Speaker system using a plurality of speaker units for directivity control

Abstract: In a speaker system capable of controlling the directivity, a first pair of speaker units are disposed at the cabinet front face, so that the diaphragm centers thereof are located at substantially the same vertical position with a specific horizontal interval between outer ends of the frames of the speaker units. A second pair of speaker units are disposed so that the diaphragm centers thereof are located at substantially the same horizontal position with a specific vertical interval between outer ends of the frames of the speaker units. The center of a line linking the diaphragm centers of the first pair of speaker units and the center of a line linking the diaphragm centers of the second pair of speaker units are located at substantially the same position.

Description: BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION The present invention relates to a speaker system using a plurality of speaker units. 2. DESCRIPTION OF THE PRIOR ART Recently, as the digital signal processing technology has been dramatically advanced, the electric signals supplied in the speaker system are notably improved in quality, and accordingly there is a mounting demand for the speaker system capable of reproducing sound at high sound quality. For high quality sound reproduction, the speaker system is desired to be free from large fluctuations in the sound pressure frequency characteristics depending on the sound listening position. For this purpose, it is required to minimize the effects of reflected sound from the walls and floor of the listening room, and it is preferred to develop a speaker system in which the directivity is controlled in a wide frequency band so that sound is not radiated to areas other than the listening position. In the low frequency range, however, the wavelength of the sound wave is long and the directivity is nondirectional, so that it is difficult to control the directivity. Especially in the speaker system using one speaker unit for bass reproduction, since the directivity is determined by the size of the diaphragm of the speaker unit, it is difficult to control the directivity in the low frequency range. As the means for solving this problem, there is a commercial speaker system which has four speaker units for bass reproduction disposed at four corners of a rectangle to virtually increasing the size of the diaphragm, and controls the directivity in the range down to the low frequency range. In such prior art, the directivity is determined by the disposition intervals of the speaker units. Therefore, to have directional directivity in the low frequency range, it is enough to widen the disposition intervals of the speaker units in the horizontal direction and the vertical direction. As the intervals become wider, however, the sound pressure level of the side lobe increases in the directivity pattern, and the side lobe is generated in relatively lower frequency range, thereby deteriorating the directivity. In the speaker system, moreover, it is desired that the sound pressure frequency characteristic be axis-symmetrical with respect to its central axis, and hence a speaker unit for sound reproduction in medium and high frequency ranges is disposed in the central part of the area surrounded by the four speaker units for sound reproduction in the low frequency range. Herein, to control the directivity characteristic in the medium and high frequency ranges, a horn speaker is generally used for the speaker for sound reproduction in the medium and high frequency ranges. To control the directivity in the frequency range from the medium frequency range by the horn speaker, the control band of the directivity is determined by the size of the horn mouth. Since the mouth is considerably large, the disposition intervals of the speaker units for sound reproduction in the low frequency range must be set larger than the diameter of the horn mouth. Therefore, when a speaker system is composed by dividing the frequency band into a low frequency band and a medium and high frequency band by a dividing network, effects of side lobe appear in the reproduction band due to the directivity of the speaker for sound reproduction in the low frequency range, and a large disturbance occurs in the sound pressure frequency characteristic near the crossover frequency with the medium and high frequency range. Therefore, to obtain favorable directivity of the speaker system, the crossover frequency of the dividing network must be set in a considerably low frequency band so as to be free from effects of side lobe of the speaker for sound reproduction in the low frequency range. However, in the horn speaker for sound reproduction in the medium and high frequency range, the sound pressure level is lowered in the low frequency range because the acoustic load of the horn is not applied, and the distortion increases, so that sufficient quality reproduction sound is not obtained from the speaker system. US-A-4885782 discloses