US2143175A - Sound reproducing system - Google Patents

Description

Jan. 10, 1939. s. A. WAITE SOUND REPRODUCING SYSTEM Filed Oct. 25, 1937 2 Sheets-Sheet l \NVENTOR uel A'.Wa1ie 5a BY 4, ATTORNEY LPF 7 Al ///l/ Jan. 10, 1939. s w n- SOUND REPRODUCING SYSTEM Filed Oct? 23, 1957 2 Sheets-Sheet 2 I u vlrvimfw rw vvvvtw 7 3 5 \NVENTOR 50m Await BY 7AM ATTQRNEY 11111. u arr; a II, '1 1111 I r Patented Jan. 10, 1939 UNITED STATES PATENT. OFFICE SOUND BEPDODUCING SYSTEM Samuel A. Waite, Beverly Hills, Calif.

Application October 23, 1937, Serial No. 170,579

5 Claims. (CL 179-1) This invention relates to a system for reproducing sound,.and especially for use in a comparatively small space, such as'in the home.

When sound reproduction and amplification by the aid of electrical energy came first into commercialuse, no particular attention was paid to the fidelity of reproduction over the entire range of audible sound. As progress was made in the art, refinements in apparatus and methods made possible a substantial improvement in this field; this progress in great measure was accelerated by the advent of talking motion pictures. In reproducing sound from recordings run simultaneously with the motion picture, the necessity of accurately and audibly recreating the recorded sounds became important; otherwise the audience finds the performance unsatisfactory.

It has been found that for entirely satisfactory.

reproduction, the loudspeakers should reproduce substantially accurately, all sound frequencies from 40 to 15000 cycles per second. Where the reproduction occurs in a large space, as in theatres or auditoriums, the size of the reproducing equipment has no practical limit. Accordingly, in order to reproduce the lower band of frequencies, it is entirely feasible to provide sufilciently large dimensions for the horn or cone. Thus a horn or cone to reproduce the lowest of these frequencies would have a mouth opening measuring six or eight feet across, corresponding to at least a material fraction of the total wave length of the lowest frequency to be reproduced. However, such dimensions do not present any particular problem in theatres or auditoriums.

To reproduce the higher frequencies, a somewhat diflerent type of problem arises. In this connection, it was early recognized that sound waves of the higher register emanating from a localized source, were projected mainly as a beam; that is, such waves had directional properties. For this reason, in order satisfactorily to transmit sound waves of the higher frequencies substantially uniformly, a plurality of sound sources for the high frequencies are utilized, arranged angularly with respect to each other.

In this way, there was some assurance that the ears of a listener, no matter where located with respect to the sound sources, would receive the desired quantities of sound waves having frequencies in the range of reproduction.

These systems, therefore, for large audiences or for large spaces, could readily be devised to re produce fairly faithfully, substantially all of the recorded sound frequencies.

For sound reproduction in the home, several additional important factors must be considered. Such home reproduction is almost exclusively utilized for the reception of radio programs and for the playing of sound records. At first, no particular attention was directed to faithfulness of the frequencies of reproduction, because the radio programs and the records were not of high fidelity to begin with. Obviously, since these programs and records inherently had a curtailed frequency range, it was impossible, even by the most faithful and accurate reproduction, to attain any greater frequency range than those present in the source. Accordingly, it was unnecessary to provide loud speakers that would reproduce beyond this curtailed range. The lower limit of bass frequencies was in the neighborhood of 100, and the upper limit was in the neighborhood of 3000 to 4000. Therefore, it was quite easy to recreate this range satisfactorily, even by a single cone speaker of approved construction.

The quality of the transmission and of recording improved to increase the frequency range; and the older reproducing systems are incapable of doing Justice to them. While it might be possible to utilize the extremely bulky reproducers developed for theatres, auditoriums and public address systems, yet several important considerations obviously militate against their utilization in the home. One of these considerations is the very high cost of the apparatus. Another is the fact that the space required is so great that an intolerable amount of the available room is preempted by the equipment.

It is one of the objects of this invention to make it possible to overcome these disadvantages, and tomake it possible to reproduce programs and records faithfully, with reproducers that can easily be accommodated in an ordinary sized cabinet or console.

