US3233695A

US3233695A - Speaker enclosure

Info

Publication number: US3233695A
Application number: US381935A
Authority: US
Inventors: Ralph E Hutchins
Original assignee: BUDSEN CORP
Current assignee: BUDSEN CORP
Priority date: 1964-07-10
Filing date: 1964-07-10
Publication date: 1966-02-08
Anticipated expiration: 1983-02-08

Description

Feb. 8, 1966 R. E. HUTCHINS SPEAKER ENCLOSURE Filed July 10, 1964 FIG. 2

FIG.

FIG. 4

FIG. 3

INVENTOR. RALPH E. HUTCHINS HIS ATTORNEYS.

United States Patent The invention relates to an improved speaker enclosure and particularly to a speaker enclosure having a vibratile panel for improving the musical sounds, and

especially the bass sounds, produced by such enclosure in cooperation with a speaker.

The physics and behavior of speaker enclosures are 'not completely understood and have been the subject of much controversy in the past. No single authoritative reference answers all the theoretic-a1 questions in the speaker enclosure field, and many variables such as different types of woods and other construction materials, glues, fasteners, shapes, braces, etc., remain relatively unexplored. There have been many prior art attempts at the design of a satisfactory speaker enclosure, but most of them have been relative failures, or rather poor compromises. They have sulfered from poor bass response, uneven response including harsh resonances or booms, and various unpleasant sounds and distortions. In addition to relatively poor performance, all of the speaker cabinets and baflles proposed thus far have drawbacks such as impractical size, weight, or cost. Also, they have failed to accomplish an optimum solution to the classic problem of cancellation of the back wave of the speaker at low frequencies. Attempts at directing back radiation from the speaker cone around a suitable baffle so as to bring it into reinforcing relation with front radiation from the speaker have been only partially successful and have produced uneven response,

One of the best comprises to date is the ported cabinet or bass reflex speaker enclosure comprising a rather large, closed cabinet as acoustically rigid as practical and having an open port for radiating the back wave of the speaker. Some of the drawbacks of a bass reflex speaker enclosure include disagreeable resonant peaks in its output and impractical size and weight.

It is an object of this invention to overcome the deficiencies of the prior art speaker enclosures in providing a relatively small, light weight, speaker enclosure of simple and inexpensive construction able effectively to use the back radiation of the speaker in reinforcing relation with the front radiation for producing a flat, full bass response without distortion or disagreeable booms, wolf notes, or resonances.

Another object of the invention is to add to and alter in a musically pleasant way the harmonic structure of musical sounds produced by a speaker.

Another object of the invention is to mechanically invert the phase of a preselected range of low frequency sound radiation from the back of a speaker and radiate such low frequency radiation from the speaker enclosure in phase with the front radiation of the speaker for reinforcing the lower frequency ranges of music produced by the speaker.

Another object of the invention is to use back radiation from a speaker cone for driving a vibratile panel substantially in phase with the speaker cone throughout a preselected low range of frequencies.

Another object of the invention is to control the resonance of a speaker enclosure so that it has a relatively uniform response to all musical frequencies and produces sound that is musically pleasing.

Another object of the invention is to provide a speaker enclosure with a panel that is vibratable in phase with the cone of the speaker throughout a predetermined low range of frequencies so as to attenuate speaker cone excursion and thereby allow more power to be applied to the speaker without overdrive or intermodulation distortions.

Another object of the invention is to use a speaker enclosure to add depth and quality to the low frequency musical sound produced by the speaker and to correlate the speaker and the enclosure so as to produce pleasing musical sounds at all musical frequencies.

Another object of the invention is to extend the high frequency response of a speaker that has a relatively low resonant frequency.

Other objects of the invention will be apparent hereinafter from the specification and from the recitals of the appended claims. To these and other ends, the invention resides in certain improvements and arrangements of parts, all as will be hereinafter more fully described, the novel features being pointed out in the claims at the end of the specification.

