US3194339A - Loudspeaker system - Google Patents

Description

3 Sheets-Sheet 1 July 13, 1965 R. J. PAwLowsKl LOUDSPEAKER SYSTEM Filed June 8. 1962 FEE-5 L56 I az 1061' /f/ July 13, 1965 R. J. PAwLowsKl LOUDSPEAKER SYSTEM Filed June 8, 1962 3 Sheets-Sheet 2 /eZuefzc/y zh Cycles /ecofK/ds Zin/ef: tor faber] j ,Pawlazasjz Bjr 5?0116, j'ermafz, ,Buff/faster jammer July 13, 1965 R. J. PAwLowsKl 3,194,339

LOUDSPEAKER SYSTEM n Filed June 8, 1962 3 Sheets-Sheet 3 In Venter faef ,I .Pula IOM 5t ope, JYz'ermarz, ,Huf-meister, fumer vfvfe S across the terminals 90 and 92. Each of the loudspeakers 84 is selected to have an impedance of approximately 8 ohms. In this manner, and with the connections illustrated in FIGURE 3, the impedance as seen at the terminals 90 and 92 will be approximately 8 ohms, and the loudspeaker system may be connected to an 8 ohm line. It is also to be noted that all of the loudspeakers are connected in phase, so that all of the cones or diaphragms 86 will be translated toward the front wall 64 at the same time by a signal of a particlular polarity.

A tweeter loudspeaker 96 is mounted on the bottom 66 of the enclosure 60 confronting the opening 74 by means of a bracket 98. Also, a second tweeter 100 is mounted on the top 68 confronting the opening 76, in a like manner. The tweeters 96 and 100 are horn tweeters, such as disclosed in Patent No. 2,873,812 of Robert C. Avedon which issued on February 17, 1959. The tweeters 96 and 100 are connected in parallel, and electrically connected to the terminals 90 and 92 through a high pass lter which comprises a capacitor 102 and a coil 104. The capacitor 102 is connected in series with the tweeters 96 and 100, and the coil 104 is connected in parallel with the tweeters 96 and 100.

The wall 70 supports a curved strip 106 adjacent to its edge remote from the rear wall 62, and the wall 72 supports a similar strip 108 confronting the strip 106. the strips106 and 108 have surfaces remote from the rear wall 62 disposed in a curved plane, and the front wall 64 is mounted on the strips 106 and 108. A screen 110 which is permeable to sound but protects the loudspeakers 84 from dirt and particles, is disposed adjacent to the side of the front wall 64 opposite the rear wall 62. A pair of strips 112 and 114 are disposed adjacent to the sidewalls 70 and 72 respectively, and a plurality of screws 116 extend through the strips 112 and 114 along lines parallel to the sidewalls 70 and 72 and are anchored in the strips 106 and 108. The screws 116 not only anchor the strips 112 and 114 on the enclosure 60, but also secure the screen 110 in position and the front wall 64 to the strips 106 and 108. Spacer strips 118 are disposed between the strips 106 and 108 in the regions of the openings 74 and 76 in order to maintain the screen 110 at the same distance from the strips 106 and 108 that is achieved by the front wall 64.

As explained in the inventors co-pending patent application, one of the advantages of a line source of audio radiation is that the radiation off of the ends of the line is very slight which permits a column speaker to be mounted above a microphone without creating excessive feedback betwen the speaker and the microphone. However, as the length of the column speaker, or line audio source, becomes more than a few wavelengths long, spurious radiation lobes appear off the ends of the line and create a feedback condition. In patent application Serial No. 118,673, the present inventor sets forth a column loudspeaker system in which the loudspeakers are disposed on a concave surface, as illustrated in FIGURES 1 and 2. The same criteria set forth in the above-referred to patent application for the elimination of spurious lobes and for the provision of a uniform radiation pattern measured in the plane of the line source apply to the speaker set forth in FIGURES 1 and 2 of this application, also. Hence, the loudspeakers 84 are placed as close together as possible centering on a common plane normal to the front wall 64 of the enclosure, and the front wall 64 of the enclosure forms an arc in the plane of the loudspeakers. The openings 74 and 76 are designed to extend the low frequency response of the loudspeaker approximately one octave, and this fact must be taken into consideration in determining the curvature of the arc of the front wall 64. For this reason, it is desirable that the length of the arc formed by the loudspeakers themselves be approximately one wave length at a frequency two octaves above the lowest frequency to be reproduced. Further, the radius of curvature of the line source should be between a wave length of sound at a frequency an octave above the lowest frequency of the range to be reproduced and a wave length of sound at the highest frequency to be reproduced by the line source, that is the loudspeakers 84 neglecting the response of the tweeters 96 and 100.

