Notes on the Development of a New Type of Hornless Loudspeaker
The paper describes a series of tests directed to the evolution of a loudspeaker, free from resonance. Various types of sound source were tried. For the most part horns were avoided. Diaphragms, when employed, were neither so light and stiff that their natural resonance was above the essential frequency range, or so flexible that their resonance was below the lowest important acoustic frequency. Best results were obtained with the latter type, and it is shown on theoretical grounds that a small diaphragm, the motion of which is controlled by intertia only, and located in an opening in a large flat wall, will give an output sound pressure proportional to the actuating force, independent of frequency. It should be possible to make an ideal sound reproducer on this principle. A practical loudspeaker which approximately fulfills the above conditions has now been evolved. It consists of a flexibly supported paper cone actuated by a coil in a magnetic field and provided with a baffle. As compared with ordinary loudspeakers, this instrument radiates much more of the low tones and more of the very high frequencies which makes for clearer articulation. The extension of the range of response of the loudspeaker to higher and lower frequencies makes defects in the remainder of the system more noticeable, particularly roughness and blasting due to overworked amplifiers. It is, therefore, important that the amplifier used with the new loudspeaker be designed to have ample capacity.
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