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Acoustic and Thermo-Acoustic

measurement equipment

A construction that provides a low-reflecting termination of the duct is a device of general need in the practice of acoustic laboratories. Many types of acoustic measurements become much easier, or even only possible, when one can provide anechoic terminations in some parts of the measurement setup. The typical application of this kind of termination is the measurement of acoustic power radiated into the duct, or transmission losses in mufflers using the impedance tube technique. Another prospective application of the low-reflecting duct termination is the stabilization of self-excited (autonomous) oscillations which can arise in systems with so-called dependent acoustic sources. Thermo-acoustically unstable appliances (like combustors, heaters, heat exchangers, etc.) or aeroacoustically unstable systems (like a pipeline with side branches, ventilation ducting, etc.) are a few examples to mention. In general, low-reflecting boundaries allow suppression of the duct eigenmodes which can be advantageous in many cases of practical interests.

Below anechoic termination, low reflecting box, BC mufflers, microphone calibration tool, and active impedance tube have been designed, made and tested. The value of the reflection coefficient of the anechoic termination is |R|< 0.05 over 20-500 Hz and |R|<0.1 over 500-2000 Hz.

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