In the drawings:

FIG. 1 shows an isometric rear view of a speaker enclosure according to the invention;

FIG. 2 shows the view of FIG. 1 with the back and side panels removed from the speaker enclosure;

FIG. 3 shows a partially sectioned side elevation of a panel of the speaker enclosure according to the invention;

FIG, 4 shows a cross section of the panel of FIG. 3 taken along the line 4-4;

FIG. 5 shows a cross section of the panel of FIG. 3 taken along the line 5-5; and

FIG. 6 shows an exaggerated flexure of the panel as viewed in FIG. 5.

Generally, the invention is accomplished by making a boundary of a speaker enclosure function as a vibratile panel having a plurality of modes of vibration including the mode of a reed and using the back radiation from the speaker to vibrate the panel substantially in inverse phase relation with the back radiation throughout predetermined low range of frequencies.

In the following description of the invention the con struction details of an illustrative speaker enclosure according to the invention will first be described, and then operation of the enclosure will be discussed.

Construction of enclosure As shown in FIGS. 1 and 2, a speaker enclosure 10 is formed of a plurality of

panels

11, 12, 13, 14, 16, and 17 that are preferably rectangular, but can be any convenient shape. The

panels

1144, 16, and 17 are preferably formed of wood but may be of any other suitable material, and are fastened together and to frame members 1843 in any acceptable manner such as by glue and screws. As oriented in FIGS. 1 and 2, the enclosure includes a top 11, bottom 12, side 13, front 14, back 16, and side panel 17. The enclosure as illustrated in FIG. 2, is shown with back panel 16 and side panel 17 removed, revealing the back of a speaker 15. Speaker 15 is mounted over an aperture (not shown) in front panel 14 for radiating sound from the front of speaker 15 into the general area in front of panel 14. Back radiation of sound from speaker 15 is exhausted into the interior of enclosure 10.

Panel 17 could form the outside panel of the speaker enclosure 10, but since structural members are outboard of panel 17, panel 24, spaced from panel 17, is added to improve the appearance of the enclosure 10 as a piece of furniture. The space between panel 17 and panel 24 can be used for mounting an amplifier or another speaker.

As shown in FIGS. 1 and 3, the back edge of vibratile panel 17 is supported or fixed in place by being connected to back panel 16 by means of screws 25. Between back panel 16 and vibratile panel 17 is preferably arranged a strip of foam rubber 27 through which screws .25 pass. Screws 25 are preferably round head screws that can be tightened or loosened for adjusting the tension or the rigidity of the connection between back panel 16 and vibratile panel 17. Screws 26 fasten back panel 16 to

frame members

18, 19, and 23, from which back panel 16 is preferably spaced by a strip of foam rubber.

As best shown in FIGS. 36, the front edge of vibratile panel 17 is free to move or vibrate and is not connected to other frame members or panels. A foam rubber strip 28 is preferably placed around the top, bottom, and front edges of panel 17 so as to extend the periphery of panel 17 to closely fit top 11, bottom 12, and front 14 so as to effectively and substantially close in a volume of air within the speaker enclosure 10. The portions of

panels

11, 12, and 14 over which panel 17 moves when vibrating are preferably finished smooth for example by sanding and coating with a smooth lacquer. Also, a dry lubricant such as talcum powder is preferably applied to foam rubber strip 23 or to the portions of

panels

11, 12, and 14 over which foam rubber strip 28 moves, to insure easy movement and vibration of panel 17 while maintaining a close fit between panel 17 and adjacent panels.

As illustrated in FIGS. 3-6 vibration of panel 17 is controlled and somewhat modified by resilient gripping means or dampers 29 engaging panel 17 along its top and bottom edges for a portion of the distance from the back edge to the front edge of panel 17. Each damper 29 is preferably formed of wood and has a strip of foam rubber Ell bonded thereto. Dampers 29 are fastened to top panel 11 and bottom panel 12 in such a way that foam rubber strips 3% face inward and engage panel 17 for controlling its vibrating motion.

