Improved membrane absorbers

Oldfield, RG

Abstract

This thesis presents research into two novel techniques for improving the low frequency performance, tunability and efficiency of membrane absorbers. The first approach uses a loudspeaker surround as the mounting for the membrane, increasing the moving mass, thereby lowering the resonant frequency of the system. Using a loudspeaker surround also allows for more accurate prediction of the absorber’s performance as the mounting conditions are such that the membrane can be more accurately represented by a lumped mass moving as a piston.
The second approach expands upon this technique and uses a loudspeaker within a sealed cabinet to act as the membrane absorber. Passive electronic components can be connected across the terminals of the loudspeaker to adapt the mechanical resonance properties of the system. Tests were performed on the absorber systems using a specially constructed low frequency impedance tube. It was found that varying a complex electrical load connected to the driver terminals enabled the range of obtainable resonant frequencies of the system to be dramatically increased. Varying a solely resistive load has also been shown to alter the absorption bandwidth. An analogue circuit analysis of the absorber system is presented and demonstrates good agreement with impedance tube measurements. A final model is shown that allows for the system to be optimised using different resistive and reactive components given a specific driver.

Citation

Oldfield, R. Improved membrane absorbers. (Dissertation). The University of Salford

• Thesis Type: Dissertation
• Deposit Date: Jan 25, 2012
• Publicly Available Date: Jan 25, 2012
• Award Date: Sep 1, 2006