Loudspeaker array with multiple drivers

Abstract

The present invention relates to a loudspeaker array comprising: a high frequency driver and a midrange driver forming a unitary assembly and configured to direct acoustic waves towards a listener in front of the loudspeaker array along an axis in a forward direction; at least one low frequency driver located generally rearwardly of the unitary assembly, and a woofer volume extending along and perpendicular to the axis between the at least one low frequency driver and the unitary assembly, in which the rear of the unitary assembly is configured and acoustically open so as to allow sound from the rear of the midrange driver to radiate rearwardly into the woofer volume.

Claims

1. A loudspeaker array, comprising: a high frequency driver and a midrange driver forming a unitary assembly and configured to direct acoustic waves towards a listener in front of the loudspeaker array along an axis in a forward direction; at least one low frequency driver located generally rearwardly of the unitary assembly, and a woofer volume extending along and perpendicular to the axis between the at least one low frequency driver and the unitary assembly, in which the rear of the unitary assembly is configured and acoustically open so as to allow sound from the rear of the midrange driver to radiate rearwardly into the woofer volume.

2. The loudspeaker array according to claim 1, in which the high frequency driver and the midrange driver are substantially coaxial.

3. The loudspeaker array according to claim 1, comprising one low frequency driver which is disposed coaxially with the unitary assembly.

4. The loudspeaker array according to claim 1, in which there is more than one low frequency driver, the low frequency drivers being adapted in combination to direct low frequency acoustic waves in a substantially forward direction.

5. The loudspeaker array according to claim 4 in which the low frequency drivers are arranged symmetrically around the axis.

6. The loudspeaker array according to claim 1 in which an acoustically absorbent material is located in but does not fill the woofer volume.

7. The loudspeaker array according to claim 6 in which the acoustically absorbent material extends so as substantially to separate the rear of the midrange driver from the low frequency driver.

8. The loudspeaker array according to claim 1, in which there is a woofer aperture extending around the unitary assembly through which low frequency acoustic waves from the low frequency driver radiate forwardly of the speaker system, and in which acoustically absorbent material is located at or within the woofer aperture.

9. The loudspeaker array according to claim 8 in which the acoustically absorbent material does not fill the woofer aperture.

10. The loudspeaker array according to claim 8, further comprising a grille extending over the woofer.

11. The loudspeaker array according to claim 8, in which the low frequency driver has a diaphragm having a first forward facing area and the woofer aperture has a second forward facing area, the second area being a proportion of the first area sufficient to limit airflow velocity of low frequency acoustic waves at the woofer aperture to less than 10 ms.sup.−1.

12. The loudspeaker array according to claim 11, in which the second area is a proportion of the first area sufficient to limit airflow velocity of low frequency acoustic waves at the woofer aperture to less than 5 ms.sup.−1.

13. The loudspeaker array according to claim 12, in which the ratio of the first and second areas is between 20% and 70%, and more preferably between 30% and 50%.

14. The loudspeaker array according to claim 1, in which there is a woofer aperture extending around the unitary assembly through which low frequency acoustic waves from the low frequency driver radiate forwardly of the speaker system, and in which a baffle is provided around the unitary assembly, extending generally rearwardly of it and configured to prevent or reduce acoustic diffraction.

15. A loudspeaker system comprising a plurality of loudspeaker arrays according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which;

(2) FIG. 1 shows a conventional three driver coaxial array loudspeaker in cross-section;

(3) FIG. 2 shows the predicted sound power response of the loudspeaker of FIG. 1;

(4) FIGS. 3a and 3b show embodiments of three driver coaxial array loudspeakers in accordance with the invention in cross-section;

(5) FIGS. 4a and 4b show the predicted sound power response of the loudspeakers of FIGS. 3a and 3b respectively;

(6) FIG. 5a shows the measured sound power response of the prior art loudspeaker of FIG. 1, and

(7) FIG. 5b shows the measured sound power response of the same driver used in the arrangement of FIG. 3b.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(8) FIG. 1 shows a prior art loudspeaker array which is described above. FIG. 2 shows the theoretical sound power response of the conventional loudspeaker array of FIG. 1, and is also explained above.

