ALFA is a software developed for the post-processing and enhancement of data measured with a new measurement method of the sound absorbption coefficient, sometimes called free-field method or echo-impulse method. ALFA can also give the reflection factor and the acoustic impedance of materials.

The method is based on the measurement of the impulse response on the material under test, using an MLS signal and a subsequent cross-correlation; then, the sampled data are post-processed with ALFA to gain directly the wanted coefficient. So the measure can be done in situ and the result of the measurement is available in real time, using only a portable computer, a good quality sampling card and, of course, an amplified loudspeaker and a microphone.

With ALFA the result of the measurement is found quite automatically. Moreover, on the sampled data, an accurate digital post-processing can be done, even later. For example, on the sampled impulse response, the so-called auto equalization or the time subtraction of the direct impulse can be done. Many calculation options are allowed, like the normalization of the window-weighted power of the time data, to have the best results.

Here are some samples from the program:

Main menu. [54 KB]

Example of MLS signal [12 KB]

Example of time impulse response. [63 KB]

Example of sound absorbtion coefficient. [72 KB]

Example of sound absorbtion coefficient (1/3 octave). [87 KB]

Example of reflection factor. [91 KB]

Example of acoustic impedance. [90 KB]

Example of the auto equalization procedure. [62 KB]

Example of study of window positioning effect on the sound absorbtion coefficient. [88 KB]

Options main menu. [69 KB]

Calculation options menu. [65 KB]

FFT main menu. [56 KB]

ALFA was developed by Paolo Guidorzi & Massimo Garai.

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This page designed by Paolo Guidorzi (C) 1996.