In an average living room the audience is often so scattered that the problem of eliminating or reducing directional effects of the reproduced sound to innocuous limits is pronounced. In the average theatre this is not a serious problem, for the audience is seated in definitely arranged places, most advantageously located as regards distance and direction from the sources of sound. But in a home there is no such predetermined spacing. A listener may be seated very close to the reproducer or quite far away; and he may be directly in front of the apparatus or to the extreme side thereof. It is thus seen that the problem of adequate volume over the whole desired frequency range, with respect to the entire room, should be considered. It is accordingly another tion over this wide range of frequencies, by the aid of compact apparatms is particularly advantageous for stereophonic systems.

This invention possesses many other advantages,.and has other objects which may be made more easily apparent from a consideration ofseveral embodiments of the invention. For this purpose there are shown a few forms in the drawings accompanying and forming part of the present specification. These forms will now be described in detail, illustrating the general princi-' ples of the invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appendedclaims.

Referring to the drawings:

Figure 1 is a diagrammatic representation of a reproducing system incorporating the invention and employed in a room of ordinary size;

Fig. 2 is a diagrammatic sectional view of the reproducing system embodying the invention, the electrical connections being also indicated;

Fig. 3 is a front elevation of the form of the invention illustrated in Fig. 2: Fig. 4 is a horizontal sectional. view, mainly diagrammatic, of another form of the invention;

Fig. 5 is a front elevation of the'form of the invention illustrated in Fig. 4;

Fig. 6 is anenlarged fragmentary view illustrating one of the reproducing units utilized in the form illustrated in Figs. 4 and 5;

- Fig. '7 is a front elevation of a still further modification of the invention; and

Fig. 8 is a horizontal sectional view illustrating the form of the invention shown in Fig. 7.

- In the form of the invention illustrated in Figs.

shown as housed or supported generally in a cabinet I. Although the reproducing system may reproduce sound within the range of from about forty cycles per second to fifteen-thousand cycles per second, yet the cabinet i is maintained of a size sufiiciently small to be readily accommodated within an average size room. The room in which it isaccommodated is shown diagrammatically by the rectangle 2 in Fig. 1. The cabinet I in this instance is indicated as being located adjacent one corner of the room.

The substantially faithful reproduction of sound frequencies without the aid of bulky apparatus and without annoying directional effects, is secured in the present instance by the aid of two reproducer units. Thus, for reproducing the higher frequency range of from about fourhundred or five-hundred cycles, up to fifteenthousand cycles, use is made of a multicellular speaker unit 3. This unit 3 is shown as appropriately supported adjacent the top of the cabinet I and forming a plurality of hom-like sound channels, such as 4 and 5. The mouth openings of these soimd channels are directed outwardly and are angularly arranged both in horizontal and vertical planes as to direct the sound waves from all of the channels substantially uniformly in the room 2. This is indicated by the dotted lines in Fig. 1. The angle of spread in a horizontal direction of the series of m'ulti-cellular channels 4. 5 is of course chosen to correspond to the spread required from the place where the reproducer is located.

The sound reproducer 3 may have acommonair actuator or diaphragm for all of the chan nels, such as 4 and 5. Since especially at the higher frequency neighboring fifteen thousand or even lower, the sound waves in a single channel tend to converge in the direction of the axis of the channel, it is apparent that the multi-channels formed by the multi-cellular structure obviate the directional effects; for there are at least as many sound beams for the higher frequencies as there are sound channels such as land 5; and each sound beam is directed in a different direction from the others, to provide the desired angular sprea'd.

It is also noted that the channels are placed in two rows, one above the other. In this way a solid angle within which substantially uniform distribution is secured, such that persons situated anywhere in the room, either sitting or standing are all within the range of the higher frequency sound waves.

The problem of reproducing the lower frequencies of sound neighboring forty cycles and by the use of comparatively small size apparatus, is by no means simple. It may be done by providing an air actuator, such as a cone 6, operated by a reproducing unit incorporating a movable voice coil in conjunction with a properly designed supporting structure. Under such circumstances the mouth opening of the cone 6 may be small enough to be readily accommodatedwithin an ordinary sized cabinet I; and yetmuch below the usual requirement of having this mouth opening of the order of one-quarter of the length of the lowest frequency sound wave. a

Thus the cabinet I serves to provide a space 8 surrounding the back of the air actuator I and having an opening 9 to the front of the cabinet I. By properly proportioning the space 8 and the opening 8 in conjunction with appropriate sound damping or absorbing material l0 on the wall of the cabinet I, the capability of the air actuator B to create substantially faithful waves corresponding to the low desired frequencies is rendered possible. This principle, known as the bass reflex, depends for its operation upon the loading of the air actuator 6 by the confined space 8. The waves carrying the energy imparted to the air in space 8 find an outlet through opening 9 for dissipation within the room. It is therefore possible by this means to enable the cone 8 to operate through the necessary'long periods of vibration without setting up disturbing harmonic frequencies; and yet without any substantial energy waste.

