Procedure for determination of sound power levels of direct-radiator loudspeakers in the low-frequency range using the sound pressure within the system enclosure

Abstract

In this paper, a method of sound power level determination in the low-frequency range applied to direct-radiator loudspeakers and using the sound pressure within the system enclosure is proposed and discussed. The procedure is based on the Thiele-Small model of the loudspeaker, whereby the emitted sound power over a 2π sr solid angle is related to the total acoustic volume velocity radiated by the system, which simultaneously can be linked to the internal sound pressure in the box. Under normal conditions, this sound pressure is independent of the acoustic environment present outside the loudspeaker. To determine the internal sound pressure, the microphone could be easily inserted into the enclosure, usually through the bass-reflex opening in vented-box systems or via a small orifice in closed-box loudspeakers. The proposed method has been tested and compared with the standard methods used commonly nowadays (the reverberation room method and the anechoic room technique) on a bass-reflex loudspeaker system whose electrical analogous circuit model and sound power response are deeply known. To assess the results, the theoretical sound power response based on the electrical analogous circuit of the loudspeaker (Thiele-Small model) has been compared with all the former measurements, obtaining high agreement in the low-frequency range when the proposed method is compared with the sound power response of the theoretical model, thus validating the procedure. Even more, the measurements on the loudspeaker using the method here proposed seem to be better in the low-frequency range than that obtained by the standard methods, that is, the reverberation and the anechoic room techniques.