The Modeling and Design of a Reactive Muffler to Reduce a Low Frequency Tone

Large reciprocating engines produce a tonal spectrum of sound radiating from their exhaust. Even after standard reactive mufflers and after-treatment devices are added, and the target A-weighted sound level has been achieved, very audible low frequency tones can remain, and their levels are sometimes even enhanced by the exhaust system, creating potential annoyance problems in neighboring communities. This paper describes a practical design approach to such a problem and demonstrates variation in critical system parameters that affect acoustical performance. These parameters include temperature, source impedance, end impedance, flow, and pipe lengths, which are explored through practical models. The results of field measurements before and after installation of a final design are included and demonstrate a significant reduction in the sound level at the frequencies of interest.