Flat-response sound source technique for using the two-microphone method in an impedance tube

In this letter, to improve the acoustic impedance measurement in a tube using the two-microphone method, a sound source technique is developed that is capable of generating incident sound waves of uniform intensity over the entire frequency range of interest. The basic principle is to use a digitally synthesized compensation input signal to achieve a flat response of the sound source provided by one or more loudspeakers. The present sound source technique has been demonstrated to be very effective and easily implemented with the current impedance tube testing systems.