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Nov 1988

Volume 84, Issue S1, pp. S2-S224

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back to top Session NNN. Noise IV and Architectural Acoustics IX: Vehicle Interior Sound and Vibration
Invited Papers
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Sound intensity measurements in a vehicle's interior sound field (A)

Ken'ichiro Suzuki and Tetsuo Maki

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S205-S206 (1988); (2 pages)

Online Publication Date: 13 Aug 2005

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Sound pressure and sound intensity in the passenger compartment of a vehicle with many standing waves are measured through piston‐plate excitation. These measurements provide the characteristics of attenuation in the free field near the sound source, which is found to be approximately −6 dB per doubling of distance. At a certain distance from the sound source, sound intensity shows an average sound‐pressure level between the maximum and minimum values in the passenger compartment. The reason for this is that, owing to the use of sound‐absorbing materials, the sound field does not consist only of standing waves, It is revealed that progressive waves dominate near the sound source. As a result, sound intensity measurements in passenger compartments provides the precise location and contribution of the sound source, even when booming sounds are present. Moreover, using the modal analysis method to investigate the behavior of the body vibration from the enforced point to the sound source is effective in improving the body structure for reducing passenger compartment noise levels.
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A method for evaluating the interior sound quality of automobiles (A)

Tsuyoshi Yamashita, Hajime Niikura, Mitsuo Nakamura, and Otoichi Kitamura

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S206-S206 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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The A‐weighted sound‐pressure level has been the conventional method of evaluating interior car noise aimed at reducing loudness. However, it is difficult to evaluate the quality of sound only by loudness. The multivariate analysis method was applied using data obtained from a semantic differential questionnaire with over 20 items about four different car models' interior sounds. The results showed that the bias from the image of the models had a larger effect on impressions than the actual sound. This shows that a blindfolded test is very important. Thus, the test procedure was modified to obtain correct results, and a blindfold test was adopted. The test was done with 48 subjects monitoring both the actual sound of the automobiles and their recorded sound. The data were analyzed using the principal component analysis, and three main factors in the sound were revealed: “beautifulness,” “powerfulness,” and “metallicness.” These factors are similar to those already found in studies of other types of sound.
Contributed Papers
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Sound reproduction in a car cabin using a digital filter network (A)

Michio Hanba, Hareo Hamada, Tanetoshi Miura, and Yoshinori Kiryu

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S206-S206 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Designs to reproduce stereo sound fields in a car cabin have many problems, such as the asymmetrical positions of loudspeakers (for the listener) and the complex characteristics of the sound transmission. Therefore, a technique is investigated in which the sound field in a car cabin is transformed using a digital filter network, keeping in mind the interaural sound pressure in both ears of the listener. The digital filter network can be realized from the transfer functions measured by a head and torso simulator in the car cabin and in the desired sound field. The purpose of using the digital filter network is to equalize the sound pressure in both ears of the listener (when the digital network is not used) to that obtained in the desired sound field. The realizability of the desired sound field in a car cabin was confirmed by computer simulation.
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A study of noise reduction of mufflers (A)

Tsuyoshi Nishimura, Masanao Ebata, and Josuke Okda

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S206-S206 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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There are two methods of analyzing the noise reduction characteristics of mufflers. One is a method based on acoustic theory. This method is widely used, because the computation is relatively simple and the noise reduction in each component of the muffler can be easily evaluated from the solution. However, the computation is carried out under assumptions that the system is linear, isentropic, and so on, and the obtained results do not agree with those obtained in practice. Another is the method of characteristics that gives a more accurate solution although the calculation is complicated. Thus the method becomes effective and convenient for practical application if the results obtained by the acoustic theory can be corrected based on the strict solutions obtained by the method of characteristics. This report deals with the method of correction for various shapes of mufflers composed of a straight pipe and an expansion chamber.
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Cockpit noise generation mechanisms in light aircraft (A)

Fred C. De Metz, Sr.

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S206-S206 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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The high noise levels occurring in the cockpits of light, powered aircraft can significantly contribute to pilot fatigue, interfere with pilot communications with passengers and air traffic control, cause permanent hearing loss, and detract from an otherwise pleasurable flight experience. The levels and spectral features of the cockpit noise field are presented for a number of popular types of light aircraft, under different operating conditions. The dominant noise generation mechanisms are identified and the effectiveness of practical and impractical noise reduction techniques for existing light aircraft are estimated. The noise control design features for a new generation of light aircraft are explored.
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