US2896736A - Acoustic system - Google Patents

Description

July 28, 1959 J. E KARLSON Acous'rxc SYSTEM Filed Aug. 15, 1955 FIG. 4.

FIG. 3.

INVENTOR JOHN E. KARLSON.

BY J

ATTORNEY.

nited States This invention relates to the acoustic art and particularly concerns a reflection type loudspeaker enclosure and means for utilizing the same.

It is a principal object of the invention to provide a reflection-type acoustic system which reproduces sound in a realistic manner.

It is a further object to provide an acoustic means for reproducing sound in a manner which closely simulates the original acoustic environment in which the sound was originated.

It is a further object to provide a means for radiating sound from a loudspeaker with maximum acoustic dispersion effect.

It is a further object to provide a reflection type enclosure for a loudspeaker.

Other and further objects of the invention will become apparent from the following description.

In sound reproduction systems utilizing loudspeakers it is desirable that the sound be produced with the utmost possible realistic effect. Many expedients have heretofore been suggested for achieving this high fidelity of sound reproduction. Conventional high fidelity acoustic systems generally employ one or more loudspeakers which give the etfect of sound emanating from one or more readily identifiable point sources. This introduces an unnatural effect which is not characteristic of sound as generally heard in a room or concert hall. When conventional conical loudspeakers radiate directly into an air space the maximum sound dispersion angle is about 90 to 120 degrees. The present invention is directed at attaining considerably greater angular dispersions in the order of 180 degrees. This is accomplished by locating a sound reproducing loudspeaker in an enclosure in such a manner that sound emanating therefrom is directed against a suitable wide sound reflecting surface. This reflector may be a flat or curved wall. The soundis dispersed from the wall in such manner that the reflected sound path avoids the loudspeaker and its enclosure. A sound image is established which gives the impression to listeners of having emanated from substantially the entire reflecting wall rather than from the loudspeaker itself. The sound Will appear to have originated from some point beyond or behind the reflecting wall and thus creates the eflect of additional acoustic spaciousness.

The invention will be best understood from the follow ing detailed description taken together with the drawing wherein:

Fig. 1 shows an external view of a loudspeaker enclosure.

Fig. 2 shows one way of using the loudspeaker .enclosure.

Figs. 3 to 9 are diagrams useful in explaining the acoustic principles underlying operation of the invention.

In Figs. 1 and 2 is shown a loudspeaker cabinet adapted for reflection-type operation. The generally cubical cabinet 10 has a front wall formed by two Wall panel members 11, 12.. The inner edges 13, 14 of the walls are curved to define a tapered or V-shaped opening. A

atent Y 2,896,736 Patented July 28, 1959 ice board 15 is mounted diagonally in the cabinet and has a circular opening 16 to which is atfixed a loudspeaker with conical diaphragm 17. The mounting board 15 may have a free edge 18 which is spaced from the rear wall of the cabinet so that sound from the rear of the loudspeaker in compartment 20 may travel over the edge 18 in path 19 to reinforce sound emitted from the front of the loudspeaker. The tapered opening defined by edges 13, 14 improves the directivity of the loudspeaker particularly for the high frequencies so that sounds of low and high frequency issue from the enclosure 10 with substantially the same angle of dispersion. Equalized phasing results from the use of the tapered opening. Suitable electrical connections (not shown) energize the loudspeaker.

In Fig. 2, the cabinet is placed on its back wall 21 adjacent a vertical Wall W. The sound which issues from the diagram 17 (which is disposed at an angle relative Y to said vertical Wall) travels at an inclined acute angle and strikes the Wall W at points A, B, C and is reflected from the wall along paths A, B and C. The dotted lines A", B, C" represent the virtual reflection paths or beams which meet at the virtual sound image point 0 located some distance behind wall W. The sound is dispersed into a room, of which wall W is a part only, by reflection because the sound issues from the enclosure 10 a Well defined path substantially directed only at the wall W. The enclosure is so placed that it is outside of the reflection paths A, B, C. Since the sound reaches its auditors only after reflection from wall W it appears the sound comes only from the wall and originates at point 0 behind the wall. The effect of spaciousness thus achieved is very striking and is due, for one reason, to the very Wide angle of dispersion of the sound.

