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Much of the literature on airborne sound transmission loss (TL) indicates that TL of a panel at a given frequency is dependent on distribution of sound intensity with angle of incidence in the incident sound field. Observed TL in most laboratory tests employing a 'diffuse' sound field yields data which may be described as lying between that to be anticipated if the energy in the sound field were concentrated at normal incidence, and that expected if the sound field were uniformly distributed over all angles of incidence (Random Incidence). An ad hoc approach to dealing with this phenomenon has involved the postulation of a 'field incidence' sound field, which assumes that the distribution of incident intensity is uniform up to a limiting angle of 75° to 80° from the normal to the panel. This approach provides a means for calculating TL which agrees with measurements, but no satisfactory analytical model has evolved which provides justification for this approach. Some careful experimental evaluations involving convolution of the cross correlation of the incident pressure field with an analytic model of panel response have shown that the fundamental approach is reasonable, but still provides no basis for explaining this phenomenon. In this paper, the recent published and unpublished data of a number of authors are reviewed, which imply that TL is more sensitive to local perturbations from a diffuse incidence sound field than from gross perturbations in the source room. One hypothesis which seems to correlate with these observations is that the aperture in which a panel is tested should be viewed as a spatial filter which limits the incident sound field in addition to the effects of 'diffusivity' present in the source room. It is postulated that the limitations produced by the aperture are more significant than those provided by the room for a 'reasonably reverberant' source room. [ABSTRACT FROM AUTHOR]

Professor L. Cremer was avidly interested in the transmission of sound through walls as part of his practice in architectural acoustics. The frequent use of masonry constructions for partitions and exterior facades in Europe, and their documented departure from ''mass law'' sound transmission performance led him to study this phenomenon in detail. He first identified what we now call the wave-coincidence effect (i.e., the matching of sound wavelengths in the surrounding fluid with the flexural wavelengths in the panel) as the mechanism which produced the non-mass-law performance in the 1940s. This work influenced London, Beranek, Watters, and Feshback in this country, leading to our present understanding of this phenomenon. His later work in impact sound transmission for masonry floors, and the transmission of flexural waves through wall junctions for flanking transmission also had a pioneering quality. Cremer systematically and significantly altered our understanding of sound propagation in buildings and other structures. This paper will review these several pioneering investigations to help us appreciate this giant of our field, on whose shoulders we all stand. [ABSTRACT FROM AUTHOR]

The design of a computer-based damping data and design system (DDDS) is described. Important features of the system are: modularity, standardized interfaces between modules based on defined information content, ease of expansion, physically based representation of material dynamic modulus, support for all users from test through analysis, and quality control to treatment design. System architecture and module function are described, followed by a detailed discussion of the material representation module. The input for this module is material test data, and the output is a set of analytic expressions for the frequency and temperature dependence of the material. The software for this module is based on the work of Rogers [J. Rheol. 27, 351-372 (1983)], which provides a rheologically consistent analytic function representation for the dynamic modulus and loss factor. The module is written within RS/1, a table-oriented, scientific software system. Damping treatment design software and approaches to system data quality issues are also addressed. [ABSTRACT FROM AUTHOR]

This paper provides an introductory framework to a session dealing with absorbing and damping materials. The opening segment describes analogs and differences between the two material concepts. Each in its respective sphere represents the principal engineering means of adding energy dissipation to control reverberation in a system. Some historical perspectives are noted, including conceptual simplicity and practical difficulties of use. Next is a brief review of major physical principles which influence performance. The analog of the role of treatment thickness on absorption and extensional damping performance is explored. The relation between normal and random incidence absorption and extensional damping performance is explored. The relation between normal and random incidence absorption coefficient is discussed. The recent work of Bliss [J. Acoust. Soc. Am. 71, 533-545 (1982)] on introducing an alternative boundary condition is explored for its relevance to this problem. An analog to coupled-room acoustics problems exist in connected structures with applied damping. Maidanik's [J. Sound Vib. 77, 245-250 (1981)] recent work in this area will be discussed for its relevance to the performance of damping treatments. The third portion of the paper reviews recent properties measurements activities including ASTM C-384, C-423, and E-756 as well as new measurement procedures. Closing remarks will deal with present and future directions of materials development. [ABSTRACT FROM AUTHOR]

