US3105569A - Loud-speaker assembly - Google Patents

Description

Oct. 1, 1963 c. R. EVANS LOUD-SPEAKER ASSEMBLY Filed May 16, 1961 my 6mm W %m M m M W 0 W m m United States Patent 3,105,569 LOUD-SPEAKER ASSEMBLY Chauncey Richard Evans, Salt Lake City, Utah, assignor to Atuh Corporation, Salt Lake City, Utah, a corporation of Utah Filed May 16, 1961, Ser. No. 110,465 3 Claims. (Cl. 181-31) This invention relates to a method of and apparatus for improving the quality of music emitted from a loudspeaker enclosure.

in recent years, there has been much interest in high fidelity systems for the reproduction of recorded music. Also, there has been a continuing demand for high quality electrical systems for use with musical instruments such as guitars. For the most part, designers of electrical sound systems have concentrated their efforts on the faithful translation of signals into sound without material alterations in quality.

However, some workers in the field have recognized that accurate reproduction of the input signals need not be the goal of a design of such a system. The real objective is the production of music that is satisfying to the human ear, and it has been found that the overall quality of the music may be improved by judiciously emphasizing particularly desirable components and :deernphasizing components that tend to be unpleasant.

One component that may be de-emphasized to good advantage has a frequency of around 3,000 c.p.s. For example, the finger noises generated in playing a guitar frequently fall in this frequency range.

An electric circuit for minimizing components in the 3,000 cps. range is disclosed in the prior application of Evans and Fowler, Serial No. 854,777, filed November 23, 1959, now abandoned. However, it now has been recognized that acoustic, rather than electric techniques for component strength control have certain advantages.

Therefore, a primary object of this invention is to provide a method of and apparatus for acoustic-ally eliminating or deemphasizing selected frequencies in music emitted by a loud speaker assembly.

This object may be accomplished by mounting two speakers in an enclosure so that the sounds from each are projected through a single opening in a wall of the enclosure and so that one of the speakers is spaced farther from the opening than the other speaker by a distance equal to one-half the wave length of the frequency to be deemphasized. When the two speakers are supplied with the same electrical signal, the spacing of the speakers results in an acoustical cancellation effect at the frequency to be deemphasized.

It is convenient to think of a sound wave as a sine curve in which the crests represent high pressure areas and the troughs represent low pressure areas. if two waves of the same frequency, but out of phase by onehalf wave length, are added together, the crests of one tends to cancel the troughs of the other. This, of course, is what happens in the present invention when the sound waves from the two speakers are brought together at the opening in the enclosure wall.

The invention is particularly suited to the deemphasis of high frequency components. In an ordinary speaker system, there will be a large speaker (called a woofer) for producing low frequency tones and a small speaker (called a tweeter) for producing high frequency tones. Since the speakers for the high frequencies are small, a plurality of them can be mounted conveniently in an enclosure of reasonable size. It is noted also that the 3,900 c.p.s. range mentioned above usually would be assigned to the tweeter.

In the preferred form of the invention, two identical tweeters are driven by identical signals. Both are mounted in an enclosure behind an opening in a wall thereof, but they are directed at angles to the axis of the opening and are disposed on opposite sides of the axis.

This arrangement provides not only for the desired cancellation effect described above but also for a dispersion of the high frequency sounds emitted from the speaker enclosure. The latter effect is a particularly desirable one, in that it substantially reduces the directional characteristic of the speaker assemblies and provides a wider sound coverage from a single compact enclosure.

A more complete understanding of the invention, and a better appreciation of its many advantages, will be gained from a consideration of the following detailed description of an embodiment illustrated in the drawings, in which:

FIG. 1 is a perspective view of the speaker cabinet or enclosure;

FIG. 2 is a perspective view of a twin tweeter mounting connected to the rear of the front wall of the cabinet;

FIG. 3 is a plan view of the speaker mounting of FIG. 2 with a part of the top wall broken away; and

FIG. 4 is a chart indicating the relative intensities of the various frequencies which may occur in the output from the twin tweeter arrangement of the present invention.

The cabinet or enclosure 10 is similar to that disclosed in the co-pending application of Evans and Fowler, Serial No. 854,777, filed November 23, 1959, now abandoned.

A large speaker (not shown) for producing low frequency sound components is mounted directly behind the large opening 12 in the front wall 11. This may be conventional in construction and it need not be described here.

The small opening 13 in the front wall provides an outlet for sounds emanating from a twin tweeter assembly designated generally by the numeral 16 in FIGS. 2 and 3. This assembly 16 may be secured to the front wall ill by any suitable means.

The mounting 16 also includes side walls 21 and 22 dispose-d in an angular relationship with respect to the front wall ll of the enclosure in and diverging rearwardly therefrom. An end wall 23 is secured to the walls l7, l8 and 21 and an end wall 24 is secured to the walls f7, 18 and 22. The side wall 21 is longer than the side wall 22 so that the end wall 23 will be spaced rear-wardly of the end wall 24.

A lateral opening 25 in the mounting l6 opposite the speaker as permits a flow of air from within the cabinet out of the enclosure through the mounting, as shown by arrow A in FIG. 3. As explained in the co-pending application of Evans and Fowler identified above, it is desirable that the low frequency pressure pulses occurring in the interior of such a cabinet or enclosure be allowed to pass to atmosphere along the path of the high frequency emissions from the tweeter speaker. This provides a pleasing effect by modulating the high frequency tones.

