損失を考慮した吸音チェンバの透過損失の推定方法

抄録

This paper describes that the network theory for an electric network with loss elements characterized by resistance r and conductance g is also applicable to the estimation of sound attenuation through a chamber with compliant walls in the lower frequency region and it is verified by the experiments. For the lumped constant system, when the ratio d_r of resistance r to inductance L is equal to the ratio d_g of conductance g to capacitance C in a network, the poles and the zeros for "Betriebsubertragungsfaktor" of the network on a complex plane move toward the left side along the real axis by the distance d, which is the average of ratio d_r and d_g, and accordingly we may directly learn the attenuation characteristic of the network in the lower frequency region. However, the ratio d_r is not equal to the ratio d_g in acoustic filter in general. Even in such cases, we can estimate the attenuation through a chamber lined with absorbing material by assuming both ratios to be equal to each other and by taking Mayers law into consideration. In the distributed constant system, we apply the same concept as mentioned above to an acoustical filter and assume both ratios d_r and d_g per unit length to be equal to d. Calculated results and measured ones show a good agreement with each other for an absorbent chamber. The same method of estimating TL is found to be a good approximation in a lined duct, too.