WO2000067524A2

WO2000067524A2 - Bending wave loudspeakers

Info

Publication number: WO2000067524A2
Application number: PCT/GB2000/001483
Authority: WO
Inventors: Henry Azima; Graham Bank; Martin Roberts
Original assignee: New Transducers Limited
Priority date: 1999-04-29
Filing date: 2000-04-28
Publication date: 2000-11-09
Also published as: AU4582300A; GB9910220D0; WO2000067524A3

Abstract

A loudspeaker combination comprising a bending-wave panel-form loudspeaker and a dipole subwoofer, the dipole subwoofer comprising a pistonic driver mounted in an open baffle.

Description

TITLE : LOUDSPEAKERS

DESCRIPTION

TECHNICAL FIELD

The invention relates to loudspeakers and more particularly to bending-wave loudspeakers, e.g. resonant panel-form loudspeakers of the kind described in International patent application O97/09842, such loudspeakers being known as distributed mode or DM panel loudspeakers .

BACKGROUND ART

Bending-wave panel loudspeakers are known to have a favourable interaction with room boundaries. This is due to a combination of diffuse sound radiation, uniform directivity with frequency and the bipolar (dipolar at low frequencies) nature of their acoustical radiation. This contrasts with the characteristics of conventional pistonic loudspeakers .

Where very low frequency reproduction is important, such as high fidelity and home theatre applications, a conventional woofer or subwoofer (hereinafter subwoofer) acting as point (monopole) source is normally used to augment the bass region. This is not an ideal sound source as it excites room modes with maximum intensity. Furthermore such a conventional subwoofer is not nearly an ideal combination with a bending-wave panel loudspeaker since a point source subwoofer behaves quite differently to the distributed mode panel loudspeaker in its interface with the room, and therefore detracts from an ideally seamless reproduction across the frequency band.

DISCLOSURE OF INVENTION According to the invention a loudspeaker combination comprises a panel -form bending-wave loudspeaker and a dipole subwoofer, the dipole subwoofer comprising a pistonic driver mounted in an open baffle.

The dipole subwoofer may comprise at least one pair of pistonic drivers. One driver of the pair may be located in the baffle in a reversed position relative to the other driver of the pair and wired out of phase with respect to the other driver of the pair. The drivers may be wired in antiphase .

Several of the drivers may be distributed over the open baffle. The open baffle may be flat or substantially so and may provide a support for the panel -form loudspeaker.

Pivot means may be provided to permit rotation of the open baffle relative to the bending-wave panel -form loudspeaker about a substantially vertical axis. The bending-wave panel -form loudspeaker is preferably a distributed mode panel loudspeaker.

Signal processing means may be provided to control time delays between the various loudspeaker drive units.

BRIEF DESCRIPTION OF DRAWINGS The invention is diagrammatically illustrated, by way of example, in the accompanying drawings in which :-

Figures la, b, and c are side views of various combinations of bending-wave panel-form loudspeaker and dipole subwoofers arrangements;

Figure 2 is a front view of a dipole subwoofer arrangement embodying the present arrangement, and

Figure 3 is a block circuit diagram showing the way in which the drivers of the subwoofer speaker array of Figure 2 may be driven.

BEST MODES FOR CARRYING OUT THE INVENTION

Dipole subwoofers and their properties are known as such but the market has tended to favour conventional monopole loudspeakers. Chiefly due to its figure-of-eight radiation pattern, a dipole speaker, placed carefully in the room can be made to behave favourably in creating an improved power response with a higher degree of uniformity across the room. Thus this behaviour is more akin to that of a bending-wave panel loudspeaker and their combination is synergistic in providing a better acoustic reproduction in real spaces .

An inherent disadvantage of dipole subwoofers, in being less efficient than their monopole counterparts, may be compensated for by the use of either more efficient drive units or more drive units. Thus a dipole subwoofer can be made more closely to match the acoustical behaviour of a bending-wave panel loudspeaker especially in its interaction in real space.

Figure la illustrates that in its basic form a dipole subwoofer for use in combination with a bending-wave panel loudspeaker 10, e.g. of the kind described in WO97/09842, can be a single conventional pistonic drive unit 12 mounted in a large substantially flat open baffle 14. Both the baffle 14 and drive unit 12 are surrounded by an acoustically transparent open grill 16. A base 18 which may be mounted on castors supports the baffle 14 and grill 16. The bending-wave panel loudspeaker 10 is supported on the baffle 14.

In the arrangement of Figure la the bending-wave panel loudspeaker 10 is shown in block form to indicate that any type of assembly, open or closed back, may be used, although ideally an open back assembly will give the optimum, near dipole, behaviour for the bending-wave panel loudspeaker at low frequencies matching that of the open baffle dipole subwoofer below.

For greater power handling and to compensate for its lower efficiency, one could utilise larger and more efficient units of subwoofer, e.g. of 250mm, 300mm or even 5 375mm diameter. In a preferred realisation, however, the subwoofer could take the form of a multi-driver array of smaller size, of say 125mm or 150mm diameter, which will provide a number of benefits.

Figure lb illustrates another loudspeaker arrangement 0 embodying the invention and which is generally similar to that already described with reference to Figure la. It will be seen that in the arrangement of Figure lb the single pistonic drive unit 12 has been replaced by a pair of pistonic drive units 12a and 12b. It is to be noted that 5 these pistonic drive units are mounted in the baffle 14 to face in opposite directions. It is envisaged that these drive units will be driven in antiphase.

