A dedicated, time dependent finite element program was used to study the absorption of sound in a viscoelastic cylinder containing a cavity. The effect on the sound absorption and the cylinder surface impedance of varying the cavity's size and shape was examined. Representative models were made and tested in a novel impedance tube and the experimental data is in good agreement with the finite element studies. We have studied such a cavity using a finite eleolent analysis supported by data obtained from a guided wave tube for experimental verification. Here we observe the changes in resonant frequency and impedance as the hole height varies from .0015 meters to .003 meters. As the hole height controls the side wall resonance, the frequency shift is most noticeable in the 20-30 kHz area where the side wall system has its resonance.

Variation of cavity size and shape significantly affects sound absorption and cylinder surface impedance in a viscoelastic cylinder, with the most noticeable frequency shift in the 20-30 kHz range.

FINITE ELEMENT STUDIES OF SINGLE CAVITY ACOUSTIC ABSORBERS

Key Takeaway: Variation of cavity size and shape significantly affects sound absorption and cylinder surface impedance in a viscoelastic cylinder, with the most noticeable frequency shift in the 20-30 kHz range.