Abstract :
The paper describes a series of tests directed to the evolution of a loud speaker, free from resonance. Various types of sound source were tried. For the most part horns were avoided. Diaphragms, when employed, were either 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 inertia 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 loud speaker which approximately fulfills the above conditions has nolo 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 loud speakers, 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 loud speaker 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 loud speaker be designed to have ample capacity.
