Acoustics FAQ

This enhanced version of the Acoustical FAQ file is provided by CampanellaAcoustics.com,acoustical consultants, as a public service to foster the worldwide dissemination of acoustical

knowledge.

/////under minor editorial revision 3 May 07 AJC.

For global compatibility, only ASCII symbols are used.

Aims:

To make acoustics accessible to a wider public.To encourage cooperation within the acoustics community.

Disclaimer: No warranty is made for the accuracy of the contents of this FAQ.

Table of Contents (Key Word Index is found in Section 7.)

0] Credits (see 10])

1] Resource Pointers

1.1 What acoustics related news groups and FAQs are there? 1.2 What World Wide Web sites are there? 1.3 What acoustics software is available on the Net? 1.4 What acoustics books and journals are there?

2] Basic Acoustics

2.1 What is sound? 2.2 What is a decibel (dB)? 2.3 How is sound measured? 2.4 What does dB(A) or "A-Weighted" mean? 2.5 How do sound levels add? 2.6 How does the ear work? 2.7 At what level does sound become unsafe? 2.8 What is sound intensity? 2.9 How does sound decay with distance? 2.10 What is the sound power level? 2.10.1 How is sound power measured? 2.11 What is the speed of sound in air, water ..? 2.12 What is meant by loudness?

3] Vibration

3.1 What is vibration? 3.2 How is vibration measured? 3.3 How is vibration isolated and controlled? 3.4 What is Seismic (Earthquake) protection?

4] Architectural & Building Acoustics

4.1 What is reverberation time? 4.2 What is the sound absorption coefficient? 4.3 What is the difference between insulation & absorption? 4.4 How is sound insulation measured? 4.5 How do I improve the noise insulation of my house/dwelling? 4.6 How does acoustics affect classrooms and meeting rooms?

5] Reserved

6] Miscellaneous Questions

6.1 What is active noise control? 6.2 What causes a sonic boom? 6.3 Can you focus sound? 6.4 What is sonoluminescence? 6.5 Why does blowing over a bottle make a note? 6.6 What is pitch? 6.7 What are musical intervals? 6.8 What causes "helium voice"? 6.9 What is structural acoustics? 6.10 What is the Doppler effect? 6.11 What is white noise, pink noise? 6.12 When should stranded wire be used for audio cables in a PA system? What is the "electricalskin effect"?

7] KEY WORD INDEX

8] Weighting Tables

8.1 Formulae for computing A Weighting and 1/3-octave frequencies. 8.2 Table of A, C and U Weightings. 8.3 Table of Absorption values.

9] List of National Acoustic Societies

10] Composers

1] Resource Pointers

*** 1.1 What acoustic related news groups and FAQs are there?

news groups

news:alt.sci.physics.acoustics - started by Angelo Campanella - now the principal group for discussion ofacoustics topics. Ang's CV is at URL http://www.CampanellaAcoustics.Com/angelo.htm .

news:sci.physics - general physics but occasionally acoustics related questions are posted.

news:rec.audio.tech - includes discussion on audio equipment, speakers etc. There are other rec.audiogroups which may be of interest.

news:alt.support.hearing-loss and news:alt.support.tinnitus - groups for sufferers of these complaints

news:bionet.audiology - matters relating to hearing and hearing loss

news:bit.listserv.deaf-l news:uk.people.deaf news:alt.society.deaf - usenet seems an ideal communicationmedium.

news:comp.dsp - the group for people interested in computing digital signal processing solutions, FFTs

FIRs IIRs etc.

news:comp.speech - speech recognition and simulation

news:comp.sys.ibm.pc.soundcard.misc - various discussion of use of internal sound cards in IBMcompatible computers.

FAQs

The main archive site for all usenet FAQs is ftp://rtfm.mit.edu/pub/usenet/

A list of mirror sites (including html) for the Acoustics FAQ is athttp://extra.newsguy.com/~consult/Acoustics_FAQ_mirrors.html

The Active Noise Control FAQ by Chris Ruckman is at http://www.xis.com/~ruckman/

The Tinnitus FAQ deals with a range of hearing disorders. It is available athttp://www.cccd.edu/faq/tinnitus.html

The Audio FAQ, with everything you ever wanted to know about the subject, from preamplifiers to speakersand listening room acoustics. It is located in the pub/usenet/rec.audio.* directories

The comp.speech faq has information on speech processing and some software linkshttp://www.speech.su.oz.au/comp.speech/

*** 1.2 What World Wide Web sites are there?

http://www.ecgcorp.com/velav/ (virtual lib for acoustics & vibration with useful links) http://online.anu.edu.au/ITA/ACAT/drw/PPofM/INDEX.html (simple acoustics introduction from David Worrall) http://www.mme.tcd.ie/~m.carley/Notes/ (theoretical basic acoustics lecture notes; difficult stuff like the wave equation etc., in hypertext for browsing,or gzipped Postscript format for downloading) http://asa.aip.org/ (Acoustical Society of America home page with several links and comprehensive career section, book listsand Society info etc.) http://pcfarina.eng.unipr.it/ (Angelo Farina has published a variety of papers - some are available in zipped MS Word format) http://eaa.essex.ac.uk/eaa/ (European Acoustics Association) http://users.aol.com/inceusa/ince.html (Institute of Noise Control Engineering home page) http://www.audiogrid.com/arsl.html (Steve Ekblad's extensive audio related BBS and Internet list) http://www.techexpo.com/ (Technical societies, conferences etc. but not specifically acoustics related) http://www.iso.ch/ (main ISO standards page) http://www.iso.ch/addresse/membodies.html (national standards organizations addresses) http://www.ansi.org/ (official ANSI site) http://www.ds.dk/public/isotc43/default.htm ISO Technical Committee 43 - all areas of acoustics and acoustical measurements. Subcommittee 1 deals with measurements including sound power. Subcommittee 2 deals with acoustical properties of buildings. http://www.ASTM.org/COMMIT/e-33.htm American Society for Testing and materials (ASTM) Committee E-33 "Environmental Acoustics". Deals with all aspects of building acoustics and some community noise measurements. http://www.noisenet.org/Noise_home.htm http://www.noisenet.org/Vibration_Introduction.htm

Some of the better search engines:

http://www.infoseek.com/ http://altavista.digital.com/ http://www.dejanews.com/ (can also be used as Usenet posting gateway) http://www.excite.com/ http://www.hotbot.com/ http://www.yahoo.com/ http://www.lycos.com/

or use your nearest Archive site to look for files you want.

*** 1.3 What acoustics software is available on the Net?

http://www.soundsoft.demon.co.uk - This is a computational acoustics resource site by Stephen Kirkupcontaining Fortran Software implementing the Boundary Element Method (BEM) for the solution of a range ofacoustic problems.

A range of programs available for downloading from the Simtel archive.

Spectrogram 4.12 - Accurate real time Win95 spectrum analysis program (freeware) by Richard Horne is ata few sites including: ftp://ftp.simtel.net/pub/simtelnet/win95/sound/gram412.zip

The comp.speech faq has several links to speech related software including speech recognition and text tospeech programs.

There are a few programs for various platforms listed at URLhttp://www.cisab.indiana.edu/CSASAB/index.html The programs listed are mainly for sound analysisand editing.

Some software is available for audio systems design at URLftp://ftp.uu.net/usenet/rec.audio.high-end/Software

Odeon is a program for architectural acoustics. A demonstration version is available by ftp. The demoincludes a large database for coefficients of absorption. A web page at URLhttp://www.dat.dtu.dk/~odeon/index.html describes the capabilities of the program and gives the ftpaddress.

Also some interactive acoustics software (e.g. room acoustics, RT, decibel conversion etc.) is available at acouple of sites.

CATT Auralization - demo version of CATT-Acoustic (room acoustics prediction / auralization). A freedownload version is available on the Web site, but it lacks a small key file which can be transferred via e-mailin return for name, address and company/organization affiliation. See www.netg.se/~catt . (4-98 perBengt-Inge Dalenback * Mariagatan 16A * S-41471 Gothenburg * SWEDEN catt@netg.se * phn/fax: +4631145154)

*** 1.4 What acoustics books and journals are there?

There is a large range of books available on the subject. Generally the choice of book will depend on whichapproach and subject area is of interest. A few books are listed below:

Introduction to Sound Speaks, C

Good foundation for acoustics principles

Acoustics Source Book Parker, S (editor)

Basic introductory articles on many topics discussed in the alt.sci.physics.acoustics group. Old book -technology a bit dated.

The Science of Sound Rossing, T

Introductory book on acoustics, music and audio

Fundamentals of Acoustics Kinsler, L Frey, A et al.

Good overall coverage of acoustics but includes lots of theory

Acoustics ... Pierce, A

Classic advanced text - lots of theory

Engineering Noise Control Bies, D & Hansen, C

Practically biased with examples. Partially updated and corrected.

Handbook of Acoustical Measurements and Noise Control Harris C (editor)

Comprehensive practical reference book.

Vibration and Sound Morse, P

Comprehensive theory of acoustic waves and vibration in materials. Good fundamentals reference book.

A list of recently reviewed noise-related books is at URL http://users.aol.com/inceusa/books.html

Some Journals

Applied Acoustics (UK - 12 per year)Acoustics Bulletin (UK - every 2 months) Acta Acustica (P.R.China) Acta Acustica / Acustica (Europe - 6 per year) Journal of the Acoustical Society of America (monthly)Journal of the Acoustical Society of Japan (E) (English edn - 2 months) Acoustics Australia (3 per year) Journal of Sound & Vibration (UK - weekly) Journal of the Audio Engineering Society (US - 10 per year) Noise Control Engineering (US - every 2 months)Technical Acoustics (http://www.ejta.org)

| Definitions used: | | 10 (̂-5) indicates 10 raised to the power of minus 5 | 1.0E-12 indicates 1.0 x 10 (̂-12) | 1 pW indicates 1 picowatt i.e. 1.0E-12 Watt | W/m 2̂ indicates Watts per square metre | lg indicates logarithm to base 10 | sqrt indicates the square root of | pi = 3.142 | Lw is sound power level, the w is subscripted

2] Basic Acoustics

*** 2.1 What is sound?

Sound is the quickly varying pressure wave within a medium that can travel widely in that medium. Weusually mean audible sound, which is the sensation (as detected by the ear) of very small rapid changes in

the air pressure above and below a static value. This "static" value is atmospheric pressure (about 100,000Pascals) which does nevertheless vary slowly, as shown on a barometer. Associated with the soundpressure wave is a flow of energy. Sound is often represented diagrammatically as a sine wave, butphysically sound (in air) is a longitudinal wave where the wave motion is in the direction of the movement ofenergy. The wave crests can be considered as the pressure maxima whilst the troughs represent thepressure minima.

How small and rapid are the changes of air pressure which cause sound? When the rapid variations in pressure occur between about 20 and 20,000 times per second (i.e. at afrequency between 20Hz and 20kHz) sound is potentially audible even though the pressure variation cansometimes be as low as only a few tens of millionths of a Pascal. Movements of the ear drum as small asthe diameter of a hydrogen atom can be audible! Louder sounds are caused by greater variation in pressure.A sound wave of one Pascal amplitude, for example, will sound quite loud, provided that most of the acousticenergy is in the mid frequencies (1kHz - 4kHz) where the human ear is most sensitive. It is commonlyaccepted that the threshold of human hearing for a 1 kHz sound wave is about 20 micro-Pascals.

What makes sound? Sound is produced when the air is disturbed in some way, for example by a vibrating object. A speaker conefrom a high fidelity system serves as a good illustration. It may be possible to see the movement of a bassspeaker cone, providing it is producing very low frequency sound. As the cone moves forward the airimmediately in front is compressed causing a slight increase in air pressure, it then moves back past its restposition and causes a reduction in the air pressure (rarefaction). The process continues so that a wave ofalternating high and low pressure is radiated away from the speaker cone at the speed of sound.

*** 2.2 What is a decibel (dB)?

The decibel is a logarithmic unit for ratios that is used in a number of scientific disciplines. Other examplesare the Richter scale for earthquake event energy and pH for hydrogen ion concentration in liquids.

In all cases the logarithmic measure is used to compare the quantity of interest with a reference value, oftenthe smallest likely value of the quantity. Sometimes that reference can be an approximate or average value.