Local computer networks (LCN's) lend themselves as a cost-efficient, growth-oriented, powerful answer to the problem of real-time control and processing of acoustic signals in a laboratory. The availability of inexpensive scientific and engineering 'off-the-shelf' software which can be structurally integrated in a shared resource environment permits the realization of large data-base management systems with micro-computers. The comparison of LCN alternatives, both hardware and software options, as it relates to specific acoustic measurement problems will be contrasted in showing E-A-R's solution for a mini/micro-computer network. Modal analysis, reverberation-time measurements, damping data reduction, hearing protection attenuation, and analytical modeling are some of the tasks which are integrated in the system. In this presentation we will discuss in detail some of the alternatives considered to date in our system development and their perceived advantages and limitations. Listings of structured programs currently under development will be provided. [ABSTRACT FROM AUTHOR]

The application of statistical energy analysis (SEA) techniques to predict the sound power radiated from point excited plates is well known. These techniques are typically restricted to plates for which thin plate approximations apply, and to the frequency region in which high modal overlap (M > 1, where M = model bandwidth/mode spacing) occurs. Experimental data are presented for three plates (0.95-cm transite, 1.3-cm aluminum, and 4.3-cm concrete) which violate either or both of the limitations, and for which the ratio of power radiated to mean square force input is significantly (as much as 10 dB) less than the SEA theory predicts. Using Mindlin's thick plate theory, modifications to the SEA theory to account for the frequency averaged driving point impedance and mode spacing have been developed. The use of these modifications gave good agreement with the experimental results for the frequency range where the plates are thick and M > 1. Several sources for the discrepancies between analytic and experimental data for low modal overlap are under investigation and will be discussed. [ABSTRACT FROM AUTHOR]

Current measurement standards do not provide adequate guidance for the evaluation of the uncertainty involved in using measured sound pressures, rather than sound intensities, to estimate the sound power radiated by a source. In this presentation, conditions are derived which are sufficient to ensure that an estimate of sound power based on close-in sound-pressure measurements over a surface enveloping the source (in a free field or free field over a reflecting plane) is, in fact, for perfect sampling, an upper bound to the true sound power. Conditions for this upper bound to be the least upper bound are also derived for the case of the absence of a priori information regarding the directivity of the source. Experimental data are presented which support the analytical findings. Some implications of sampling error in the measurement process are also discussed. [ABSTRACT FROM AUTHOR]

This workshop, sponsored by the Noise Technical Committee of The Acoustical Society, is intended to provide a summary of current state-of-the-art in reverberation room qualification for ANSI S1.21-1972. This standard prescribes evaluation procedures for the qualification of a reverberation room measurement system for the measurement of broad-band noise and discrete frequency sound. In this introduction, the evaluation procedures are reviewed and the performance requirements are discussed. [ABSTRACT FROM AUTHOR]

The purpose of the microphone system is to provide an estimate of the space average sound pressure level with the minimum possible variance for measurement of a tone. The variance in the estimate for measurement of a tone in a given room is a function of the number of independent samples taken, and the effectiveness of the rotating diffuser at the frequency of interest. Theoretical considerations indicate that the number of independent samples produced by an array is equal to the number of microphones (separated by more than one-half wavelength) which are used. For a microphone traverse, the number of half-wavelengths along the traversing path gives approximately the number of independent samples. Thus, there is always a frequency above which a traverse should provide a lower variance in the estimate than a given array. Experience suggests, however, that the lowest frequency of interest determines the accuracy requirements for the microphone system, assuming a reasonably effective rotating diffuser. In this presentation, it is shown that for 'ideal'-shaped rooms with reasonably effective rotating diffusers the difference between the accuracy of the estimate of a large array or traverse is small. However, for rooms with less than 'ideal' shape, it is shown that an array can provide substantially improved accuracy in comparison to a traverse due to the increased number of samples which can be generated at low frequencies. [ABSTRACT FROM AUTHOR]

The exact description of sound transmission through an enclosure depends, in general, on the details of the source radiation characteristics, coupling of the source to the enclosure acoustic space, and coupling of the acoustic space to the resonant and nonresonant motion of the enclosure walls. Moreover, for an extended source, and a relatively small and absorptive enclosed space, an exact description is beyond the present state of the art. In this paper, a simple design procedure based on an energy flow analysis is described, which provides good lower bound estimates of enclosure performance. The performance parameter that is calculated is the lower bound of a space average, or radiated power insertion loss. When formulated in this way, the performance is reciprocal in the sense that it is independent of whether transmission is from outside to inside or inside to outside. Above the first enclosure volume resonance, the result is PIL >= TL + 10 log A/S where PIL is the power insertion loss, TL is the field incidence transmission loss of the enclosure walls, A is the sabine absorption of the enclosure interior, and S is the radiating area of the walls. A result that is applicable below the first enclosure resonance is also presented. A number of experimental results are presented which confirm the analysis procedures. [Work supported in part by General Electric Co., Aircraft Engine Group, Cincinnati, Ohio, and NASA-Langley Research Center.] [ABSTRACT FROM AUTHOR]