a loud speaker driver configuration in which a high frequency driver is symmetrically located between lower frequency drivers. In one configuration, the high frequency driver is located mid-way between two lower frequency drivers positioned one above the other. In another configuration, there are four lower frequency drivers positioned around the high frequency driver, all being the same distance from the high frequency driver. GB-A-1303602 discloses loudspeaker assemblies comprising a plurality of identical first speakers spaced equally around a second loudspeaker. In particular, in the case that there are more than two of the first loudspeakers, the centres of the first speakers are arranged at the apices of a regular polygon. The present invention comprises a speaker system comprising: a cabinet having a front surface; first and second speaker units disposed on the front surface of the cabinet at a specific horizontal spacing and such that there is a difference of less than the radius of the diaphragms of the first and second speaker units between the vertical positions of the centres of the diaphragms of the first and second speaker units; and third and fourth speaker units disposed on the front surface of the cabinet at a specific vertical spacing and such that there is a difference of less than the radius of the diaphragms of the third and fourth speaker units between the horizontal positions of the centres of the diaphragms of the third and fourth speaker units; the first through fourth speaker units being arranged such that the centre of a line which links the centres of the diaphragms of the first and second speaker units and the centre of a line which links the centres of the diaphragms of the third and fourth speaker units are located at a distance apart of less than the radius of the diaphragms; characterised in that the horizontal spacing between the centres of the diaphragms of the first and second units and the vertical spacing between the centres of the diaphragms of the third and fourth speaker units are different from each other. The invention thus realises a speaker system in which the directivity can be controlled in a wide frequency band including the low frequency range. Further, an additional speaker unit may be disposed on the front face of the cabinet at a center of an area surrounded by the first and second pairs of speaker units. In this case, each of the first and second pairs of speaker units may be a speaker unit for sound reproduction in a low frequency range lower than a specific crossover frequency and the additional speaker unit may be a speaker unit for sound reproduction in a middle and high frequency range higher than the crossover frequency. In this arrangement, a speaker system having an arbitrary desired directivity can be obtained in a wide frequency band including-the low frequency range and the middle and high frequency range. In this constitution, the directivity of the set of the four speaker units for sound reproduction in the low frequency range in the horizontal direction is dominated not only by the horizontal spacing of the first pair of speaker units, but also by the second pair of speaker units separated in the vertical direction. Likewise, the directivity in the vertical direction is dominated not only by the vertical spacing of the second pair of speaker units, but also by the first pair of speaker units separated in the horizontal direction. As a result, sharpness of the directivity in each of the horizontal direction and vertical direction is smoothed, so that the frequency at which the side lobe is generated becomes high, and the sound pressure level is lowered. Therefore, by keeping wide spacings between the positions of the four speaker units for sound reproduction in the low frequency range, and by disposing a speaker unit for sound reproduction in the medium and high frequency range with a wide mouth such as a horn speaker in the central part of the area surrounded by the four speaker units, it is possible to suppress the disturbance of the directivity by the side lobe near the crossover frequency of the dividing network, so that a directivity free from disturbance even in the low frequency range can be realized. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front perspective view of a speaker system in a first embodiment of the invention. Fig. 2 is a sectional diagram showing a structure of a general speaker unit. Fig. 3 is a diagram showing a directivity angle of a speaker system. Figs. 4a and 4b are respectively directivity diagrams in the horizontal direction and vertical direction of the speaker system in the first embodiment. Fig. 5 is a front perspective view of a speaker system in a second embodiment of the invention. Figs. 6a and 6b are respectively directivity diagrams in the horizontal direction and vertical direction of the speaker system in the second embodiment. DESCRIPTION OF THE PREFERRED EMBODIMENTS The appearance of a speaker system of a first embodiment of the invention is shown in Fig. 1. Speaker