Sound absorption of resonators or perforated panels with multiple folded long tubes crammed in small module by additive manufacturing

Abstract

Resonators or perforated panels give a large sound absorption at a resonant frequency tuned by opening area of the pores, neck length and a cavity depth behind the neck. The author has studied the sound absorption of thin tile-like resonators tuned at low frequencies by including a folded long neck in its surface panel. The resonators are made by an additive manufacturing with a fused deposition modeling (FDM). This paper makes the resonators or the perforated panels with multiple folded long tubes and discusses its measured sound absorption characteristics. One of the multiple folded long tubes is crammed in 12 mm × 12 mm × 19.2 mm of rectangular module even if the tube has 2 mm × 2 mm of opening area and 288 mm of length. A perforated panel consisted of planar periodic arrays of this module gives a large sound absorption at 69 Hz when a 40 mm depth of cavity behind the perforated panel. Furthermore, when the planar periodic arrays of small Helmholtz resonators applied single module and single cavity tuned at different resonant frequency, it has potential to form an acoustic metasurface with sound absorption at broadband frequencies.