Trane TRG-TRC007-EN manual Weighting Example

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period two

Sound Perception and Rating Methods

notes

A–Weighting Example

octave

center

actual sound

 

A-weighting

A-weighted

 

 

 

band

frequency (Hz)

pressure (dB)

 

factor (dB)

sound pressure (dB)

 

1

63

63

 

– 26

37

 

2

125

52

 

– 16

36

 

3

250

45

 

– 9

36

 

4

500

38

 

– 3

35

 

5

1,000

31

 

+ 0

31

 

6

2,000

24

 

+ 1

25

 

7

4,000

16

 

+ 1

17

 

8

8,000

10

 

+ 0

10

 

 

 

 

 

 

42 dBA

Figure 24

 

 

 

 

 

 

 

 

 

 

 

The following steps describe how to calculate an A-weighted value.

1Starting with the actual sound-pressure levels for the eight octave bands, add or subtract the decibel values represented by the A-weighting curve shown in Figure 23. These weighting factors are also listed in the table in Figure 24. Subtract 26 dB from the 63 Hz sound-pressure level, 16 dB from the 125 Hz level, 9 dB from the 250 Hz level, and 3 dB from the 500 Hz level. Then, add 1 dB each to the sound-pressure levels in the 2,000 Hz and 4,000 Hz octave bands.

2Logarithmically sum all eight octave bands together to arrive at an overall A-weighted sound-pressure level. This value is then expressed using the units of dBA.

For the sound-pressure data in this example, the A-weighted sound-pressure level is 42 dBA.

Most sound meters can automatically calculate and display the A-weighted sound-pressure level, providing a simple and objective means of verifying acoustical performance. However, as mentioned earlier, one of the drawbacks of a single-number descriptor is that data about the relative magnitude of each octave band is lost when the eight octave bands are combined into one value. Therefore, even if the target dBA level is achieved, an objectionable tonal quality or spectrum imbalance may exist.

TRG-TRC007-EN

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Contents Air Conditioning Clinic Fundamentals of Hvac Acoustics Business Reply Mail Comment Card One of the Fundamental SeriesFundamentals of Hvac Acoustics Preface Fundamentals of Hvac AcousticsContents TRG-TRC007-EN Fundamentals of Sound Fundamentals of SoundWhat is Sound? What is Sound?Sound Wave and Frequency Wavelength Broadband Sound Broadband Sound and TonesOctave Bands Octave BandsLogarithmic sums One-Third Octave Bands Sound Power and Sound Pressure Sound Power and Sound PressureAn Analogy DB = 10 log DecibelLogarithmic Scale 10 ´ logEquation for Sound Power Equation for Sound PressureLogarithmic Addition of Decibels 50 dB + 44 dB = 51 dBHuman Ear Response Sound Perception Rating MethodsHuman Ear Loudness Contours Single-Number Rating Methods Response to TonesSingle-Number Rating Methods C Weighting Sound Perception and Rating MethodsWeighting Example Weighting Noise Criteria NC Curves NC-39 Room Criteria RC Curves MPa DB ref Pressure Sound Perception and Rating Methods RC-31 R Phon and Sone Octave-Band Rating Method Octave-Band Rating MethodAcoustical Analysis Acoustical AnalysisSetting a Design Goal Setting a Design GoalAcoustical Analysis Acoustical Analysis Source-Path-Receiver AnalysisSource-Path-Receiver Model Typical Sound Paths AirborneExamples of a Single Sound Path Example of Multiple Sound PathsIdentifying Sound Sources and Paths Modeling Sound Paths Sound-Path ModelingSupply Algorithms for Sound-Path Modeling Computerized Analysis Tools Attenuation and Regeneration Terms Used in Sound-Path ModelingSound Transmission Insertion loss IL Noise reduction NR Transmission loss TL Absorption Reflected Sound Receiver Sound Correction Equipment Sound Rating Equipment Sound RatingFree Field Fields of Measurement= L p1 20 log Distance Correction in a Free FieldLot Near Field Reverberant Field Semireverberant Field Rating Hvac Equipment Hvac Equipment Sound RatingReverberant-Room Method Free-Field Method Industry Standards Ducted Air-Handling Equipment Air Handler Test Configurations Former Methods of Sound Testing ARI Standard Sound Power by Octave Band Review Review-Period OneReview-Period Two Noise criteria NC Room criteria RCReview-Period Three Review-Period Four Review Quiz Questions for PeriodOctave-band frequency, Hz Answers Glossary Glossary Room effect See receiver room correction Glossary Trane