Acoustic Pulse Testing

In the testing of electro-acoustic transducers such as microphones one desires to find the generated electrical signal in the presence of an incident plane wave sound field. Likewise, in testing loudspeakers, one wishes to measure the generated sound field. In practical testing systems, reflections which interfere with the measurement are in general present even in the best of “dead” rooms. The pulse testing procedure has been successful in acoustic measurements in eliminating the effects of reflections from the boundaries of the medium. The method consists of generating in the medium a short finite train of sinusoidal waves whose wave-length corresponds to the frequency at which the measurement is desired. The directly transmitted pulse is measured before any reflected signal reaches the sound pickup. The reverberation level is allowed to become negligible before the next pulse is generated and measured. Electronic circuits for generating the applied electrical signal and for continuously recording the received signal level will be described. The system also has been designed so that the direct signal may be discriminated against and any reflection measured, thus providing a means of measuring reflection coefficients of acoustic materials. The limitations of the pulse method will be discussed and compared with those of frequency warble and noise methods of vitiating reflections.