Measured performance and predicted transmission loss of plug mufflers

Abstract

Predicted transmission loss characteristics of plug mufflers are compared to measurements of both transmission loss and insertion loss. A plug muffler is a cross flow expansion and a cross flow contraction perforated tube element connected in series. The predictions were based on transfer matrix calculations using a decoupling approach which gives closed form expressions for the matrix terms [K. Jayaraman and K. Yam, J. Acoust. Soc. Am. 69, 390–396 (1981)]. Transmission loss measurements with and without flow were made on an impedance tube with a horn‐driver as a noise source. Insertion loss measurements were made on the impedance tube, a cold flow facility, and on an engine. Results (zero) are shown for Mach numbers from 0–0.18 at ambient and elevated temperatures. The agreement between the measured and predicted results is excellent.