As all drivers show some degree of asymmetry in their operation, higher linearity and thus reduced acoustic 0 distortion is also achieved by the use of a pair of drivers with antiphase electrical connection facilitated by the opposing physical placement of the drivers. If the vibration and distortion reduction benefit is thought to be of benefit then both odd and even numbers of drivers might 5 be used on the baffle 14.

An even number array of such smaller drive units will further spread the excitation points of the room, and have the advantage of lesser room mode resonance generation, making it even more compatible as a partnering reproducer to a bending-wave panel loudspeaker. This may be described as adding to a "spatially diffuse" radiation behaviour. Signal processing (preferably digital signal processing) may also be used to manipulate the delay between different drive units for further enhancement of the diffuse nature of the low frequency reproduction. This may be described as adding "temporal diffusion" . The combination of the two will provide a powerful method of simulating a distributed mode panel form of radiation.

Yet another advantage will be gained by mounting the drive units with half of them facing forward and half of them facing backwards (and electrically connected out of phase) within the baffle. This will reduce the even harmonic distortion content of the acoustic output at higher reproduction levels.

In order to ensure the best possible integration with the distributed mode panel loudspeaker partnering speaker, a preferred construction method is to have the dipole subwoofer directly beneath the bending-wave panel loudspeaker, and acting as its supporting structure at the same time. It may, however, be placed separately in some applications still with good results.

For optimum performance of dipole subwoofers it is desirable to be able to rotate them in the azimuth plane to find the optimum angle for the null axis of the system with respect to the room boundaries. To achieve this an arrangement such as is shown in Figure lc may be provided in which again parts similar to those already described are given the same reference numerals. It will be seen in the arrangement of Figure lc that the baffle 14 is supported on the base 18 and in turn supports the bending-wave panel loudspeaker 10 by means of rotatable couplings 20 which enable the baffle 14 to be rotated whilst leaving the bending-wave panel loudspeaker in a relatively fixed position. The provision of this arrangement allows the separate angling of the subwoofer and bending-wave panel loudspeaker sections and enables the best alignment of the directional radiation patterns with the room modal resonances according to the placement of both the speaker (s) and listener (s) with the intention of producing an optimised frequency characteristic. This may not be necessary for the partnering bending-wave panel loudspeaker, or possible even detrimental in some instances. To provide maximum flexibility for an optimised sound performance the subwoofer section may be made to pivot independently of the bending-wave panel loudspeaker. Given that the acoustic radiation from a bending-wave panel loudspeaker is not wholly dipolar even at low frequencies a further embodiment of the invention configures the base section as partially dipolar and partially diffuse by employing an array of smaller bass drivers. The number of drivers is preferably at least three and may be as many as ten. Figure 2 shows an arrangement in which six such speakers are provided with three (B) facing forwardly and three (A) facing rearwardly of the baffle. When these speakers are driven by audio signals, variously delayed to generate sources of differing effective position, the acoustic sum is the equivalent to diffuse radiation. Figure 3 illustrates how such a delay may be achieved and provides that an input signal at 30 is passed via delay stages tl, t2 , t3 etc. to output amplifiers 32, 32', 32" etc. coupled to the drivers held in the baffle 14.

Fig lc also shows the baffle 14 with optional rearward wings 22 from the opposite vertical edges, the purpose of which is to increase the pressure component of the sound radiation without significantly altering the dipolar radiation pattern. This increase in the pressure content may help in filling-in gaps in the room response. It will be appreciated that such baffle wings 22 are also applicable to the embodiments of Figures la and lb.

INDUSTRIAL APPLICABILITY The present invention thus provides a synergistic combination of bending-wave panel loudspeaker and subwoofer .

Claims

1. A loudspeaker combination comprising a bending-wave panel -form loudspeaker and a dipole subwoofer, the dipole subwoofer comprising a pistonic driver mounted in an open baffle.

2. A loudspeaker combination according to Claim 1, wherein the dipole subwoofer comprises at least one pair of pistonic drivers.

3. A loudspeaker combination according to Claim 2, wherein one pistonic driver of the pair is located in the baffle in a reversed position relative to the other pistonic driver of the pair and is electrically connected out of phase with respect to the other driver of the pair.

4. A loudspeaker combination according to Claim 3, wherein the pistonic drivers are electrically connected in antiphase .

5. A loudspeaker combination according to Claim 2, Claim 3, or Claim 4 comprising several pairs of pistonic drivers distributed over the open baffle.

6. A loudspeaker combination according to any preceding claim, wherein the open baffle provides a support for the bending-wave panel-form loudspeaker.

7. A loudspeaker combination according to Claim 5, comprising means permitting rotation of the open baffle relative to the bending-wave panel -form loudspeaker about a substantially vertical axis.

8. A loudspeaker combination according to any preceding Claim, wherein the bending-wave panel -form loudspeaker is a distributed mode panel loudspeaker.

9. A loudspeaker combination according to any preceding claim, comprising a plurality of pistonic drive units mounted on the open baffle and, signal processing means for controlling the time delays between the pistonic loudspeaker drive units.

10. A loudspeaker according to any preceding claim, wherein the baffle comprises at least one wing extending therefrom and at an angle to the plane of the baffle.