In professional audio applications, small loudspeakers are often mounted on or near large solid surfaces, such as mixing consoles, desktops, and work surfaces. When mounted in this manner, the surface is in the near field of the loudspeaker and thus may detrimentally modify its frequency response by acoustic loading. In a majority of cases, analysis reveals that the magnitude response changes in a predictable and systematic way. Changes in acoustic loading raise the magnitude response in the 100–250-Hz region, and reflections cause combing effects at mid to high frequencies. A statistical study of 89 active near-field loudspeakers, located in 45 different installations, revealed that in 80% of the cases a one-sixth-octave-wide peak in the magnitude response at 141 Hz of about 4–6 dB was exhibited. The development of an active correction method is described which minimizes this low-frequency loading problem. It uses a single second-order notch filter to equalize the low-frequency loading effects.
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https://aes2.org/publications/elibrary-page/?id=13683
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