GB2191065A - Sound generating system - Google Patents

Abstract

A bass-enhancer/sub-woofer (10) in a loudspeaker system dispenses with a cabinet and comprises a multiple dipole array in which the dipoles are positioned in line one behind the other in the manner of an aerial. By setting the array at an appropriate angle within a room the effect of the room characteristics can be matched. A satellite loudspeaker (12) is preferably mounted to be adjustable in angular position independently of the sub- woofer (10). <IMAGE>

Description

SPECIFICATION Sound generating systems This invention relates generally to sound generating systems, and is particulariy concerned with systems which will generate low frequencies without the use of a cabinet.

It has been generally recognised for a long time that the materials used in the construction of a loudspeaker cabinet can markedly affect the overall sound. Much research has been conducted into the design of loudspeaker cabinets, as well as into the interaction of loudspeaker cabinets with different room configurations. Attempts have been made to make loudspeakers with cabinet materials having high stiffness and low mass. However, for practical purposes, improvements in this direction can only be achieved to a limited degree.

Sub-woofers are known in loudspeaker systems, with a view to enhancing the bass response.

However, existing sub-woofers are monaural, and although extending the bandwidth do tend to have an adverse effect on the stereo quality of stereophonic systems. Although equalised bass can achieve increased extension and power, one still has problems arising from the interaction of the speaker and the room within which it is operating.

Most domestic rooms for example result in the production of standing waves which will give rise to boom in the acoustic response.

It is an object of the present invention to provide a sound generating system which is able to produce the sort of sound quality that would be achieved if one could have the ultimate in cabinet noncontribution.

It is a further object of the present invention to provide a sound generating system which can be integrated appropiatelywith the room acoustics so that the system maintains its capabilities down to the lowest frequencies regardless of the room in which it is functioning.

In accordance with the present invention this is achieved by the provision of a sound generating system comprising a multiple dipole array in which the dipoles are positioned in line one behind the other.

Preferably, the array is a double dipole array.

The dipoles may be mounted on a common base plate.

According to one preferred embodiment of the invention the system includes a satellite loudspeaker mounted above the dipole array and capable of orientation independently of the dipole array. By this means the base extender system constituted by the dipole array can be positioned to give the optimum sound pressure and polar response for a particular room, and then the satellite loudspeaker can be rotated relative to the dipole array to give the optimum stereo effect.

In order that the invention may be fully understood, an embodiment of sound generating system in accordance with the invention will now be described by way of example and with reference to the accompanying drawing, in which: Fig. 1 shows a number of typical dipole arrays as used in a sound generating system in accordance with the invention; and, Fig. 2 is a schematic side view of a loudspeaker system comprising a sub-woofer and satellite loudspeaker.

The sound generating system of the present invention can be put into practical effect either as a bass-enhancerforan existing loudspeaker system, or alternatively as an integrated part of a loudspeaker system. Because the sound generating system is particularly designed for use at low frequencies, it is hereinafter referred to as a subwoofer. As referred to above, it is an object of the present invention to remove the effect of the cabinet in the loudspeaker. The solution of the present invention is to use an array of dipoles, as illustrated in Fig. 1,with the dipoles arrayed like the elements of an aerial. Preferably, a double dipole is used, but one could alternatively have a quadruple or sextuple array.The primary advantage of this arrangement is that one can tune the system both in respect of its polar response and frequency response. The low frequency dipole array source is designed to have a falling sound pressure response, at 6dB/octave below the turnover, determined by the effective path length of the dipole and double dipole array. A simple filter can be used to correct for this response, and even when correction stops, the source still only falls at 6dB/octave. A number of different lower turnover frequencies can be used in order to achieve an ideal match with a large number of different listening room characteristics.

Fig. 2 shows a full loudspeaker system comprising the sub-woofer which is indicated generally at 10, and a satellite loudspeaker which is indicated generally at 12. The sub-woofer comprises a metal base plate 14 and a pair of support plates 16 and 18 which carry the respective dipoles. Each support plate 16, 18 is also provided with a curved grille 20.

In one preferred embodiment of the invention, each dipole comprises a baffle-less longthrow bass driver. The bass drivers are positioned front and back of a column 22 which provides a stand for the satellite loudspeaker 12. The satellite loudspeaker 12 is fastened to the column 22 by adjustable means which allows the satellite loudspeaker to be angled independently of the sub-woofer 10. This means that the sub-woofer 10 can be positioned and rotated to interface with the room, after which the satellite loudspeaker 12 can be turned to give the optimum stereo effect.

As an alternative to using large, for example 12 inch, baffle-less long-throw base driversforthe subwoofer, one can alternatively use two or more small-baffle single dipoles.

Experimental evidence has been produced to determine the effect of six room boundaries on such a source. The addition of boundaries has been found to have a detrimental effect upon a double dipole which is set normal to the front wall.

Similarly, with the source parallel to the wall, neither the sound pressure response curve nor the polar response are ideal. However, by rotating the sub-wooferto an intermediate angle relative to the wall it has been found that an optimum angle exists forthe positioning of such a dipole array in any particular room. At this optimum intermediate angle the horizontal polar response curve and sound pressure response curve begin to approach the response which one would expect from a theoretical ideal source measured in free space. Thus, using the present invention, it is possible to site a low frequency multiple dipole array, preferably a double dipole array, and to preserve the directivity characteristics as if the source was unbounded. As the dipoles are only generating bass in one dimension, the interaction of three room standing waves which one finds in other systems is minimised, thus preventing boom and giving a deeper, more powerful and cleaner bass response regardless of the room characteristics.

Claims (7)

1. A sound generating system comprising a multiple dipole array in which the dipoles are positioned in line one behind the other.

2. A system as claimed in claim 1, in which the array is a double dipole array.

3. A system as claimed in claim 1 or 2, in which the dipoles are mounted on a common base plate.

4. A system as claimed in any preceding claim, in which each dipole comprises a baffle-less longthrow bass driver.

5. A system as claimed in claim 1,2 or 3, in which the array comprises two or more small-baffle single dipoles.

6. A system as claimed in any preceding claim, which includes a satellite loudspeaker mounted above the dipole array and capable of orientation independently of the dipole array.

7. A sound generating system substantially as hereinbefore described with reference to the accompanying drawings.