Transmission loss measurement by small reverberation chambers

Abstract

Even though the measurement of transmission loss by the two-room method is well established and documented, the application has traditionally been applied to architectural structures such as wall panels and doors. This requires the construction of rooms of large volume with thick walls, which was severally reported in acoustic journals. Nevertheless, there exist panels whose sizes are small with respect to the wall thickness due to their inherent applications or other considerations such as costs or difficulties in fabrication. These panels are not apt to be tested in large rooms with thick walls because of the resulting deterioration in diffusivity due to the existence of a tunnel between the chambers. In such cases, smaller rooms with correspondingly thinner walls may be used to advantage in the determination of the transmission loss. This paper describes the construction of a pair of twin reverberation chambers in the shape of a pentagonal parallelepiped with an inclined roof. Acoustic characteristics such as diffusivity, cutoff frequency, and reverberation time of the rooms are presented. Results of transmission loss measurements in aluminum and carbon-epoxy composite specimens are also reported. [Supported by NASA Grant NGR 21-002-350.]