Trane TRG-TRC007-EN manual Lot

Page 57

period four

Equipment Sound Rating

notes

Distance Correction in a Free Field

air-cooled chiller

Lp1 = 95 dB

Lp2 = 83 dB

 

 

r1

= 30 ft

 

 

 

 

 

lot

 

 

 

 

 

 

 

(9.1 m)

 

 

line

 

 

 

 

 

r2

= 120 ft

 

 

 

 

 

 

 

(36.6 m)

 

Figure 55

 

 

 

 

 

 

 

 

In practice, this equation is commonly used to determine how loud a piece of equipment will be at a given distance. For example, the manufacturer of an air- cooled chiller lists the sound-pressure level of the chiller as 95 dB at a distance of 30 ft (9.1 m) from the chiller. This equation can be used to estimate the sound-pressure level at a lot line, which is 120 ft (36.6 m) from the chiller. In this example, the sound-pressure level at the lot line is 83 dB.

Lp2 = 95 dB – 20 log10 [120 ft / 30 ft] = 83 dB

(Lp2 = 95 dB – 20 log10 [36.6 m / 9.1 m] = 83 dB)

This equation is only valid for sound pressure. It cannot be used to convert sound power (Lw) to sound pressure (Lp). Also, it is only valid in a free-field environment.

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TRG-TRC007-EN

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Contents Air Conditioning Clinic Fundamentals of Hvac Acoustics Business Reply Mail One of the Fundamental Series Comment CardFundamentals of Hvac Acoustics Fundamentals of Hvac Acoustics PrefaceContents TRG-TRC007-EN Fundamentals of Sound Fundamentals of SoundWhat is Sound? What is Sound?Sound Wave and Frequency Wavelength Broadband Sound and Tones Broadband SoundOctave Bands Octave BandsLogarithmic sums One-Third Octave Bands Sound Power and Sound Pressure Sound Power and Sound PressureAn Analogy Decibel DB = 10 log10 ´ log Logarithmic ScaleEquation for Sound Pressure Equation for Sound Power50 dB + 44 dB = 51 dB Logarithmic Addition of DecibelsSound Perception Rating Methods Human EarHuman Ear Response Loudness Contours Response to Tones Single-Number Rating MethodsSingle-Number Rating Methods Sound Perception and Rating Methods C WeightingWeighting 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 Source-Path-Receiver Analysis Acoustical AnalysisSource-Path-Receiver Model Airborne Typical Sound PathsExample of Multiple Sound Paths Examples of a Single Sound PathIdentifying Sound Sources and Paths Sound-Path Modeling Modeling Sound PathsSupply Algorithms for Sound-Path Modeling Computerized Analysis Tools Terms Used in Sound-Path Modeling Attenuation and RegenerationSound Transmission Insertion loss IL Noise reduction NR Transmission loss TL Absorption Reflected Sound Receiver Sound Correction Equipment Sound Rating Equipment Sound RatingFields of Measurement Free FieldDistance Correction in a Free Field = L p1 20 logLot Near Field Reverberant Field Semireverberant Field Hvac Equipment Sound Rating Rating Hvac EquipmentReverberant-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-Period One ReviewNoise criteria NC Room criteria RC Review-Period TwoReview-Period Three Review-Period Four Review Questions for Period QuizOctave-band frequency, Hz Answers Glossary Glossary Room effect See receiver room correction Glossary Trane