Small dimension low frequency folded exponential horn loudspeaker with unitary sound path and loudspeaker system including same

摘要

A small dimension low frequency loudspeaker has a folded exponential horn which provides a unitary curved sound path from an electroacoustic transducer at the throat of the horn to a volume into which sound is radiated at the mouth of the horn. The length of the horn is such that, at an exponential rate of expansion between the throat and the mouth, the mouth, when it is bounded by at least one planar surface, such as a floor, a ceiling, and/or walls of a room, has adequate area to enable reproduction of low audible frequencies. An illustrative embodiment of the low frequency loudspeaker has an effective low end cut- off frequency of 55 Hz. A loudspeaker system, including a low frequency loudspeaker as well as midrange and high frequency loudspeakers and an LC crossover network, is also disclosed. The LC crossover network includes an autotransformer which not only serves as a component to determine a crossover frequency but which also boosts the electrical signal that is input to the electroacoustic transducer of a less efficient loudspeaker. The autotransformer increases the output of the less efficient loudspeaker and accommodates its use with more efficient loudspeakers so that the overall loudspeaker system operates at optimum efficiency. An illustrative embodiment of the loudspeaker system affords 108 dB SPL output at 1 meter with 1 watt input which corresponds to about 20% overall efficiency. The smoothness of amplitude response over the range of audible frequencies that is necessary for high fidelity sound reproduction is improved by inclusion of peaking circuits in the LC crossover network of the loudspeaker system to enhance amplitude response in the regions of crossover frequencies. Side wings are additionally provided to eliminate cavities at the sides of the loudspeaker system which would otherwise cause deterioration of smoothness of amplitude response.