LOUD SPEAKER CABINET
United States Patent 3712411
A loudspeaker system is provided comprising a vibration-free cabinet of minimum interior size having a relatively thick front wall including two spaced parallel sound exit apertures. A loudspeaker is attached to the rear of the front wall with its cone communicating directly with one of the exit apertures, and a sound-delay chamber of constant cross-section throughout its length is interposed between the second exit aperture and the interior of the cabinet, leading to the rear of the speaker cone. Sound waves from the two resulting sound paths reinforce each other in a slightly out-of-phase relationship which enhances the quality and depth of the resulting overall sound and utilizes the full power of the speaker. Also, microphone-speaker feedback is substantially eliminated at normal power and at locations beyond approximately one foot from the front of the cabinet.
US Patent References:
Sound translating device
Thuras - July 1932 - 1869178
Radio speaker unit support
Dumas - April 1943 - 2315896
Loudspeaker system
Novak - August 1959 - 2900040
Loud speaker
Sieler - February 1961 - 2971598
Vented enclosure type loudspeaker system providing improved low frequency response
Carlsson - May 1962 - 3037081
Sound translating device
Thuras - July 1932 - 1869178
Radio speaker unit support
Dumas - April 1943 - 2315896
Loudspeaker system
Novak - August 1959 - 2900040
Loud speaker
Sieler - February 1961 - 2971598
Vented enclosure type loudspeaker system providing improved low frequency response
Carlsson - May 1962 - 3037081
Application Number:
05/235714
Publication Date:
01/23/1973
Filing Date:
03/17/1972
View Patent Images:
Export Citation:
Primary Class:
International Classes:
H04R1/28; G10K13/00; H04R1/28
Field of Search:
181/31B
Primary Examiner:
Tomsky, Stephen J.
Claims:
I claim
1. A loudspeaker system comprising a cabinet including front, rear, side, and end walls, each of said walls being of a thickness sufficient to substantially prevent vibration thereof,
2. A loudspeaker system according to claim 1 wherein said apertures are circular and are each on the order of 4 inches in diameter and said front wall is on the order of 11/4inches thick.
3. A loudspeaker system according to claim 1 wherein said chamber extends parallel to said first wall and has an outlet opening communicating with said other of said apertures and an inlet opening communicating with said interior of said cabinet.
4. A loudspeaker system according to claim 3 wherein said delay chamber has a cross-sectional area on the order of 61/4square inches and a length on the order of 51/4inches.
5. A loudspeaker system according to claim 3 wherein the interior of said cabinet is on the order of 121/4inches high, 61/4inches wide and 6 inches deep.
6. A loudspeaker system according to claim 5 wherein said inlet opening is adjacent the said end wall remote from said first mentioned aperture.
7. A loudspeaker system according to claim 6 wherein said chamber extends across said other aperture.
1. A loudspeaker system comprising a cabinet including front, rear, side, and end walls, each of said walls being of a thickness sufficient to substantially prevent vibration thereof,
2. A loudspeaker system according to claim 1 wherein said apertures are circular and are each on the order of 4 inches in diameter and said front wall is on the order of 11/4inches thick.
3. A loudspeaker system according to claim 1 wherein said chamber extends parallel to said first wall and has an outlet opening communicating with said other of said apertures and an inlet opening communicating with said interior of said cabinet.
4. A loudspeaker system according to claim 3 wherein said delay chamber has a cross-sectional area on the order of 61/4square inches and a length on the order of 51/4inches.
5. A loudspeaker system according to claim 3 wherein the interior of said cabinet is on the order of 121/4inches high, 61/4inches wide and 6 inches deep.
6. A loudspeaker system according to claim 5 wherein said inlet opening is adjacent the said end wall remote from said first mentioned aperture.
7. A loudspeaker system according to claim 6 wherein said chamber extends across said other aperture.
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to loudspeakers and has particular reference to loudspeaker systems capable of being universally used for music, paging, and public address applications.
2. Description of the Prior Art
One of the most perplexing problems encountered in microphone -- loud speaker combinations, as found, for example, in paging and public address systems, is the development of undesired feedback noise which occurs when the microphone is placed in the neighborhood of the speaker to which it is electrically connected. Although attempts have been made to solve this problem, such solutions have generally resulted in expensive construction, impaired sound quality and/or reduced power output of the speaker. Also, heretofore, in order to provide clear and faithful or authentic reproduction of sound throughout the normal audio range and at relatively full power, various expedients have been used. For example, combinations of different size loudspeakers are employed in many cases, in which larger speakers are used for transmitting lower frequency sounds and smaller speakers are used for transmitting higher frequency sounds. Such combinations have come into almost universal use for several reasons. One is that two or three of such speakers could be crowded into a smaller cabinet of prior design than could a single full-range speaker. Another is that maximum power rating increases with each added speaker, making it possible for less expensive speakers to be used.
