VRIJE UNIVERSITEIT BRUSSEL Acoustics - the Dept. of ...

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26 CHAPTER 2. THE HUMAN HEARING SYSTEMFigure 2.2: The anatomy of the cochlea. Source : Encarta Winkler Prins2004is chosen as the reference frequency for the dB-scale. The pain threshold isvirtually independent of the frequency and corresponds to 130 or 140 dB.Speech is above all a complex mixture of tones, with a frequency spectrumrangingfrom200to4000Hz. Thiszoneintheauditoryfieldiscalledthezoneof speech. The protection of the ear in this zone is of the utmost importancefor a persons the social life (Figure 2.4).2.2.2 Amplification of signals in hearingThe amplification of sound happens in the external ear (external auditorycanal), middle- and inner ear. The amplification in the external auditorycanal relies on resonator-operation and happens predominantly in the speechintelligibility area(Figure2.4). Intheexternal auditorycanal, thatresemblesa open-closed tube, a standing wave originates with if the wavelength of thesound isgiven by λ = 4L, with L ≈ 0.03mthe lengthof the external auditory
2.2. PHYSIOLOGY OF THE EAR 27Figure 2.3: The organ of Corti. Source : anatomie.med.vu.nl andwww.audiologieboek.nlcanal. This means that the resonance frequency of the acoustic system canbe found as follows :f = c4L = 340m/s ≈ 3000Hz (2.1)4∗0.03mBecause the inner ear contains a liquid, there is an impedance mismatchbetween the outer and inner ear. To overcome this mismatch the hearingsystem has two mechanisms that are used to amplify the force that can beexerted on the liquid. The first amplification in the middle ear relies on themechanical amplification of the vibrations of the ossicles. The system of ossicles(hammer - anvil - stirrup) weakens low and high tones and amplifies
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Chapter 5Sound InsulationWhen consi
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5.3. THE ACOUSTICAL BARRIER 95For t
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Chapter 6Noise control6.1 Origin of
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6.1. ORIGIN OF NOISE 101Figure 6.2:
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6.4. RADIATION NOISE 115Figure 6.17
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6.4. RADIATION NOISE 117Figure 6.20
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Part IIINoise directives119
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124CHAPTER 7. DIRECTIVE 2000/14/EG:
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128 CHAPTER 8. NOISE ON THE WORK FL
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140 CHAPTER 9. COMMUNITY NOISE2. No
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142 CHAPTER 9. COMMUNITY NOISE
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144 APPENDIX A. MATERIAL PROPERTIES
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152 BIBLIOGRAPHY[12] Bruel and Kjae
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