units 11, 12, 13, 14 are disposed on a flat cabinet front face 15a of a rectangular parallelepiped cabinet 15. The speaker units 11, 12 are disposed so that the centers 11c and 12c of their diaphragms are located substantially on the same horizontal line, and the speaker units 13, 14 are disposed so that the centers 13c and 14c of their diaphragms are located substantially on the same vertical line. A horizontal line 16 and a vertical line 17 shown in Fig. 1 are respectively a horizontal axis and a vertical axis passing through a specified origin O on the cabinet front face 15a. Prior to specific description of the embodiment, the construction of a general speaker unit is briefly explained below. Fig. 2 is a structural sectional view of a dynamic speaker unit. An under-plate 22 is affixed to a lower surface of a magnet 21. A center pole 23 is disposed to be integrated with the middle part of the under-plate 22. A top plate 24 forming a magnetic gap with the center pole 23 is affixed to an upper surface of the magnet 21. A voice coil 25 responsive to an electric signal is held in the magnetic gap. A voice coil bobbin 26 transmits a driving force generated in the voice coil 25 to the vibration system. A conical diaphragm 27 having a dome shape in its central region is affixed to a front end of the voice coil bobbin 26. A frame 28 is affixed to an upper surface of the top plate 24. A damper 29 has an inner circumference affixed to an intermediate position of the voice coil bobbin 26, and an outer circumference affixed to the frame 28. An edge 30 has an inner circumference affixed to an outer circumference of the diaphragm 27, and an outer circumference affixed to the frame 28. A terminal 31 is affixed to the frame 28. A tinsel cord 32 for supplying the electric signal to the voice coil 25 is connected at one end thereof to the terminal 31 and at the other end to a mid part of the voice coil bobbin 26. Screw holes 33 for mounting the speaker unit on the cabinet front face are opened in the outer circumference of the frame 28. A speaker unit as shown in Fig. 2 may be used as each of the speaker units 11, 12, 13 and 14 shown in Fig. 1. Of course, speaker units having other structures may equally be employed. In the speaker system shown in Fig. 1, two speaker units 11 and 12 are disposed on the cabinet front face 15a, at a specific horizontal spacing between outer ends of the frames of the speaker units so that the centers 11c and 12c of the diaphragms of the speaker units are located on the same horizontal line (i.e., at the same vertical position). The spacing of the speaker units 11 and 12 is defined so that the distance between the centers 11c, 12c of the diaphragms is Lh. The other two speaker units 13 and 14 are disposed at a specific vertical spacing between outer ends of the frames of the speaker units so that the centers 13c and 14c of the diaphragms of the speaker units are located on the same vertical line (i.e., at the same horizontal position). The spacing of the speaker units 13 and 14 is defined so that the distance between the centers 13c, 14c of the diaphragms is Lv. The speaker units 11, 12, 13, 14 are disposed so that the center of a line linking the centers 11c, 12c of the diaphragms and the center of a line linking the centers 13c, 14c of the diaphragms substantially coincide with each other. In other words, the horizontal position and vertical position of the center of the line linking the centers 11c, 12c of the diaphragms, or the horizontal position and vertical position of the center of the line linking the centers 13c, 14c of the diaphragms are substantially the same as the origin O at the intersection of the horizontal axis 16 and the vertical axis 17 on the cabinet front face 15a. Besides, the line linking the centers 11c, 12c of the diaphragms and the horizontal axis 16 are parallel to each other, while the line linking the centers 13c, 14c of the diaphragms and the vertical axis 17 are parallel to each other. If the distance between a plane fully contacting with the cabinet front face 15a and each of the diaphragm centers 11c, 12c, 13c, 14c can be ignored, the line linking the diaphragm centers 11c and 12c and the horizontal axis 16 may be regarded to coincide with each other, and the line linking the diaphragm centers 13c and 14c and the vertical axis 17 may be regarded to coincide with each other. In this constitution, according to the speaker system of the invention, since the two speaker units 13, 14 disposed in the vertical direction at a distance Lv between the centers 13c and 14c of the diaphragms are located at the horizontal position in the middle between the two speaker units 11, 12 disposed in the horizontal direction at a distance Lh between the centers 11c and 12c of the diaphragms, the sharpness of the directivity in the horizontal direction of the pair of the speaker units 11, 12 is smoothed. Likewise, since the two speaker units 11, 12 disposed in the horizontal dircction at a distance Lh between the centers 11c and 12c of the diaphragms