Index of content:
Volume 130, Issue 4, April 2011
- NOISE: ITS EFFECTS AND CONTROL 
130(2011); http://dx.doi.org/10.1121/1.3624823View Description Hide Description
Active control of sound can be employed globally to reduce noise levels in an entire enclosure, or locally around a listener’s head. Recently, spherical loudspeaker arrays have been studied as multiple-channel sources for local active control of sound, presenting the fundamental theory and several active control configurations. In this paper, important aspects of using a spherical loudspeaker array for local active control of sound are further investigated. First, the feasibility of creating sphere-shaped quiet zones away from the source is studied both theoretically and numerically, showing that these quiet zones are associated with sound amplification and poor system robustness. To mitigate the latter, the design of shell-shaped quiet zones around the source is investigated. A combination of two spherical sources is then studied with the aim of enlarging the quiet zone. The two sources are employed to generate quiet zones that surround a rigid sphere, investigating the application of active control around a listener’s head. A significant improvement in performance is demonstrated in this case over a conventional headrest-type system that uses two monopole secondary sources. Finally, several simulations are presented to support the theoretical work and to demonstrate the performance and limitations of the system.
130(2011); http://dx.doi.org/10.1121/1.3621180View Description Hide Description
Road traffic noise in urban areas is a major source of annoyance. A quiet façade has been hypothesized to beneficially affect annoyance. However, only a limited number of studies investigated this hypothesis, and further quantification is needed. This study investigates the effect of a relatively quiet façade on the annoyance response. Logistic regression was performed in a large population based study (GLOBE, N∼18 000), to study the association between road traffic noise exposure at the most exposed dwelling façade (L den) and annoyance in: (1) The subgroup with a relatively quiet façade (large difference in road traffic noise level between most and least exposed façade (Q > 10 dB); (2) the subgroup without a relatively quiet façade (Q < 10 dB). Questionnaire data were linked to individual exposure assessment based on detailed spatial data (GIS) and standard modeling techniques. Annoyance was less likely (OR Q >10 < OR Q < 10) in the subgroup with relatively quiet façade compared to the subgroup without relatively quiet façade. The difference in response between groups seemed to increase with increasing Q and L den. Results indicate that residents may benefit from a quiet façade to the dwelling.