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Biomedical subjects

L L Beranek

Publications and source records attributed to L L Beranek.

5 recordsLinked to original sources
PubMed2001

Relation of acoustical parameters with and without audiences in concert halls and a simple method for simulating the occupied state.

Five acoustical parameters-reverberation time RT, early decay time EDT, clarity C80, strength G, and interaural cross-correlation coefficient IACC-were measured using identical procedures with and without audiences in six concert and opera halls. Reverberation times without audiences were measured in 15 additional halls using the same measuring techniques as for the six halls above, but for full occupancy the data were taken from musical stop chords at symphonic concerts. This paper shows that in all halls (1) the occupied RT can be predicted from the unoccupied RT using a linear regression equation, y = a - b exp(x), within acceptable limits, at low- and mid-frequencies. It is also shown for the six halls that (2) occupied C80's are predicted accurately from unoccupied values by the newly proposed equation; (3) G's with and without audiences are highly correlated by a first degree linear regression equation; and (4) IACCs have nearly the same value in both occupied and unoccupied halls. As a separate subject, the successful use of a cloth covering for seats in a concert or opera hall to simulate the occupied condition has been developed.

Acoustics↗
PubMed2001

Mechanism of sound absorption by seated audience in halls.

Four methods are explored for predicting the reverberation times in fully occupied halls for music as related to the sound absorption by their audiences. The methods for providing audience absorptions include two that use reverberation chambers, namely, the ISO 354 method (and other similar standards) (ISO) and Kath and Kuhl's method (K & K) [Acustica 15, 127-131 (1965)], and two that use average data from halls, i.e., Beranek's method (COH) [Concert and Opera Halls: How They Sound (Acoustical Society of America, Melville, NY, 1996)], and the average audience power-per-seat absorption which in practice is multiplied by the number of seats (AA). These methods are applied to the calculation of reverberation times in six existing halls, fully occupied, and the results were compared with actual measurements. The COH method was best for predictions over the entire frequency range. The K & K method showed the highest accuracy at mid-frequencies. Both the ISO and the K & K methods yielded wide differences for the measurements in the 125- and 250-Hz bands. The AA method was as good as the COH method when the measurements for the six halls were averaged, but showed a wide spread in the predictions around the average because it does not consider the degree of upholstering of the seats. It was hypothecated by the authors that the principal reasons for the ISO and K & K discrepancies at low frequencies were (a) differences between the degree of sound diffusion in actual halls and that in reverberation chambers, and (b) lack of information on the mechanisms of absorption of sound by people seated side-by-side in rows, particularly for near-grazing incidence sound fields. First, this article explores the sound diffusivity in a reverberation chamber and in the halls using CAD models. A probability density function of the incident angles of the sound rays that impinge on the audiences is defined and was measured for each case. Using a unique method, the sound absorption coefficient of each portion of the body and chair in a seated audience was determined in an anechoic chamber as a function of the incident angle of a sound wave. With adjustments from these findings, the K & K method can be made to equal the COH method in accuracy at all frequencies. Its forte is that it can be used for the determination of the sound absorption of occupied chairs from measurements of a limited number in a reverberation chamber.

Journal Article↗
PubMed1998

Relations among interaural cross-correlation coefficient (IACCE), lateral fraction (LFE), and apparent source width (ASW) in concert halls.

Relations are determined between one of the important subjective attributes of concert hall acoustics, the apparent source width, ASW, and three acoustical measures, interaural cross-correlation coefficient IACCE, LFE, and strength factor G. Although these measures previously have been found to correlate with ASW, their relations with it have not been examined sufficiently, especially in respect to their frequency characteristics. Herein, ASW's are directly determined for electronically reproduced musical sound fields with extensive ranges of values for IACCE and LFE. Investigated as parameters are angles of incidence, the time delay difference between a pair of symmetric early lateral reflections, and the number of early lateral reflections. These studies indicate the relative efficacy of IACCE and LFE for determining ASW under conditions that are realistically encountered in concert halls. The results were compared with measured IACCE's, LFE's, and also the strength factor G's in existing concert halls. It is concluded that the arithmetic average of [1-IACCE]'s at 500, 1 k and 2 k Hz combined with the strength factor Glow of the sound field at frequencies below 250 Hz are physical measures highly correlated with the subjective rank ordering of concert halls and that they cover the effects on ASW of the entire octave-band frequency range from 125 to 4 k Hz.

Acoustics↗
PubMed1966

Noise.

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Hearing Loss, Noise-Induced↗