Relationship between subjective

responses and physical parameters for air-

conditioner noise

Yoshiharu Soeta

National Institute of Advanced Industrial Science and Technology (AIST)

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Subjective and physical evaluation of air-conditioner noise

Introduction

• Air conditioners are regarded as major noise

sources in building environments. Considerable

efforts reduced the sound levels

• People may feel uncomfortable by certain

aspects of the sound quality

• Both the sound levels and the sound quality of

an air conditioner are important for the user’s

acoustic comfort2

Subjective and physical evaluation of air-conditioner noise

Purpose of this study

• To clarify the most dominant factor for subjective

evaluation caused by air-conditioner noise

• Physical evaluation

• Autocorrelation function (ACF) factors

• Sound quality indices (loudness, sharpness,

roughness, fluctuation strength)

• Subjective evaluation

• Annoyance to air-conditioner noises in buildings

• Preference to air-conditioner sounds in cars3

Subjective and physical evaluation of air-conditioner noise

Autocorrelation function (ACF)

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Signal

ACF

Correlation between a signal

and a delayed version of itself.

Sinusoidal wave Brain wave White noise

Subjective and physical evaluation of air-conditioner noise

ACF factors (Ando 2009)

Spectrum ACF

• F(0) : rms of the zero delay LAeq

• t1 : delay time of the first peak Pitch

• f1 : amplitude of the first peak Pitch strength

• Wf(0) : widths of the first decay Spectral centroid

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Subjective and physical evaluation of air-conditioner noise

Sound quality indices (Zwicker and

Fastl 1999)

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• Loudness

• psychological counterpart of the physical strength

• Sharpness

• a measure of the high-frequency content

• Roughness

• rapid (15-300 Hz) amplitude modulation sensation

• Fluctuation strength

• slower (up to 20 Hz) amplitude modulation sensation

Subjective and physical evaluation of air-conditioner noise

Methods for noise measurements

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• Number of measured noises

• cassette type air-conditioner, 2 (CT1 and CT2),

• split type air-conditioner, 5 (ST1, ST2, ST3, ST4, ST5),

• central air conditioning system, (CA)

• Microphone: Omni-directional microphone

CTST

ST

Subjective and physical evaluation of air-conditioner noise

Results of ACF factors, t1 and f1

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Lower pitch

Stronger pitch

Weaker pitch

Higher pitch

Subjective and physical evaluation of air-conditioner noise

Results of ACF factor Wf(0) and LAeq

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Lower spectral

centroid

Higher spectral

centroid

Subjective and physical evaluation of air-conditioner noise

Subjective annoyance test

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• Sources: 8 types of air-conditioner noise (2.5 sec)

• Procedures: Scheffe’s paired comparison method

• Task: Compare the two stimuli based on seven grade

Subjective and physical evaluation of air-conditioner noise

Relationship between physical

parameters and annoyance

Subjective and physical evaluation of air-conditioner noise

Multiple regression analysis using

physical parameters

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• Model A: ACF factors

• Model B: Sound quality indices

SVannoyance ≈ a0 + a1t1 + a2f1 + a3SD_f1

a1 a2 a3

Standardized partial

regression coefficient

-1.17 -0.61 0.20

SVannoyance ≈ b0 + b1loudness + b2SD_roughness + b3roughness

b1 b2 b3

Standardized partial

regression coefficient

0.50 0.35 0.12

Subjective and physical evaluation of air-conditioner noise

Subjective preference test

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• Types of noise: 9 types of sounds from air-conditioner in cars

• Procedures: Paired comparison method

• Task: Which of two sounds was more preferred?

Subjective and physical evaluation of air-conditioner noise

Relationship between physical

parameters and preference

Subjective and physical evaluation of air-conditioner noise

Multiple regression analysis using

physical parameters

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• Model A: ACF factors

• Model B: Sound quality indices

SVannoyance ≈ a0 + a1Wf(0) + a2LAeq

a1 a2

Standardized partial

regression coefficient

0.65 -0.52

SVannoyance ≈ b0 + b1loudness + b2sharpness

b1 b2

Standardized partial

regression coefficient

-0.58 -0.45

Subjective and physical evaluation of air-conditioner noise

Summary

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• Subjective annoyance for air-conditioner noises

in buildings can be predicted by

• t1 (pitch) and f1 (pitch strength)

• loudness and roughness

• Subjective preference for air-conditioner sounds

in cars can be predicted by

• Wf(0) (spectral centroid) and LAeq

• loudness and sharpness

Subjective and physical evaluation of air-conditioner noise

Thank you for your attention

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