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Trane TRG-TRC007-EN manual Attenuation and Regeneration, Acoustical Analysis, period three

Models: TRG-TRC007-EN

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Attenuation and Regeneration

period three

Acoustical Analysis

notes

Attenuation and Regeneration

return	heat pump
return	(source)	supply
duct		supply
		duct

return-air grille

diffuser

Figure 46

Terms Used in Sound-Path Modeling

This section introduces several terms that are fairly specific to the science of acoustics.

Attenuation refers to the reduction in sound level as sound travels along the path from a source to a receiver. It is typically used to refer to the reduction of sound as it travels through a duct system. Straight ducts, elbows, junctions, and silencers are examples of elements that attenuate sound.

Regenerated sound results from components of the duct system that create turbulence in the air stream. Turbulence is caused by an abrupt change in airflow direction or velocity with a corresponding static-pressure loss. Regenerated sound increases with air velocity or when the air is forced to make sharp turns. Elbows, junctions, diffusers, silencers, and dampers are all examples of elements that regenerate sound.

Notice that some elements can both attenuate and regenerate sound. For example, as air makes a 90-degree turn in a rectangular duct elbow, some of the sound is reflected back upstream, attenuating the airborne sound downstream of the elbow. At the same time, however, the turbulence created by the air turning the sharp corner causes some regenerated sound.

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Trane TRG-TRC007-EN Attenuation and Regeneration, Acoustical Analysis, period three, Terms Used in Sound-PathModeling