Most often in common acoustics, the decibel is used to compare the sound pressure level (SPL) in air witha reference pressure. The reference level for sound intensity (I), sound power level (PWL) and sound pressurein water are amongst others that are in common use:

Reference sound pressure (in air) = 0.00002 = 2E-5 Pa (rms)

" " intensity = 0.000000000001 = 1E-12 W/m^2

" " power = 0.000000000001 = 1E-12 W

" " pressure (water) = 0.000001 = 1E-6 Pa

Acousticians use the dB scale for the following reasons:

1) Quantities of interest often exhibit such huge ranges of variation that a dB scale is more convenient than alinear scale. For example, sound pressure radiated by a submarine may vary by eight orders of magnitudedepending on direction; expression in linear units carries with it the confusion of the location of the decimalpoint. Decibels values are characteristically between only -999 to +999.

2) The human ear interprets loudness more easily represented with a logarithmic scale than with a linearscale.

*** 2.3 How is sound measured?

A sound level meter (SLM) is the principal instrument for general noise measurement. The indication on aSLM (aside from weighting considerations) indicates the sound pressure, p, as a level referenced to 0.00002Pa, calibrated on a decibel scale.

Sound Pressure Level = 20 x lg (p/0.00002) dB

Often, the "maximum" level and sometimes the "peak" level of the sound being measured is quoted. During

any given time interval the peak level will be numerically greater than the maximum level and the maximumlevel will be numerically greater than the (rms) sound pressure level;

peak>max>rms.

*** 2.4 What does dB(A) or "A-Weighted" mean? C-Weighted?

A sound level meter that measures the sound pressure level with a "flat" response will indicate the strength oflow frequency sound with the same emphasis as higher frequency sounds. Yet our ear perceives lowfrequency sound to be of less loudness that higher frequency sound. The eardrum- stapes-circular windowsystem behaves like a mechanical transformer with a finite pass band. In EE parlance, the "3 dB" rolloverfrequencies are approximately 500 Hz on the low end and 8 kHz on the high end. By using an electronic filterof attenuation equal to that apparently offered by the human ear for sound each frequency (the 40-phonresponse curve), the sound level meter will now report a numerical value proportional to the human perceptionof the strength of that sound independent of frequency. Section 8.2 shows a table of these weightings.

Unfortunately, human perception of loudness vis-a-vis frequency changes with loudness. When sound is veryloud - 100 dB or more, the perception of loudness is more consistent across the audible frequency band. "B"and "C" Weightings reflect this trend. "B" Weighting is now little used, but C-Weighting has achievedprominence in evaluating annoying community noises such as low frequency sound emitted by artillery fireand outdoor rock concerts. C-Weighting is also tabulated in 8.2.

The first electrical sound meter was reported by George W Pierce in Proceedings of the American Academyof Arts and Sciences, v 43 (1907-8) A couple of decades later the switch from horse drawn vehicles toautomobiles in cities led to large changes in the background noise climate. The advent of "talkies" - filmsound - was a big stimulus to sound meter patents of the time, but there was still no standard method ofsound measurement. "Noise" (unwanted sound) became a public issue.

The first tentative standard for sound level meters (Z24.3) was published by the American StandardsAssociation in 1936, sponsored by the Acoustical Society of America. The tentative standard shows twofrequency weighting curves "A" and "B" which were modeled on the response of the human ear to low andhigh levels of sound respectively.

With the coming of the Walsh-Healy act in 1969, the A-Weighting of sound was defacto presumed to be the"appropriate" weighting to represent sound level as a single number (rather than as a spectrum). With theadvent of US FAA and US EPA interests in the '70's, the dBA metric was also adapted by them. (Along withthe dBA metric has come an associated shortfall in precision in accurately presenting the capacity of a givensound to produce hearing loss and the capacity to create annoyance.)

[Editor's Note: A single number metric such as dBA is more easily understood by legal and administrativeofficials, so that promulgation, enforcement and administrative criteria and actions are understandable bymore parties, often at the expense of a more precise comprehension and engineering action capability. Forinstance, enforcement may be on a dBA basis, but noise control design demands the octave band or eventhird-octave band spectral data metric.]

The most commonly referenced weighting is "A-Weighting" dB(A), which is similar to that originally definedas Curve "A" in the 1936 standard. "C-Weighting" dB(C), which is used occasionally, has a relatively flatresponse. ""U-Weighting"" is a recent weighting which is used for measuring audible sound in the presenceof ultrasound, and can be combined with A-Weighting to give AU-Weighting. The A-Weighting formula isgiven in section 8 of this FAQ file.

In addition to frequency weighting, sound pressure level measurement can be time weighted as the "Fast","Slow" or "Impulse" response. Measurements of sound pressure level with A-Weighting and fast responseare also known as the "sound level".

Many modern sound level meters can measure the average sound energy over a given time. this metric iscalled the "equivalent continuous sound level" (Leq). More recently, it has become customary in some circlesto presume that this sound measurement was A-Weighted if no weighting descriptor is listed.

*** 2.5 How are decibel sound levels added?

If there are two uncorrelated sound sources in a room - for example a radio producing an average sound levelof 62.0 dB, and a television producing a sound level of 73.0 dB - then the total decibel sound level is alogarithmic sum i.e.

Combined sound level = 10 x lg ( 10 (̂62/10) + 10 (̂73/10) )

= 73.3 dB

Note: for two different sounds, the combined level cannot be more than 3 dB above the higher of the twosound levels. However, if the sounds are phase related ("correlated") there can be up to a 6dB increase inSPL.

*** 2.6 How does the ear work?

The eardrum is connected by three small jointed bones in the air filled middle ear to the oval window of theinner ear or cochlea, a fluid- filled spiral shell about one and a half inches in length. Over 10,000 hair cells onthe basilar membrane along the cochlea convert minuscule movements to nerve impulses, which aretransmitted by the auditory nerve to the hearing center of the brain.

The basilar membrane is wider at its apex than at its base near the oval window; the cochlea tapers towardsits apex. Groups of the delicate hair sensors on the membrane, which membrane varies in stiffness along itslength, respond to different frequencies transmitted down the spiral. The hair sensors are one of the few celltypes in the body which do not regenerate. They can therefore be irreparably damaged by large noise doses.Refer to the Tinnitus FAQ for more information on associated hearing disorders.

http://www.mankato.msus.edu/dept/comdis/kuster2/audiology.html http://oto.wustl.edu/cochlea ftp://rtfm.mit.edu/pub/usenet/news.answers/medicine/tinnitus-faq

*** 2.7 At what level does sound become unsafe?

It is strongly recommended, to avoid unprotected exposure to sound pressure levels above 100dBA. Usehearing protection when exposed to levels above 85dBA (about the sound level of a lawn mower when you arepushing it over a grassy surface), and especially when prolonged exposure (more than a fraction of an hour)is expected. Damage to hearing from loud noise is cumulative and is irreversible. Exposure to high noiselevels is also one of the main causes of tinnitus.

The safety aspects of ultrasound scans are the subject of ongoing investigation. One metric that has beenexpressed is that exposure to ultrasound should not exceed 85dB in the 16kHz octave band.

Health hazards also result from extended exposure to vibration. An example is "white finger" disease, whichis found amongst workers who frequently use hand-held machinery such as chain saws.

*** 2.8 What is sound intensity?

Sound intensity is expressed in decibels with respect to one pico-watt (10 -̂12 watts) per square meter. Thisis very nearly* numerically equal to the sound pressure level (SPL) in decibels when measures one foot fromthe noise source (viz. the inlet of a noisy fan) . An intensity estimate using SPL measurement only presumesno standing waves or reflections where the effective impedance can differ from that of free space air. In itscomplete form, intensity include the unit vector of the propagation direction, i.e. intensity is a vector quantity.

*For a plane wave, the sound power that passes through a surface of A square meters is defined as the ratioof the pressure squared to the air impedance

I = p 2̂/(rho*c)

When combined with the propagation unit vector, this defines the rate of sound energy transmitted in aspecified direction per unit area normal to the direction. When measured in practical units, we can computeintensity after the relation that

Numerically, the sound intensity is related to the sound power as follows: In free air space, a source emittingLw dB re 1 picowatt produces the sound pressure level Lp at a distance R feet as

Lp=Lw-20logR-0.6

At a one foot radius, that sound power is distributed over a surface of 4*pi = 12.57 square feet or(*.3048 2̂=.0920*) 1.17 square meters. 10log1.17=0.7dB. So within 0.1 dB, the coincidence exists that thesound intensity in picowatts per square meter is numerically equal to the sound pressure level in dB!

NOTE: This identity holds true only when the impedance, rho*c is exactly 400 mks rayls. This occurs for sealevel at 39 degrees C. For 22 C, rho*c = 412; a 0.13 dB difference arises. But at higher elevations, air densitydecreases for a given temperature. At an elevation of 840 feet above sea level, rho*c reduces to 400 at 22 C.(fortunate for much of Midwestern US!). The 0.13 dB difference at sea level is not usually significant foracoustical measurements.

Sound intensity meters are popular for determining the quantity and location of sound energy emission.

*** 2.9 How does sound decay with distance?

At distances large compared to the size of the source, sound intensity diminishes according to the inversesquare law.

I = Io/D 2̂

This is relatively simple to reliably calculate, provided the source is small and outdoors where no echoesoccur. (But indoor calculations in a reverberant field are rather more complex. )

If the noise source is outdoors and its dimensions are small compared with the distance to the monitoringposition (ideally a point source), then as the sound energy is radiated it will spread over an area which isproportional to the square of the distance. This is an 'inverse square law' where the sound level will decline by6dB for each doubling of distance.

Line noise sources such as a long line of moving traffic will radiate noise in cylindrical pattern, so that thearea covered by the sound energy spread is directly proportional to the distance and the sound will declineby 3dB per doubling of distance.

Close to a source (the near field) the change in SPL will not follow the above laws because the spread ofenergy is less, and smaller changes of sound level with distance should be expected.

If the observation position very close to the source, at a distance that is small compared to the size of thesource, the sound level changes very little with location in that source area. One may be able to determinethe "virtual center" of the whole sound field, whence inverse square law calculations can proceed in referenceto that distance, for locations outside the source area.

The surrounding environment, especially close to the ground, and in the presence of wind & verticaltemperature gradients, has a great effect on the sound received at a distant location. Ground reflectionaffects sound levels more than a few feet away (distances greater than the height of the sound source or thereceiver above the ground). Wind and air temperature gradients affect all sound propagation beyond 100meters over the surface of the earth. Sound propagates well downwind (traveling with the wind), and verypoorly upwind. When the ground surface is cooler than the air just above it ("inversion"), typically late atnight and just before dawn, sound will travel great distances across the landscape even without any wind.

In addition it is always necessary to take into account attenuation due to the absorption of sound by the air,which may be substantial at higher frequencies. For ultrasound, air absorption may well be the dominantfactor in the reduction.

*** 2.10 What is the sound power level?

(See ACCULAB Reference Sound Source on this site: http://www.campanellaacoustics.com/rssman.htm )

Sound power level, Lw, is often quoted on machinery to indicate the total sound energy radiated per second.It is quoted in decibels with respect to the reference power level. The reference level is 1pico-watt (pW)[1x10 (̂-12) watts]. One watt of radiated sound power is represented as "Lw=120 dB re one picowatt". If thereported sound power is in terms of A-Weighted spectral weighting, a suffix, A, is applied to form dB(A).

The sound pressure level (SPL) resulting from sound power (Lw) being radiated into free space, e.g. over apaved surface, is computed from

SPL = Lw - 20*log(R) - 11 dB re 20 uPa (R in meters)

SPL = Lw - 20*log(r) - 0.7 dB re 20 uPa (r in feet)

If instead the sound is emitted over a reflecting plane such as a hard surface, three (3) decibels are added tothe SPL.

For example, a lawn mower with sound power level 100 dB(A) will produce at a sound pressure level (SPL) ofabout 89dB(A) at the operator (you) position over grass and 92 dB(A) when the mower is operated over a hardsurface such as your driveway. At your neighbor's yard 50 feet (15m) away, the SPL will be is 65 dBA.

*** 2.10.1 How is sound power measured?

Sound power is usually measured indirectly as the sound pressure level found at a specific distance, and inevery direction that sound can be radiated. The sound power emitted by Items that can be carried to alaboratory is usually measured in a hemi-anechoic room or a reverberation room.

Either the "comparison" or the "direct" method is used.

In the comparison method, the SPL that the item causes in that room is compared the SPL created by astandard "Reference Sound Source" (see the 'Acculab' portion of this web page) to determine the soundpower emitted by the item. This is the most common and economical method.

