1Architectural Board Exam Reviewer

ARCHITECTURAL ACOUSTICScompiled & edited by Arch. Jenaro A. Villamor, uap

Definitions of ACOUSTICS:1. branch of physics concerned with sound2. deals with the production, control, transmission, reception, and effects of sound

Almost all acoustical situations are described in 3 parts (elements):1. Sound Source ( e.g. human speech, HVAC equipment)2. Transmission Path (e.g. air, earth, building materials)3. Receiver (e.g. humans, animals, sensitive medical equipment)

ARCHITECTURAL ACOUSTICS1. technology of designing spaces, structures and mechanical systems to meet hearing needs2. effect of building design on the control of sound in buildings

3 Aspects of Acoustical Design in Buildings1. Planning to keep noise sources as far as possible from quiet area2. Internal acoustics of rooms3. Structural precautions to reduce noise penetrations

Essential Elements of Architectural Acoustics:1. Room Acoustics the qualities or characteristics of a room, auditorium, or concert hall that determinethe audibility of speech or fidelity of musical sound in it Cubic volume (and coupled spaces) Shape and proportion (length-to-width, height-to-width) Finishes (selection and placement) Audience layout ( floor slope, speaker-to-listener distances) Special treatment ( suspended reflectors, resonant absorbers, quadratic-residue diffusers)

2. Sound Isolation the use of building materials and construction assemblies designed to reduce thetransmission of airborne and structure-borne sound from one room to another or from the exterior to theinterior of a building (Sound Insulation) Site noise characteristics (sound level, character, duration) Outdoor barriers, nearby buildings, vegetation, and earth berms Location of activities within buildings (zoning, buffer spaces) Background noise criteria (HVAC system, electronic)

3. Mechanical system noise and vibrations Equipment noise characteristics Location of mechanical equipment Vibration isolation ( springs, pads) Air duct and pipe treatment ( linings, mufflers, laggings) Background noise from air outlets (coordination with sound isolation)

24. Electronic sound systems System compatibility with room acoustics Loudspeaker selection, placement and orientation System components and controls Background masking (loudspeaker layout, sound spectra)

Definitions of SOUND1. physical wave in an elastic medium, usually air2. the sensation stimulated in the organs of hearing by mechanical radiant energy transmitted aslongitudinal pressure waves through the air or other medium3. a vibration in an elastic medium such as air, water, most building materials, and the earth4. physically, sound is a rapid fluctuation of air pressure

Types of Sound1. Wanted Sound (speech, music) heard properlyo considered desirableo heard properly

2. Unwanted Sound (noise) annoyanceo annoyance or not desired or objectionable

Characteristics of Sound1. Audible2. Inaudible

Basic Principles of Sound - understanding the characteristics of sound is essential in designing for goodacoustics)

1. Generation - of sound is generated when an object vibrates, causing the adjacent air to move, resultingin a series of pressure waves radiating out from the moving object

oWave a disturbance or oscillation that transfers energy progressively from point to point in a mediumor space without advance by the points themselves, as in the transmission of sound or light

o Sound Wave a longitudinal pressure wave in air or an elastic medium esp. one producing an audiblesensation

2. Frequency - the no. of times the cycle of compression and rarefaction of air occurs in a given unit oftime (e.g. 1000 cycles in the period of 1 second = 1000 cps = 1000 Hertz)

o the no. of cycles per unit time of a wave

o oscillation - the no. of complete cycles per second (frequency of vibration)

o the rate of oscillation of molecules by sound (frequency of vibration) measured in cycles per second(Hertz)

3o Pitch frequency of sound vibration; the predominant frequency of a sound as perceived by the humanear

o Vibration the back and forth motion of a complete cycleo Cycle full circuit by a displaced particleo Period the time required for one complete cycleo 20 20,000 Hz approx. audio frequency range of human hearing;o 600 40,000 Hz critical frequency for speech communicationo Tone composed of a fundamental frequency with multiples of the fundamental, called Harmonicso Pure Tone sound composed only of 1 frequencyo Musical sounds are combination of many pure toneso Frequency bands used to express division of sounds into sections (Octave bands are the mostcommon)o 9 Octave Bands 31.5, 63, 125, 250, 500, 1000, 2000, 4000, 8000 Hz

3. Velocityo varies according to the medium of transmission; approx. 1100 fps in air at normal temperature andpressure

4. Wavelengtho Distance between similar points on successive waves; the distance the sound travels in one cycleo Relationship between wavelength, frequency, and velocity: = c/f = wavelength, ft.2c = velocity of sound, fpsf = frequency of sound, Hz (cps)o Low frequency sounds: characterized by long wavelengthso High frequency sounds: characterized by short wavelengthso Sounds with wavelengths ranging from 50 can be heard by humans

5. Magnitudeo Sound power (watts) amount of energy produced by a sourceo Intensity describes the energy level; unit is watts/cm2o Loudness (what is perceived) related to the Intensity Level (IL) or Sound Pressure Level (SPL)o The Sound Pressure Level (SPL) is equivalent to the Sound Intensity Level (IL)o Intensity Level is expressed in decibelso Decibel dimensionless unit used to express the ratio of two numerical values of a logarithmic scale

Comparison of decimal, exponential, and logarithmic statements of various acoustic intensitiesIntensity (watts/cm2) Intensity LevelDecimal Notation Exponential Notation Logarithmic Notation Examples0.001 10-3 130 dB Painful0.0001 10-4 120 dB0.00001 10-5 110 dB 75-piece orchestra0.000001 10-6 100 dB0.0000001 10-7 90 dB Shouting at 5 ft.0.000000001 10-9 70 dB Speech at 3ft.0.00000000001 10-11 50 dB Average office