Contents

Air Conditioning Clinic Fundamentals of HVAC AcousticsOne of the Fundamental Series TRG-TRC007-ENBUSINESS REPLY MAIL BUSINESS REPLY MAILTRANE Attn Applications Engineering 3600 Pammel Creek Road La Crosse WIComment Card Response CardFundamentals of HVAC AcousticsOne of the Fundamental Series A publication of Trane, an American Standard CompanyFundamentals of HVAC Acoustics Preface Fundamentals of HVAC AcousticsA Trane Air Conditioning Clinic Contents period two Sound Perception and Rating Methodsperiod three period fiveTRG-TRC007-EN period one Fundamentals of SoundFundamentals of Sound period oneWhat is Sound? period oneWhat is Sound? Fundamentals of SoundSound Wave and Frequency Fundamentals of Soundperiod one Wavelength Fundamentals of Soundperiod one Broadband Sound Broadband Sound and TonesFundamentals of Sound period oneOctave Bands Fundamentals of Soundperiod one Octave BandsFundamentals of Sound period oneOctave Bands Octave bands compress the range of frequencies between the upper and lower ends of the band into a single value. Sound measured in an octave band is the logarithmic sum of the sound level at each of the frequencies within the bandOne-ThirdOctave Bands Fundamentals of Soundperiod one Sound Power and Sound Pressure Sound Power and Sound PressureFundamentals of Sound period oneAn Analogy Fundamentals of Soundperiod one K Correlates to bulb wattagedB = 10 log10 DecibelFundamentals of Sound period oneLogarithmic Scale Fundamentals of Soundperiod one ratioEquation for Sound Power = 10 log10= 20 log10 Equation for Sound PressureLogarithmic Addition of Decibels 50 dB + 44 dB = 51 dBFundamentals of Sound period oneperiod two Sound Perception and Rating MethodsSound Perception and Rating Methods period twoperiod two Loudness ContoursSound Perception and Rating Methods Response to Tones Single-NumberRating MethodsSound Perception and Rating Methods period twoA-B-CWeighting Sound Perception and Rating Methodsperiod two A-WeightingExample Sound Perception and Rating Methodsperiod two A-Weighting Sound Perception and Rating Methodsperiod two Noise Criteria NC Curves Sound Perception and Rating Methodsperiod two Sound Perception and Rating Methods period twoNoise Criteria NC Curves NC-39Room Criteria RC Curves Sound Perception and Rating Methodsperiod two Sound Perception and Rating Methods period twoRoom Criteria RC Curves dB refSound Perception and Rating Methods period twonPerceptible vibration RV The sound level in the octave bands between 16 Hz and 63 Hz falls in the shaded regions A and B. These regions indicate sound-pressurelevels at which walls and ceilings can vibrate perceptibly-rattlingcabinet doors, pictures, ceiling fixtures, and other furnishings in contact with them Sound Perception and Rating Methods period twoRoom Criteria RC Curves RC-31RPhon and Sone Sound Perception and Rating Methodsperiod two Octave-BandRating Method Sound Perception and Rating Methodsperiod two Octave-BandRating Methodperiod three Acoustical AnalysisAcoustical Analysis period threeSetting a Design Goal period threeSetting a Design Goal Acoustical AnalysisSetting a Design Goal When defining the acoustical design goal for an outdoor environment, to meet a local noise ordinance for example, the A-weightedscale is typically used. This generally takes the form of a maximum A-weighted sound-pressurelevel at the lot line of the propertyAcoustical Analysis period threeAcoustical Analysis Acoustical Analysisperiod three Source-Path-ReceiverAnalysisSource-Path-ReceiverModel Acoustical Analysisperiod three Typical Sound Paths Acoustical Analysisperiod three IAirborneExamples of a Single Sound Path Example of Multiple Sound PathsAcoustical Analysis period threeIdentifying Sound Sources and Paths Acoustical Analysisperiod three packaged rooftop air conditionerModeling Sound Paths Acoustical Analysisperiod three Sound-PathModelingAcoustical Analysis period threeExample of Multiple Sound Paths supplyAlgorithms for Sound-PathModeling Acoustical Analysisperiod three Computerized Analysis Tools Acoustical Analysisperiod three Attenuation and Regeneration Acoustical Analysisperiod three Terms Used in Sound-PathModelingSound Transmission Acoustical Analysisperiod three Acoustical Analysis period threeSound Transmission IInsertion loss IL INoise reduction NRAbsorption Acoustical Analysisperiod three Reflected Sound Acoustical Analysisperiod three Receiver Sound Correction Acoustical Analysisperiod three period four Equipment Sound RatingEquipment Sound Rating period fourperiod four Free FieldEquipment Sound Rating Fields of Measurement= Lp1 20 log10Distance Correction in a Free Field Equipment Sound RatingEquipment Sound Rating period fourDistance Correction in a Free Field Lp2 = 95 dB - 20 log10 120 ft / 30 ft = 83 dBNear Field Equipment Sound Ratingperiod four Reverberant Field Equipment Sound Ratingperiod four source reflective wallsSemireverberant Field Equipment Sound Ratingperiod four Rating HVAC Equipment Equipment Sound Ratingperiod four HVAC Equipment Sound RatingReverberant-RoomMethod Equipment Sound Ratingperiod four Free-FieldMethod Equipment Sound Ratingperiod four Industry Standards Equipment Sound Ratingperiod four Ducted Air-HandlingEquipment Equipment Sound Ratingperiod four supply-airoutletAir Handler Test Configurations Equipment Sound Ratingperiod four Former Methods of Sound Testing Equipment Sound Ratingperiod four I ASHRAE generic fan algorithmARI Standard Equipment Sound Ratingperiod four IUses reverberant- room methodSound Power by Octave Band Equipment Sound Ratingperiod four 1 2 3period five ReviewReview period fiveperiod five Review-PeriodTwoReview TRG-TRC007-ENReview-PeriodThree Reviewperiod five Review-PeriodFour Reviewperiod five Review period fivenTrane Acoustics Program TAP Quiz Questions for PeriodQuestions for Period Quiz Questions for PeriodQuestions for Period 7True or False Sound can only travel from a source to the receiver along one pathAnswers Glossary Glossary hertz Hz The unit of measure for frequency. One hertz is equal to one cycle per secondGlossary reverberant field A uniform, or diffuse, sound field that is the opposite of a free field. In a perfectly reverberant field, the sound-pressurelevel is equal at all pointsGlossary the receiver, and everything it encounters as it travels along the way, constitutes the pathLiterature Order Number TRG-TRC007-ENFile Number E/AV-FND-TRG-TRC007-1101-EN