Furthermore, it is wellknown that within the lower range of frequencies from neighboring forty cycles to two-hundred or three-hundred cycles, no material directional sound effect is produced. Accordingly, a single reproducer system 6! may be utilized without danger of producing annoying directional efi'ects for the low frequencies.

As shown most clearly in Fig. 2, the reproducers 8 and 'l are fed in parallel from a common source connected to mains II and II. This common source, of course, provides a current modulated inv accordance with the sound frequencies corresponding to the sound to be reproduced. This pass filter i5 and the low pass nlter- II. The circuits may also be provided, if desired, with equalizer circuits, to insure that no particular frequency or band of frequencies be unduly emphasized by the reproducers.

By the present arrangement it is obvious that the necessity of an extremely bulky low frequency reproducer is avoided. It is a simple matter to design the circuits for substantially uniform frequency responses over the entire range covered by both the high reproducer I and the low frequency reproducer I. The cabinet I is maintained of reasonably small size. Although the low frequency reproducer 1 requires but low power for its operation (due to its high efhciency), yet its use in the comparatively small room 2 is sufficient to provide any reasonable requirement as regards volume. The mouth openings of the several speakers may, if desired, be so spaced as to obtain the desirable stereophonic effects; or a plurality of cabinets I may be simultaneously used for this purpose.

In Figs. 4, 5 and 6 a modified form of the system is illustrated. In this form, instead of having separate reproducer units for the high and low frequency range from fifteen thousand cycles down to forty cycles per second, a plurality of substantially uniform sized reproducing units H to 24 inclusive are utilized. These may take the form of cone speakers having the air actuators 25. The units I! to 24 inclusive may be placed, if desired, in two rows, one above the other, to distribute uniformly in a vertical plane the higher frequencies of sound. Furthermore, these units are all shown as supported in a console or cabinet 26 and fed from a common source of modulated current, as by way-of the amplifier system 21.

Each of the air actuators 28 in the form of cones is so designed as to reproduce both the high and low frequencies. This is illustrated for example in Fig. 6. There are two voice coils 28 and 29 in series in each unit, one of the voice coils being shunted by an appropriate condenser II. The voice coils are carried on separate portions of the tubular support 3| which is joined to the cone 25. The tubular support 3| intermediate the coils 28 and 29 is provided with a flexible portion 32. Accordingly, the coils 28 and 29 may substantially independently reproduce vibrations in the cone 2!. i

The bass reflex principle is also incorporated herein by providing the space 33 in back of all of the air actuators 25. This space opens through the opening 34 in the front of the cabinet 26. The space 33 and the opening 34 are designed to insure substantially faithful reproduction of the low frequencies. By appropriate angular spacing of each of the cone reproducers H to 24 inclusive, the objectionable directional effect of the high frequency waves is obviated.

In the form of the invention illustrated in Figs. '7 and 8, the individual reproducers 35 are provided with individual spaces 35, 31, I8 and 39 opening through the individual openings 40, H, 42 and U to the front of the cabinet support 44. In other respects this form is similar to the form illustrated in Figs. 4, 5 and 6.

The principle described may equally as well be utilized to systems utilizing a stereophonic system, by the aid of proper spacing of the individual units, or any other equivalent scheme.

What is claimed is:

1. In a sound reproducing system for use in a space having a size corresponding substantially to a room in the home, means forming a plurality of sound wave transmitting channels, a plurality of electrical power actuated means for producing sound waves in all of said channels, including vibratory air actuators having one side thereof directed toward the corresponding channel, at least one of the electrical power actuated means being capable of propagating undistorted waves in the lower audible frequency hand, up to several hundred cycles and at least some of the electrical power actuated means being capable of propagating waves in the higher audible frequency band, the combination of the two bands corresponding to a satisfactory wide range of audible frequency substantially greater than that of either band alone, the channels for propagating waves in the higher audible frequency band being so angularly displaced with respect to each other as substantially uniformly to direct the waves in the higher frequency band in all directions within the space, and means forming a restricted chamber back of that air actuator that is adapted for propagating waves in the lower frequency band, said chamber having an opening directly communicating with said chamber, said chamber and its opening having a size such as to cause a loading of the actuator to satisfy the requirements for propagating the lowest undistorted frequency in the low frequency band, and such that harmonics of said low frequencies are substantially entirely prevented from being generated by the action of the low frequency unit, the channel for said air actuator having a mouth opening with dimensions considerably smaller than that required by other means for substantially faithfully reproducing said lowest frequency.

