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Sound Insulation Evaluation Using Transfer Function Measurements

The accepted methods for measurement of sound insulation between rooms, audiometric cabins and other adjacent closed spaces deal with average sound pressure measurements and random sound excitation. The acoustic field can be as diffuse as found in reverberation chambers or form well-determined stationary waves in rectangular rooms. The use of random noise excitation requires averages in time to reduce the expected inherent uncertainties. The use of techniques, such as MLS or swept sine excitation, can avoid time consuming averaging processes and reduce measurement. With the advent of new front-end devices and signal analyzers it is now relatively easy to obtain acoustic transfer functions between two points in space, which can be in adjacent enclosures. With these transfer functions, it is possible to obtain the level differences, required by the international standard, as suggested in a new draft ISO document. This paper presents results obtained for the insulation of a cabin, tested in a reverberation chamber, using random noise and swept sine excitation. An analysis is given of the viability of using fewer positions of sound sources when measuring the transfer function. Repeatability tests, for both methods, are also presented.