GB1245541A - Sound producing device - Google Patents

Abstract

1,245,541. Loud-speakers. L. WALSH. 9 Jan., 1969, No. 1402/69. Heading H4J A conical loud-speaker has substantially all the energy radiated from its interior surface absorbed. The cone is generated by rotation of a curved or straight line about an axis and may be of elliptical type. A11 of the slant lines connecting the smaller end and larger end of the cone are at least 50 degrees in relation to a plane perpendicular to the axis. Preferably the speed of sound in the diaphragm is greater than in air so that over a range of frequencies sound is radiated "coherently". A steep angled cone (Fig. 1) has a voice coil 3 in an air gap 5 and is held by flexible webs 6, 7 to a framework 2. A baffle 9 containing sound absorbent material 10, together with the web 7, encloses the lower end of the diaphragm 1. Material 8, which may be solid or foamed elastomer, e.g. polyurethane foam, also absorb internal energy. A disc 11 of sound absorbent material absorbs any energy reflected back towards the voice coil 3. In use the loud-speaker axis is vertical. By appropriate choice of the material and angle of the cone a cylindrical wave front is radiated horizontally (Fig. 6, not shown). Alternatively, the wave front may tilt upwardly or downwardly. Energy absorption at the diaphragm edge may be effected by elastomer ring sections 28, 29 (Fig. 4) enclosing fluid in which a ring 31 moves, or by magnetic damping (not shown). An alternative loud-speaker (Fig. 5) has an aluminium diaphragm 1 to which is bonded a paper layer 32 and a tapered layer 33 of foamed polyurethane. The cone angle is 80 degrees or more. Alternative diaphragm materials are paper, plastics and hard fibre. The diaphragm may be made in segments with the grain of the diaphragm material properly oriented, or it may be moulded, pressed or formed from flat sheet with one or more seams.