are located at the vertical position in the middle between the two speaker units 13, 14 disposed in the vertical direction at a distance Lv between the centers 13c and 14c of the diaphragms, the sharpness of the directivity in the horizontal direction of the pair of the speaker units 13, 14 is smoothed. Therefore, by the arrangement of the four speaker units 11, 12, 13, 14 in this embodiment, the frequency at which the side lobe is generated is higher than in the conventional constitution. The directivity angle of the speaker system of the embodiment is described below with reference to Fig. 3. Fig. 3 shows a central axis 34 as the normal of the cabinet front face 15a passing-through the origin O, a horizontal plane 35 formed by the horizontal axis 16 and the central axis 34, and a vertical plane 36 formed by the vertical axis 17 and central axis 34. The same constituent elements as in Fig. 1 are identified with the same reference numbers. The angle h formed when the central axis 34 is rotated within the horizontal plane 35 about the origin O is defined as a directivity angle in the horizontal direction, and the angle v formed when the central axis 34 is rotated within the vertical plane 36 about the origin O is defined as a directivity angle in the vertical direction. Examples of the directivity in the horizontal direction and vertical direction of the first embodiment are shown in Figs. 4a, 4b, respectively. The directivity at each of directivity angles of 0, 20, 40 and 60 degrees are shown. The shown directivity patterns are calculated by assuming the distance between the diaphragm centers 11c, 12c of the speaker units 11, 12 to be Lh = 290 mm, the distance between the diaphragm centers 13c, 14c of the speaker units 13, 14 to be Lv = 400 mm, and each of the diaphragms of the speaker units 11, 12, 13, 14 to be a circular plane surface sound source having a radius of 54 mm. In Figs. 4a, 4b, the relative sound pressure level refers to the difference of the sound pressure level at each of the directivity angles 20, 40 and 60 degrees from the sound pressure level at directivity angle 0 degree assumed to be 0 dB. It is known from the characteristics in Figs. 4a, 4b that the frequency at which the side lobe is generated is relatively high, and that the sound pressure level of the side lobe is low. Generally, in a listening room, the distance between the ceiling and the floor is small, and the sound radiated from the speaker is likely to be reflected by the ceiling and floor. Hence, in the embodiment, the speaker units 11, 12, 13, 14 are disposed so that the distance Lv between the diaphragm centers 13c, 14c of the two speaker units 13, 14 is longer than the distance Lh between the diaphragm centers 11c, 12c of the other two speaker units 11, 12, thereby making the directivity in the vertical direction narrower than the directivity in the horizontal direction. By varying the disposition intervals of the speaker units 11, 12, 13, 14 depending on the ambient environments, the directivity can be varied arbitrarily in each of the horizontal direction and vertical direction. In the above embodiment the speaker units 11, 12 are disposed so that their diaphragm centers 11c, 12c are located at the same vertical position (positioned on the same horizontal line), but the speaker units 11, 12 may be disposed substantially at the same vertical position by allowing a difference of less than the radius of the diaphragm in the vertical position of their diaphragm centers 11c, 12c. Likewise, the speaker units 13, 14 are disposed so that their diaphragm centers 13c, 14c are located at the same horizontal position (positioned on the same vertical line), but the speaker units 13, 14 may be disposed substantially at the same horizontal position by allowing a difference of less than the radius of the diaphragm in the horizontal position of their diaphragm centers 13c, 14c. In the above embodiment, moreover, the speaker units 11, 12, 13, 14 are arranged so that the center of the line linking the diaphragm centers 11c, 12c of the speaker units 11, 12, and the center of the line linking the diaphragm centers 13c, 14c of the speaker units 13, 14 coincide with each other, but a distance difference of less than the radius of a diaphragm may be allowed between the center of the line linking the diaphragm centers 11c, 12c and the center of the line linking the diaphragm centers 13c, 14c, and the speaker units 11, 12, 13, 14 may be disposed so that the center of the line linking the diaphragm centers 11c, 12c and the center of the line linking the diaphragm centers 13c, 14c may substantially coincide with each other. Further, in the above embodiment, the shape of the cabinet 15 is a rectangular parallelepiped, and the shape of the front face 15a is a flat plane, but such shape is not limitative, and, for example, the cabinet front face 15a may be a curved surface or a polyhedron. In the above embodiment, still further, the frame upper surfaces of the four speaker units 11, 12, 13, 14 are disposed so as to contact