In the particular loudspeaker described in FIGURES 1 through 3, the radius of curvature of the line source, or the front wall 64, is approximately 10 feet. Oval speakers having a major axis of 9 inches and a minor axis of 5 inches are employed, so that the total length of the line, or the arc length of the line radiator is approximately 45 inches.

FIGURE 5 illustrates the impedance in ohms along the vertical axis for the loudspeaker system of FIGURES 1 through 3, and its relation to frequency plotted along the horizontal axis. It will be noticed that the dashed line, which represents the frequency response of the loudspeaker with the ports 74 and 76 sealed closed, exhibits a peak at a frequency of about 150 cycles per second, and this peak represents the frequency of mechanical resonance of the loudspeakers 84 which constitute the line source of audio energy. The ports 74 and 76 are designed to create an anti-resonance with the volume ofthe enclosure at the resonant frequency of the speakers in free air, which is cycles per second in this construction, and hence cause the loudspeakers to radiate energy down to a frequency of 50 cycles per second. The solid line curve of FIGURE 5 indicates a relatively smaller peak at 50 cycles per second. In addition, the principal frequency of mechanical resonance has been shifted upward in the solid line of FIGURE 5 to approximately 175 cycles per second.

The net result of the ports 74 and 76 is clearly visible from the frequency response curve of FIGURE 4. The dashed line in FIGURE 4 represents the response of this loudspeaker system with the ports 74 and 76 closed. The solid line represents the frequency response of the system with the ports open. In FIGURE 4, the output of the loudspeaker is plotted along the vertical axis and the frequency of the signal producing this response is plotted along the horizontal axis. It is to be noted that the frequency response has been extended downwardly from a frequency of approximately 100 cycles per second to a frequency of approximately 50 cycles per second as a result of the acoustical energy radiated from the ports 74 and 76.

Each of the ports 74 and 76 has a dimension of approximately 61/2 inches by 61/2 inches. The distance between the sidewalls 70 and 72 within the enclosure 60 is approximately 91/2 inches, the distance between the bottom 66 and the top 68 is approximately 5 81/2 inches, and the distance between the rear surface of the front wall 64 and the confronting surface of the rear wall 62 is approximately 8 inches. Also, a layer of sound absorbent material is disposed upon the surface of the rear wall 62 confronting the front wall 64.

The size of the openings 74 and 76 may be varied to accentuate or attenuate the magnitude of the low frequency response. A small port will extend to the low frequency range to a lower frequency but with smaller amplitude, while a large port will increase the low frequency response to a greater extent but not extend the frequency range as far.

It is to be noted that the horn tweeters 96 and 100 confront the openings 74 and 76 and therefore, the high frequency response of these tweeters also passes through these openings. Since the horn tweeters 96 and 100 are not affected by back waves, the low frequency energy also present at these openings has no appreciable effect upon the performance of the horn tweeters. It is also to be noted that the horn tweeters are disposed within the enclosure and spaced from the plane of the front wall 64. In the embodiment of FIGURES 1 and 2, the horn tweeters are recessed a distance of approximately onefourth inch from the screen 110. In this manner, the

horn tweeters 96 and 100 have a negligible effect upon the acoustical operation of the openings 74 and 76.

Since the sound emerging from the ports74 and 76 will be in phase, it is imperative that the distance between these openings beone-half wavelength at the frequency in which sound is emitted from the openings. This is a requirement since it is desired'that energy off the ends of the line source of acoustical energy be avoided, and the energy radiated in this direction from the ports will cancel if the ports are one-half wavelength apart. However, the energy from the ports 74 and 76 is in phase in a plane normal to the axis between the ports and will not cancel but reinforce. The frequency of the radiation from the ports 74 and,76,is peaked at the frequency of anti-resonance, 100 cycles per second in the construction described herein, and the ports are'spaced from each other by a half wave-length at this frequency.

