Abstract
Acoustic transmission loss is a common parameter utilized throughout several studies to evaluate the acoustic characteristics of a given test element. Transmission loss has been frequently referred to as a source independent parameter. However, this work presents evidence that the incident acoustic pressure amplitude does, in fact, have an effect on the measured transmission loss for some passive damping devices. The transmission loss was experimentally measured utilizing the two-source location method and the specimens tested include an expansion chamber, a quarter wave resonator, a Herschel–Quincke tube and various Helmholtz resonators. When varying the power supplied to the acoustic source, it was noted that all the devices exhibited nearly constant values of transmission loss, with the exception of the Helmholtz resonators. The Helmholtz resonators had a significant variance of transmission loss with respect to the acoustic source power. This decrease in performance is caused by the “jet-flow” phenomenon occurring at the Helmholtz resonator neck, which results in increased acoustic losses. The present work illustrates that the assumption of source independence, which is often made when using transmission loss to evaluate damping devices, must be taken with caution, as this assumption is case dependent and may be crucial when scaling experimental studies to an industrial setting.
Highlights
Transmission loss (TL) is an acoustic parameter which is widely used throughout industry and research applications
This paper focuses on the TL of the Helmholtz resonator (HR), a device that is ubiquitous in research because of its geometric simplicity and ability to target low frequencies while maintaining relatively small dimensions [2,3,4]
To begin clarification of this behaviour, the experimental measurement of the transmission loss spectra was first conducted for three reactive damping devices: an expansion chamber (EC), a quarter wave resonator (QWR) and a Herschel–Quincke (HQ) device
Summary
Transmission loss (TL) is an acoustic parameter which is widely used throughout industry and research applications. It is a measure of the ratio of incident to transmitted acoustic sound power levels, as described in Equation (1) [1]: TL = 10 log Wi Wt (1). This paper will highlight that the assumption of source and system independence should be taken with caution, considering that the effect of incident acoustic pressure amplitudes on the transmission loss of damping devices can be overlooked. The effect of incident acoustic pressure amplitude may be crucial when attempting to extrapolate the transmission loss measured in an experimental setup to that which is estimated for an industrial setting.
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