*U.S. Patent No. 2,612,558 , 09/30/1952 [DjVu111KB]
Crossover Filter Network
Klipsch, Paul W.
     This invention relates to electroc filters and particulary to crossover filter networks used to allocate power in different frequency ranges to different loads, especially to two or more loudspeakers.
     An object is to provide a simplified crossover network of low cost but with frequency response performance comparable with one using costly "high-fidelity" components.
     A further object is to provide a crossover network operable at a high impedance level where capacitor sizes are small and hence inexpensive.

*U.S. Patent No. 2,713,396 , 07/19/1955 (app. 05/24/1950) [DjVu167KB]
NOVEL, SMALL, EXTENDED LOW FREQUENCY (class: 181/199, 181/163)
Tavares, Ernest A.
Abstract: Generally speaking, the present invention relates the sound reproduction art. More specifically, it relates to a novel, small loudspeaker enclosure arranged and so related to a loudspeaker as to greatly extend the low frequency range of useful acoustic radiation thereœrom into a listening region. A great many prior art sound reproducing arrangements have been developed, including a number of different types of speakers and a number of different types of speaker enclosures. However, most such prior art speakers and/or speaker enclosures are incaoable of radiating any substantial amount of usable acoustic power in the very low frequency range. This is true for several reasons. The first and major reason arises from the fact that the vibrating loudspeaker cone, customarily used as the sound reproducer, has a front and a back surface, and acoustic radiation from the front surface of said cone is one hundred eighty degrees (180 ø ) out of phase with respect to acoustic radiation from the back surface thereof. This one hundred eighty degree (180 ø ) phase difference between the front acoustic radiation and the back acoustic radiation is relatively unimportant at high frequencies, since a very small baffle interposed between the front and back radiation, in a manner such as to cause the back radiation to travel a slightly longer distance than the front radiation (or vice versa) before combining therewith, will cause the one hundred eighty degree (180 ø ) phase difference to be completely nullified and the front and back radiation to reinforce each other. However, in the lower frequency range, this one hundred eighty degree (180 ø ) phase difference between the front and back acoustic radiation becomes important and leads to serious loss of useful low frequency acoustic output power because of cancellation occurring when the out of phase front and back radiation combines between the loudspeaker and the listening region. This can be prevented only by the use of very large baffles effectively separating the front and back radiation and causing the back radiation to travel a considerable longer path than the front radiation (or vice versa) before combining therewith. The additional length of travel required for the back radiation being half a wave length or an odd multiple thereof so as to cause the front and back acoustic radiation to be additive and reinforce each other. It will be understood that, since at very low frequencies half an acoustic wave length will be quite long, the baffles which must be used in such a system, if the useful low frequency output is to be good, will be very large. This size requirement, which cannot be met in most cases, for practical reasons, is the major reason why most prior art sound reproducing systems do not radiate substantial useful quantities of low frequency acoustic radiation.

*U.S. Patent No. 2,718,931 , 09/27/1955 (app. 11/28/1952) [DjVu66KB]
LOUD SPEAKER FOR OUTDOOR THEATERS (class: 181/31)
Boudouris, Angelo

Abstract: This invention relates to loud speakers for outdoor theaters and is particularly directed to a unit that is resistant to deterioration from the usual conditions encountered in service. Loud speakers for outdoor theaters are subject to rapid deterioration. not only from direct rain from which they may be partially shielded by the housing in which they are contained but by condensed moisture, dust accumulations, deposits by spiders, wasps and other insects, and by vandalism on the part of the patrons. The primary object of the present invention is to provide a means for mounting and protecting a loud speaker for outdoor theaters so that it is not readily damaged by any of the above causes. Another object of the invention is to provide a mounting for a loud speaker for outdoor theaters which completely protects the vital parts of the speaker against rain, condensation and all other outside influences. Still another object is to provide a mounting by which the loud speaker is fixed in its case without the use of screws through or into the front face of the housing in which the speaker is contained.

*U.S. Patent No. 2,727,949 , 12/20/1955 [DjVu58KB]
Loudspeaker
Lokkesmoe, Julius B
     My invention relates to improvements in loudspeakers, and particularly to loudspeakers of the electro-dynamic type.
     An object of my invention is to provide a novel and improved electro-dynamic loudspeaker having high fidelity response at both the low and high frequency ends of the audio frequency range.

*U.S. Patent No. 2,797,766 ,  07/02/1957 (app. 10/20/1953) [DjVu94KB]
LOUD SPEAKER (class: 181/151; 181/152; 381/345)
Sullivan, Herbert W. (assignee: David Bogen & Company, Inc.)
Abstract: One of the objects of this invention is to improve the response characteristic of an acoustic diaphragm by causing at least one side of said diaphragm to vibrate in a medium other than air, adapted by its characteristic impedance or capacitance to extend the lower frequency end as compared to that prevailing in air. Another object of the invention is to cause at least one side of an acoustic diaphragm to vibrate in a gaseous medium which is heavier than air. Another object of the invention is to vibrate at least one side of a diaphragm in a gas or gas mixture reducing the velocity of sound waves as compared to that prevailing in air. Still further an object of the invention is to increase the characteristic impedance of the diaphragm as compared to that prevailing in air. Still another object of the invention is to increase the acoustic capacitance of the diaphragm as compared to that prevailing in air.