SUMMARY OF THE INVENTION
According to the present invention, a loudspeaker cabinet is provided which substantially eliminates microphone - speaker feedback, produces a clear and authentic reproduction of substantially all sounds within the normal audio range and at all volume levels, is capable of utilizing maximum power of a single full-range speaker substantially throughout such range and is of minimum size. This is accomplished by providing a vibration-free enclosure of minimum size having a relatively thick front wall, i.e., on the order of 11/4inches thick, in which two spaced parallel sound exit apertures, on the order of 4 inches in diameter each are formed. Because of the thickness of the front wall, the exit apertures assume the form of sound conduits, each having a length of approximately one-third of its diameter.
A loudspeaker is attached behind the front wall in line with one of the sound exit apertures and a sound delay chamber having a constant cross-section throughout its length is formed intermediate the second sound exit aperture and the interior of the cabinet leading to the rear of the speaker cone. Such chamber has a cross-sectional area of substantially 61/4square inches and an effective length of substantially 51/4inches. It has been found that this size chamber is effective to slightly delay the passage of substantially all sound waves within the normal audio spectrum. The resulting two sound paths appear to reinforce each other to utilize substantially the full power of the speaker. Also, due to the resulting slight out-of-phase relationship of the two sounds thus emanated, a slight echo effect results which adds to the depth and richness of the overall sound. This, combined with the particular size and configuration of the cabinet results in a clear and authentic or faithful reproduction of music or the like throughout substantially the entire audio range. Further, and of considerable importance, is the absence of any microphone - speaker feedback tendencies beyond a distance of approximately 1 foot from the front wall of the speaker. Apparently, this is due to the fact that the two sounds, when combined at a short distance from the front of the speaker, result in a total sound which is somewhat out of phase with the feedback characteristics of the microphone - speaker combination.
It has been found, in using a five inch speaker with sound exit apertures on the order of 4 inches in diameter, that it is essential to maintain the length of the opening of such openings (thickness of the front wall) at least 11/4inches in order to restrict the point at which feedback occurs to within 1 foot of such exit apertures, which is well within desirable limits and well within the limits of other speaker cabinets of which applicant is aware.
Accordingly, a principal object of the present invention is to reduce microphone - loudspeaker feedback tendencies in loudspeaker systems.
Another object is to provide a loudspeaker system capable of faithfully reproducing all sounds within the normal audio range and at all normal volume levels.
Another object is to reduce the size of a loudspeaker cabinet without impairing its sound propagating qualities.
Another object is to provide a loudspeaker system having pleasing resonance qualities throughout the normal audio range and at all normal volume levels.
Another object is to provide a simple and economically manufactured loudspeaker cabinet capable of faithfully reproducing all sounds within the normal audio range and at all normal volume levels.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view with one side section cut away, illustrating a preferred form of the present invention.
FIG. 2 is a sectional elevation view taken along line 2--2 of FIG. 3.
FIG. 3 is a sectional plan view taken along line 3--3 of FIG. 2.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
Referring in detail to the drawings, the cabinet, generally indicated at 11, comprises top and bottom walls 12, 13, front and back walls 14 and 15 and side walls 16, 17. The various walls are formed of a dense material commercially available under the names "high density particle board" or "high density flake board". Such walls, except the front wall 14, are at least 3/4 inches thick and are chosen to prevent absorption of sound and to substantially prevent any undesirable or uncontrolled vibrations from being set up in the walls which would otherwise tend to distort the sound emanating from the cabinet. Thin sheets of hard wood veneer (not shown) are bonded to opposite surfaces of the walls to prevent warpage and to reflect rather than absorb sound waves impinging thereon.
Although the side, top and front walls are rigid enough to prevent any unwanted vibrations from being set up therein, they resonate in the same manner as a violin or guitar sound box to enhance all sounds generated by the back of the speaker cone.
The front wall 14 is formed of two panels 18 and 20 having a combined thickness of 11/4inches. Two parallel cylindrical apertures 21 and 22 of 4 inches diameter each, are formed through the two panels 18 and 20. A decorative cloth fabric 23 is interposed between the two panels to extend across the apertures 21 and 22. Such panels are integrally secured together by a suitable adhesive which also supports the fabric 23 in a relatively taut condition across the apertures 21 and 22.