The dampers 29 require that panel 17 not vibrate in one piece in the motion of a swinging door but rather in a more complex manner including a plurality of modes. To facilitate such vibration it is preferred that panel 17 be formed of flexible material, and in one successful embodiment of the invention, panel 17 was formed of /8" plywood with the grain of the outer layers of the plies running from front to back of the panel 17. With proper adjustment of dimensions and other parameters, other materials, woods, or grain orientations may be used for panel 17. 7

Operation All the details as to the operation of the inventive speaker enclosure, and the complete theoretical explanation of its functioning are not known. The invention was arrived at empirically after many inoperable variations and unsuccessful attempts. As mentioned above, acoustic theory with respect to speaker enclosures generally is incomplete and somewhat confused. The following de scription of the operation of the inventive enclosure is as complete and accurate as presently known, and is offered to make the operation of the invention as clearly understandable as possible. However, applicant does not wish to be limited to any particular theory or rationale as to the operation of the inventive speaker enclosure or the reasons for its improved sound producing ability. There is a great deal of empirical evidence and expert opinion in support of the fact that the inventive speaker enclosure does cooperate with a speaker to produce musical sounds that are more pleasing to listeners, and many presently known and possible future explanations help account for this.

Panel 17 is driven or vibrated by the back wave or back radiation from speaker 15. The mass, flexibility, rigidity of mounting, and other factors contributing to the reluctance of panel 17 to move are arranged so that for frequencies from about 30 cycles per second or the bottom of the range of musical sounds up to about 200 to 250 cycles per second, panel 17 is vibrated substantially in phase with the cone of speaker 15. This occurs in part because when the cone of speaker 15 moves into the enclosure so as to cause a compression within the enclosure, such compression is transmitted by the enclosed volume of air to the walls of the enclosure and within a finite time produces an outward push on panel 17. Because of the delay in the transmission of the compression, and because of the size and reluctance of panel 17 to move, by the time panel 17 starts its actual outward motion in response to the push from the compression, the speaker cone is also moving or about to move outward. The outward movement of the speaker cone causes a rarefaction within the enclosure which effectively exerts an inward pull on panel 17. By the time panel 17 actually moves inward in response to such pull, the speaker cone is also moving inward.

The in-phase relationship of panel 17 with the cone of speaker 15 is maintained throughout a range of three or four octaves at the bottom of the musical scale so that panel 17 has a fiat response to such frequencies without any sharp peaks or pronounced amplitude in its resonance.

The panel 17 is not always exactly in phase with the front radiation of speaker 15 but has various small phase angles relative to the speaker cone throughout the three to four octaves at the bottom of the musical scale. By such an in-phase relationship the panel 17 reinforces and adds to sound radiated from the front of speaker 15.

A mechanical analogy to the in-phase relationship between panel 17 and the cone of speaker 15 can be made by depending a weight from a spring. By correct selection of weight and spring, it is possible to oscillate the weight in-phase with the oscillation of the top of the spring so that the top of the spring and the weight move toward and away from each other similarly to the way the cone of speaker 15 and vibratile panel 17 move toward and away from each other.

It would be possible to vary the size, mass, flexibility, etc., of vibratile panel 17 so as to tune it for in-phase vibration with speaker 15 at frequencies other than low frequency ranges, but it is the musical lows rather than the highs and medium highs which most need boosting or reinforcing by the speaker enclosure. This is caused in part by the fact that the resistive component of air relative to cone diameter is reduced for frequencies below which the cone diameter is about one-half wave length.

FIGS. 4-6 partially illustrate the vibration of panel 17. The basic low frequency phase inversion, or in-phase vibration of panel '17 as described above can be characterized as a predominantly reed-type vibration. Thus, panel 17 can be considered as a relatively long, wide reed fastened at its back edge by screws 25 and free to vibrate at its front edge. FIG. 6 shows a view of an exaggerated flexure of panel 17 in response to such vibration. This basic, reed-type vibration is somewhat modified by dampers 29 which tend to form funnel or valley configurations in the panel as the front portion vibrates. This can be seen from the view of FIG. 4 showing that the forward portion of panel 17 can vibrate with the greatest amplitude at the center of the panel and with reduced amplitude toward its top and bottom edges. The valley or funnel configurations produce corresponding, but smaller, hill portions raised in the rearward sectors of the panel. This can be seen in FIG. 6 where, in the illustrated position of panel 17, the foam rubber strips 30 of dampers 29 are shown compressed at the lower forward edge and the upper central portion of the dampers 29, the upper central compression being the hill portions mentioned above. In other words, as the front portion of panel 17 moves in one direction, some portions of its rearward area move in the opposite direction. Partly because of the anchoring of the rear edge of the panel by screws 25; panel 17 is bent or flexed in the performance of such vibration rather than moving as one solid piece around a fulcrum point established by the dampers 29.