with the same plane, and all normals of the speaker units 11, 12, 13, 14 passing through the diaphragm centers 11c, 12c, 13c, 14c are parallel to one another, but the normals passing through the diaphragm centers 11c, 12c, 13c, 14c of the speaker units 11, 12, 13, 14 may not be always parallel to one another as far as the speaker units 11, 12, 13, 14 are disposed on the cabinet front face 15a, and may not be parallel to the normal direction of the cabinet front face 15a. A second embodiment is shown in Fig. 5. In Fig. 5, the same constituent parts as in the first embodiment in Fig. 1 are identified with the same reference numbers. What is different from the first embodiment is that a speaker unit 18 different from the speaker units 11, 12, 13, 14 is newly added to the speaker system of the first embodiment so that its diaphragm center 18c is located at the origin O. The four speaker units 11, 12, 13, 14 are used for sound reproduction in the low frequency range, and the speaker unit 18 is used for sound reproduction in the medium and high frequency range. The speaker unit for sound reproduction in the low frequency range refers to a speaker unit which is capable of obtaining a sufficient reproduction sound pressure level stably in the low frequency range, inclined to increase harmonic distortion components in the reproduction sound as the reproduction sound pressure level drops in the higher frequency range, and incapable of obtaining such a satisfactory reproduction sound as in the low frequency range. On the other hand, the speaker unit for sound reproduction in the medium and high frequency range refers to a speaker unit which is capable of obtaining a sufficient reproduction sound pressure level stably in the medium and high frequency range, inclined to increase harmonic distortion components in the reproduction sound as the reproduction sound pressure level drops in the lower frequency range, and incapable of obtaining such a satisfactory reproduction sound as in the medium and high frequency range. Therefore, when adding the speaker unit 18 for sound reproduction in the medium and high frequency range to the speaker system of the first embodiment, only the signals in the low frequency range are fed into the speaker units 11, 12, 13, 14 for sound reproduction in the low frequency range so that a sufficient reproduction sound is reproduced in the low frequency range by the speaker units 11, 12, 13, 14, and only the signals in the medium and high frequency range are fed into the speaker unit 18 for sound reproduction in the medium and high frequency range so that a sufficient reproduction sound is reproduced in the medium and high frequency range by the speaker unit 18. At this time, by adjusting the reproduction sound pressure level of the entire set of the speaker units 11, 12, 13, 14 for sound reproduction in the low frequency range, and the reproduction sound pressure level of the speaker unit 18 for sound reproduction in the medium and high frequency range, a stable reproduction sound pressure level is obtained in the wide band from the low frequency range to the medium and high frequency range. An electric circuit for dividing a signal into a low frequency band and a medium and high frequency band and for feeding the band divided signal components into the set of the speaker units 11, 12, 13 and 14 and the speaker unit 18 is called a dividing network, and the frequency at which the signal frequency band is divided into two bands is called the crossover frequency. The dividing network itself is a known art, and the practical electric circuit thereof may be composed in various known manners. In the second embodiment, the behavior of the set of the speaker units 11, 12, 13, 14 in the low frequency range is the same as in the first embodiment. Therefore, in the directivity of the set of the speaker units 11, 12, 13, 14 in the low frequency range, the frequency at which the side lobe is generated is high, and the sound pressure level of the side lobe is lowered. Therefore, it is easier to set the crossover frequency of the dividing network for the speaker units 11, 12, 13, 14 and the speaker unit 18 in a band free from effects of the side lobes of the set of the speaker units 11, 12, 13, 14. Hence, directivity free from disturbance from the low frequency range can be obtained. Shown below is an example of a calculation of the directivity of the speaker system in which the band is divided into the low frequency band and the medium and high frequency band by the dividing network. In the same way as in the first embodiment, assuming the distance between the diaphragm centers 11c, 12c of the speaker units 11, 12 to be Lh = 290 mm, the distance between the diaphragm centers 13c, 14c of the speaker units 13, 14 to be Lv = 400 mm, each of the diaphragms of the speaker units 11, 12, 13, 14 to be a plane surface sound source having a radius of 54 mm, the diaphragm of the speaker unit 18 to be a plane surface sound source having a diameter of 110 mm, and the crossover frequency of the