Helmholtz Resonators as a tool for suppressing the Mass-Air-Mass resonance in Cavity Walls

Abstract

In this exploratory research project we report on initial encouraging results of using HRs to reduce the loss of insulation in lightweight cavity walls in the region of the mass-air-mass resonance. This resonance results from the two wall leaves enclosing an air spring on which they can resonate. Often the wall insulation in this critical low frequency band is significantly poorer than if it were only a single leaf wall. Many light weight propriety wall systems are designed so that this region is sited just outside the range assessed by the single figure values (STC and Rw) used to set building code requirements. Such walls, although meeting code requirements, can be subjectively undesirable when insulating against sounds from low frequency loudspeakers which are a ubiquitous feature of modern living. So far the work has comprised using 3D printed HRs tuned to the M-A-M and coupled into an experimental cavity to demonstrate proof of principle, and then moved to investigating designs which would fit into typical wall studs so as to minimise any disruption of standard wall construction processes.