Index of content:
Volume 120, Issue 4, October 2006
- NOISE: ITS EFFECTS AND CONTROL 
Broadband noise reduction of piezoelectric smart panel featuring negative-capacitive-converter shunt circuit120(2006); http://dx.doi.org/10.1121/1.2259791View Description Hide Description
A broadband noise reduction of a piezoelectric smart panel featuring a negative capacitance converter (NCC) shunt circuit is experimentally investigated. Piezoelectric shunt damping utilized on the panel structure is attractive for noise reduction especially at low resonance frequencies of the structure. To achieve a broadband noise reduction, however, a multimode shunt is necessary. The NCC circuit can be an ideal broadband shunt circuit by nullifying the capacitance of the piezoelectric patch with the circuit. Since the intrinsic capacitance of the patch is not constant with the frequency, the broadband shunt performance of the NCC can be deteriorated. Thus, we introduce the dual-patch NCC circuit on the smart panel. The proposed concept is explained and the tuning and implementation procedures are addressed. The noise reduction performance of the panel is tested in terms of transmission loss according to the standard transmitted noise measurement. The broadband damping performance of the smart panel featuring a dual-patch NCC shunt is compared with the panels featuring resonant shunt circuit and ordinary NCC shunt circuit in terms of acceleration and noise transmission loss. It is found that the dual-patch NCC shunt is more efficient than ordinary NCC and resonant shunt for achieving broadband noise reduction with smart panels.
120(2006); http://dx.doi.org/10.1121/1.2259790View Description Hide Description
A hybrid active noise reduction(ANR) architecture is presented and validated for a circumaural earcup and a communication earplug. The hybrid system combines source-independent feedback ANR with a Lyapunov-tuned leaky LMS filter (LyLMS) improving gain stability margins over feedforward ANR alone. In flat plate testing, the earcup demonstrates an overall C-weighted total noise reduction of and , respectively, for sum-of-tones noise and for aircraft or helicopter cockpit noise, improving low frequency performance by up to over either control component acting individually. For the earplug, a filtered- implementation of the LyLMS accommodates its nonconstant cancellation path gain. A fast time-domain identification method provides a high-fidelity, computationally efficient, infinite impulse response cancellation path model, which is used for both the filtered- implementation and communication feedthrough. Insertion loss measurements made with a manikin show overall C-weighted total noise reduction provided by the ANR earplug of for sum-of-tones and from for UH-60 helicopternoise, with negligible degradation in attenuation during speech communication. For both hearing protectors, a stability metric improves by a factor of 2 to several orders of magnitude through hybrid ANR.
120(2006); http://dx.doi.org/10.1121/1.2266539View Description Hide Description
A study of community annoyance caused by exposures to railway noise was carried out in 18 areas along railway lines to accumulate social survey data and assess the relationship between railway noise levels and annoyance responses in Korea. Railway noise levels were measured with portable sound-level meters. Social surveys were administered to people living within of noise measurement sites. A questionnaire contained demographic factors, degree of noise annoyance, interference with daily activities, and health-related symptoms. The question relating to noise annoyance was answered on an 11-point numerical scale. The randomly selected respondents, who were aged between 18 to 70 years of age, completed the questionnaire independently. In total, 726 respondents participated in social surveys. Taking into consideration the urban structure and layout of the residential areas of Korea, Japan, and Europe, one can assume that the annoyance responses caused by the railway noise in this study will be similar to those found in Japan, which are considerably more severe than those found in European countries. This study showed that one of the most important factors contributing to the difference in the annoyance responses between Korea and Europe is the distance between railways and houses.