Volume 130, Issue 1, July 2011
Index of content:
- ARCHITECTURAL ACOUSTICS 
On the acoustic properties of parallel arrangement of multiple micro-perforated panel absorbers with different cavity depths130(2011); http://dx.doi.org/10.1121/1.3596459View Description Hide Description
The acoustic properties of a compound micro-perforated panel (MPP) absorber array are investigated. The absorber array consists of three parallel-arranged MPP absorbers with different cavity depths. A finite element procedure is used to simulate its acoustic behaviors under normal incidence. Experimental studies are carried out to verify the numerical simulations. Due to different reactance matching conditions in the absorber array, strong local resonance occurs and the corresponding local resonanceabsorption dominates. Compared with single MPP absorber, the absorber array requires lower acoustic resistance for good absorption performance, and the resonance frequencies shift due to inter-resonator interactions. The different acoustic resistance requirement is explained by considering the reduced effective perforation rate of the MPP in the absorber array. The performance of the absorber array varies with the sizes and spatial arrangement of the component absorbers. When the distance between component absorbers is larger than a quarter-wavelength, the above-mentioned parallel absorption mechanism diminishes. In the experimental study, the normal incidence absorption coefficients of a prototype MPP absorber array are tested. The measured results compare well with the numerical predictions. The experimental study also shows that although other absorption mechanisms may exist, dissipation by the MPP is dominant in the MPP absorber array.
130(2011); http://dx.doi.org/10.1121/1.3598455View Description Hide Description
In the present study, the effects of interference from combined noises on speech transmission were investigated in a simulated open public space. Sound fields for dominant noises were predicted using a typical urban square model surrounded by buildings. Then road traffic noise and two types of construction noises, corresponding to stationary and impulsive noises, were selected as background noises. Listening tests were performed on a group of adults, and the quality of speech transmission was evaluated using listening difficulty as well as intelligibility scores. During the listening tests, two factors that affect speech transmission performance were considered: (1) temporal characteristics of construction noise (stationary or impulsive) and (2) the levels of the construction and road traffic noises. The results indicated that word intelligibility scores and listening difficulty ratings were affected by the temporal characteristics of construction noise due to fluctuations in the background noise level. It was also observed that listening difficulty is unable to describe the speech transmission in noisy open public spaces showing larger variation than did word intelligibility scores.
130(2011); http://dx.doi.org/10.1121/1.3598429View Description Hide Description
The indirect auditory feedback from one’s own voice arises from sound reflections at the room boundaries or from sound reinforcement systems. The relative variations of indirect auditory feedback are quantified through room acoustic parameters such as the room gain and the voice support, rather than the reverberation time. Fourteen subjects matched the loudness level of their own voice (the autophonic level) to that of a constant and external reference sound, under different synthesized room acoustics conditions. The matching voice levels are used to build a set of equal autophonic level curves. These curves give an indication of the amount of variation in voice level induced by the acoustic environment as a consequence of the sidetone compensation or Lombard effect. In the range of typical rooms for speech, the variations in overall voice level that result in a constant autophonic level are on the order of 2 dB, and more than 3 dB in the 4 kHz octave band. By comparison of these curves with previous studies, it is shown that talkers use acoustic cues other than loudness to adjust their voices when speaking in different rooms.
130(2011); http://dx.doi.org/10.1121/1.3596465View Description Hide Description
This paper investigates both theoretically and experimentally the sound radiation from an aperture placed in an enclosure wall for the particular case of low modal sound field. The incidence field is composed of the enclosed sound field, which is calculated using the theoretical modal model presented. The transmitted sound is calculated by the Rayleigh radiation equation after continuity conditions have been applied in the aperture plane, assuming the condition of a thin wall. The model is experimentally validated by measuring the directivity and sound pressure radiated from an aperture in the side of a rectangular box. Because the walls of the enclosure are not rigid, an experimental procedure to determine its admittance is also presented. The experiments have been carried out for the first four modes of the enclosed sound field, and good agreement is found between the theoretical and experimental results. These results indicate that the admittance of the aperture, its radiation efficiency, and its directivity are all functions of the predominant mode shape, and the frequency, as well as the location and shape, of the aperture relative to the predominant enclosed mode shape.