To test the adequacy of French regulations for sound isolation in buildings, subjects were asked to rate their annoyance with samples of music filtered by electronic "insulation curves" representing different party walls. The insulation curves differed in their shape but all provided an A-weighted le•,el difference of 51 dB with a pink noise source, measured over a 1/3-octave bandwidth of 40 Hz-10 kHz. However, the different insulation curves did not provide the same degree of sound isolation with various music samples due to source spectral differences. A statistically significant correlation was observed between annoyance and the A-weighted level difference ratings of the insulation curves when bandlimited pink noise (125 Hz-4 kHz)was used as a source. This correlation was not present when broadband (40 Hz-10 kHz) pink noise was used for the performance rating. Subjects showed a preference for insulation curves with steeper slopes (9 and 12 dB/oct), thus preferring a greater relative attenuation at higher frequencies. Additionally, the presence of coincidence dips was found to have an effect on subject preference that appeared to depend upon both the frequency range at which they occurred and the slope. The bandwidth of the music signals and the intelligibility of speech in the intruding sounds were also found to influence the annoyance ratings. These results indicate that the level difference method for rating sound insulation could better predict occupant response if the above results were accounted for in the procedure.
A geometrical cone-tracing method associated with the signal processing technique is used to calculate the binaural impulse response of a concert hall. Some inaccuracy and the computation time of the geometrical algorithm tend to limit the method for the high-reflection orders which are necessary to provide a good listening effect. In order to extend the response, a new approach is presented based on different statistical processes that depend on both the acoustical and geometrical characteristics of the hall. After a theoretical presentation (new statistical results are proposed to describe the sound field behavior in a concert hall), some simulations are given in order to illustrate the different statistical processes. This simulation technique seems to be a very convenient tool both for the design of a new concert hall and for the study of the important parameters in auditory spaciousness.
Many performing art centers and multipurpose halls with poor acoustics cannot be improved for economical reasons by architectural correction works or by mechanical moving devices. The principle of virtual acoustic wall [Guicking et al., J. Acoust. Soc. Am. 78 (1985)] has been successfully applied to control the reflectivity and diffusivity of concert halls existing walls. Several independent active cells composed of a microphone, an electronic unit, and a loudspeaker form a virtual wall. By appropriately controlling the open loop gain in the cells of each virtual wall it is possible to create different sound fields fully coherent in space and time with the preexisting one. The first reflections can thus be reinforced and a natural reverberation enhancement effect is obtained by the acoustic exchange between the virtual walls. Computer sound simulation of three virtual walls in a concert hall was performed and experimental results, both objective and subjective, are shown for two concert halls in which a virtual wall system was installed.
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