Is There a Systematic Disagreement between Intensity-Based and Pressure-Based Sound Transmission Loss Measurements?

Abstract

Conventional and intensity-based sound transmission loss measurements have frequently been compared in the literature. Looking at published results determined under laboratory conditions, one would come to the conclusion that it is only possible to obtain good agreement between the two methods in a very restricted frequency range. It has often been reported that the intensity method gives lower values of the sound reduction index than the conventional method at low frequencies and higher at high frequencies. The purpose of this paper is to demonstrate with experimental data that excellent agreement between the two methods can be obtained in a fairly wide frequency range (80 Hz-6.3 kHz), provided that the measurements are carried out under optimum conditions. As pointed out by several authors, the only reason for systematic deviations between the two methods is the effect of having a partition that is highly absorbing in the receiving room.

Airborne sound insulation of vacuum insulating glazing: General observations from measurements

“…Although the measurements were made in a laboratory, the procedure followed might be better described as a field measurement mainly because the sample size was smaller than required for standard laboratory measurements, and the sample was held in place with closed cell foam and metal clamps rather than putty. The intensity method has been shown to give results consistent with the conventional pressure method of measuring sound reduction index, 18 apart from a systematic difference that can occur when the receiving room in conventional measurements is not large. 12,17,19 An adaptation term, K c , is included in ISO 15186 to compensate for this discrepancy, including a set of suggested values for a typical receiving room volume.…”