In the direct method two processes may apply. For the hemianechoic method, the SPL is measured in everydirection on a surface encompassing the test item. These measurements are then combined to compute theemitted sound power. For the reverberation room, the SPL is measured at several locations in the that room,then averaged. The sound power is computed from that average as:

PWL = SPL + 10Log(A)-C.

A = absorption in the reverberation room, sabins or square meters. C = 16.3 for A as sabins (square feet) C = 6.2 for A in square meters.

See ISO Technical Committee Web Site for acoustical measurement information.

*** 2.11 What is the speed of sound in air & water ?

**** AIR ****

A convenient formula for the speed of sound in air is

c = 20*sqrt(273 + T), T in Centigrade and c in meters/sec

or

c = 49*sqrt(459 + T), T in Fahrenheit and c in feet/sec

The speed of sound in air at a temperature of 0 degrees C and 50% relative humidity is 331.6 m/s. The speedis proportional to the square root of absolute temperature and it is therefore about 12 m/s greater at 20degrees C. The speed is nearly independent of frequency and atmospheric pressure but the resultant soundvelocity relative to the ground may be substantially altered by wind velocity.

A good approximation for the speed of sound in other gases at standard temperature and pressure can beobtained from

c = sqrt (gamma x P / rho)

where gamma is the ratio of specific heats, P is 1.013E5 Pa and rho is the density.

**** WATER ****

The speed of sound in water is approximately 1500 m/s. It is possible to measure changes in oceantemperature by observing the resultant change in speed of sound over long distances. The speed of sound inan ocean is approximately:

c = 1449.2 + 4.6T - 0.055T 2̂ + 0.00029T 3̂ + (1.34-0.01T)(S-35) + 0.016z

T temperature in degrees Celsius, S salinity in parts per thousand z is depth in meters

See also CRC Handbook of Chemistry & Physics for some other substances and Dushaw & WorcesterJASA (1993) 93, pp255-275 for sea water.

*** 2.12 What is meant by loudness?

Loudness: Loudness is one of the more difficult aspects of domestic acoustics to learn and understand. Iwill try me best to get things straight. Loudness is the human impression of the strength of a sound. Theloudness of a noise does not always correlate with its sound level.

A-Weighting: The A-weighting scale attempts to balance the electronic pass band of a sound level meterto respond to sound at various frequencies as the human ear actually hears it after passing through theeardrum, the middle and into the inner ear (cochlea).

Loudness Weighting: The actual weighting curve for the human ear is much more complex than thesimplistic A-weightng curve. The ear canal creates a resonance around 4,000 Hz, and the low frequencyresponse depends on sound level, being flatter for the highest sound levels, and cutting off rapidly at lowfrequencies for low sound levels.

Phons: The loudness level of any sound, in phons, is the decibel level of an equally loud 1kHz tone, heardbinaurally by an otologically normal listener.

(NOTE: Historically, it was with reluctance that a simple frequency weighting "sound level meter" curve(A-Weighting) was accepted as giving a representative approximation to loudness.

One phon curve is especially selected; that which has a 1,000Hz threshold of 40 decibels (referenced to20 micropascals). This curve is assigned the special name of "the 40-phone curve" (no surprise).

More on Loudness: The ear senses noise on a different basis than simple energy summation, and thiscan lead to discrepancy between the loudness of certain repetitive sounds and their sound level.

A 10dB sound level increase is perceived to be about "twice as loud" in many cases.

Sone: And that leads us to the "sone" which happens to be the same metric, but with a different nameand a different number sequence. The sone is another unit of comparative loudness with

0.5 sone = 30 phons,

1 sone = 40 phons,

2 sones = 50 phons,

4 sones = 60 phons etc.

The sone "10dB rule" is inappropriate at very low and high sound levels where human subjective perception does notfollow it. This can lead to a discrepancy between the loudness of certain repetitive sounds and their sound level..

Loudness Calculation: Loudness level calculations, typically according to ANSI S3.4, take account of"masking" - the process by which the audibility of one sound is reduced due to the presence of another at aclose frequency. The redundancy principles of masking are applied in digital audio broadcasting (DAB),leading to a considerable saving in bandwidth with no perceptible loss in quality.

3] Vibration

*** 3.1 What is vibration?

When something moves periodically about a static position it can be said to vibrate. Examples of unwantedvibration are the movement of a building near a railway line when a train passes, or the vibration of the floorcaused by a washing machine or spin dryer. Floor vibration can be reduced with vibration isolators,sometimes at the risk of increased machinery vibration and subsequent deterioration.

*** 3.2 How is vibration measured?

Vibration is often measured with an accelerometer. This is a device that is securely attached to the surfaceunder investigation. The accelerometer produces an electrical charge proportional to the surface acceleration,which is then amplified by a charge amplifier and recorded or observed with a meter. The frequencies ofinterest are generally lower than sound, and range from below 1 Hz to about 1 kHz.

It is sometimes more useful to know the vibration velocity or displacement. Often, moving coil transducersare used to directly measure vibration velocity. A single integration of that signal provides a measure ofdisplacement.

If only an accelerometer is available, it is necessary to integrate the acceleration signal once for velocity andtwice for displacement. If the vibration is sinusoidal at a known frequency, f, then an integration is calculatedby dividing the original by 2 x pi x f (noting that there is also an associated phase change).

Example: A machine is vibrating with sinusoidal motion at 79.6 Hz with an rms acceleration of 10 m/s 2̂.

Its rms velocity is therefore 10/(2 x pi x 79.6) = 20 mm/s Its rms displacement is 10/(4 x pi^2 x 79.6^2) = 0.04 mm

The final result may also be expressed in terms of zero-to-peak, which is found as the square root of two[sqrt(2)] times the rms value. The peak-to-peak value is twice again that.

Thus, one has three measures (acceleration, velocity, displacement) and three scales (rms, 0-p, p-p) totalingnine possible explicit measures of one and the same vibration. Couple that with three possible directions(E-W, N-S, up-down) one faces 27 separate possible values... and then there are inches, mils, microns andmillimeters... Needless to say, one must be eternally vigilant and explicit in their vibration measurement andreporting nomenclature!

*** 3.3 How is vibration isolated or controlled?

Vibration problems are solved by considering the system as a number of connected springs and masses withdamping. The vibration source is included within, e.g. the engine of a motor car, or the environment on whichthis assembly is mounted is presumed to vibrate, e.g. a scanning electron microscope.

If the vibration is produced by a motor inside a machine, it is necessary that the natural frequency of thesupporting system is well below frequency of motor oscillations (the forcing frequency). This is achieved byincreasing the mass or decreasing the stiffness of the system as appropriate.

The method of vibration isolation is demonstrated with a weight held from a rubber band. If the band is movedup and down very slowly the suspended weight will move by the same amount. At resonance the weight willmove much more and possibly in the opposite direction. But as the frequency of vertical movement is furtherincreased, the weight will become almost stationary. Springs are more commonly used in compression thanin tension.

Important:-

Intuitive attempts to reduce vibration from machinery can sometimes instead aggravate the problem. This isespecially true when care was originally taken to minimize vibration at the time of design, manufacture andinstallation.

Another method of vibration control is to cancel the forces involved using a Dynamic Vibration Absorber. Herean additional "tuned" mass-spring combination is added so that it exerts a force equal and opposite to theunwanted vibration. They are only appropriate when the vibration is of a fixed frequency.

Recently, "Active Vibration Control", using techniques akin to Active Noise Control has evolved. This sensesthe unwanted vibration of a structural member to produce a reversed phase signal to drive a transducerattached to the same member to counter the motion. In that way, for instance, the vibration of rolling wheelsof a vehicle is prevented from being transmitted into the body of that vehicle through the chassis

*** 3.4 What is Seismic (Earthquake) protection? Earthquakes can producevertical and sidewise vibrations up tp perhaps one G or more, though it is usually much less. The immediateconcerns can be divided into two categories, "Operating, Basic Earthquake" (OBE) and "Safe Shutdown,Earthquake" (SSE). OBE protection seeks to have equipment operate during and survive an earthquake. SSEprotection merely assures that equipment that shuts down during an earthquake will survive to be usedanother day. Unfortunately, the amount of vibration items experience in a building can be worsened by thatbuilding, the higher in the building, the worse the vibration amplitude, since the elasticity of the joists andcolumns act as springs, only to resonate with the masses supported at anywhere from 5 Hz to 15 Hz. Thebest place to be is in the basement, on bedrock. Equipment bolted to the floor and walls ("hard mounted"),survive best, provided the bolts, walls or floor do not break. Equipment mounted on isolator springs areparticularly vulnerable since those soft isolators easily allow the equipment to sway due to the earthquake,only to suddenly crash into the sprung motion stops or nearby objects. Special seismic isolator springscontaining soft stops (like the rubber stops accompanying automobile suspension springs) that cushion theimpact.

4] Architectural & Building Acoustics*** 4.1 What is reverberation time?

The time for sound in a room to decay 60 decibels. Scientific work on room acoustics was pioneered byWallace Clement Sabine 1868-1919 (see his Collected Papers on Acoustics, 1922). The reverberation time,T, is defined as the time taken for sound energy to decay in a room by a factor of one million in energy (60dB). It is dependent on the room volume and the total amount of sound absorption contained in the room. Inmetric units

0.161 x room Volume T = --------------------------------------------------------------------- sum of Surface areas x absorption coefficients

In US English units, dimensions are in feet and the constant is 0.049.

*** 4.2 What is the sound absorption coefficient?

The absorption coefficient of a material is ideally the fraction of the randomly incident sound power which isabsorbed, or otherwise not reflected. It is standard practice to measure the coefficient at the preferred octavefrequencies over the range of at least 125Hz - 4kHz.

It can be determined on small material samples with an "impedance tube" or on large samples in a laboratory"reverberation room". The impedance tube evaluates sound absorption at normal incidence only, andproduces absorption values that are slightly lower than those found in the reverberation room where the"Sabine coefficient" is measured over a wide range of incidence angles.

For the purposes of architectural design, the Sabine coefficient is preferred, though the normal incidenceabsorption may be used in the absence of any other information. Interestingly some absorbent materials arefound to have a Sabine coefficient in excess of unity at higher frequencies. This is due to diffraction effects.Where this occurs the value can be taken at face value for small material patches and as 1.0 for very largeabsorbers (entire walls). The Odeon computer program includes a file of absorption coefficients.

*** 4.3 What is the difference between sound absorption & sound insulation ?

There is often confusion between sound insulation and sound absorption.

Sound is absorbed when it encounters a material which will convert some or all of it into heat, or which allowsit to pass through not to return. For this reason good sound absorbers do not of themselves make goodsound insulators. Sound insulators rarely absorb sound. Sound absorbers contribute little to soundinsulation. They are treated separately in sound control design.

Sound insulation prevents sound from traveling from one place to another, such as between apartments in abuilding, or to reduce unwanted external noise inside a concert hall. Heavy materials like concrete are themost effective materials for sound insulation - doubling the mass per unit area of a wall will improve itsinsulation by about 6dB. It is possible to achieve good insulation over most of the audio frequency range withless mass by instead using a double leaf partition (two independent walls separated by an air gap filed with asound absorber).

*** 4.4 How is sound insulation measured?

////The measurement method depends on the particular situation. There are standards for the measurementof the insulation of materials in the laboratory, and for a number of different field circumstances. Usually

Test procedures (e.g. ASTM E-90 in the lab and E336 in the field) generate a loud and consistent broad bandspectrum of steady noise on one side of a partition or specimen of the material under test, then measure theamount of this sound that passes through that material. The ratio of the incident sound to the transmittedsound is the "noise reduction", usually expressed as 10 time the logarithm of this ratio. If the noise reductionis also corrected for the amount of sound absorption to be found in the receiving room, 10 times the logarithmof the corrected ratio is called the "transmission loss. This is performed for 1/3 octave bands of noise from100 to 4000 Hz.

A single-number rating of that range of noise reductions or transmission losses van be had by fitting them toa segmented curve.

In North America, this procedure is ASTM E413. The fitted range is from 125-4000 Hz. The value of that curveat 500 Hz is called the Noise Isolation Class (NIC) or Sound Transmission Class (STC) respectively.Internationally, ISO140-3 produces the noise reduction and transmission loss data in the same way. But thesingle number rating is according to ISO 717 which uses data in the 100-3150 Hz range. This single numberrating is called "R'" and "R" respectively.