Reference is made to Figs. 3 and 4 in further explaining this phenomenon. In a room R a direct radiating loudspeaker L directs sound outwardly in an average beam dispersion angle S of to 90 degrees. Certain areas in the room outside of the beam path are not exposed to the direct sound radiation. Sound reaches these areas only after numerous reflections and thus differs in phase and intensity from the directly radiated sound waves. Fig. 3 should be contrasted with Figs. 2 and 4 which show the invention. In Fig. 3 the path of some of the sound waves is normal to the reflecting wall and consequently the sound is dispersed from the wall in such manner and direction that it does not entirely avoid the loudspeaker and its enclosure. In other words, much of the sound is reflected back into its source. In Figs. 2 and 4 on the other hand, the sound waves are inclined at an angle to the vertical wall and the reflected sound path completely avoids the loudspeaker and its enclosure.

In Fig. 4, the loudspeaker enclosure 10 is disposed so that sound Waves are directed at Wall W. The sound reflected back into the room has a dispersion angle S considerably greater than the previous dispersion angle S. In effect the reflected sound fills substantially the entire room so that the listening qualities of the sound are substantially the same at all points in the room. The arrangement shown in Fig. 4 produces another desirable effeet in that the sound is reproduced in an acoustic environment which simulates a concert hall, studio or other place where the sound originated. When the sound waves are reflected from Wide Walls W and W the effect of the a wall W. Another purpose of this view is to illustrate how this effect can be approximated by loudspeakers not mounted in an enclosure having a taperedopening. The reflected sound beams establish virtual pathsA", B", C" which meet at the virtual origin 0; Point O is a virtual sound source located beyond wall W as explained in connection with Fig. 2. In order that the virtual sound paths'may meet at the common point 0 it is necessary that the loudspeaker enclosure be such that the sound originatesfrorn an equivalent acoustic point source. Reference is made to Patent No. 2,816,619 issued to me on December 17, 1957 on patent application Serial No. 259,831, filed December 4, 1951.

This is probably best accomplished by the structure shown in Fig. 2. The sound which is radiated upon wall W is substantially equalized in phase for all reproduced sound frequencies, and the wall is irradiated with sound beams of uniform intensity. The reflected waves are equalized in phase with a virtual sound source located behind the reflecting surface. Thus the sound a pears to emanate from the entire wall to produce the desired realistic acoustic effects inherent in and characteristic of the original sound. In other words it is important that the sound appear to issue from as large a wall area as possible rather than from a readily identifiable directly radiating point source as in conventional loudspeaker arrangements. 'In the present system this area sound source as contrasted with a directly radiating point sound source produces most impressive acoustic effects.

In Fig. 7 the loudspeaker enclosure 10 is shown placed on its back 21 so that the sound beams are reflected up- Ward from wall W above the enclosure. In Fig. 8 the loudspeaker enclosure is located in a corner formed by walls W, W. The enclosure is shown placed on its back but it can be disposed upright in the position shown in Figs. 1 and 6. This arrangement produces very interesting dual sound source effects because each of the walls appears to be an individual sound source. A minor image effect is also created in the corner. The composite effect is considerably difierent than when a single wall is used as the principal reflecting plane as shown in Figs. 2, 4-7. The corner placement arrangement produces less realistic and natural acoustic efiects and should not be regarded as wholly equivalent to the use of a single reflecting wall.

In Fig. 9 the wall W is parabolic in form and the loudspeaker enclosure is located at the focal point P so that the reflected sound beams issue in parallel paths P. The wall W" may have a difierently curved surface such as elliptical, hyperbolic, etc. depending on the distribution and sound characteristics desired. These curved surfaces will permit projection of sound over considerable distances with minimal losses.

Other modifications of the invention will readily occur to those skilled in the art.

What is claimed and desired to protect by Letters Patent of the United States is:

An acoustic system comprising a loudspeaker, an enclosure for said speaker having a tapered opening through which the sound waves issue and by which the several frequencies. thereof are equalized in phase and confined in a limited dispersion pattern, and a vertical sound-reflecting surface, said enclosure being disposed with its speaker and tapered opening in such positions relative to the vertical sound-reflecting surface as to direct the sound waves at an inclined acute angle against said reflecting surface for reflection therefrom in a path which avoids the said speaker and its said enclosure, the reflected waves being thereby also equalized in phase with a virtual sound source located behind said reflecting surface.

References Cited in the file of this patent UNITED STATES PATENTS 1,936,396 Jefferis Nov. 21, 1933 1,945,710 Smoot Feb. 6, 1934 1,984,550 Sandeman Dec. 18, 1934 2,124,575 Karnes July 26, 1938 2,292,424 Abrahams Aug. 11, 1942 2,643,727 Leon June 30, 1953 2,701,025 Kuhl Feb. 1, 1955 2,710,662 Camras June 14, 1955 2,722,990 West Nov. 8, 1955 OTHER REFERENCES Publication by Karlson, Radio & Television News, pages 58-60, January 1954. (Copy in Library.)

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