Noise Criteria Calculator Documentation _ Michael Schwob

Acoustical Engineer

Noise Criteria Calculator Documentation

The Noise Criteria Calculator is a web application that calculates certain single number ratings and generatesgraphs based on the input of a sound pressure level (SPL) spectrum. The Noise Criteria Calculator is located athttp://michaelschwob.com/noise-criteria-calculator

The criteria calculated are the traditional noise criteria (NC), the extended NC (eNC), the room criteria (RC MarkII), A-weighted level (dBA) and C-weighted level (dBC). The equations, calculation procedures and algorithms arebased on the references cited below.

Because the Noise Criteria Calculator is a web application it will operate on any computing device that uses one ofthe following web browsers with Javascript enabled: Microsoft Internet Explorer, Mozzila Firefox, Opera Browser,Google Chrome. Calculations and image generation are performed on the web server so your computersprocessor and memory are not used for analysis. The application was not developed to be used on devices withvery small screens, such as smart phones. Although it will work, it may be cumbersome to use on these devices.

Input

The Noise Criteria Calculator input form has two components: the sound pressure level input fields and the graphoption buttons. (The form directly below is not operable. It is used, on this page, for illustration purposes.)

The sound pressure level input fields correspond to the standard octave bands from 16Hz to 8kHz. This frequencyrange is inclusive of the bands required for the NC, eNC and RC Mark II. The bands use for each criteria are:

Criteria Required Frequency Bands

NC 63Hz, 125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz, 8kHz

eNC 16Hz, 31.5Hz, 63Hz, 125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz, 8kHz

RC Mark II 16Hz, 31.5Hz, 63Hz, 125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz

If you are only interested in a particular criterion then you only need to provide the levels in the bands required forthat criterion. dBA and dBC are averages and have no band limitations.

Noise Criteria Calculator Documentation | Michael Schwob http://michaelschwob.com/noise-criteria-calculator/documentation/

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The sound pressure level input fields will accept any number from 0.0 to 99.9. Negative numbers andnon-numeric characters (other than a decimal point) are not allowed to be entered. If a field is left blank then it willbe interpreted as 0.0.

The graph options produce the following results:

OptionButton

Effect Example

NC Graph the input sound pressure levels over the traditional NCcurves as described in Reference 4.

eNC Graph the input sound pressure levels over the extended NC(eNC) curves as described in ANSI S12.2-2008.

RC

Mark II

Graph the input sound pressure levels over the RC Mark II curvesas described by Reference 7.

None Graph the input sound pressure levels without reference criteriacurves.

Results

The Noise Criteria Calculator results section contains four parts: the calculated noise criteria, notes, errors and thedata graph. Following are the possible results for each criterion:


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Criteria PotentialResults

Description

NC70 A level in the spectrum is higher than the NC-70 curve, which is the highestlevel curve. The input spectrum cannot be rated.

eNC70 A level in the spectrum is higher than the eNC-70 curve, which is the highestlevel curve. The input spectrum cannot be rated.

RC50 A level in the spectrum is higher than the RC-50 curve, which is the highestlevel curve. The input spectrum cannot be rated.

dBAdBC

XdBA,YdBC

X is the A-weighted sound level of the input spectrum.Y is the C-weighted sound level of the input spectrum.

The notes section, just below the criteria, will appear if there is a possibility of acoustically induced vibrations andrattles in lightweight structures as determined according to the procedure in ANSI S12.2-2008. If this sectionappears, there are two possible messages:

Probability of clearly perceptible acoustically induced vibration and rattle in lightweight wall andceiling construction.

or


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Probability of moderately perceptible acoustically induced vibration and rattle in lightweight wall andceiling construction.

The error section will appear just below the notes if there is an error is encountered while processing on the server.If there are no errors, this section will not appear.

The graph section at the bottom of the page will contain a PNG image of a line graph showing the input spectrumgraphed according to the selected options described above. The octave band center frequencies are indicated onthe x-axis (abscissa) according to the graph option. The sound pressure levels are indicated on the y-axis(ordinate) from 0dB to 100dB in 10dB increments. The selected criteria curves are shown in silver gray. The valueof the criteria curve is shown at the end of each curve to the right. The input spectrum levels are shown in blue.

References

ANSI S12.2-2008 American National Standard Criteria for Evaluating Room Noise1.ASHRAE 2005 Handbook, Fundamentals, Chapter 7, Sound and Vibration2.ASHRAE 2007 Handbook, HVAC Applications, Chapter 47, Sound and Vibration Control3.Beranek, L.L., Revised criteria for noise in buildings. Noise Control 3, 19-27 (1957).4.Beranek, L.L. and Ver, I.L., Noise and Vibration Control Engineering, Principles and Applications, John Wileyand Sons, Inc., 1992.

5.

Blazier, W.E., Revised noise criteria for application in the acoustical design and rating of HVAC systems.Noise Control Eng. J. 16(2), 64-73 (1981).

6.

Blazier, W.E., RC Mark II: A refined procedure for rating the noise of heating, ventilating, and air-conditioning(HVAC) systems in buildings. Noise Control Eng. J. 45(6), 243-250 (1997).

7.

Schaffer, M.E., A Practical Guide to Noise and Vibration Control for HVAC Systems, American Society of8.


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Heating, Refrigeration and Air-Conditioning Engineers, Inc., 2005.


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Noise Criteria Calculator Documentation _ Michael Schwob

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