Similar methods are applied to impact ("footfall") noise (a problem in multifamily residential buildings). Astandard tapping machine is used to hammer on the floor, lightly and steadily at the rate of 10 taps persecond. The sound pressure level in the room below are measured. ASTM E492 and ISO 140-4 and 717apply. (See ASTM e-33 Web Site .)

*** 4.5 How do I improve the noise insulation of myhouse/dwelling?

This is one of the most commonly asked questions of noise consultants. Firstly you should consider whetherit is noise insulation or sound absorption (see 4.3) that is really required. Sound insulation is most oftenasked for in order to keep out unwanted noise, but is occasionally requested for the purpose of minimizingdisturbance to others.

The method of noise insulation will depend on the exact situation; generalities are extremely difficult todevise. Situations are more often than not unique, depending on the nature of the building infrastructure thatthe architect or his informal successors have devised. More often than not, successful noise isolation

improvement requires the advice of a competent and experiences person and at an early stage of therenovation. The following ideas may serve as initial guidelines.

When the noise is from an external source such as a main road it may be possible, if planning authoritiespermit, to screen with a noise barrier. These can be effective providing that the direct line of sight betweentraffic and house is concealed by the barrier.

The weak point for sound transmission to and from a building is most often via the windows. Double glazingwill usually afford noticeably better protection than single glazing, but in areas of high external noise it mightbe preferable to have double windows with a large air gap (25 to 100 mm) and acoustic absorbent material onthe perimeter reveal around that gap. For a few people, the resultant lower room background noise level canmake noise transmitted through party walls more apparent. The fitting of new windows may reduce the levelof air ventilation, and it will be vital to compensate for this, if necessary with by improving the noise insulationof certain party walls.

Noise through party walls can be reduced by the addition of a false wall. This is constructed from a layer ofsound insulating material, commonly plasterboard, separated from the party wall by a large void containingacoustic quilting. The false wall must not be connected to the party wall because that would allow soundtransmission paths. The quality of construction is an important consideration if optimal levels of attenuationare desired. It is advisable to contact an independent noise consultant before allowing any building works tocommence.

*** 4.5 How does acoustics affect classrooms and meeting rooms?

This question is less common, but now known to be a significant factor in modern public education.Basically, the degree that we hear well in a room depends on the background noise level and thereverberation of sound in that room. An example of a good listening environment is outdoors in a quiet backyard in the country . Here, the background noise level can be as low as 35 dBA and the reverberation timewill be a tiny fraction of a second, if any. A class or meeting of 20 to 30 persons will proceed quite well, thegroup acting in harmony most if not all of the time. Repartee vital to learning can be rapid and 2-way. /////recompose the following The weak point for sound transmission to and from a building is most often via the windows. Double glazingwill usually afford noticeably better protection than single glazing, but in areas of high external noise it mightbe preferable to have double windows with a large air gap (25 to 100 mm) and acoustic absorbent material onthe perimeter reveal around that gap. For a few people, the resultant lower room background noise level canmake noise transmitted through party walls more apparent. The fitting of new windows may reduce the levelof air ventilation, and it will be vital to compensate for this, if necessary with by improving the noise insulationof certain party walls.

Noise through party walls can be reduced by the addition of a false wall. This is constructed from a layer ofsound insulating material, commonly plasterboard, separated from the party wall by a large void containingacoustic quilting. The false wall must not be connected to the party wall because that would allow soundtransmission paths. The quality of construction is an important consideration if optimal levels of attenuationare desired. It is advisable to contact an independent noise consultant before allowing any building works tocommence.

6] Miscellaneous Questions*** 6.1 What is active noise control?

ANC is an electronic method of reducing or removing unwanted sound by the production of a pressure waveof equal amplitude but opposite sign to the unwanted sound. When the electronically produced inverse waveis added to original unwanted sound the result is nil sound at that location.

This method of noise control is sometimes considered a "cure-all" for noise problems. But this is not thecase. Noise cancellation in 3D spaces such as living areas is difficult to impossible to achieve. However itcan be more successful locally, e.g. for a passenger sitting in an aircraft or car. Many institutions world wideare developing technology to increase the circumstances where ANC can be effective. The award winning"Active Noise Control FAQ" is maintained by Chris Ruckman and available at a number of sites worldwide

including:

http://www.erols.com/ruckman/

*** 6.2 What causes a sonic boom?

(from "Aircraft Noise" by Michael T Smith, Cambridge, 1989)

" .. When the speed of an aircraft is supersonic, the pressure waves cannot get away ahead of the aircraft astheir natural speed is slower than that of the aircraft. Slower, in this context, means just over 1200 km/hr atsea level and about 10% less at normal cruising altitude. Because they cannot get away, the pressuredisturbances coalesce and lag behind the airplane, which is in effect traveling at the apex of a conical shockwave. The main shock wave is generated by the extreme nose of the airplane, but ancillary shocks aregenerated by all the major fuselage discontinuities. .. "

Ken Plotkin (kplotkin@access2.digex.net) on 24th July 1995 wrote:

[snip] .. A body moving through the air pushes the air aside. Small disturbances move away at the speed ofsound. Disturbances from a slowly moving body go out in circles, like ripples from a pebble in a pond. If thebody moves faster, the circles are closer in the direction of travel. If the body is supersonic, then the circlesoverlap. The envelope of circles forms a cone. The vertex angle of the cone is determined by its vertex movingin the travel direction of, and with the speed of the body, while the circles grow at the sound speed. [snip]The existence of the "Mach cone", "Mach waves" and the corresponding angle, was discovered by ErnstMach in the nineteenth century. [snip]

*** 6.3 Can you focus sound?

Sound can be focused like light, but in the case of sound the "optics" must be much larger because you aredealing with longer wavelengths. This effect is heard in some domed buildings such as the Capitol inWashington, and St. Paul's Cathedral in London providing noise background conditions permit.

Large parabolic reflectors 1/2 meter or more in diameter can be used to send and receive sound oversignificant distances. Your local science museum or exploratorium may have a demonstration of thismethod. It is also possible to refract and focus sound with an "acoustical lens. The lens is constructed fromparallel plates which locally decrease the speed of sound. Also, a large thin bubble, say 2 metres across,filled with carbon dioxide will focus sound. The effect is not very pronounced.

Sound can be directed by assembling several loudspeakers in an organized array. See "Acoustics" by LeoBeranek, 1954 and 1986, pp 93-115. This principle is used in column speakers, and commercial systems forreducing noise levels outside the dance floor area of discos.

*** 6.4 What is sonoluminescence?

In the early 1930s Frenzel and Schultes discovered that photographic plates became "fogged" whensubmerged in water exposed to high frequency sound. More recent experiments have succeeded insuspending a single luminous pulsating bubble in a standing wave acoustic field, visible in an undarkenedroom. Generally sonoluminescence is light emission from small cavitating bubbles of air or other gas in wateror other fluids, produced when the fluid is acted upon by intense high frequency sound waves. Themechanism is not completely understood, but very high pressures and temperatures are thought to beproduced at the center of the collapsing bubbles.

See "Science" 14 October 1994 page 233, "Scientific American" (International Edition) February 1995 Page32 or "Physics Today" September 1994 Page 22, all quite readable articles.

See also the following URLs:

http://ne43.ne.uiuc.edu/ans/sonolum.html http://www.wdv.com/Sono

James Davison (TKGN58A@prodigy.com) on 28th June 1995 wrote:

[snip] .. I have been sufficiently interested to reconstruct the apparatus for producing this effect -- using a pairof piezoelectric transducers, an old oscilloscope and a signal wave generator -- materials costing only a fewhundred dollars.

I am proud to say that tonight I managed to reproduce this effect -- the tiny bubble has the appearance of atiny blue star trapped in the middle of the flask. It is distinctly visible to the unadapted eye in a dark room,and it is a very startling thing to see. [snip]

*** 6.5 Why does blowing over a bottle make a note?

Resonance in acoustics occurs when some mass-spring combination is supplied with energy. Many musicalinstruments rely on air resonance to improve their sonority. If you blow across the mouth of a bottle you canoften get a note. The bottle behaves as a Helmholtz resonator. The main volume of air inside the bottle isanalogous to a spring, whilst the "plug" of air in the neck acts as an attached mass. The resonant frequencyis roughly given by:

f = { c sqrt (S/LV) } / 2pi

c is velocity of sound S is the surface area of the neck opening V is bottle volume L is the effective length of the neck i.e. the actual length plus ends correction. Ends correction ~ 1.5 timesradius of neck opening

Example: A 75 cl (7.5E-4 m 3̂, approx. a "fifth") sized wine bottle with neck diameter 19 mm, bottle necklength 8 cm, air temp = 20 degrees C. The calculated resonant frequency is 109Hz, actual resonance was105Hz.

Helmholtz resonators are sometimes employed as a means of passive noise control in air conditioning ducts.They may also be hidden in the wall design of auditoria and offices in order to improve the acoustics.

*** 6.6 What is pitch?

The term "pitch" has both a subjective and an objective sense. Concert pitch is an objective termcorresponding to the frequency of a musical note A (at present 440Hz). Using such a standard will define thepitch of every other note on a particular musical scale. For example, with Equal Temperament eachsemi-tone is higher or lower in frequency than the previous semi-tone by a factor of 2 (̂1/12). An octave is apitch interval of 2:1. Many sounds with no obvious tonal prominence are considered by musicians to be ofindeterminate pitch; for example, the side drum, cymbals, triangle, castanets, tambourine, and the spokenword.

Pitch is also a subjective frequency ordering of sounds. Perceived pitch is dependent on frequency, waveform and amplitude or changing amplitude. Numbers can be assigned to perceived pitch relative to a purefrontal tone of 1000Hz at 40dB (1000 mels) thereby establishing a pitch scale.

*** 6.7 What are musical intervals?

An interval is the fractional frequency ratio between musical notes.

The ratio of frequency intervals for Just Intonation is demonstrated below in the scale of C major, though thesame ratios apply to all the major keys:

C (9:8)

D (10:9)

E (16:15)

F (9:8)

G (10:9)

A (9:8)

B

(16:15) C <- Octave

The interval between E & F and between B & C is a semi-tone, whilst the other intervals are tones. Theinterval between any two notes above can be found by multiplying the intervening ratios; thus if all the aboveratios are multiplied together the resultant is 2 because an octave is twice the original frequency.

Intervals are also sequentially labeled; the interval. For instance, in the scale of C major: C D E F G A B C,the note 'E' is the third note of the scale and the interval from C to E is therefore called a third. For the scaleD major: D E F# G A B C# D, the third will be F#. The term 'interval' can also be used to indicate that thenotes are sounded together, in which case there are consonant intervals and dissonant intervals.

The notes of minor scales differ from their major counterparts; one important difference being the flattenedthird. E flat is a minor third above the note C.

The use of Just Temperament causes serious problems of intonation when music modulates between keys.Equal Temperament is nearly always used as a compromise to the problem of tuning (see question 6.6).

See The Oxford Companion to Music, Percy A Scholes, "interval".

*** 6.8 What causes "helium voice"?

Many people, on hearing the voice of someone who has breathed helium, believe that the person's speechpitch has increased.

WARNING - Breathing helium can be very dangerous.

A cavity will have certain resonant frequencies. These frequencies depend on the shape and size of the cavityand on the velocity of sound within the cavity. Human vocal cords vibrate impulsively (pulse rate is the voicefundamental) in the vocal tract, generating a range of frequencies above that fundamental. The vocal tract andcavities enhances various frequency components imparting the recognizable voice spectrum.

The velocity of sound in helium is more than twice that in air. The characteristic resonant frequencies of thevocal tract cavities will be raised in that ratio. The mechanical resonant frequency of any solid or fleshy tractcomponent will not be altered by helium, but the result of the higher resonance frequency of the several vocaltract cavities is to alter substantially the relative amplitudes of the voice spectrum components andharmonics thus leading to a significant voice timbre change and also an apparent pitch change.

*** 6.9 What is structural acoustics?

Structural acoustics is concerned with the coupled dynamic response of elastic structures in contact withnon-flowing fluids into which vibrations or sound is consequentially emitted. Conversely, sound in the fluid canexcite vibrations in the structure.

The fluid, although non-flowing, undergoes small amplitude vibration relative to some equilibrium position.) Forheavy fluids like water, the coupling is two-way, since the structural response is influenced by the fluidresponse, and vice versa. For lighter fluids like air, the coupling may be either one-way (where the structuralvibration affects the fluid response, but not vice versa) or two-way (as occurs, for example, in the violin.