The distances between the front wall 11 of the enclosure is and the two speakers 19 and 20 are functions of the wave lengths to be deemphasized. The distance from the middle of the wall 23 supporting speaker 19 to a point in the middle of the opening 13 is greater than the distance from the middle of the wall 24 supporting speaker 24) to the same point in the middle of the opening 13. In order that the sound waves may be degrees out of phase at the opening 13, the difference in the two distances should be one-half the wave length of the unwanted frequency.

It is to be understood that this condition does not exist for all sound waves emitted at this frequency from each speaker. Since sound waves are transmitted from all sound Waves of this frequency will not intersect at the point described. Therefore, some sound waves will not have the complete cancellation effect described above but there will nevertheless be some cancellation tendency. It has been proven, in actual practice that this structural arrangement results in a great improvement of the tone quality of high frequency speakers.

FIG. 4 represents the output from a twin tweeter assembly of the type shown in FIGS. 2 and 3 set so as to deemphasize frequencies in the range of 3,000 c.p.s. This curve is the actual output sound intensity resulting from signals of uniform intensity fed to the tweeters.

Note that frequencies above 3,000 c.p.s. also are affected by the novel disposition of the twin tweeters of this invention. This is to be expected. Av difference in spacing numerically equal to one-half the length of a 3,000 c.=p.s. sound wave would be numerically equal.

to the length of a 'full wave of 6,000 cps. frequency, etc. Thus, some of the higher frequencies will be accentuated and some will be deemphasized along with the 3,000 c.p.s. sounds. These variations have not been found, to be unpleasant or to detract from the. desirability of the invention. e

The angular relationship of the speakers also provides a larger area of coverage of the sound emitted therefrom. The speakers 19 and 20 will project beams angularly from the enclosure It) in opposite directions. This provides a flaring pattern for the high frequency emissions from the enclosure, and permits these tones to be heard clearly at various pointsin the room.

In view of the many variations and modifications which will suggest themselves to persons skilled in the art, it is intended that the foregoing description of an illustrated embodiment of the invention be considered as exemplary only and that the scope of the invention be ascertained from the following claims.

I claim: i

1. In combination with'a loud speaker enclosure having an opening in the front wall, a loud speaker mounting secured to the front wall of the enclosure and communicating with an opening therein, said mounting having parallel top and bottom walls, a pair of side walls diverging 'rearwardly from the front wall of said enclosure, an end wall secured to each of said side walls,

a loud speaker secured to each of said end walls, the

length of one of said side walls being such that one'of said speakers will be spaced from the enclosure opening 4 a distance greater than that of the other speaker so that the 'differencein the two distances is equal to one-half the wave length of a frequency in the range of 3,000 cycles per second. 1

2. In combination with a loud speaker enclosure having a front wall with an opening therein, a tweeter assembly comprisinga mounting secured to the front wall W of said enclosure, said mounting having parallel top and bottom walls, a pair of side walls diverging rearwardly from said front wall, an end wall secured to each side wall, a tweeter attached to each of said end walls, one of said side walls being longer than the other side wall so as to space the adjacent tweeter a distance from the opening of said enclosure greater than that of the other tweeter, the difference in said distances being equal to one-half the wvave length of a predetermined frequency, and said mounting having an opening therein opposite said one of said side walls.

3. A loud speaker assembly mounting, comprising parallel top and bottom walls, a pair of diverging side walls, an end wall secured to each side Walls, said walls forming an enclosure having a rectangular opening opposite saidend Wall s, loud speakers attached to each end wall, the angle of divergence of the Side walls being such that sound waves emitted from the central portion.

to space the adjacent loud speaker a distance from'said opening greater than that of the other loud speaker, the difference in said distances being equal to one-half the wave length of a predetermined frequency, and said mounting having an opening therein opposite said first side wall.

References Cited in the file of this patent UNITED STATES PATENTS 1,808,174 Maxam June 2, 1931 2,172,871 Giannini Sept. 12, 1939 2,872,516 Hoffman a Feb. 3, 1959 FOREIGN PATENTS 100,124 Australia Ian. 18, 937 1,000,450 Germany Ian. 10, 1937 OTHER REFERENCES Custom Sound Installation, Radio and Television News, May 1950', pages 3-5.

Claims (1)

1. IN COMBINATION WITH A LOUD SPEAKER ENCLOSURE HAVING AN OPENING IN THE FRONT WALL, A LOUD SPEAKER MOUNTING SECURED TO THE FRONT WAL OF THE ENCLOSURE AND COMMUNICATING WITH AN OPENING THEREIN, SAID MOUNTING HAVING PARALLEL TOP AND BOTTOM WALLS, A PAIR OF SIDE WALLS DIVERGING REARWARDLY FROM THE FRONT WALL OF SAID ENCLOSURE, AN END WALL SECURED TO EACH OF SAID SIDE WALLS, A LOUD SPEAKER SECURED TO EACH OF SAID END WALLS, THE LENGTH OF ONE OF SAID SIDE WALLS BEING SUCH THAT ONE OF

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