Equalization for Central Phantom Images and Dependence on Loudspeaker Spacing: Reformatting from Three Loudspeakers to Two Loudspeakers
The problem of properly equalizing the centered phantom image (e.g., centered vocalist or virtual center loudspeaker in a home theater) is examined in detail. The strong dependence of the correct EQ on loudspeaker spacing is emphasized. Applying the theory of head-related stereophony, correct EQ curves are derived for several common loudspeaker spacings. Complete results are presented as magnitude responses of second- and fourth-order analog and digital filters as well as poles and zeros, making possible cookbook implementations. A surface plot shows magnitude responses for correct EQ for loudspeaker spacings from ±90° to 0°. Results are also presented for the situation in which the correct EQ has been applied for a particular loudspeaker spacing, but the loudspeakers are at other spacings. Filters realizing the inverses of these results will correct the mistake. A modest standardization effort will allow manufacturers to build user-adjustable correction filters into their equipment.:
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