Structural acoustics problems of interest involving water include the vibration of submerged structures,acoustic radiation from mechanically excited, submerged, elastic structures; acoustic scattering fromsubmerged, elastic structures (e.g., sonar echoes); acoustic cavity analysis; and dynamics of fluid-filledelastic piping systems. These problems are of interest for both time-harmonic (sinusoidal) and generaltime-dependent (transient) excitations. Water hammer in pipes can be thought of as a transient structuralacoustics problem.

Structural acoustics problems of interest involving the air medium include determining and reducing noiselevels in automobile and airplane cabins.

Reference (for simple geometry problems): "Sound, Structures, and Their Interaction," Second Edition, byM.C. Junger and D. Feit, MIT Press, Cambridge, Mass (1986).

*** 6.10 What is the doppler effect?

When a sound source is moving, a stationary observer will hear a frequency that differs from that which isproduced by the source. The doppler effect will be noticed as a marked drop in pitch when a vehicle passesat high speed. An interesting fact is that doppler for any straight line movement always sweeps down inpitch!

If one approaches a sound source by moving toward it with a velocity, v, the frequency of the sound heard isF=Fo(c+v)/c, where Fo is the emitted sound frequency, c is the speed of sound in still air and v is the speedof the observer or the moving source. if one moves away from a sound source, the sign of v is reversed.

But for an approaching sound source, the frequency of the sound heard is F=Fo*c/(c-v). For a recedingsource the sign of the velocity, v, term is reversed.

The speed of sound in air is approximately 340 m/s (see 2.11).

Example 1: A sound source, S, emits 1000 waves per second (1 kHz) and is moving directly towards anobserver, O, at a speed of 100 metres per second (equivalent to approximately 225 miles per hour).

After 1 second the wave front, which is traveling at the speed of sound, will have traveled 340 metres from theoriginal source position. Also after that second the sound source will have moved 100 metres towards theobserver.

0 m 340 m

S | | | | | | | | | Obs.

<-------------- 1000 waves ------------------>

100 m 340 m

S | | | | | | | | | Obs.

<------- 1000 waves --------->

Therefore the same number of waves will occupy a space of 340-100 = 240 metres and the wavelength will be240/1000 = 0.24 metres. To the observer the frequency heard will be the speed of sound divided by itswavelength = 340/0.24 = 1416.7 Hz.

Example 2: An observer moving at 100 metres per second directly approaches a stationary sound source, S,which is emitting 1000 waves per second (1 kHz). In this example there is no change in wavelength. In onesecond, the observer will hear the number of waves emitted per second plus the number of waves which s/hehas passed in the time (1000+100/0.34) = 1294.1 Hz.

Note the interesting result - a stationary observer with moving source will not hear the same frequency as awould a moving observer with a stationary source.

Interesting corollaries are that if one is confined to movement velocities equal to or less than the speed ofsound, on approaching a sound source, one will observe frequencies up to only twice the radiating frequency,but if one is stationary and approached by a sound source, there is no upper frequency limit.

Thought teaser: Apply these principles to light, aether, red shift and quasars. What would cause a "blueshift"?

*** 6.11 What is white noise, pink noise?

The power spectral density of white noise is independent of frequency. There is the same amount of energywithin any two different but identically sized frequency intervals. E.g. 84-86Hz and 543-545Hz. A narrow bandFFT analysis of white noise will show as flat. However octave band analysis will show the level to rise by 3dBper octave because each band has twice the frequency range of the preceding octave.

Pink noise is produced by filtering white noise to have the same power within each octave. Narrow band

analysis will show a fall in level with increasing frequency, but third-octave band or octave band analysisresults will be "flat".

See Joseph S. Wisniewski's Colors of noise FAQ at:- http://capella.dur.ac.uk/doug/noisecols13.txt

*** 6.12 When should stranded wire be used for audio cables in aPA system? What is the "electrical skin effect"?

Q:Tim <2207leung@hknet.com> wrote: When should solid core or stranded audio cables be used in thepublic addressing system that broadcasts an audio with sound bandwidth 7kHz? Any reasons for thechoice?

A: Art Ludwig - aludwig@silcom.com - provided the following answer and analysis:

For higher audio frequencies, the "skin effect" in practical conductors forces the current to be close to thesurface. This increases the effective resistance of that wire. The "Skin depth" - for planar geometry and wirediameters much larger than this depth - is where the ac current diminishes to 1/e of the surface value. Roundwire conductors should be less than three times that planar skin depth in diameter for there to be a "small"effect.

One way to circumvent the problem is to use stranded wire, each stand insulated from the other and woven ina special pattern that varies the radius and thus the magnetic linkage. This is called "Litz wire".

Audio designers may bundle several smaller gauge insulated wires, stranded or solid, to form a largercapacity conductor with minimal skin effect. Also, thinner or stranded wire has a nice flexibility andworkability.

The skin depth, delta, is given by: delta = a/sqrt(f) where delta is in meters, f in Hertz. The constant, a, is.0642 for silver, .0660 for copper, .0826 for aluminum, .127 for brass, and .185 for a representative solder. Myreference is "Fields and Waves in Communications Electronics," Ramo, Whinnery, and Van Duzer, Wiley,1965, page 289.

It is important to note that for a wire diameter comparable to the skin depth, The current does not fall offnearly as rapidly as for the planar case. The Bessel function solution must be used to get reasonableaccuracy. >From the same reference, define T=sqrt(2/j)/delta. The current in a cylindrical conductor isproportional to J0(Tr) where J0 is the Bessel function of order zero, and r is the radius. For a wire 3.2 skindepths in diameter, the current at the skin depth is 73% that at the surface, and it is not much lower at thecenter. (For a planar surface, current at the skin depth is only 37% of that at the surface and drops furtherwith depth.) The table below indicates the increase of resistance and inductance caused by the skin effect fora single strand of solid copper wire 20,000 Hz. The values of resistance and inductive reactance are given asfractions of the DC resistance. The results are a function of the wire radius in skin depths, so the results canbe scaled to other frequencies by scaling the diameter by sqrt(20000/freq)

AWG diameter(in.) Resistance Ratio Inductive Reactance Ratio

8 .1285 2.02 1.72

10 .1019 1.65 1.34

12 .0808 1.35 1.00

14 .0641 1.17 .70

16 .0508 1.07 .46

18 .0403 1.03 .30

(Ed. Notes: 1-Lowering the frequency increases the effective diameter at which each ratio cited applies. Vizthe 18 gauge 20 kHz effect would be the same for a wire of diameter 0.0641 (14 gauge) at 8 kHz.)

2-From the coefficient, a, it is apparent that: Silver conductors will perform about the same as copper

conductors. The skin depth is about 25% greater in aluminum (0.0826 vs 0.0660) so that for instance therelative skin effect in #12 aluminum wire is the same as in #14 copper wire. For brass and solder, the skindepth is double that of copper or silver.)

Art Ludwig concludes with: "Litz wire - a bundle of woven insulated wires - is designed to reduce the skineffect. Ordinary stranded wire will not help since the wire strands are in electrical contact and tend to stay atthe same radius from the center.

"My web site contains a Glossary including entries on skin effect and Litz wire, in addition to other sounddata. The address is http://www.silcom.com/~aludwig

"A Matlab program is available (Requires Matlab 5) for computing skin depth effects, current density, effectiveresistance, etc., etc. for cylindrical copper wires of any diameter and at any frequency. Easily changed forother conductors. It is available on request from aludwig@silcom.com .

7] INDEXA-Weighting 2.4 2.12 8.1 8.2 absorption coefficient 4.1 4.2 absorption coefficients, Table of 8.3 accelerometer 3.1 acoustic energy 2.1 2.8 2.10 4.1 4.3 Acoustical Society of America 2.4 http://asa.aip.org/ active noise control 6.1 active vibration control 3.3 addition of sound 2.5 air absorption 2.9 ANC 6.1 atmospheric attenuation 2.9 atmospheric pressure 2.1 2.11 audibility 2.1 2.12 auralization 1.3 C-Weighting 8.2 column speaker 6.3 concert pitch 6.6 dB(A) 2.4 8.1 decibel (dB) 2.2 2.3 2.4 Doppler effect 6.10 dynamic vibration absorber 3.3 ear 2.1 2.2 2.6 2.7 http://oto.wustl.edu/cochlea/ elastic structures 6.9 equal temperament 6.6 6.7 equivalent continuous sound level 2.4 focusing sound 6.3 frequency 2.1 2.4 2.12 6.6 6.7 hearing conservation 2.7 http://www.globaldialog.com/~nhca/index.html hearing damage 2.6 2.7 Helmholtz resonator 6.5 historical notes 2.4 2.12 insulation 4.3 4.4 4.5 interference 6.3 interval (music) 6.6 6.7 inverse square law 2.9 just intonation 6.7 Leq 2.4 logarithmic scale 2.2 2.3 loudness 2.1 2.2 2.12 loudspeaker 2.1 6.3 longitudinal wave 2.1 Lw 2.10 major and minor keys 6.7

masking 2.12 mel 6.6 musical scale 6.6 6.7 ocean sound velocity 2.11 octave 6.6 6.10 PA cable 6.12 pascal 2.1 2.2 2.8 passive noise control 6.1 6.5 peak level 2.3 phon 2.12 physical constants http://physics.nist.gov/PhysRefData/contents.html Pierce, George W 2.4 pink noise 6.11 pitch 6.6 6.8 resonance 6.5 6.8 reverberation time 4.1 Sabine, Wallace C 4.1 semi-tone 6.6 6.7 skin effect 6.12 sone 2.12 sonic boom 6.2 sonoluminescence 6.4 sound 2.1 sound absorption 4.1 4.2 4.3 sound cancellation 6.1 sound decay 2.9 sound insulation 4.3 4.4 4.5 sound intensity 2.2 2.8 sound intensity meter 2.8 sound level 2.4 2.5 2.12 sound level meter 2.3 2.4 2.8 2.12 sound power level 2.10 sound pressure 2.1 2.2 sound pressure level 2.3 2.4 2.5 speech 6.6 6.8 speaker 2.1 6.3 speed of sound 2.1 2.11 6.8 6.11 structural acoustics 6.9 supersonic 6.2 tapping machine 4.4 third-octave band 8.2 tinnitus 2.6 2.7 U-Weighting 8.2 ultrasound 2.9 ultrasound scans 2.7 velocity of sound 2.1 2.11 6.8 6.10 vibration & Seismic (3.4) 2.1 2.7 3.1 3.2 vibration control 3.3 voice 6.6 6.8 wave 2.1 weighting 2.4 2.12 8.1 white finger 2.7 white noise 6.11

8] Weighting Tables*** 8.1 A-Weighting

A-Weighting can be found from the following formulae

For A-Weighting: A(f) =

12200^2 f^4

------------------------------------------------------------------

(f^2 +20.6^2) (f^2 +12200^2) (f^2 +107.7^2)^0.5 (f^2 +737.9^2)^0.5

The weighting in dB relative to 1000Hz is now given by

A(f)

20 lg ------- where A(1000) = 0.794

A(1000)

It is convenient to list A-Weighting at nominal octave or 1/3-octave ("third-octave") frequencies, for example1250 Hz or 2500 Hz. Ideally weightings should be calculated for the exact frequencies which may bedetermined from the formula 1000 x 10 (̂n/10), where n is a positive or negative integer. Thus the frequencyshown as 1250 Hz is more precisely 1258.9 Hz etc.

