The basic properties of acoustics in small rooms and the effects leading to uneven frequency responses are described. The principles underlying possible equalization schemes are outlined. This paper concentrates on the underlying causes of response irregularities rather than discussing proprietary solutions. It is shown that additional low-frequency loudspeakers can help to optimize the low-frequency responses without detriment to the higher frequency image localization. By using several low-frequency sources, some response control can be achieved over a limited region. At high frequencies, the objective responses of rooms do not match the subjective impressions, and equalization based on measured parameters is likely to be unsuccessful. Equalization schemes based on relatively wide-band or short-term response parameters are likely to match the auditory perception mechanisms better and, thus, to be more successful. Automatic or active control of equalization is essential for complex schemes. However, it adds little to the fundamental principles and the inherent limitations of either low- or high-frequency equalization.
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