2. In a sound reproducing system for use in a space having a size corresponding substantially to a room in the home, means forming a plurality of sound wave transmitting channels, a plurality of electrical power actuated means for producing sound waves in all of said channels, including vibratory air actuators having one side thereof directed toward the corresponding channel, at least one of the electrical power actuated means being capable of propagating undistorted waves of a frequency as low as neighboring forty cycles per second, and up to several hundred cycles and at least some of the electrical power actuated means being capable of propagating waves of a frequency as high as neighboring fifteen thousand cycles per second, the combination of the two frequency bands overlapping, the channels for propagating waves in the higher frequency band being so angularly displaced with respect to each other as substantially uniformly to direct the waves in the higher frequency band in all desired directions within the space, and means forming a restricted chamber back of that air actuator that is adapted for propagating the lowest frequency wave, said chamber having an opening directly communicating with said chamber, said chamber and its opening having a size corresponding to the requirements for propagating an undistorted wave having a frequency neighboring forty cycles per second, and such that harmonics of said low frequencies are substantially entirely prevented from being generated by the action of the low frequency unit, the channel for said air actuator having a mouth opening with dimensions considerably smaller than required by other means for substantially faithfully reproducing said low frequency wave.

3. In a sound reproducing system for use in a space having a size corresponding substantially to a room in the home, a plurality of electrically actuated reproducers, angularly spaced from each other to provide air wave channels directed so as to direct sound substantially uniformly to all parts of the room where a listener may be stationed, and adapted to be fed from a common source of sound frequency modulated electrical current, at least some of said reproducers having a low frequency voice coil, a high frequency voice coil, and a common air actuator substantially independently affected by said coils, said coils cooperating to cover a wide range of frequencies, and a cabinet support for said reproducers, said cabinet support forming a confined space around the back of the air actuators, said cabinet having an opening communicating with the space, said space and opening being proportioned to enable the reproducers to reproduce substantially faithfully sound frequencies neighboring forty cycles, said reproducers havingdimensions sufllciently small to be readily accommodated by the cabinet.

4. In a sound reproducing system for use in a space having a size corresponding substantially to a room in the home, a plurality of electrically actuated reproducers, angularly spaced from each other to provide air wave channels directed so as to direct sound substantially uniformly to all parts of the room where a listener may be stationed, and adapted to be fed from a common source of sound frequency modulated electrical current, at least some of said reproducers having a low frequency voice coil, a high frequency voice coil, and a common air actuator substantially independently aifected by said coils, said coils cooperating to cover a wide range of frequencies, and a cabinet support for said reproducers, said cabinet support forming a plurality of spaces corresponding respectively with the back of the air actuators, each of said spaces opening independently from the cabinet, the said spaces and the openings being so proportioned that the reproducers may reproduce substantially faithfully sound frequencies neighboring forty cycles, said reproducers having dimensions sufficiently small to be readily accommodated by the cabinet.

5. In a stereophonic sound reproducing system, 7

means forming a plurality of sound wave transmitting channels, at least some of said channels being sufflciently separated from the others to produce the desired stereophonic effect, a plurality of electrical power actuated means for producing sound waves in said channels, including vibratory air actuators having one side thereof directed toward the corresponding channel, at least one of the electrical power actuated means being capable of propagating waves of a frequency as low as neighboring forty cycles per second, and at least some of the electrical power actuated means being capable of propagating waves of a frequency as high as neighboring fifteen thousand cycles per second, the combination of the two frequency bands overlapping at about several hundred cycles, the channels for propagating waves in the higher frequency band being so directed as substantially uniformly to direct the waves in the higher frequency band in all desired directions within the space, and means forming a restricted chamber back of that air actuator that is adapted for propagating the lowest frequency wave, said chamber having an opening directly communicating with said chamber, said reproducers being thereby capable of having reduced dimensions for adapting them for separation to obtain said stereophonic effect.

SAMUEL A. WAI'I'E.

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