At these precise frequencies, the A- and C-Weighting values are as follows:

*** 8.2 A, C & U Weighting Table (dB) Nominal Exact

Frequency Frequency A-Weight C-Weight U-Weight

(4)* *

10 10.00 -70.4 -14.3 0.0

12.5 12.59 -63.4 -11.2 0.0

16 15.85 -56.7 - 8.5 0.0

20 19.95 -50.5 - 6.2 0.0

25 25.12 -44.7 - 4.4 0.0

31.5 31.62 -39.4 - 3.0 0.0

40 39.81 -34.6 - 2.0 0.0

50 50.12 -30.2 - 1.3 0.0

63 63.10 -26.2 - 0.8 0.0

80 79.43 -22.5 - 0.5 0.0

100 100.00 -19.1 - 0.3 0.0

125 125.9 -16.1 - 0.2 0.0

160 158.5 -13.4 - 0.1 0.0

200 199.5 -10.9 0.0 0.0

250 251.2 - 8.6 0.0 0.0

315 316.2 - 6.6 0.0 0.0

400 398.1 - 4.8 0.0 0.0

500 501.2 - 3.2 0.0 0.0

630 631.0 - 1.9 0.0 0.0

800 794.3 - 0.8 0.0 0.0

1000 1000.0 0.0 0.0 0.0

1250 1259 + 0.6 0.0 0.0

1600 1585 + 1.0 - 0.1 0.0

2000 1995 + 1.2 - 0.2 0.0

2500 2512 + 1.3 - 0.3 0.0

3150 3162 + 1.2 - 0.5 0.0

4000 3981 + 1.0 - 0.8 0.0

5000 5012 + 0.5 - 1.3 0.0

6300 6310 - 0.1 - 2.0 0.0

8000 7943 - 1.1 - 3.0 0.0

10000 10000 - 2.5 - 4.4 0.0

12500 12590 - 4.3 - 6.2 - 2.8

16000 15850 - 6.6 - 8.5 -13.0

20000 19950 - 9.3 -11.2 -25.3

25000 25120 -37.6

31500 31620 -49.7

40000 39810 -61.8

* There is some reason to believe that a very low frequency rollover frequency of 4 Hz may be appropriate forinstruments that are to be used to measure sound affecting humans.

===========================================================

*** 8.3 Table of Absorption Values SOUND ABSORPTION COEFFICIENTS: COMMON BUILDING MATERIALS\\

Values accumulated circa 1990-2003, various sources /Material\\\--->OctaveBands 125 250 500 1000 2000 4000 NRC ------------------CEILINGS---------------------------------------- IntCell K-13 5/8" 0.05 0.16 0.44 0.79 0.90 0.91 0.57 IntCell K-13 1.0" 0.08 0.29 0.75 0.98 0.93 0.96 0.74 DrywallGypsm,1/2",Nailed/2x4, 0.29 0.10 0.05 0.04 0.07 0.09 0.07 Treated(abs.Face)WallPanel 0.30 0.12 0.22 0.27 0.30 0.40 0.23 Fiss/Pntd5/8 0.07 0.22 0.81 0.76 0.58 0.43 0.59 Armstrong Minatone Celtic 0.1 0.33 0.40 0.47 0.77 0.84 0.71 0.62 ArmstrongFissuredFireguard#7 0.38 0.41 0.50 0.77 0.87 0.87 0.64 ArmsCortyegaMinatone 0.44 0.30 0.46 0.63 0.74 0.77 0.53 Armstrong Ultima RH90 0.32 0.34 0.76 0.87 0.86 0.84 0.71 CAPAUL HD-90, #7 MOUNT 0.84 0.94 0.69 0.88 1.00 1.00 0.88 SAME, EST # 4 MOUNT 0.12 0.31 0.74 0.98 0.99 1.00 0.76 1.25"C-4CelotexFurdPerfPaint 0.25 0.58 0.99 0.75 0.58 0.50 0.73 Ceil'gBafl1.5"thk,each16SqFt 0.12 0.40 0.70 0.95 0.90 0.95 0.74 Armstrong Cortega CAC35 0.30 0.31 0.48 0.75 0.75 0.70 0.57 Kinetics PAB Sabines/2x4 unit 2.10 5.00 9.90 14.5 15.2 15.6 11.15 54"Velour28ozSqYd 0.23 0.62 1.00 1.0 1.1 1.30 0.93

-------------STRUCTURAL WALLS:------------------------------------ Brick Wall, Unpainted, 18"thk 0.02 0.02 0.03 0.04 0.05 0.05 0.04 Brick Wall, Painted , " 0.01 0.01 0.02 0.02 0.02 0.02 0.02 Concrete Block, Coarse (Unpai 0.36 0.44 0.31 0.29 0.39 0.25 0.36 Concrete Block, Painted 0.10 0.05 0.06 0.07 0.09 0.08 0.07 Drapes,10ozVelour,HungFlatOnW 0.04 0.05 0.11 0.18 0.30 0.35 0.16 " 14 oz 0.05 0.07 0.13 0.22 0.32 0.35 0.19 " 18 oz 0.05 0.12 0.35 0.48 0.38 0.36 0.33 " Pleated to Half Area, 14 o 0.07 0.31 0.49 0.75 0.70 0.60 0.56 " 18 oz 0.14 0.35 0.55 0.75 0.70 0.60 0.59 Drywall, 1/2" 0.29 0.10 0.05 0.04 0.07 0.09 0.07 Plaster:Gyp,Lime,Smooth/Tile, 0.01 0.02 0.02 0.03 0.04 0.05 0.03 " :Gypsum or Lime, on Lath 0.14 0.10 0.06 0.05 0.04 0.03 0.06 " : Same with 3/8" Plywood P 0.28 0.22 0.17 0.09 0.10 0.11 0.15 Plaster on Hollow Tile Blocks 0.02 0.02 0.02 0.03 0.04 0.04 0.03 Plaster,Gyp,MetalLath/WoodStu 0.04 0.04 0.04 0.06 0.06 0.03 0.05 Plaster, Lime on Metal Lath, 0.04 0.05 0.06 0.08 0.04 0.06 0.06 Plaster on Wood Wool 0.40 0.30 0.20 0.12 0.10 0.10 0.18 Plaster, Fibrous, 2" thk 0.35 0.30 0.20 0.55 0.10 0.04 0.29 Poured Concrete, Unpainted 0.01 0.01 0.02 0.02 0.02 0.03 0.02 " Painted 0.01 0.01 0.01 0.02 0.02 0.02 0.02

------PRACTICAL WALL TREATMENTS:---------------------------------- 1/4"Cork/Drywall(Simulation) 0.02 0.03 0.08 0.18 0.45 0.63 0.19 1"Tect 15x15,FAB-TUF Blocks,2 0.10 0.14 0.30 0.57 0.58 0.57 0.40 1" TECTUM, FLUSH, A-(OLD#4) 0.06 0.13 0.24 0.45 0.82 0.64 0.41 1.5"Tectum,Flush, A-(Old#4) 0.07 0.22 0.48 0.82 0.64 0.96 0.54 1"Tectum,Flush,"FABRI-TOUGH"( 0.07 0.13 0.28 0.59 0.91 0.75 0.48 1"TectmC-20(3/4"Fur)"FAB-TUF" 0.12 0.18 0.44 0.83 0.82 0.85 0.57 1"TECT:C-40+R-8ins 0.40 0.84 1.18 0.84 0.94 0.88 0.95 1"TectmC-40(8_FG)"FABRI-TOUGH 0.37 0.72 1.03 0.96 0.82 0.96 0.88 1"Tectm-#7Mnt+R11FG 0.93 0.86 0.91 0.82 0.94 0.97 0.88 2"Tectum 0n 3/4" Sleeper Only 0.13 0.20 0.50 0.70 0.58 0.72 0.50 2"Tectum 0n 1-1/2"+Ins 0.42 0.89 1.19 0.85 1.08 0.94 1.00 2" PERF METAL FACE, #4 MOUNT 0.80 0.61 0.96 0.93 0.77 0.86 0.82 4" PERF METAL FACE, #4 MOUNT 0.76 0.99 0.99 0.99 0.99 0.84 0.99 ArmstrongSonotrol 10S(AntAbus 0.09 0.36 0.84 0.99 0.99 0.93 0.80 AmstrgSonotrol 11H(ImpctRes) 0.21 0.53 0.97 1.04 1.01 0.97 0.89 AmstrgSonotrol 10F(VaprBarr) 0.23 0.69 0.61 0.64 0.47 0.35 0.60 AmstrgSonotrol 20S(Standard) 0.40 0.97 1.16 1.08 1.01 1.00 1.06 ARMSRONG TRAVERTONE #7 MOUNT 0.45 0.50 0.56 0.78 0.77 0.91 0.65 Armstrong Soft-Look (C-Mount) 0.40 0.34 0.67 0.93 0.90 0.81 0.71 Armstrong Sanserra 3/4" #1Mtg 0.09 0.25 0.70 0.85 0.83 0.89 0.66 Kinetics Panels, 1-3/4" 0.26 0.31 0.86 1.13 1.03 0.85 0.83 Kinetics Panels, 2-3/4" 0.32 0.82 1.21 1.10 1.02 1.05 1.04 Kinetics 1/2" 'HARDSIDE' 0.06 0.13 0.48 0.91 0.94 0.76 0.62 Kinetics 1" 'HARDSIDE' 0.10 0.46 0.93 1.09 1.02 0.85 0.88 Kinetics 1.5" 'HARDSIDE' 0.15 0.82 0.99 1.03 0.97 0.90 0.95 Kinetics 2" 'HARDSIDE' 0.39 0.98 1.15 1.09 1.00 1.00 1.06 Soundblox, Type "A"(Bare) 0.62 0.84 0.36 0.43 0.27 0.50 0.48 Sound Blocks Type "BR" 8"+- 0.70 0.77 0.61 0.48 0.44 0.41 0.58 Soundblox, Type "Q"(120Hz) 1.07 0.57 0.61 0.37 0.56 0.55 0.53 Soundblox, Type "R"(BdBnd) 0.39 0.99 0.65 0.58 0.43 0.45 0.66 12"Wd,3/4"tk,1/2"Slt/2" FG 0.15 0.52 0.87 0.45 0.15 0.04 0.50 8"Wd,3/4"tk,1/2"Slt/2" FG 0.15 0.50 0.85 0.50 0.17 0.06 0.51 6"Wd,3/4"tk,1/2"Slt/2" FG 0.14 0.35 0.65 0.80 0.40 0.20 0.55 WallTechA108wp 0.13 0.40 0.88 1.08 1.07 1.03 0.86 WallTechA208wp 0.42 0.90 1.23 1.21 1.00 1.08 1.09 WallCovering, Generic 0.05 0.06 0.16 0.20 0.20 0.28 0.16 Almute by "PEER",2"+F.G. 0.36 0.86 1.13 1.06 0.90 0.71 0.99 RULON.Pln.SltWood 0.40 0.50 0.36 0.45 0.33 0.27 0.41 RULON.Ins.SltWood 0.79 0.86 0.98 0.88 0.59 0.49 0.83

-----------------FIBERGLASS, Generic------------------------------ 1" Duct Liner Board 1.5 pcf 0.23 0.54 0.68 0.83 0.92 0.89 0.74 2" Duct Liner Board 1.5 pcf 0.42 0.83 1.02 1.05 1.04 0.48 0.99 R-6 = 2" (4'or 6'x125' rolls) 0.31 0.58 0.86 0.81 0.83 0.85 0.77 R-8 = 2-1/2" (Thinnest common 0.33 0.68 0.96 0.95 0.95 0.99 0.89 R-11 = 3-1/2" est 0.40 0.70 0.96 0.96 0.98 0.99 0.90 R-13 3-5/8" est 0.50 0.80 0.97 0.98 0.99 0.99 0.94

R-19 = 6 " est 0.60 0.85 0.98 0.98 0.99 0.99 0.95 R-25 = 8" est 0.70 0.88 0.98 0.99 0.99 0.99 0.96 R-30 9" (2'x4' Batts)est 0.75 0.90 0.99 0.99 0.99 0.99 0.97 B-38 12" (2'x4' Batts)est 0.80 0.95 0.99 0.99 0.99 0.99 0.98 Lay-in (#7 Mount, Typical) 0.75 0.75 0.80 0.85 0.80 0.70 0.80 '3/4" F-glassPanel, Est. 0.09 0.09 0.46 0.78 0.77 0.80 0.53 Fiberglass, 1" 0.23 0.50 0.73 0.88 0.91 0.97 0.76 Fiberglass Batting, 4" 0.80 0.99 0.99 0.99 0.99 0.95 0.99

-----------------CURTAINS----------------------------------------- 0.04psf polyester @ 30" 0.28 0.22 0.34 0.45 0.55 0.71 0.39 0.04psf polyester @ 6" 0.02 0.22 0.50 0.50 0.52 0.65 0.44 0.12psf polyester @ 30" 0.42 0.43 0.64 0.75 0.86 0.93 0.67 0.12psf polyester @ 6" 0.17 0.46 0.63 0.80 0.76 0.78 0.66 0.194psf DblLayer Nomex @ 30" 0.53 0.57 0.82 1.05 1.30 1.53 0.94 0.194psf DblLayer Nomex @ 6" 0.23 0.62 1.00 1.00 1.10 1.30 0.93