As illustrated in FIGURES 1 and 2, the loud speaker system employs a plurality of loud speakers mounted in a line with a concave contour. The present invention may also be practiced with a loudspeaker system of the type illustrated in FIGURE 6. FIGURE 6 shows an embodiment of a loudspeaker system in which an enclosure 60A is provided with a straight rear wall 62A, straight front wall 64A and bottom and top walls 66A and 68A, respectively. The loudspeakers 84 are mounted in a straight line and the ports 74A and 76A are disposed at the ends of the line. The ports are spaced from eacli other by a distance of approximately one-half wavelength at the frequency in which the ports effectively radiate acoustical energy.

Those skilled in the art may devise many modifications and improvements upon the invention hereinbefore set forth. It is therefore intended that the scope of the present invention be not limited by the foregoing disclosure, but rather only by the appended claims.

The invention claimed is:

1. In a loudspeaker system for reproducing a continuous range of frequencies in the audible range having an elongated enclosure with an elongated'wall, a plurality of loudspeakers mounted and sealed on the wall of the enclosure in a line parallel to the axis of elongation of the enclosure, said enclosure having opening means confronting each of the loudspeakers, each loudspeaker having a diaphragm confronting the opening means and acoustically sealed on the enclosure, said loudspeakers being electrically connected to respond in phase to an electrical signal and forming a line source of acoustical radiation, the construction wherein the enclosure includes two ports in said Wall located on opposite ends ofthe line of loudspeakersy along the axis of elongation of the enclosure, said enclosure and ports resonating at a frequency at the low end of the frequency response range of the loudspeaker system and the ports being spaced from each other by a distance of approximately a half wave length at said frequency of resonance.

2. A loudspeaker system for reproducing a continuous range of frequencies in the audible range comprising, in combination, an elongated enclosure having an elongated wall, a plurality of loudspeakers mounted on the enclosure and sealed on the wall of the enclosure in a line parallel to the axis of elongation of the enclosure, said enclosure having opening means confronting each of the loudspeakers, each loudspeaker having a diaphragm confronting the opening means and acoustically sealed in the enclosure, said loudspeakers being electrically connected to respond in phase to an electrical signal and forming a line source of acoustical radiation, said enclosure having two ports in said wall located on the axis of elongation of the enclosure on opposite ends of the line of loudspeakers, said enclosure and ports resonating at a frequency at the low end of the frequency response range of the loudspeaker system and the ports being spaced from each other by a distance of approximately a half wave length at said frequency of resonance, and a horn-type loudspeaker mounted within the enclosure with the horn directed toward and confronting one of the ports, said horn having a frequency response extending above the frequency response of the other loudspeakers. k

3. A loudspeaker system comprising, in combination, an elongated enclosure having a plurality of adjacent openings in one wall thereof disposed in a plane traversing the axis of elongation of the enclosure, a loudspeaker mounted on the enclosure confronting each opening, each loudspeaker having a diaphragm acoustically sealed about the confronting opening, said loudspeakers being electrically connected to respond in phase to an electrical signal and forming a line source of acoustical energy, said enclosure including a pair of ports located in said wall and in the plane of the loudspeaker openings on opposite sides of the loudspeakers, said enclosure and ports resonating at a frequency at the low end of the frequency response range of the speaker system and the ports being spaced from each other by a distance of approximately a half wave length at said frequency of resonance.

4. A loudspeaker system having a frequency of response range extending between anupper and a lower limit comprising, in combination, an elongated enclosure having a curved concave wall with a radius of curvature equal to a wave length of a frequency within the response range of the loudspeaker system, said curved wall having a plurality of adjacent openings thereindisposed in a plane traversing the axis of elongation of the enclosure, said openings extending through an arc having a length at least equal to a wave length at a frequency two octaves above the lower limit of the response range of the loudspeaker system, a loudspeaker mounted on the enclosure confronting each opening, each loudspeaker having a diaphragm acoustically sealed about the confronting open-y ing, said loudspeakers being electrically connected to respond in phase to an electrical signal, and forming a line source of acoustical energy, the enclosure including a pair of ports located in said curved wall and in the plane of the loudspeakers on opposite sides of the loudspeakers, said enclosure and ports resonating at a frequency at the low end of the frequency response range of the speaker system and the ports being spaced from each other by a distance of approximately a half wave length at said frequency rof resonance.

