a multi - driver , coaxially mounted loud speaker array utilizing a high frequency bi - morph driving element that is totally contained within the hollow core of the voice coil former of a lower frequency loud speaker . the outwardly radiating conical edge of the high frequency device &# 39 ; s diaphragm is annularly fixed by a compliance to the inner surface of the referenced voice coil former or to the diaphragm which radiates outwardly therefrom and is excited by the former . a significant advancement in the art is acquired by the realization of a cavity between the situs of the bi - morph driving element and the back of the former -- excited diaphragm , behind the annular compliance . this feature allows a design engineer to literally tune the response of the higher frequency loud speaker by deliberately varying the volume of the cavity .