Recently, a desktop procedure for measuring the transmission loss of automotive door seals was proposed. In that procedure, a door seal is placed in a square-section, four-microphone standing wave tube, and is held between a movable clamp and the opposite tube wall. Since the clamp partially blocks the tube cross-section, it is necessary to correct the measured transmission loss to obtain the transmission loss of the seal alone. Initially, the correction factor was determined by measuring transmission losses of samples having known properties, and that were clamped in the tube in the same way as the seals. It would be desirable if those samples had transmission losses comparable to the seals, but the original materials had transmission losses much lower than the seals. Since it was not possible to find materials having the desired, high transmission loss, the correction factor has now been determined by using a finite element model of the measurement arrangement, in which the “sample” was represented as a porous material whose properties were adjusted to yield transmission losses similar to the door seals. The procedure by which the new correction factor was determined will be described in detail and a general expression for the correction factor will be given.
Door Seals, Sound Transmission, Standing wave tube, Finite element model
Acoustics and Noise Control
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