-----------------WINDOWS------------------------------------------ GlasWindws, Heavy Plate Glass 0.18 0.06 0.04 0.03 0.02 0.02 0.04 " Ordinary Window Galss 0.35 0.25 0.18 0.12 0.07 0.04 0.16 GypDwll,1/2",Nailed/2x4,16"oc 0.29 0.10 0.05 0.04 0.07 0.09 0.07 Marble or Glazed Tile 0.01 0.01 0.01 0.01 0.02 0.02 0.01 Openings, Stage,0.25 to 0.75 0.25 0.35 0.45 0.55 0.65 0.75 0.50 Opngs,DeepBalc.,UphSeats 0.50 0.60 0.70 0.80 0.90 1.00 0.75 Grilles, Vents 0.15 0.25 0.30 0.40 0.50 0.50 0.36

------------FLOORS------------------------------------------------ Concrete or Terrazo 0.01 0.01 0.02 0.02 0.02 0.20 0.02 Linl,Asplt,Rubr,CrkTile/Cncr 0.02 0.03 0.03 0.03 0.03 0.02 0.03 Linl,Gyp,Rubr,Crk,3/16"/Solid 0.04 0.03 0.04 0.04 0.03 0.02 0.04 WOOD Block, Pitch Pine 0.05 0.03 0.06 0.09 0.10 0.22 0.07 WOOD, on Joist or Sleeper 0.15 0.11 0.10 0.07 0.06 0.07 0.09 PARQUET in Asphalt or Concret 0.04 0.04 0.07 0.06 0.06 0.07 0.06 Wood Platform, Space Beneath 0.40 0.30 0.20 0.17 0.15 0.10 0.21 WOOD, Solid and Polished 0.10 0.07 0.05 0.05 0.04 0.04 0.05 Carpet, Heavy, on Concrete 0.02 0.06 0.14 0.37 0.60 0.65 0.29 Crpt,Hvy/40ozHrflt orFoamRbr 0.08 0.24 0.57 0.69 0.71 0.73 0.55 Crpt/LatxBck/40ozHF orFoamRbr 0.08 0.27 0.39 0.34 0.48 0.63 0.37 Crpt,WoolPile/Undrpd, 5/8"thk 0.20 0.25 0.35 0.40 0.50 0.75 0.38 Crpt,WoolPile,/Cncrt, 3/8"thk 0.09 0.08 0.21 0.26 0.27 0.37 0.21 Water Surface (Pool) 0.01 0.01 0.01 0.02 0.02 0.03 0.01 WoodPnl,3/8-1/2",2-4"Airgap 0.30 0.25 0.20 0.17 0.15 0.10 0.19

---Pews, Seats and Chairs----------------------------------------- ORCHESTRA WOOD STICK-CHAIRS 0.02 0.03 0.04 0.04 0.04 0.03 0.04 CHAIRS, Metal or Wood, Unocc 0.02 0.03 0.04 0.07 0.07 0.07 0.05 1.5" SEAT CUSHIONS, PEW 0.20 0.30 0.34 0.34 0.32 0.28 0.33 SEATS(CHAIRS)ClothUpholstd 0.49 0.66 0.80 0.88 0.82 0.70 0.79 Chairs, Leather 0.44 0.54 0.60 0.62 0.58 0.50 0.59 Pews without people 0.14 0.12 0.10 0.26 0.32 0.40 0.20 People, Seated 0.43 0.49 0.65 0.60 0.59 0.46 0.58 WOOD PEWS, OCCUPIED 0.57 0.61 0.75 0.86 0.91 0.86 0.78 AUDIENCE,Seated,Uphlstd Chrs 0.60 0.74 0.88 0.96 0.93 0.85 0.88 PeopleOverPads 0.16 0.20 0.28 0.34 0.35 0.35 0.29

---ROOF Decking, Acoustical--------------------------------------- Vulcraft + Ins 1.5 BIA 0.51 0.95 1.00 0.98 0.62 0.27 0.89 Vulcraft + Ins: 3 NIA 0.53 1.00 1.00 0.93 0.57 0.33 0.88 RollFormB 15, 1" 0.25 0.59 1.07 0.91 0.56 0.20 0.78 RollFormB15,2" 0.52 0.96 1.00 0.91 0.61 0.30 0.87 Roll Form B15, 1" 0.14 0.35 0.77 1.00 0.75 0.47 0.72 Roll Form C33, 2" (High TL) 0.36 0.79 1.00 1.00 0.88 0.60 0.92 AlPro Slat Panls (DeepCavity) 0.37 0.69 0.97 0.93 0.92 0.93 0.88 Sheetmetal, common 0.15 0.08 0.02 0.01 0.01 0.01 0.03 Sheetmetal, Heavy 0.12 0.08 0.02 0.01 0.01 0.01 0.03

/////////ADDENDUM\\\\\\\\\\\\\////// From: Matthew_J._stead@ieaust.org.au (Matthew J. stead): Subject: Acoustic Database (re-sent message) Date: 02 Nov 1995 23:46:17 GMT Centre Octave Band Frequency 125 250 500 1000 2000 4000

alphabetic listing (UK) Acoustic plaster (SBI) 0.15 0.25 0.40 0.55 0.60 0.60 0.45 Acoustic plaster 12mm thick ( 0.10 0.15 0.20 0.25 0.30 0.35 0.23 Acoustic plaster on solid wal 0.10 0.15 0.20 0.25 0.30 0.35 0.23 Acoustic tiles on solid wall 0.15 0.42 0.65 0.72 0.70 0.60 0.62 Acoustic tiles suspended 0.40 0.50 0.70 0.77 0.80 0.75 0.69 Brick-unglazed 0.03 0.03 0.03 0.04 0.05 0.07 0.04 Brickwork (pointed) 0.05 0.04 0.02 0.04 0.05 0.05 0.04 Carpet 6mm pile bonded to ope 0.03 0.09 0.20 0.54 0.70 0.72 0.38 Carpet-indoor outdoor-foam ba 0.02 0.02 0.15 0.39 0.74 0.77 0.33 Carpet-loop pile-medium heavy 0.06 0.21 0.67 0.55 0.56 0.60 0.50 Ceramic tiles with smooth sur 0.01 0.01 0.01 0.02 0.02 0.02 0.02 Compressed mineral fibre susp 0.40 0.50 0.65 0.75 0.80 0.75 0.68 Concrete 0.01 0.01 0.02 0.02 0.02 0.03 0.02 Concrete block-course 0.36 0.44 0.31 0.29 0.39 0.25 0.36 Concrete block-painted, seale 0.10 0.05 0.06 0.07 0.09 0.08 0.07 Concrete breeze or Cinder blo 0.20 0.30 0.60 0.60 0.50 0.50 0.50 Cork tiles 25mm on solid wall 0.05 0.10 0.20 0.55 0.60 0.55 0.36 Curtains in heavy folds 0.10 0.35 0.55 0.70 0.70 0.65 0.58 Curtains in medium folds 0.05 0.15 0.35 0.55 0.65 0.65 0.43 Face brickwork 0.05 0.04 0.04 0.04 0.05 0.05 0.04 Glass (1 m2) 4 mm 0.20 0.25 0.20 0.10 0.05 0.05 0.15 Glass (1 m2) 6 mm 0.15 0.06 0.04 0.08 0.05 0.05 0.06 Glass fibre acoustic blanket- 0.18 0.65 0.95 0.95 0.95 0.95 0.88 Glass pane 4mm (average) 0.35 0.25 0.18 0.12 0.07 0.04 0.16 Glass pane 6mm (large) 0.18 0.06 0.04 0.03 0.02 0.02 0.04 Hardcord carpet on hard floor 0.02 0.03 0.05 0.10 0.30 0.50 0.12 Hardcord carpet on underfelt 0.05 0.05 0.10 0.20 0.45 0.65 0.20 Heavy carpet on concrete 0.02 0.06 0.14 0.37 0.60 0.65 0.29 Heavy curtains in folds again 0.06 0.10 0.38 0.63 0.70 0.73 0.45 Heavy pile carpet on underfel 0.07 0.25 0.50 0.60 0.70 0.70 0.51 Light curtains against solid 0.04 0.07 0.11 0.18 0.30 0.35 0.17 Linoleum or vinyl stuck to co 0.02 0.02 0.03 0.04 0.04 0.05 0.03 Marble or Glazed Tiles 0.01 0.01 0.01 0.01 0.02 0.02 0.01 Marble slabs (SBI) 0.01 0.01 0.01 0.01 0.02 0.02 0.01 Medium pile carpet on underfe 0.08 0.15 0.40 0.55 0.60 0.70 0.43 Medium pile carpet on underfe 0.11 0.14 0.37 0.43 0.27 0.25 0.30 Curtain (medium weight) 14oz/ 0.07 0.31 0.49 0.75 0.70 0.60 0.56 Mineral fibre (medium density 0.45 0.75 0.80 0.85 0.85 0.85 0.81 Mineral fibre (medium density 0.10 0.35 0.60 0.70 0.75 0.80 0.60 Mineral fibre (medium density 0.20 0.45 0.65 0.75 0.80 0.85 0.66 Occupied auditorium seats-ful 0.20 0.40 0.46 0.46 0.51 0.46 0.46 Occupied auditorium seats-woo 0.16 0.25 0.40 0.40 0.45 0.40 0.38 Occupied metal or wooden seat 0.15 0.19 0.22 0.39 0.38 0.30 0.30 Orchestra player with instrum 0.37 0.80 1.10 1.30 1.20 1.10 1.10 Painted Brickwork 0.01 0.02 0.02 0.02 0.03 0.03 0.02 People (per person) 0.10 0.20 0.35 0.30 0.30 0.30 0.29 Person in padded office chair 0.15 0.25 0.40 0.40 0.45 0.40 0.38 Plaster acoustic tile suspend 0.25 0.50 0.80 0.80 0.60 0.50 0.68 Plaster on concrete block 0.12 0.09 0.07 0.05 0.05 0.04 0.07 Plaster on solid wall 0.02 0.02 0.02 0.03 0.04 0.05 0.03 Plaster on studs 0.02 0.03 0.04 0.06 0.06 0.03 0.05 Plaster on wall 0.04 0.05 0.06 0.08 0.05 0.05 0.06 Plaster-gypsum or lime-smooth 0.14 0.10 0.06 0.04 0.04 0.03 0.06 Plasterboard as a suspended c 0.20 0.15 0.10 0.05 0.05 0.05 0.09 Plasterboard ceiling 13 mm 0.29 0.10 0.05 0.04 0.07 0.09 0.07 Plasterboard on battens 9mm 0.30 0.15 0.10 0.05 0.04 0.05 0.09 Plasterboard Partitioning (mi 0.30 0.20 0.15 0.05 0.05 0.05 0.11 Plywood 9 mm 0.28 0.22 0.17 0.09 0.10 0.11 0.15 Plywood on battens 12mm 0.30 0.20 0.15 0.10 0.15 0.10 0.15 Plywood on battens 5mm 0.40 0.35 0.20 0.15 0.05 0.05 0.19 Plywood with airspace behind 0.32 0.43 0.12 0.07 0.07 0.11 0.17 Polished marble or glazed til 0.01 0.01 0.01 0.01 0.01 0.01 0.01 Rockwool 25mm + 25mm air gap 0.40 0.90 0.80 0.63 0.68 Rockwool 25mm + 25mm air gap 0.53 0.92 0.60 0.30 0.59 Rockwool blanket 100mm 0.45 0.75 0.80 0.85 0.85 0.90 0.81 Rockwool blanket 25mm 0.10 0.35 0.60 0.70 0.75 0.80 0.60 Rockwool blanket 25mm with 10 0.15 0.30 0.75 0.85 0.75 0.40 0.66 Rockwool blanket 25mm with 5p 0.10 0.35 0.85 0.85 0.35 0.15 0.60 Rockwool blanket 50mm 0.20 0.45 0.65 0.75 0.80 0.80 0.66 Rockwool blanket 50mm with 10 0.40 0.80 0.90 0.85 0.75 0.40 0.83