The vibratile panel 17 is known to have other vibra- I tion modes at some frequencies. For example, substantial portions of it can vibrate substantially in one piece with little fiexure in the mode of a piston or plate with smaller amplitude vibrations that are most easily detected at-higher frequencies. Also, the front portion of panel 17 can have a central node around which its upper and lower portions travel in opposite directions. Furthermore, above the range of frequencies for which the basic reed-type vibration of panel 17 is in phase with' the cone of speaker 15, central and rearward areas of panel 17 were found to be in phase with the speaker cone. All the vibrations of the panel have not been analyzed, and much time, equipment, and study would be required to analyze definitively all the vibrations in response to all frequencies and all combinations of musical tones. It has been clearly determined, however, that the vibrations of the panel are basically in phase with the speaker cone throughout the lower three to four octaves of the musical scale, and that it cooperates with the speaker and the rest of the enclosure to alter or add to the harmonic structure of the musical input to the speaker. This is particularly true for the music produced by electronic instruments such as organs, accordions, and guitars.

For many musical tones, particularly in the low musical ranges, the vibrations of panel 17 increase the amplitude of harmonics in such a way as to produce a resultant lower tone apparently an octave below the fundamental and thus deepen and add quality to bass notes in a musically pleasant way. Bass tones produced by the panel 17 in cooperation with the speaker enclosure have authority, volume, and quality adjudged remarkable and exceptionally pleasing and desirable by musicians and musical experts.

An important effect of the above described in-phase vibration of panel 17 relative to the cone of speaker is that speaker cone excursion is attenuated. As the cone of speaker 15 is moving inward to produce a compressioninside the enclosure 10, panel 17 also is moving inward and also produces a compression within the enclosure 10. This effectively cushions the cone of speaker 15. An opposite, similar effect is obtained for the outward travel of the speaker cone. Several important advantages result from such cone excursion attenuation. Speaker 15 can be driven with more than normal power without its cone excursion exceeding the limits within which the speaker response is linear. Distortion introduced by the cones spider is also reduced, and harsh, unpleasant intermodulation distortion is substantially eliminated.

In effect, the speaker cone is coupled to the panel 17, so that some of the power applied to the speaker is used to drive panel 17 in an in-phase relationship rather than merely to force the speaker cone through a long excursion. The relatively large area of panel 17 (approximately three or four times the area of the speaker cone) is used as the primary radiator of low frequencies, thus substantially solving the well known problem of long speaker cone excursion for low frequencies. As illustrating the capacity of the inventive speaker enclosure to eliminate various distortions by reducing speaker cone excursion, a 21 watt speaker mounted in speaker en closure 10 has been driven at peaks of 90 watts and with an average input of 50 watts without any substantial distortion or unpleasantness in the musical output. This capacity of the inventive speaker enclosure can reduce the expense and complexity of speakers and enclosures for high powered output.

Back panel 16 cooperates with the speaker 15 and with side panel 17 and the rest of the speaker enclosure to act as a musical sounding board. A speaker enclosure such as enclosure 10 previously would have to have been built as acoustically rigid as practical to avoid unpleasant distortions and objectionable resonant peaks at a few particular frequencies. In contrast, back panel 16 can be formed of fairly light material, for example /2 plywood, and can be resiliently mounted as by interposing a foam rubber strip around the periphery of back panel 16 between it and panel 17 and the

frame members

18, 19, and 23 to which it is fastened. Side panel 17, by consuming much of the power input to the speaker 15 at low frequencies and by vibrating in an in-phase relation with the cone of speaker 15 so as to reduce the excursion of such cone, thereby not only reduces intermodulation distortion in the speaker cone, but also similar intermodulation distortion in the vibration of back panel 16. In effect, the large amplitude, long vibrations for the bass tones are provided by side panel 17, and back panel 16, relieved of such forces, can respond as a resonant sounding board having generally plate-type vibrations that are more responsive to higher frequencies and are relatively uniform with musically pleasant characteristics.

