Objective:

Measuring sound absorption is essential to performing acoustic measurements and experiments under controlled acoustic conditions, especially considering the acoustic influence of room boundaries.

So-called "in-situ" methods allow measurement of the reflection and absorption coefficients under real conditions in a single measurement procedure. The method proposed captures the direct signal and reflections in one measurement. These reflections not only include the direct, interesting one, but also others from the surroundings. To separate the reflections coming from the tested surface, the influence of the direct signal and other reflections must be cancelled.

One known separation method uses a time-windowing technique to separate the direct signal from the reflections. When the impulse response of the direct signal and reflections overlap in time, this method is no longer satisfactory. Frequency-dependent windowing is necessary to separate the different parts of the signal. However, in the wavelet domain, it is possible to observe separation of the interesting reflection.

The objective of this project is to study how the use of wavelet multipliers could improve the efficiency of the in-situ methods in this context .

Method:

A demonstrator system will be built to acquire the necessary measurements for the evaluation of absorption coefficients. This demonstrator will be used to evaluate the usefulness of the new methods in a semi-anechoic room.

A systematic numeric study will be carried out on the acquired signals, in order to manually determine the symbol of a wavelet multiplier for the extraction of the reflected signal. The best parameters for optimal separation will then be investigated. This, in combination with the use of physical models, will help design a semi-automatic method for the calculation of the optimal multiplier symbol.

Application:

The improved measurement method will be available for in-situ measurement of reflection and absorption coefficients