Rough concrete (SBI) 0.02 0.03 0.03 0.03 0.04 0.07 0.03 Rubber floor tiles 0.05 0.05 0.10 0.10 0.05 0.05 0.08 Seated high school student 0.22 0.30 0.33 0.40 0.44 0.45 0.37 Seated primary school student 0.18 0.23 0.28 0.32 0.35 0.40 0.30 Single pane of glass-3 mm (SB 0.08 0.04 0.03 0.03 0.02 0.02 0.03 Smooth brickwork with flush p 0.02 0.03 0.03 0.04 0.05 0.07 0.04 Smooth brickwork-10 mm deep p 0.08 0.09 0.12 0.16 0.22 0.24 0.15 Smooth concrete-painted or gl 0.01 0.01 0.01 0.02 0.02 0.02 0.02 Smooth unpainted concrete (SB 0.01 0.01 0.02 0.02 0.02 0.05 0.02 Standing adult 0.12 0.24 0.59 0.98 1.13 1.12 0.74 Thin cork or Vinyl tiles on c 0.02 0.02 0.03 0.03 0.04 0.04 0.03 Tight loop pile carpet 0.05 0.05 0.08 0.15 0.25 0.45 0.13 Tile-asphalt-linoleum or conc 0.02 0.03 0.03 0.03 0.03 0.02 0.03 Timber boards on joists 0.10 0.11 0.10 0.08 0.08 0.11 0.09 Tufted pile carpet 9mm on fel 0.08 0.08 0.30 0.60 0.75 0.80 0.43 Unoccupied auditorium seats-f 0.12 0.19 0.30 0.30 0.30 0.35 0.27 Unoccupied auditorium seats-w 0.03 0.05 0.05 0.10 0.15 0.10 0.09 Unpainted Brickwork 0.02 0.02 0.02 0.04 0.05 0.05 0.03 Vinyl or hard composition flo 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Water surface (pool) 0.01 0.01 0.01 0.02 0.02 0.02 0.02 Water surface in swimming poo 0.01 0.01 0.01 0.01 0.02 0.02 0.01 Wood parquetry on solid floor 0.04 0.04 0.07 0.06 0.06 0.07 0.06 Wooden floor on joists (SBI) 0.15 0.11 0.10 0.07 0.06 0.07 0.09

9] List of National Acoustical SocietiesFor standards organizations addresses see section 1.2

Please let us know if any information in this list needs amending.

Argentina Argentina Acoustical Association

Asociacion de Acusticos Argentinos c/o Prof A. Mendez, Laboratorio de Acustica, Camino Centenario Y 506, 1897 - Gonnet, Argentina

Tel: +54 21 84 2686 Fax: +54 21 71 2721 e-mail: ciclal@gba.gov.ar

Web: http://www.eie.fceia.unr.edu.ar/~acustica/adaa/index.htm LABORATORIO DE ACÚSTICA Y ELECTROACÚSTICA: http://www.eie.fceia.unr.edu.ar/~acustica/

Australia Australian Acoustical Society

Private Bag 1, Darlinghurst, NSW 2010 Tel: +61 2 331 6920 Fax: +61 2 331 7296

Austria Austrian Acoustics Association

c/o Prof Ewald Benes, Technische Universitat Wien, Institut fur Allgemeine Physik, Wien, Austria

Tel: +43 1 58801-5587 Fax: +43 1 5864203

Belgium Belgian Acoutics Assosciation (ABAV)

Av. P Holoffe 21, 1342 Limelette, Belgium Tel: +32 2 653 88 01 Fax: +32 2 653 07 29

e-mail: bbri.lim@pophost.eunet.be

Brazil Sociedade Brasileira de Acustica

Attn Prof Samir Gerges, Universidade Federal de Santa Catarina, Departamento de Engenharia Mecanica, Campus Univeritario, C.P 476

CEP 88040-900, Florianopolis - SC, Brazil Tel: +55 48 2344074 Fax: +55 48 2341519

e-mail: gerges@mbox1.ufsc.br

Canada Canadian Acoustical Association

PO Box 1351, Station F, Toronto, Ontario, M4Y 2V9, Canada Tel: +1 514 343 7559 or +1 613 993 0102

Chile Sociedad Chilena de Acustica

San Francisco # 1138, Santiago, Chile . Tel/Fax: +56 2 555 63 66 or +56 2 551 79 20

e-mail: acusticos@entelchile.net with copy (Cc) to: crooke@cmet.net

China (PRC) Acoustical Society of China

17 Zhongguancun St., Beijing 100080, China

Czech Republic Czech Acoustical Society

Technicka 2, 166 27 Prague 6, Czech Republic. Tel: +420 2 24352310 Fax: +420 2 3111786

e-mail: csas@feld.cvut.cz

Denmark Acoustical Society of Denmark

c/o Department of Acoustic Technology, Bldg. 352 - Technical University of Denmark, DK-2800 Lyngby, Denmark Tel: +45 4588 1622 Fax: +45 4588 0577

e-mail: atc.das@dat.dtu.dk

Finland Acoustical Society of Finland

c/o Helsinki University of Technology, Acoustics Laboratory, Otakaari 5 A, FIN-02150 Espoo, Finland

Tel: +358 9 451 2499 Fax: +358 9 460 224 e-mail: akustinen.seura@hut.fi

France French Acoustical Society

Societe Francaise d'Acoustique 23 avenue Brunetiere, 75017 Paris, France

Tel +33 1 48 88 90 59 Fax: +33 1 48 88 90 60 e-mail: sfa@cal.enst.fr

Germany German Acoustical Society

Deutsche Gesellschaft fur Akustik c/o Department of Physics Acoustics, University of Oldenburg,

D-26111 Oldenburg, Germany Tel: +49 441 798 3572 Fax: +49 441 798 3698

e-mail: dega@aku.physik.uni-oldenburg.de

Greece Hellenic Acoustical Society

Patision 147, 112 51 Athens, Greece Tel or Fax: +30 1 8646 065

Hong Kong Hong Kong Institute of Acoustics

PO Box 7261 Hong Kong

Fax: +852 2886 3777 e-mail: hkioa@hk.super.net

Hungary Scientific Society for Optics, Acoustics... (OPAKFI)

Fo utca 68, H-1027 Budapest, Hungary Tel/Fax: +36 1 202 0452

e-mail (c/o Andras Illenyi): illenyi@sparc.core.hu

India Acoustical Society of India

c/o Dr S Agrawal, CEERI Centre, CSIR Complex, Hillside Road, New Delhi-110012, India

Tel: +91 11 5784642 e-mail (c/o National Physical Lab): Agrawals%npl@sirnetd.ernet.in

Italy Associazione Italiana di Acustica Istituto di Acustica "O.M. Corbino"

Area della ricerca di Roma Tor Vergata Via del Fosso del Cavaliere

00133 Roma Italy Tel. +39 6 49934480 (ask Mrs. Cappelli)

Fax: +39 6 20660061 E-mail: aia@idac.rm.cnr.it

Japan Acoustical Society of Japan

Nippon Onkyo Gakkai 4th Floor, Ikeda Building, 2-7-7 Yoyogi, Shibuya-ku, Tokyo, Japan

Tel: +81 3 3379 1200 Fax: +81 3 3379 1456

Korean Republic The Acoustical Society of Korea,

c/o 302-B, The Korean Federation of Science and Technology, 635-4, Yeoksam-dong, Kangnam-gu, Seoul-city, 135-080, Rep. of Korea

Tel: +82 2 565 1625 Fax: +82 2 569 9717

Mexico Mexican Institute of Acoustics Instituto Mexicano de Acustica

c/o Sergio Beristain, P.O. BOX 75805, Col. Lindavista 07300 Mexico, D.F.

Tel +52 5 682 28 30 Fax: +52 5 523 47 42 e-mail: SBERISTA@vmredipn.ipn.mx

Netherlands Netherlands Acoustical Society

Nederlands Akoestisch Genootschap Postbus 162, NL-2600 AD, Delft, Netherlands Tel: +31 15 26 92 442 Fax: +31 15 26 92 111

e-mail: nag@tpd.tno.nl

New Zealand New Zealand Acoustical Society

c/o J. Quedley, CPO Box 1181, Auckland, New Zealand Tel: +64 9 623 3147 Fax: +64 9 623 3248

e-mail: mms@bitz.co.nz

Norway Acoustical Society of Norway

Norsk Akustisk Selskap Sintef Telecom and Informatics, N-7034 Trondheim, Norway

Tel: +47 73 59 26 45 Fax: +47 73 59 14 12

e-mail: truls.gjestland@informatics.sintef.no

Peru Acoustical Society of Peru

Sociedad Peruana de Acustica Garcilazo de la Vega 163, Salamanca de Monterrico, Lima 3, Peru

Tel: +51 1 4351151 Fax: +51 1 4675625 e-mail: cjim@mail.cosapidata.com.pe

Poland Polish Acoustical Society

Polskie Towarzystow Akustyki Instytut Akustyki, Uniwersytet Adama Mikiewicz, ul J.Matejki 48/49,

60-769 Poznan, Poland Tel or Fax: +48 61666 420

e-mail: ula@phys.amu.edu.pl

Portugal Portuguese Acoustical Society

SPA - CAPS/Instituto Superior Tecnico, Av. Rovisco Pais 1096 Lisboa CODEX, Portugal

tel: +351 1 841 9393/39 fax: +351 1 352 3014 e-mail: capsist@alfa.ist.utl.pt

Romania Romanian Acoustical Society

Societatea Romana de Acustica c/o Nicolae Enescu, Universitatea Politehnica Bucuresti, Splaiul Independentei nr. 313, 77206 Bucuresti, Romania

Tel: +40 1 4101615 Fax: +40 1 4104488 e-mail: enescu@cat.mec.pub.ro

RussiaEast-European Acoustical Association (http://webcenter.ru/~eeaa/)

44, Moskovskoe Shosse, Saint Petersburg, 196158, RussiaFax: +7 (812) 1279323e-mail: eeaa@online.ru

Russian Acoustical Society 4 Shvernik ul, Moscow, 117036 Russia

Tel: +7 095 126 7401 Fax: +7 095 126 8411 e-mail: bvp@asu.acoins.msk.su

Singapore Society of Acoustics Singapore

c/o W Gan, Acoustical Services Pte Ltd 209-212 Innovation Centre, NTU Nanyang Ave, Singapore 639798

Fax +65 791 3665 e-mail: wsgan@singnet.com.sg

Slovakia Slovak Acoustical Society

c/o Prof Stefan Markus, Racianska 75, PO Box 95, 830 08 Bratislava 38, Slovakia

Tel: +421 7 254751 Fax: +421 7 253301 e-mail: markus@umms.savba.sk

South Africa South African Acoustics Institute

c/o John R. Hassall Acoustics, Noise and Vibration Consultancy

Email: jhassall@pixie.co.za Tel: +27 11 403 1163

Spain Spanish Acoustical Society

Sociedad Espanola de Acustica Serrano 144, E-28006 Madrid, Spain

Tel: +34 1 5618806 Fax: +34 1 4117651 e-mail: a.perezlopez@mad.servicom.es

Sweden Swedish Acoustical Society

Svenska Akustiska Sallskapet c/o Ingemansson AB, Box 47 321

S-100 74 Stockholm, Sweden Tel: +46 8 744 5780 Fax: +46 8 18 26 78

e-mail: sas@ingemansson.se

Switzerland Schweizerische Gesellschaft fur Akustique

Societe Suisse d'Acoustique Postfach 251, 8600 Dubendorf

Tel: +41 1 823 4743 Fax: +41 1 823 4793 e-mail: kurt.heutschi@empa.ch

Turkey Turkish Acoustical Society - TAS

Y.T.U. Mimarlik Fakultesi Yildiz, 80750, ISTANBUL/TURKEY Tel: +90 212 259 70 70 ext: 2772

Fax: +90 212 26105 49 e-mail: takder@ana.cc.yildiz.edu.tr

UK Institute of Acoustics

5 Holywell Hill, St Albans, Herts, AL1 1EU, UK Tel: +44 1727 848195 Fax: +44 1727 850553

e-mail: Acoustics@clus1.ulcc.ac.uk

USA Acoustical Society of America

500 Sunnyside Blvd., Woodbury, NY 11797, USA Tel: +1 516 576 2360 Fax: +1 516 576 2377

e-mail: asa@aip.org

10] FAQ Contributors

** Andrew Silverman* Angelo Campanella a.campanella@att.net

Michael Carley Gordon Everstine Johan L Nielsen Torben Poulsen Larry Royster

Chris Ruckman Asbjoern Saeboe Jesper Sandvad

** Originator and original architect of this acoustics FAQ file!

* Acoustics FAQ file Editor January 1998 ff

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