An observed characteristic of the speaker enclosure according to the invention, the reasons for which are presently unknown, is that the speaker enclosure 10 also extends the high frequency response of a woofer type speaker having a relatively low resonant frequency, for example 30 to 40 cycles per second.

Conventional speaker enclosures and baflle structures exhibit two response peaks in their musical output, one peak corresponding to the natural resonant frequency of the enclosure or baffle structure, and the other corresponding to the natural resonant frequency of the speaker cone. The usual procedure is to design the baffie or enclosure so that it has a natural resonant frequency below that of the speaker cone in order to separate the two response peaks, providing a smoother frequency response and minimizing the boom effect characteristic of a sharp peak in the frequency response in the bass region. Speaker enclosure 10 adds three resonant bodies not present in the conventional enclosure or bafile structures: 1) the natural resonance of the back panel sounding board 16, (2) the natural resonance of the volume of air confined in the enclosure, and (3) the resonance of vibratile panel 17 with its complex vibrations in the modes of both a reed and a plate. By properly spacing the naturally resonant frequencies of all five bodies, a relatively flat response can be produced over a wider range of frequencies than can be obtained from an enclosure or baflie structure of conventional design.

Final tuning of any speaker enclosure or bafiie, like tuning of a musical instrument, has always required some empirical modification and adjustment to produce optimum musical quality. Variation in size, shape, materials, construction techniques, etc, in the manufacture of speaker enclosures according to the invention will probably also require some tuning for best results. In addition to tuning by changing dimensions such as panel and enclosure sizes and the length of dampers 29, tuning can also be effected by the tension of screws 25 connecting back panel 16 and side panel 17, compression of foam rubber strips 30 of dampers 29 against the top and bottom edges of panel 17 and changes in materials, wood grain orientations, and speaker characteristics.

Obviously, vibratile panel 17 and other enclosure panels such as back panel 16 can be changed in orientation or position. Thus, vibratile panel 17 can be located at the back, top, bottom, or front of enclosure 10, or could be secured at its front edge and have its back edge free to move. The back panel sounding board 16 can be arranged and secured in many other ways, and can even be made relatively rigid with excellent sound production resulting. Variations in the ways of securing vibratile panel 17 and controlling or damping its vibrations are also possible within the spirit of the invention.

Accordingly, while the invention has been disclosed herein by reference to the details of a preferred embodiment thereof, it is to be understood that such disclosure is intended in an illustrative rather than a limiting sense, and it is contemplated that various modifications in the construction and arrangement of the parts will readily ocour to those skilled in the art within the spirit of the invention and the scope of the appended claims.

I claim:

1. A substantially closed speaker enclosure a boundary of which comprises a substantially rectangular panel resiliently supported along one edge thereof and along adjacent portions of each edge of said panel that adjoins said one edge, so that said panel is vibratile in the mode of a relatively wide reed and in the mode of a plate.

2. A speaker enclosure substantially confining a volume of air and including a speaker having a vibratile cone the back of which is in communication with said volume of air, a boundary of said enclosure comprising a substantially rectangular panel resiliently supported along one edge thereof and along adjacent portions of each edge of said panel that adjoins said one edge, said panel being actuatable by sound waves from said back of said cone for vibration in the mode of a reed substantially in phase with said cone throughout a predetermined low range of frequencies.

3. A substantially closed speaker enclosure formed of a plurality of substantially rectangular panels a first one of which is resiliently supported around its periphery for acting as a sounding board, and a second one of which is resiliently supported along one edge thereof and along adjacent portions of each edge thereof that adjoins said one edge, so that said second panel is vibratile in the mode of a relatively wide reed.

4. A substantially closed speaker enclosure a boundary of which comprises a substantially rectangular panel supported along a first edge thereof and being free for vibrational movement along a second, opposite edge thereof, said vibrational movement being damped by resilient members engaging said panel along each of the edges of said panel leading from said first edge to said second edge for a portion of the distance from said first edge to said second edge.