5. A loudspeaker system comprising the elements of claim 3 in combination with a horn-type loudspeaker mounted within the enclosure with the horn directed toward and confronting one of the ports, said horn having a frequency response extending above the frequency response of the other loudspeakers in said system, said horn-type loudspeaker being electrically connected to the other loudspeakers in said loudspeaker system through a high pass filter.

6. A loudspeaker system having a frequency response range extending between an upper and a lower limit cornprising, in combination, an elongated enclosure having a curved concave wall with a radius of curvature equal to a wave length of a frequency within the response range of the loudspeaker system, said curved wall having a plurality of adjacent oval openings therein, said openings having parallel major axes and being disposed in a plane traversing the axis of elongation of the enclosure, said openings extending through an arc having a length at least equal to a Wave length at a frequency two octaves above the lower limit of the response range of the loudspeaker, a loudspeaker mounted on the enclosure confronting each opening, each loudspeaker having an oval diaphragm acoustically sealed about the confronting opening with its major axis parallel to the major axis of the opening, said loudspeakers being electrically connected to each other to respond in phase to an electrical signal and forming a line source of acoustical energy, said enalsaso closure including a pairaof ports located in said curved wall and in the plane of the loudspeakers on opposite sides of the loudspeakers, said enclosure and ports resonating at a frequency at the low end of the frequency response range of the speaker system and the ports being spaced from each other by a distance of approximately a half wave length at said frequency of resonance, a horntype loudspeaker mounted within the enclosure with the horn directed toward and confronting each of the ports, each of said horn-type loudspeakers having a frequency response extending above the frequency response of the other loudspeakers, a high pass filter electrically connected between the other loudspeakers and the horntype loudspeakers to electrically connect the horn-type loudspeakers in phase with the other loudspeakers, and a layer of sound absorbent material disposed within the References Cited in the tile of this patent UNITED STATES PATENTS 2,114,680 Goldsmith Apr. 19, 1938 2,143,175 Waite Jan. 10, 1939 2,441,425 Lawrence May 1l, 1948 2,808,121 Goettner Oct. l, 1957 2,927,963 Jordan et al Mar. 8, 196() FOREIGN PATENTS 272,869 Switzerland Jan. 15, 1951 781,637 Great Britain Aug. 21, 1957 575,492 Germany Apr. 28, 1933 868,921 Germany Mar. 2, 1953 883,299 Germany Iuly 16, 1953

Claims (1)

1. IN A LOUDSPEAKER SYSTEM FOR REPRODUCING A CONTINUOUS RANGE OF FREQUENCIES IN THE AUDIBLE RANGE HAVING AN ELONGATED ENCLOSURE WITH AN ELONGATED WALL, A PLURALITY OF LOUDSPEAKERS MOUNTED AND SEALED ON THE WALL OF THE ENCLOSURE IN A LINE PARALLEL TO THE AXIS OF ELONGATION OF THE ENCLOSURE, SAID ENCLOSURE HAVING OPENING MEAN CONFRONTING EACH OF THE LOUDSPEAKERS, EACH LOUDSPEAKER HAVING A DIAPHRAGM CONFRONTING THE OPENING MEANS AND ACOUSTICALLY SEALED ON THE ENCLOSURE, SAID LOUDSPEAKERS BEING ELECTRICALLY CONNECTED TO RESPOND IN PHASE TO AN ELECTRICAL SIGNAL AND FORMING A LINE SOURCE OF ACOUSTICAL RADIATION, THE CONSTRUCTION WHEREIN THE ENCLOSURE INCLUDES TWO PORTS IN SAID WALL LOCATED ON OPPOSITE ENDS OF THE LINE OF LOUDSPEAKERS ALONG THE AXIS OF ELONGATION OF THE ENCLOSURE, SAID ENCLOSURE AND PORTS RESONATING AT A FREQUENCY AT THE LOW END OF THE FREQUENCY RESPONSE RANGE OF THE LOUDSPEAKER SYSTEM AND THE PORTS BEING SPACED FROM EACH OTHER BY A DISTANCE OF APPROXIMATELY A HALF WAVE LENGTH AT SAID FREQUENCY OF RESONANCE.

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