The top, side and bottom walls are integrally secured together with a suitable adhesive and are recessed as indicated at 24 to receive the front wall 14 which is integrally secured within such recesses by a suitable adhesive to form an acoustically insulated cabinet.
The top, bottom and side walls are also recessed at 25 to receive the rear wall 15 which is removably secured in place by suitable screws 19 or the like to permit access to the interior of the cabinet. Sealing material may be interposed between the rear wall 15 and the recess 25 to insure adequate sound insulation at such point. A layer of sponge rubber 26 approximately 1/2inch thick and having a substantially smooth sound reflecting inner surface is suitably bonded to the inner surface of the rear wall 15 to dampen any unwanted vibrations which might possibly otherwise be set up in the rear wall. It will be noted, however, that the layer 26 will reflect substantially all sound waves generated by the speaker cone.
A 5inch heavy duty loudspeaker 27 of conventional construction and having the usual air moving cone (not shown) is secured by bolts 28 to the rear panel 18 directly in line with the upper aperture 21. For example, such a speaker may be commercially obtained under the tradename "Trusonic Lifetime Speaker" from Trusonic Audio of Huntington, Ind. Such speaker has a cone capable of a maximum excursion of approximately 1/4 inch and is rated at 40 watts, peak power.
A sound delay conduit or chamber 30 of constant cross-section throughout its length is provided, opening into the lower sound exit opening 22, and is formed by parallel walls 31 and 32 which extend across the interior of the cabinet 11 and are integrally secured to spacer strips 33 and 34 attached to the side walls 16 and 17. Such chamber 30 has a cross-sectional opening of 11/8inches deep and 51/2inches wide. The chamber has an effective length of 51/4inches.
The rear chamber wall 32 is spaced above the bottom wall 13 to form a sound entrance 35 and is attached at its upper end to a horizontal wall section 36 secured to the rear panel 18 of the front wall. The front chamber wall 31 is spaced inwardly from the panel 18 and terminates below the wall section 36 to form a sound outlet 37 leading to the exit aperture 22. All such chamber walls have smooth, non-sound absorbing surfaces.
The cabinet 11 has the following internal dimensions:
Height (A) equals 121/2inches.
Width (B) equals 61/2inches.
Depth (C) equals 53/4inches.
The above dimensions and resultant interior volume of the cabinet have been found to be minimal and critical in order to provide faithful sound reproduction at all normal volume levels throughout the normal audio range and with pleasing resonance characteristics throughout such range. Preferably, these dimensions should be maintained within a tolerance of plus or minus one-eighth of an inch in order to obtain the results noted herein.
With the foregoing construction, sound at substantially all frequencies within the normal audio range is transmitted both from the front of the loudspeaker cone and from the rear thereof without noticeable attenuation at any point in such range. Apparently, although the sound waves transmitted by delay chamber 30 are slightly delayed or out-of-phase, they reinforce the sound waves emanating through the aperture 21 at some distance in front of the cabinet to fully utilize the air moving capabilities of the speaker 27. This out-of-phase relationship creates a slight echo effect to produce a pleasing, clear and natural sound which appears to have considerable depth and in which no distortion is detectable by the human ear. Of considerable importance is the fact that microphone - speaker feedback is eliminated at distances greater than approximately one foot from the front of the speaker apertures 21 and 22. That is, if a microphone which is connected in circuit with the speaker 27 through an amplifier is held directly in front of the aperture 21 and substantially within 1 foot of the front wall 14, the usual high pitched feedback will be heard. If the microphone is held directly in front of the aperture 22 and substantially within 1 foot fro the front panel, a much lower pitched feedback will be heard. However, if the microphone is held in any position relative to the cabinet, but beyond a boundary of approximately 1 foot from the front wall 14, no feedback is discernible.
It should be noted that the size and length of the sound exit apertures 21 and 22, the size and location of the sound delay chamber 30 and the size of the interior of the cabinet are found substantially critical to the above noted elimination of feedback tendencies outside of said 1 foot boundary.
As an example of the power handling capabilities of the speaker-cabinet it has been found in actual tests that two such loudspeaker-cabinets provide adequate sound for transmission of music and voice communication to an assemblage of 200 people. Also, two such speaker-cabinets provide adequate sound for paging persons within an area of 12,000 square feet.
1. Field of the Invention
This invention relates to loudspeakers and has particular reference to loudspeaker systems capable of being universally used for music, paging, and public address applications.
