New Methodology for the Acoustic Design of Compression Driver Phase Plugs with Concentric Annular Channels

摘要

Compression drivers couple a radiating diaphragm to a horn throat of smaller area, resulting in high efficiency. When coupled to a suitable horn, this area reduction improves the match between the output mechanical impedance of the driver and the loading acoustic-radiation impedance. Early workers had devised a phase plug to fill most of the cavity volume. Applying both an equal path-length and a modal approach to a phase plug with concentric annular channels coupled to a cavity shaped as a flat disk is explored. The assumption that the cavity may be represented as a flat disk is investigated by comparing its behavior with that of an axially vibrating rigid spherical cap radiating into a curved cavity. It is demonstrated that channel arrangements derived for a flat disk are not optimum for use in a typical compression driver with a curved cavity. A new methodology for calculating the channel positions and areas giving least modal excitation is described. The impact of the new approach is illustrated with a practical design.