A loud-speaker of a closed or a bass-reflex type, wherein a plurality of speaker units are intensively arranged behind an opening of a baffle board or a throat of a sounding horn with the sound wave radiating direction thereof being concentrated toward the center axis of the opening of throat, and the...http://www.google.com/patents/US4391346?utm_source=gb-gplus-sharePatent US4391346 - Loud-speaker
