US Patent 7624839 Enclosure for symbiotic active/passive operation of an acoustic driver

A compact loudspeaker enclosure combines planar type devices for high frequency sound reproduction and cone type active devices for low frequency sound reproduction. The low frequency cone type transducers are mounted in baffles between forward and rear enclosed spaces and thus do not directly radiate into the environment. The first enclosed space is acoustically coupled to the environment by the planar device which is mounted between the first enclosed space and the environment with one major face mounted to radiate either directly into the environment or to be horn loaded. The planar operates as a passive radiator to the LF devices at low frequencies and an active device above a crossover frequency.