2. Description of the Prior Art
One of the most perplexing problems encountered in microphone -- loud speaker combinations, as found, for example, in paging and public address systems, is the development of undesired feedback noise which occurs when the microphone is placed in the neighborhood of the speaker to which it is electrically connected. Although attempts have been made to solve this problem, such solutions have generally resulted in expensive construction, impaired sound quality and/or reduced power output of the speaker. Also, heretofore, in order to provide clear and faithful or authentic reproduction of sound throughout the normal audio range and at relatively full power, various expedients have been used. For example, combinations of different size loudspeakers are employed in many cases, in which larger speakers are used for transmitting lower frequency sounds and smaller speakers are used for transmitting higher frequency sounds. Such combinations have come into almost universal use for several reasons. One is that two or three of such speakers could be crowded into a smaller cabinet of prior design than could a single full-range speaker. Another is that maximum power rating increases with each added speaker, making it possible for less expensive speakers to be used.
SUMMARY OF THE INVENTION
According to the present invention, a loudspeaker cabinet is provided which substantially eliminates microphone - speaker feedback, produces a clear and authentic reproduction of substantially all sounds within the normal audio range and at all volume levels, is capable of utilizing maximum power of a single full-range speaker substantially throughout such range and is of minimum size. This is accomplished by providing a vibration-free enclosure of minimum size having a relatively thick front wall, i.e., on the order of 11/4inches thick, in which two spaced parallel sound exit apertures, on the order of 4 inches in diameter each are formed. Because of the thickness of the front wall, the exit apertures assume the form of sound conduits, each having a length of approximately one-third of its diameter.
A loudspeaker is attached behind the front wall in line with one of the sound exit apertures and a sound delay chamber having a constant cross-section throughout its length is formed intermediate the second sound exit aperture and the interior of the cabinet leading to the rear of the speaker cone. Such chamber has a cross-sectional area of substantially 61/4square inches and an effective length of substantially 51/4inches. It has been found that this size chamber is effective to slightly delay the passage of substantially all sound waves within the normal audio spectrum. The resulting two sound paths appear to reinforce each other to utilize substantially the full power of the speaker. Also, due to the resulting slight out-of-phase relationship of the two sounds thus emanated, a slight echo effect results which adds to the depth and richness of the overall sound. This, combined with the particular size and configuration of the cabinet results in a clear and authentic or faithful reproduction of music or the like throughout substantially the entire audio range. Further, and of considerable importance, is the absence of any microphone - speaker feedback tendencies beyond a distance of approximately 1 foot from the front wall of the speaker. Apparently, this is due to the fact that the two sounds, when combined at a short distance from the front of the speaker, result in a total sound which is somewhat out of phase with the feedback characteristics of the microphone - speaker combination.
It has been found, in using a five inch speaker with sound exit apertures on the order of 4 inches in diameter, that it is essential to maintain the length of the opening of such openings (thickness of the front wall) at least 11/4inches in order to restrict the point at which feedback occurs to within 1 foot of such exit apertures, which is well within desirable limits and well within the limits of other speaker cabinets of which applicant is aware.
Accordingly, a principal object of the present invention is to reduce microphone - loudspeaker feedback tendencies in loudspeaker systems.
Another object is to provide a loudspeaker system capable of faithfully reproducing all sounds within the normal audio range and at all normal volume levels.
Another object is to reduce the size of a loudspeaker cabinet without impairing its sound propagating qualities.
Another object is to provide a loudspeaker system having pleasing resonance qualities throughout the normal audio range and at all normal volume levels.
Another object is to provide a simple and economically manufactured loudspeaker cabinet capable of faithfully reproducing all sounds within the normal audio range and at all normal volume levels.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view with one side section cut away, illustrating a preferred form of the present invention.
FIG. 2 is a sectional elevation view taken along line 2--2 of FIG. 3.
FIG. 3 is a sectional plan view taken along line 3--3 of FIG. 2.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
Referring in detail to the drawings, the cabinet, generally indicated at 11, comprises top and bottom walls 12, 13, front and back walls 14 and 15 and side walls 16, 17. The various walls are formed of a dense material commercially available under the names "high density particle board" or "high density flake board". Such walls, except the front wall 14, are at least 3/4 inches thick and are chosen to prevent absorption of sound and to substantially prevent any undesirable or uncontrolled vibrations from being set up in the walls which would otherwise tend to distort the sound emanating from the cabinet. Thin sheets of hard wood veneer (not shown) are bonded to opposite surfaces of the walls to prevent warpage and to reflect rather than absorb sound waves impinging thereon.
Although the side, top and front walls are rigid enough to prevent any unwanted vibrations from being set up therein, they resonate in the same manner as a violin or guitar sound box to enhance all sounds generated by the back of the speaker cone.
