The results of an extensive series of laboratory measurements of sound transmission throul windows are presented. By reference to these data, the systematic dependence of the sound transmission loss on glass thickness and interpane spacing is evaluated.

Des donn'ees exp'erimentales concernant l'att'enuatiori des sons par les fenetres 3 double vitrage ont Bt6 compar'ees aux pr'edictions de plusieurs modeles th'eoriques. On a trouvg des equations simples qui permettent un ajustage empirique satisfaisant aux donniks. L'att'enuation des sons par un vitrage double a Ct'e compar'ee Zi 1 'at t'enuat ion correspondante pour un vitrage triple; les rCsultats sont semblables lorsque le total des espaces entre les panneaux d'une fengtre triple est 6gal 3 l'espace entre les panneaux d'une fenetre double. Cependant, 11att5nuation rhlis'ee par un vitrage triple est toujours sup'erieure aux frhuences en

sponse in order to obtain accurate phase information. SYSid then uses FFT techniques to deconvolve the stimulus from the measured response and to further analyze the data. From this basic mode of operation SYSid can perform many types of analyses including phase responses, group delay, impulse response, Hilbert envelope, reverse energy time curve, RT60, waterfall displays, electrical impedance, etc. In addition to these linear measurements, SYSid also provides the capabilities to make distortion measurements due to nonlinearities in the system. These include harmonic distortion, intermodulation distortion, THD+ N, and input-output functions. With the current incarnation of SYSid each channel can be up to 32k sample points. Each channel is 16 bits and can be sampled at a maximum rate of 50 kHz. Examples of measurements made in areas of room acoustics, transducer design, and auditory physiology will be presented. 2:15 $pAA6. Measuring and predicting the effect of an audience. J.S. Bradley (Acoust. Lab., Inst. for Res. in Construction, Natl. Res. Council, Ottawa, ON K1A 0R6, Canada)

Measurement of sound transmission through a building facade requires determination of the incident sound power. Interpretation of sound pressure level measurements near a facade is, however, complicated by interference between the incident sound waves and those reflected from the facade. Experimental data and a simple mathematical model are used to examine systematic effects associated with reflections from a large flat facade and, subsequently, to investigate deviations from this simple situation. Although the original motivation for the work was the investigation of problems pertinent to measurements of facade sound transmission, many of the results are relevant for other applications involving measurement of noise near a highly reflective surface.

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