A High Efficiency Receiver for a Horn-Type Loud Speaker of Large Power Capacity

Abstract

Synopsis: This paper describes a telephone receiver of the moving coil type which is particularly adaptable to the horn type of loud speaker and which represents a notable advance over similar devices at present available. Its design is such as to permit of a continuous electrical input of 30 watts as contrasted with the largest capacity heretofore available of about 5 watts. In addition, measurements show that the receiver has a conversion efficiency from electrical to sound energy varying between 10 and 50 per cent in the frequency range of 60 to 7,500 cycles. Throughout most of this range, its efficiency is 50 per cent or better. This contrasts with an average efficiency of about 1 per cent for other loud speakers either of the horn or cone type. Combining the 50 fold increase in efficiency with a 5 or 6 fold increase in power capacity, a single loud speaker unit of the type here described is capable of 250 to 300 times the sound output of anything heretofore available. This device is in commercial use in connection with the Vitaphone and Movietone types of talking motion pictures. As commercially produced in quantities numbering several thousand, an average efficiency of the order of 30 per cent has been realized.

A New Methodology for the Acoustic Design of Compression Driver Phase Plugs With Radial Channels

“…Thus far we have not considered the effect of modal excitation in the compression cavity. In the next section we shall refine the design to account for this in a similar way to [4].…”

“…Many commercial designs, either by design or inheritance, are based on the geometry proposed by Smith. Recent work by the authors has extended Smith's method to account for the curvature of the compression cavity common with modern domed membranes [4]. The authors work also employs numerical models to illustrate the importance of using phase plug design methods that take account of the compression chamber modes.…”

“…Surprisingly, the only published work on the acoustical behaviour is by Henricksen [8] [9] in his two comparisons to annular phase plugs. However, the analysis presented in these papers uses an equivalent technique to the equal path-length approach, which was originally proposed by Wente [10], superseded by Smith [2], and shown to be inadequate by the authors [4].…”

“…It is demonstrated that modes in the compression cavity are excited by the radiating membrane and that the phase plug must be carefully constructed to compensate for this excitation. The geometry of the channel entrance is derived in order to minimise the excitation of these modes in an equivalent analysis to that presented by the authors for annular phase plug designs [4]. Numerically modelled examples of the new phase plug geometry are presented.…”

Shape Optimization of a Compression Driver Phase Plug

“…While improving the impedance match at moderately high frequencies, this simple setup suffers from radial resonances in the compression chamber, which cause frequency response irregularities and limit the upper operational frequency. Wente and Thuras [44] introduced a phase plug with one annular channel between the compression chamber and the horn throat, and could thus partly avoid the radial resonances and push the usable frequency limit further up.…”