Volume 8, Issue 2, October 1936
Index of content:
8(1936); http://dx.doi.org/10.1121/1.1915879View Description Hide Description
Distributions of loudness judgments are shown for a large group of observers comparing 100‐ and 5000‐cycle tones with a 1000‐cycle reference tone. The tests were made with automatic equipment for conducting the constant stimuli type of test. Additional tests show how experience, hearingacuity, time variations, and other factors affect deviations of loudness judgments.
A Method of Eliminating Cavity Resonance, Extending Low Frequency Response and Increasing Acoustic Damping in Cabinet Type Loudspeakers8(1936); http://dx.doi.org/10.1121/1.1915883View Description Hide Description
When a direct‐radiator loudspeaker is mounted in a cabinet, as in the conventional radio receiver, response irregularities are introduced because of resonances in the space behind the loudspeaker. With a cabinet and a speaker diaphragm of ordinary size, the acoustic load at low frequencies is highly reactive, the radiation efficiency is very low and diaphragm amplitudes become excessive. In the method described, the rear of the loudspeaker diaphragm is tightly coupled to one end of a folded conduit lined with sound‐absorbing material and terminating in an opening in the bottom of the cabinet. This arrangement is called an acoustical labyrinth. By suitably proportioning the conduit, an extension downward of the reproduced frequency range is secured. The acoustic impedance of the conduit is shown by measurement to offer a diaphragm load having desirable characteristics, it being predominantly resistive over nearly the entire measured low frequency range (40–350 cycles). Measurements of the important acoustic and electrical impedances of a conventional and a labyrinth loudspeaker system also are reported. The improvement in the frequency characteristic of a cabinet type loudspeaker afforded by the use of the acoustical labyrinth is shown by response curves.
8(1936); http://dx.doi.org/10.1121/1.1915885View Description Hide Description
This paper gives some data on the absorbing material used in a room recently completed and intended for acoustical measurements under essentially free field conditions. The absorbing material, which consists of a number of layers of cloth separated by air spaces, is shown to have an absorption coefficient of the order of 98 to 99 percent over a wide frequency range. Some data are also given showing the degree of departures of the sound field in the room from the field to be expected in free space. It is shown that it may not be possible to duplicate a free field in an enclosed room, regardless of the freedom from interference obtained, because of the fact that the pressure may decrease more rapidly than the inverse distance law applying to a free field.
8(1936); http://dx.doi.org/10.1121/1.1915886View Description Hide Description
The extension of both frequency and volume range in large scale sound reproduction has imposed severe limitations on the performance characteristics of loudspeakers employed in these applications. This paper discusses some of the problems that arise under such conditions and what means have been taken for their solution. The limitations of single speakers to cover the entire frequency range are mentioned and the advantages of multispeaker systems are pointed out.
8(1936); http://dx.doi.org/10.1121/1.1915887View Description Hide Description