Efficient Resonant Loudspeakers with Large Form-Factor Design Freedom
Small cabinet loudspeakers with a flat response are quite inefficient. Assuming that the frequency response can be manipulated electronically, systems that have a nonflat soundpressure level (SPL) response can provide greater usable efficiency. Such a nonflat design can deal with very compact housing, but for small drivers it would require a relatively large cone excursion to obtain a high SPL. A new solution is presented that uses a resonant combination of a coupling volume and a long pipe-shaped port. In this structure the efficient resonant coupling of the driver to the acoustic load enables small drivers with modest cone displacement to achieve a high SPL. Due to the high and narrow peak in the frequency response, the normal operating range of the driver decreases considerably. This makes the driver unsuitable for normal use. To overcome this, a second measure is applied. Nonlinear processing essentially compresses the bandwidth of a 20–120-Hz 2.5-octave bass signal down to a much narrower span, which is centered where the driver efficiency is maximum. This system allows very compact loudspeakers. An experimental example of such a design is described, and a working prototype is discussed. The new loudspeaker is compared with a closed cabinet and a bass-reflex cabinet using the same drivers. It appears that the new loudspeaker has the highest output in its working range.
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