5. A speaker enclosure having the structure specified in claim 4 wherein said panel is resiliently connected along said first edge thereof to a sounding board forming another boundary of said enclosure, said sounding board being resiliently supported around its periphery.

6. A speaker enclosure substantially confining a volume of air and including a speaker having a vibratile cone the back of which is in communication with said volume of air, a boundary of said enclosure comprising a substantially rectangular panel supported along a first edge thereof and free for vibrational movement along a second, opposite edge thereof, said vibrational movement being damped by resilient members engaging said panel along each of the edges of said panel leading from said first edge to said second edge for a portion of the distance from said first edge to said second edge, the sound waves from said back of said cone acting through said volume of air for causing said vibration of said panel substantially in phase with said cone throughout a predetermined low range of sound frequencies.

7. A substantially closed speaker enclosure formed of a plurality of substantially rectangular panels, a first one of said panels being resiliently supported around its periphery for acting as a sounding board, and a second one of said panels being resiliently supported along a first edge thereof and freely movable for vibration along a second opposite edge thereof, vibratile movement of said second panel being warped by resilient members engaging said second panel along each of the edges of said panel leading from said first edge to said second edge for a portion of the distance from said first edge to said second edge. I

8. A speaker enclosure substantially confining a volume of air and supporting a speaker having a vibratile cone the front of which is in communication with ambient air outside said enclosure and the back of which is in communication with said volume of air, vibration of said cone being transmitted by said volume of air to the boundaries of said enclosure, a first one of said boundaries comprising a sounding board resiliently secured around its periphery to said enclosure through a strip of resilient material, and a second one of said boundaries comprising a panel a first edge of which is secured to said sounding board through a strip of resilient material, a second opposite edge of said second panel being free for vibration, said vibration of said second panel being warped by resilient cleats engaging the edges of said panel leading from said first edge to said second edge for a portion of the distance from said first edge to said second edge, whereby vibration of said second panel in response to vibration of said cone produces sound waves in reinforcing relation with sound waves from said front of said cone throughout a predetermined low range of frequencies.

9. A substantially closed speaker enclosure a boundary of which comprises a resilient panel held substantially in place continuously along approximately one half its periphery and freely movable along the remainder of its periphery.

10. The speaker enclosure of claim 9 wherein said panel is substantially rectangular and is held along one edge thereof and along adjacent portions of each edge of said panel that adjoins said one edge.

11. A substantially closed speaker enclosure formed of a plurality of panels, a first one of whichis held substantially in place around substantially its entire periphery and a second one of which is held substantially in place continuously along approximately one half its periphery and freely movable along the remainder of its periphery.

12. The speaker enclosure of claim 11 wherein said first and second panels are mutually adjacent and sub,- stantially rectangular, and said second panel is held in place along one edge thereof and along adjacent portions of each edge thereof that adjoins said one edge.

References Cited by the Examiner UNITED STATES PATENTS 1,923,870 8/1933 Kressmann l8131.l 2,476,572 7/ 1949 Wenzel 181-3 1.1 2,713,396 7/1955 Tavares 181-31.1 2,757,751 8/1956 Tavares 18l--31.1 2,811,215 10/1957 Rudd et al. 181-31.1 2,834,423 5/ 1958 Bradford 181-311 3,090,461 5/1963 Gray 18131.1 3,150,739 9/1964 Dones 18131.1

LEO SMILOW, Primary Examiner.

Claims

1. A SUBSTANTIALLY CLOSED SPEAKER ENCLOSURE A BOUNDARY OF WHICH COMPRISES A SUBSTANTIALLY RECTANGULAR PANEL RESILIENTLY SUPPORTED ALONG ONE EDGE THEREOF AND ALONG ADJACENT PORTIONS OF EACH EDGE OF SAID PANEL THE ADJOINS SAID ONE EDGE, SO THAT SAID PANEL IS VIBRATILE IN THE MODE OF A RELATIVELY WIDE REED AND IN THE MODE OF A PLATE.