The front wall 14 is formed of two panels 18 and 20 having a combined thickness of 11/4inches. Two parallel cylindrical apertures 21 and 22 of 4 inches diameter each, are formed through the two panels 18 and 20. A decorative cloth fabric 23 is interposed between the two panels to extend across the apertures 21 and 22. Such panels are integrally secured together by a suitable adhesive which also supports the fabric 23 in a relatively taut condition across the apertures 21 and 22.
The top, side and bottom walls are integrally secured together with a suitable adhesive and are recessed as indicated at 24 to receive the front wall 14 which is integrally secured within such recesses by a suitable adhesive to form an acoustically insulated cabinet.
The top, bottom and side walls are also recessed at 25 to receive the rear wall 15 which is removably secured in place by suitable screws 19 or the like to permit access to the interior of the cabinet. Sealing material may be interposed between the rear wall 15 and the recess 25 to insure adequate sound insulation at such point. A layer of sponge rubber 26 approximately 1/2inch thick and having a substantially smooth sound reflecting inner surface is suitably bonded to the inner surface of the rear wall 15 to dampen any unwanted vibrations which might possibly otherwise be set up in the rear wall. It will be noted, however, that the layer 26 will reflect substantially all sound waves generated by the speaker cone.
A 5inch heavy duty loudspeaker 27 of conventional construction and having the usual air moving cone (not shown) is secured by bolts 28 to the rear panel 18 directly in line with the upper aperture 21. For example, such a speaker may be commercially obtained under the tradename "Trusonic Lifetime Speaker" from Trusonic Audio of Huntington, Ind. Such speaker has a cone capable of a maximum excursion of approximately 1/4 inch and is rated at 40 watts, peak power.
A sound delay conduit or chamber 30 of constant cross-section throughout its length is provided, opening into the lower sound exit opening 22, and is formed by parallel walls 31 and 32 which extend across the interior of the cabinet 11 and are integrally secured to spacer strips 33 and 34 attached to the side walls 16 and 17. Such chamber 30 has a cross-sectional opening of 11/8inches deep and 51/2inches wide. The chamber has an effective length of 51/4inches.
The rear chamber wall 32 is spaced above the bottom wall 13 to form a sound entrance 35 and is attached at its upper end to a horizontal wall section 36 secured to the rear panel 18 of the front wall. The front chamber wall 31 is spaced inwardly from the panel 18 and terminates below the wall section 36 to form a sound outlet 37 leading to the exit aperture 22. All such chamber walls have smooth, non-sound absorbing surfaces.
The cabinet 11 has the following internal dimensions:
Height (A) equals 121/2inches.
Width (B) equals 61/2inches.
Depth (C) equals 53/4inches.
The above dimensions and resultant interior volume of the cabinet have been found to be minimal and critical in order to provide faithful sound reproduction at all normal volume levels throughout the normal audio range and with pleasing resonance characteristics throughout such range. Preferably, these dimensions should be maintained within a tolerance of plus or minus one-eighth of an inch in order to obtain the results noted herein.
With the foregoing construction, sound at substantially all frequencies within the normal audio range is transmitted both from the front of the loudspeaker cone and from the rear thereof without noticeable attenuation at any point in such range. Apparently, although the sound waves transmitted by delay chamber 30 are slightly delayed or out-of-phase, they reinforce the sound waves emanating through the aperture 21 at some distance in front of the cabinet to fully utilize the air moving capabilities of the speaker 27. This out-of-phase relationship creates a slight echo effect to produce a pleasing, clear and natural sound which appears to have considerable depth and in which no distortion is detectable by the human ear. Of considerable importance is the fact that microphone - speaker feedback is eliminated at distances greater than approximately one foot from the front of the speaker apertures 21 and 22. That is, if a microphone which is connected in circuit with the speaker 27 through an amplifier is held directly in front of the aperture 21 and substantially within 1 foot of the front wall 14, the usual high pitched feedback will be heard. If the microphone is held directly in front of the aperture 22 and substantially within 1 foot fro the front panel, a much lower pitched feedback will be heard. However, if the microphone is held in any position relative to the cabinet, but beyond a boundary of approximately 1 foot from the front wall 14, no feedback is discernible.
It should be noted that the size and length of the sound exit apertures 21 and 22, the size and location of the sound delay chamber 30 and the size of the interior of the cabinet are found substantially critical to the above noted elimination of feedback tendencies outside of said 1 foot boundary.
As an example of the power handling capabilities of the speaker-cabinet it has been found in actual tests that two such loudspeaker-cabinets provide adequate sound for transmission of music and voice communication to an assemblage of 200 people. Also, two such speaker-cabinets provide adequate sound for paging persons within an area of 12,000 square feet.