dividing network to be 1.2 kHz, the directivity patterns in the horizontal direction and vertical direction calculated at the speaker system directivity angles of 0, 20, 40 and 60 degrees are respectively shown in Figs. 6a, 6b. It is known from Figs. 6a, 6b that there is no significant disturbance due to effects of the side lobes in the directivity pattern along with the increase in the directivity angle in the vicinity of the crossover frequency. Here, the reason why the diameter of the diaphragm of the speaker unit 18 is made large as 110 mm will be described. When the directivity is calculated by using a flat plane sound source, the sharpness of the directivity will be loosened more and the frequency at which the side lobe is generated will become higher with an increase of the area of the diaphragm. Accordingly, the speaker unit having a large diaphragm can be regarded as a speaker unit whose directivity is controlled to a certain extent. In other words, if the speaker unit 18 has the same directivity as that of the flat plane sound source having a large diameter as 110 mm, it is possible to realize a directivity of the entire speaker system controlled to be less disturbed in the wide frequency band including the low frequency range in the arrangement shown in Fig. 5. Incidentally, even if the distance Lh between diaphragm centers 11c, 12c of the speaker units 11 and 12, and the distance Lv between diaphragm centers 13c, 14c of the speaker units 13 and 14 are made sufficiently large, the disturbance of directivity due to effects of side lobe is small. Accordingly, a horn speaker with a wide mouth can be used for the speaker unit for sound reproduction in the medium and high frequency range, so that the directivity can be sufficiently controlled in a wide range. In this embodiment, the horizontal position and vertical position of the diaphragm center 18c of the speaker unit 18 are matched with the horizontal position and vertical position of the origin O on the cabinet front face 15a, but a slight difference may be allowed between the horizontal position or vertical position of the diaphragm center 18c and the horizontal position or vertical position of the origin O, as far as the positions substantially coincide each other.

Claims: A speaker system comprising: a cabinet (15) having a front surface (15a); first and second speaker units (11,12) disposed on the front surface of the cabinet at a specific horizontal spacing and such that there is a difference of less than the radius of the diaphragms of the first and second speaker units (11, 12) between the vertical positions of the centres of the diaphragms of the first and second speaker units; and third and fourth speaker units (13, 14) disposed on the front surface of the cabinet at a specific vertical spacing and such that there is a difference of less than the radius of the diaphragms of the third and fourth speaker units (13,14) between the horizontal positions of the centres of the diaphragms of the third and fourth speaker units; the first through fourth speaker units (11-14) being arranged such that the centre of a line which links the centres of the diaphragms of the first and second speaker units (11,12) and the centre of a line which links the centres of the diaphragms of the third and fourth speaker units (13,14) are located at a distance apart of less than the radius of the diaphragms; characterised in that the horizontal spacing (Lh) between the centres of the diaphragms of the first and second units (11,12) and the vertical spacing (Lv) between the centres of the diaphragms of the third and fourth speaker units (13,14) are different from each other. A speaker system according to Claim 1 wherein said line which links the centres of the diaphragms of the first and second speaker units (11,12) is horizontal and said line which links the centres of the diaphragms of the third and fourth speaker units (13,14) is vertical. The speaker system of Claim 1 or 2 wherein said centres of said lines coincide. A speaker system according to Claim 1, 2 or 3, wherein the vertical spacing (Lv) between the centres of the diaphragms of the third and fourth speaker units (13,14) is longer than the horizontal spacing (Lh) between the centres of the diaphragms of the first and second speaker units (11,12). A speaker system according to Claim 1, 2, 3 or 4, further comprising a fifth speaker unit (18) which is disposed on the front surface (15a) of the cabinet (15) at a centre of an area surrounded by the first through fourth speaker units (11-14). A speaker system according to Claim 5, wherein each of the first through fourth speaker units (11-14) is a speaker unit for reproducing sound in a first frequency range and the fifth speaker unit (18) is a speaker unit for reproducing sound in a second frequency range which is higher in frequency than said first frequency range.

Inventors: KOURA SATOSHI, SAIK SHUJI, SATOH KAZUE, KOURA, SATOSHI, SAIK, SHUJI, SATOH, KAZUE
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: H04R1
IPC codes: H04R1