A platform to measure transmission loss of mufflers with flow

Abstract

Mufflers are widely used to reduce the exhaust noise of Internal Combustion Engines. Every muffler has to be tailored carefully to the engine to which it is connected. One very important tool of muffler design is the measurement of its acoustic transmission loss. Introduction of flow is a key issue as it simulates a real engine situation. Transmission loss is defined as the ratio between the inlet sound power to the output sound power provided that the terminations are anechoic. This condition is hard to realize, especially in the presence of flow. The two source-location method has been proven to be the most stable and most efficient technique to measure muffler transmission loss. At several companies and research institutes, this has become a standard measurement which is repeated frequently throughout the design process. This paper describes a new platform, which is based on LABVIEW and National Instruments Data Acquisition cards, to automate the measurement accounting for different theoretical and practical considerations. Different excitations can be used, and all results are stored for advanced post processing.