Noise Criteria Calculator Documentation

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

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

Because the Noise Criteria Calculator is a web application it will operate on any computing device that uses one of the 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 computer’s processor and memory are not used for analysis. The application was not developed to be used on devices with very 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 graph option buttons. (The form directly below is not operable. It is used, on this page, for illustration purposes.)

Noise Criteria Calculator Input Form

The sound pressure level input fields correspond to the standard octave bands from 16Hz to 8kHz. This frequency range 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 for that criterion. dBA and dBC are averages and have no band limitations.

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

The graph options produce the following results:

Option Button Effect Example
NC Graph the input sound pressure levels over the traditional NC curves as described in Reference 4. Noise Criteria (NC) Graph
eNC Graph the input sound pressure levels over the extended NC (eNC) curves as described in ANSI S12.2-2008. Noise Criteria (NC) Graph
RC Mark II Graph the input sound pressure levels over the RC Mark II curves as described by Reference 7. Room Criteria (RC) Graph
None Graph the input sound pressure levels without reference criteria curves. Sound Pressure Level Graph

Results

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

Criteria Potential Results Description
NC<15 All levels in the input spectrum are less than the NC-15 curve, which is the lowest level curve. The input spectrum cannot be rated.
NC NC-Y at X Hz Y is the NC value as determined by tangency at the X Hz octave band.
NC>70 A level in the spectrum is higher than the NC-70 curve, which is the highest level curve. The input spectrum cannot be rated.
eNC<15 All levels in the input spectrum are less than the eNC-15 curve, which is the lowest level curve. The input spectrum cannot be rated.
eNC eNC-Y at X Hz Y is the eNC value as determined by tangency at the X Hz octave band. If the X Hz octave band is not indicated then the eNC value was determined by the SIL according to the procedure in ANSI S12.2-2008.
eNC>70 A level in the spectrum is higher than the eNC-70 curve, which is the highest level curve. The input spectrum cannot be rated.
RC<25 All levels in the input spectrum are less than the RC-25 curve, which is the lowest level curve. The input spectrum cannot be rated.
RC Mark II RC-Y, QAI-X Y is the RC value as determined by the SPIL. X is the Quality Assessment Index and has the format ND where N is the magnitude of the QAI and D is the sound quality descriptor. D may have the values of:

N = Neutral

L = Low Frequency (Rumble)

M = Mid Frequency (Roar)

H = High Frequency (Hiss)

RC>50 A level in the spectrum is higher than the RC-50 curve, which is the highest level curve. The input spectrum cannot be rated.
dBA
dBC
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 and rattles in lightweight structures as determined according to the procedure in ANSI S12.2-2008. If this section appears, there are two possible messages:

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

or

Probability of moderately perceptible acoustically induced vibration and rattle in lightweight wall and ceiling 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 spectrum graphed according to the selected options described above. The octave band center frequencies are indicated on the 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 value of the criteria curve is shown at the end of each curve to the right. The input spectrum levels are shown in blue.

Noise Criteria (NC) Graph

References

  1. ANSI S12.2-2008 “American National Standard Criteria for Evaluating Room Noise”
  2. ASHRAE 2005 Handbook, Fundamentals, Chapter 7, “Sound and Vibration”
  3. ASHRAE 2007 Handbook, HVAC Applications, Chapter 47, “Sound and Vibration Control”
  4. Beranek, L.L., “Revised criteria for noise in buildings.” Noise Control 3, 19-27 (1957).
  5. Beranek, L.L. and Ver, I.L., “Noise and Vibration Control Engineering, Principles and Applications”, John Wiley and Sons, Inc., 1992.
  6. 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).
  7. 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).
  8. Schaffer, M.E., “A Practical Guide to Noise and Vibration Control for HVAC Systems”, American Society of Heating, Refrigeration and Air-Conditioning Engineers, Inc., 2005.