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Trane TRG-TRC007-EN = Lp1, 20 log10, Distance Correction in a Free Field, Equipment Sound Rating

Models: TRG-TRC007-EN

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period four

Equipment Sound Rating

notes

Distance Correction in a Free Field

Lp2	= Lp1	– 20 log10			r2
					r1

Figure 54

This type of relationship between distance and surface area provides the following simple mathematical model for estimating how sound will change as the distance from the source increases.

Lp2 = Lp1 - 20 log10 [r2 / r1]

where,

Lp2 = sound-pressure level at distance r2

Lp1 = sound-pressure level at distance r1

r1 = distance from the source where Lp1 was measured

r2 = distance from the source to where the sound pressure (Lp2) is desired

Using this expression, it can be shown that doubling the distance from the sound source results in a 6 dB reduction in the sound-pressure level. This is a handy fact to know when making estimates of outdoor sound levels.

Lp2 = Lp1 - 20 log10 [2 /1] = Lp1 - 6

TRG-TRC007-EN

Page 56

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Trane TRG-TRC007-EN manual = Lp1, 20 log10, Distance Correction in a Free Field, Equipment Sound Rating, period four

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 AcousticsFundamentals of HVAC Acoustics One of the Fundamental Series A publication ofTrane, an American Standard Company A Trane Air Conditioning Clinic PrefaceFundamentals of HVAC Acoustics 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 Soundperiod one Sound Wave and FrequencyFundamentals of Sound period one WavelengthFundamentals of Sound 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 bandperiod one One-ThirdOctave BandsFundamentals of Sound 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 twoSound Perception and Rating Methods period twoLoudness Contours Response to Tones Single-NumberRating MethodsSound Perception and Rating Methods period twoperiod two A-B-CWeightingSound Perception and Rating Methods period two A-WeightingExampleSound Perception and Rating Methods period two A-WeightingSound Perception and Rating Methods period two Noise Criteria NC CurvesSound Perception and Rating Methods Sound Perception and Rating Methods period twoNoise Criteria NC Curves NC-39period two Room Criteria RC CurvesSound Perception and Rating Methods Sound Perception and Rating Methods period twoRoom Criteria RC Curves dB refnPerceptible 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 Methodsperiod two Sound Perception and Rating Methods period twoRoom Criteria RC Curves RC-31Rperiod two Phon and SoneSound Perception and Rating Methods 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-ReceiverAnalysisperiod three Source-Path-ReceiverModelAcoustical Analysis 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 supplyperiod three Algorithms for Sound-PathModelingAcoustical Analysis period three Computerized Analysis ToolsAcoustical Analysis Attenuation and Regeneration Acoustical Analysisperiod three Terms Used in Sound-PathModelingperiod three Sound TransmissionAcoustical Analysis Acoustical Analysis period threeSound Transmission IInsertion loss IL INoise reduction NRperiod three AbsorptionAcoustical Analysis period three Reflected SoundAcoustical Analysis period three Receiver Sound CorrectionAcoustical Analysis 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 dBperiod four Near FieldEquipment Sound Rating Reverberant Field Equipment Sound Ratingperiod four source reflective wallsperiod four Semireverberant FieldEquipment Sound Rating Rating HVAC Equipment Equipment Sound Ratingperiod four HVAC Equipment Sound Ratingperiod four Reverberant-RoomMethodEquipment Sound Rating period four Free-FieldMethodEquipment Sound Rating period four Industry StandardsEquipment Sound Rating Ducted Air-HandlingEquipment Equipment Sound Ratingperiod four supply-airoutletperiod four Air Handler Test ConfigurationsEquipment Sound Rating 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-ENperiod five Review-PeriodThreeReview period five Review-PeriodFourReview nTrane Acoustics Program TAP Reviewperiod five Questions for Period QuizQuestions 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

Distance Correction in a Free Field

= Lp1

– 20 log10