Reducing low frequency boiler stack noise in the community

摘要

Noise complaints were received from the two closest residences in the adjacent community whenever certain boilers were operated by the client. Complaints were described as low frequency or rumbling with observable physical vibration. Measurements in the community showed strong multiple tonal peaks starting at 15 Hz in the infrasound range (<20 Hz) and many tones throughout the low frequency range of 20 to 200 Hz. Diagnostic measurements inside the boiler stacks quantified the acoustic power and frequency spectrum of each of the five boiler stacks on both gas and oil fuel. The measurements also demonstrated that the lowest tone was an acoustic resonance, ala “organ pipe” mode driven by the high temperature exhaust flow. A special tuned cavity muffler was designed and installed on the three loudest units, and performance verification measurements showed that the resonance was eliminated and reductions of 21 dBA and 22 dBC were demonstrated. No complaints have been received since the muffler installation was completed.