Random Incidence Transmission Loss of Miniature Helmholtz Resonator Embedded Acoustic Meta-material
* Presenting author
An array of light-weight miniature Helmholtz resonators (HRs), was shown to significantly enhance the low frequency absorption, when embedded in a PU foam material; this test was carried out in an impedance tube. This concept was then used to study the sound absorption in a cylindrical cavity. A series of tests were carried out by changing number of HRs, embedded circumferentially in PU foam, at various radial distances on top of the cavity, with a noise source at the bottom. About 8-14 dB reduction in noise levels was observed at the lower frequencies. In this paper, the idea is now extended to examine the random incidence transmission loss of such an array of embedded HRs. Towards, this purpose a twin room reverberation chamber with a 30 cm x 30 cm panel in between is used; random incidence tests will be done for a panel with 20 mm foam alone and the same foam with an array of miniature resonators. The effectiveness of this concept to increase transmission loss at lower frequencies will be demonstrated. Also, by adjusting the resonator frequencies, by intruding the neck into resonator cavity, s shown to yield increased tranmission loss over a broader range of frequencies.