(9) FIGS. 3a and 3b show two embodiments of loudspeaker arrays in accordance with the present invention; elements of these embodiments which are substantially the same as those in the loudspeaker array of FIG. 1 bear the same reference numerals as the elements in FIG. 1. In these drawings the front, as that term is applied herein to any element of the loudspeaker array, and the forward direction, as that term is applied herein to any direction, mean the right hand side of the drawing, and the terms back, rear and rearwardly mean the left hand side of the drawing. The axis referred to herein runs horizontally, left to right in the drawings. As in FIG. 1, the tweeter 2 is located on the left/right horizontal axis with an annular midrange driver 4 arranged concentrically around the tweeter 2, the two being substantially in the same plane, and mounted in a single, unitary assembly 6. The diaphragms of the midrange driver and the tweeter are arranged so as to be closely spaced where they are adjacent. A conventional woofer 8 is located coaxially with and behind the assembly 6 and spaced axially from it; this positioning leaves a woofer front cavity 10 between the woofer diaphragm 12 and the rear of the assembly 6, through which cavity acoustic waves generated by the woofer 8 can propagate forwardly and radially outwardly towards a woofer aperture 14 (which forms an annulus around the assembly 6) and thence towards a listener positioned in front of the system (i.e. to the right hand side of the drawing). In FIG. 3a the midrange driver shield 16 of the conventional loudspeaker array of FIG. 1 is removed, leaving nothing but empty space in the woofer front cavity 10 between the rear of the midrange driver 4 (and the rear of the tweeter 2) and the front of the woofer 8.

(10) In FIG. 3b the shield of FIG. 1 is replaced with an enclosure 32 formed of an open cell foam 34 which interrupts the acoustic path from the rear of the midrange driver 2 towards the woofer 8 and a curved baffle 36, but is adapted to not substantially obstruct acoustic waves travelling rearwardly from the rear of the midrange driver 4. Additional acoustically absorbent material 38 (it can be made of the same material as or of a different material to the material 34 forming part of the enclosure 32) is provided at the woofer aperture 14 and a grille 40 is provided overlying the front of this material 38 (or it may extend over the entire woofer aperture 14) to conceal it from view and to protect it.

(11) FIGS. 4a and 4b show the theoretical sound power response of the loudspeakers of FIGS. 3a and 3b, respectively. As can be seen, the large (−10 dB) dip in the response at around 950 Hz present in FIG. 2 should be substantially removed. This has been confirmed in our experiments, in which the sound power response of the midrange driver assembly shown in FIG. 1 was measured and is shown in FIG. 5a; this plot conforms closely to the predicted result shown in FIG. 2. The same midrange assembly was then used in the arrangement of FIG. 3b, and the resulting sound power response is shown in FIG. 5b; again it can be seen that this result conforms closely to the predicted response shown in FIG. 4b, and represents a significant improvement in performance over the conventional loudspeaker arrangement of FIG. 1.

(12) The choice of the area of the woofer aperture as a proportion of the area of the woofer diaphragm 12 is significant: if this proportion is too small then diffraction occurs, and this is detrimental to sound quality. If the proportion is too high then there is a high airflow velocity in the woofer aperture 14, which causes undesirable noise. We have found that an area ratio range of between 20% and 70% is suitable for an acceptable product, but that a range of between about 30% and about 50% is preferable.

(13) It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention. For example, the embodiment above is a substantially circular loudspeaker array, but the illustrated circular midrange driver diaphragm can be any shape (e.g. square, oval, cloverleaf) provided its rear acoustic radiation is directed into the woofer front cavity. Preferably the shape of the tweeter is the same as that of the midrange driver, as may be the shape of the or each low frequency driver. We have mentioned the possibility of providing multiple woofers, these may be arranged symmetrically, such as in the known front-to-front and back-to-back arrangements of two woofers (force cancelling arrays), or multiple woofers may be arranged around a cavity and arranged to direct their aggregated acoustic waves forwardly (as in US 2020/0396536, for example). The tweeter and midrange driver may be coplanar, or their respective planes may be spaced along the axis provided they are in a single assembly and there is no significant distance between the inner edge of the midrange driver and the outer edge of the tweeter. The way the unitary assembly 6 is supported is not clearly shown in the drawings; however, it is well-known in the art that this support may comprise a generally radial, “spider” assembly. The support may also be one which is substantially axial, where the assembly is supported on a stalk which extends rearwardly or generally rearwardly, or a number of stalks which extend generally rearwardly.

(14) Where different variations or alternative arrangements are described above, it should be understood that embodiments of the invention may incorporate such variations and/or alternatives in any suitable combination.