Sound absorption of Helmholtz resonators included a neck extension built in surface panel

Acoustic resonant absorber like a perforated panel or a Helmholtz resonator can be tuned at a low frequency by extending its neck or enlarging cavity volume. However, a total size of the resonators is often quite large when the neck or the cavity is simply extended for tuning at a low frequency. Previous researchers have studied Helmholtz resonator shortened in its size by subsided neck into back air cavity, and confirm that this resonator is tuned at low frequency without a deep cavity. The author has studied the effects of a winding built-in neck extension to sound absorption of perforated panels, which shows same effects as the subsided neck into back cavity. This study obtains sound absorption coefficient by measuring surface acoustic impedance at Helmholtz resonator, and discusses sound absorption of the resonator included various neck extensions built in a surface panel. Discussions in this paper focus effects of path length, patterns, or number of turns of the winding neck extension and cavity volume to the sound absorption of the Helmholtz resonator.