40.0000000000001 10-13 30 dB Quiet unoccupied office0.00000000000001 10-14 20 dB Rural ambient0.000000000000001 10-15 10 dB0.0000000000000001 10-16 0 dB Threshold of hearing

o The fundamental relationship that determines the decibel level is ten times the logarithm to the base 10of the numerical ratio of the two intensities. For example:IL = 10 log II0IL = intensity levelI = intensity, watts/cm2I0 = reference intensity, 10-16 watts/cm246. Time Characteristics of Soundo Some sounds remain constant with time (e.g. fan may produce a sound with constant frequency andintensity characteristics a steady state sound)o Sounds (traffic, voices, musical instruments) vary as a function of timeo Vehicular traffic sounds: maximum levels/levels exceeded for 90% of the timeo Speech sounds: 1% peakso Orchestras sound: long-term average levelsBehavior of Sound in a Free Field Sound intensity is reduced to one-quarter each time the distance doubles:

I1 and I2 are the intensities at distances d1 and d2 from the source The intensity of a sound at a distance from the source is expressed as the power (P) of the sourcedivided by the area over which it has spread (A)I = P/A If the sound radiates freely in all directions from a source the area is a sphere. The intensity isrepresented as:I = P4 r2P = power in wattsr = distance from source in cmIn English units, the conversion factor is 930 cm2/ft4 r2Using this, the equation for spherical direction is:I = P/930 x 4 r2As the intensity is reduced to one-quarter with each doubling of distance, the sound pressure level (IL) isreduced by 6 dB. Quartering the intensity reduced the intensity level by 6 dB Sound attenuation is due to distance, absorption, or barriers Barriers, to be effective must be solid, quite large as compared to the wavelength of sound and near tothe source or receiver Shrubs, hedges, small groves: visual barriers only; no value acoustically Sound Combining. Sounds from separate sources may combine. Two violins produce a louder soundthan 1 instrument; 3 violins are louder still. Decibels are not added directly to make the perceived leveltwice as loud for 2 sources or 3 times as loud for 3. The level for combined sources is determined byadding powers, intensities or pressures; and subsequently converting to decibels. Doubling of intensitiesresults in a 3 dB increase (e.g. 50 dB plus 50 dB is 53 dB, not 100 dB)

5

5ROOM ACOUSTICSSound Indoors Acoustics of Room Sound in an enclosure radiates out from the source until it hits a surface that reflects or absorbs it If the source is continuous, a state of equilibrium will be reached Levels are constant throughout most spaces except at points very near the source (for a given source,the built-up or reverberant levels will be highest in a space with a few absorptive surfaces lobby withmarble walls/floors; in a space with large areas of sound absorbing materials, the levels will be lowest1. Sound Absorption Materials varying sound absorption characteristics Some absorb low frequency energy Some absorb high frequency energy Others absorb energy equally over a broad spectrum Mechanism of Absorption: 3 families of devices for sound absorption; all types absorb sound bychanging sound energy to heat energy Fibrous materials (Porous materials): absorption provided by a specific material depends on thickness,density, porosity, resistance to air flow (e.g. materials must be thick to absorb low frequency soundseffectively; suspending an acoustical ceiling tile a foot below the structure results in better broad bandabsorption than cementing the tile directly to the structure; acoustic paints with sand or walnut shellsare useless as sound absorbers Panel resonators: built with a membrane (thin plywood, linoleum in front of a sealed airspace); panel isset in motion by the alternating pressure of the impinging sound wave; sound energy is converted intoheat through internal viscous damping; used where efficient low frequency absorption is required/ midand high frequency absorption is unwanted; used in recording studios Volume resonators Coefficient of Absorption (): Knowing the amount of absorption at different frequencies for eachmaterial in a room is essential in designing the room acoustics The absorption coefficient is the fraction of incident energy that is absorbed by a surface expressed as = IaIiIi = incident energy, watts/cm2Ia= absorbed energy, watts/cm2 = absorption coefficient (no units) Total absorption (A) provided by a surface (S) is expressed in sabinsA = SA = Total absorption, sabinsS = Surface area, sq ft = Coefficient of absorption

6Coefficients of General Building Materials and FurnishingsCoefficients for absorption in auditorium is shown for both empty and occupied seating conditions

Many products are prefabricated for sound absorbing treatment (suspended ceilings/wall mountedtreatments 3 kinds of custom-designed treatments that are often used in auditoriums/churches (the deep air spaceinsures adequate low frequency performance

62. Noise Reduction by Absorption Noise levels in a room are highest for a given source if the rooms surfaces are primarily soundreflecting; lowest if there are large areas of sound absorbing materials (e.g. sound absorbing ceilings3. Reflections4. Reverberation

6

2. Noise Reduction by Absorption Noise levels in a room are highest for a given source if the rooms surfaces are primarily soundreflecting; lowest if there are large areas of sound absorbing materials (e.g. sound absorbing ceilings3. Reflections4. Reverberation

6

2. Noise Reduction by Absorption Noise levels in a room are highest for a given source if the rooms surfaces are primarily soundreflecting; lowest if there are large areas of sound absorbing materials (e.g. sound absorbing ceilings3. Reflections4. Reverberation