Effect of inserting a Helmholtz resonator on sound insulation in a double-leaf partition cavity

We investigated the improvement of sound insulation of a double-leaf partition using Helmholtz resonators. We proposed a method of predicting the sound reduction index R0 at normal incidence using impedance transfer, under the assumption that the resonators installed in the air cavity between the two leaves were independent components of a wall, similarly to boards and studs. Furthermore, for experimentation, a small sample without studs was used to prevent flanking transmission through them. Theoretical and empirical examinations revealed that installing the resonators in the cavity in the following manner was sufficient to control sound insulation at low frequencies. High sound insulation occurred at the resonance frequency f0 of resonators; the sound insulation decreased at higher and lower frequencies than f0. The sound insulation at f0 depended on the acoustic resistance of resonators. When an air layer existed behind the resonators, other peaks and dips appeared at higher frequencies than f0. Installing both a fibrous absorber and resonators in the cavity was sufficient to recover the decreased performance of sound insulation owing to the installation of resonators.