This report introduces a new database of room impulse responses (RIRs) measured in an empty rectangular room using subwoofers as sound sources. The purpose of this database, publicly available for download, is to provide acoustic measurements within the frequency region of modal resonances. Performing acoustic measurements at low frequencies presents many difficulties, mainly related to ambient noise and to unavoidable nonlinearities of the subwoofer. In this report, it is shown that these issues can be addressed and partially solved by means of the exponential sine-sweep technique and a careful calibration of the measurement equipment. A procedure for estimating the reverberation time at very low frequencies is proposed, which uses a cosine-modulated filterbank and an approximation of the RIRs using parametric models in order to reduce problems related to low signal-to-noise ratio and to the length of typical band-pass filter responses. [7] contain binaural and head-related RIRs, and are useful in hearing-aids applications. Other databases present specific configurations of the microphones, usually arranged into arrays. What is common to all these databases is that they use fullrange loudspeakers, whose frequency response typi-* To whom correspondence should be addressed. Tel: +32-16-321817; e-mail: giacomo.vairetti@esat.kuleuven.be cally has a lower bound of 50-100 Hz. While these databases cover a frequency range sufficient for the development and evaluation of speech enhancement algorithms, information about a significant portion of the modal response of the room is missing.
INTRODUCTIONNowadays, home audio systems generally include a subwoofer, which is intended for the reproduction of low-frequency content typically in the region between 20 Hz and 150 Hz. In this frequency range, small-sized typical rooms operate within the modal frequency region [8]. In small-sized rooms, most of the acoustical problems are actually due to poor acoustics at very low frequencies (LFs). The modal resonances are usually well separated, energetic, and detectable by the human ear [9], thus degrading the perceived sound quality. A subwoofer with small enough lower cut-off frequency can even partially excite the so-called cavity mode (i.e. the modal resonance centered at 0 Hz). Therefore, algorithms for home audio system applications, such as room compensation algorithms, should be validated also on