Trane TRG-TRC007-EN manual Semireverberant Field

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period four

Equipment Sound Rating

notes

Semireverberant Field

semireverberant

near

field

field

source

wall

Figure 58

Most rooms in buildings are somewhere between a free field and a reverberant field environment. Called a semireverberant field, these spaces have some characteristics of both free field and reverberant field environments. The walls, floor, and ceiling prevent the sound from behaving as it would in a free field. These surfaces are not, however, perfectly reflective. Some of the sound is reflected by these surfaces, but a portion of the sound is absorbed or transmitted.

An understanding of how sound behaves in a semireverberant field is important when taking sound measurements. The characteristics of the sound field change with distance when a small sound source is placed in the center of a room. Close to the source, in the near field, sound measurement is unpredictable. Near the wall, in the reverberant field, the reflected sound begins to add to the sound coming directly from the source. The reduction in sound level due to the distance from the source tends to be cancelled out by the addition of the sound reflecting off the wall. This results in a near-constant sound-pressure level near the wall.

In the semireverberant field, sound behaves similarly to how it would in a free field. The sound level will decrease as the distance from the source increases, but not as much as it would in an ideal free field.

The construction of the room plays a significant role in determining what portion of the room behaves as a reverberant field, and what portion behaves as a semireverberant field. Small rooms with hard, reflective surfaces behave similarly to reverberant rooms. This description often fits a mechanical equipment room that is constructed of concrete and is small with respect to the size of the sound source.

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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 dBSound Perception Rating Methods Human EarHuman Ear Response Loudness Contours Response to Tones Single-Number Rating MethodsSingle-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