Loudspeaker parameter measurement in reverberant environments

Abstract

Loudspeaker driver small-signal parameter measurement is required to design and quantitatively measure loudspeaker enclosures. Such measurements are conventionally performed in an anechoic chamber with the intent of eliminating the acoustic response of the room from influencing the measurement. A novel procedure is proposed to perform the measurements in arbitrary untreated enclosures using a standard sound card. Aoshima’s optimal time stretched pulse [Aoshima, J. Acoust. Soc. Am. (1981)] [Suzuki et al., J. Acoust. Soc. Am. (1995)] is used to excite the loudspeaker. The response is captured by a high-quality flat response microphone. Knowledge of the minimum first reflection time of the enclosure is used to filter out the effects of room response without affecting the measurement of loudspeaker response. A sliding window is used to remove reverberent effects similar to time delay spectrometry (TDS) [Heyser, J. Audio Eng. Soc. (1967)]. The filtered signal is fit against a complex rational polynomial transfer function, inspired by the method described by Leach et al. [IEEE Trans. ASSP Dec. (1979)] and Jain et al. [IEEE Trans. ASSP Feb. (1983)]. The fit is performed by a nonlinear least-squares method written in AMPL [Fourer et al., 1993], a language for mathematical programming.