EP1138175A2

EP1138175A2 - Bending wave panel-form loudspeaker

Info

Publication number: EP1138175A2
Application number: EP99958386A
Authority: EP
Inventors: Henry Azima
Original assignee: New Transducers Ltd
Current assignee: NVF Tech Ltd
Priority date: 1998-12-09
Filing date: 1999-12-09
Publication date: 2001-10-04
Also published as: WO2000035242A2; CN1329809A; TW457826B; WO2000035242A3; JP2002532993A; AU1576000A

Abstract

A window loudspeaker combination comprising a pane of glass or other transparent material adapted to be supported at its periphery in a surround and a vibration exciter coupled to the pane to cause bending wave vibration therein to produce an acoustic output, characterised in that the vibration exciter is an electrodynamic inertial device having a low mass voice coil, a magnet system associated with the voice coil, and a suspension for mounting voice coil in the magnet system for movement relative thereto, the vibration exciter being mounted wholly on the plane.

Description

TITLE: LOUDSPEAKER

DESCRIPTION

TECHNICAL FIELD

The invention relates to loudspeakers and more particularly to panel -form loudspeakers.

BACKGROUND ART It is known to suggest driving the transparent face of a wristwatch to act as a buzzer or sounder i.e. to emit simple sound tones, e.g. to act as an alarm for the wearer of the wristwatch.

It is also known to apply high mass unitary mertial exciters to windows, i.e. to window glass to form a loudspeaker, but with relatively poor results. Two problems may be identified, namely the high mass at the exciter/glass coupling point due to intermediaries such as plate like fixings and/or bolts or screws which restrict the upper frequency range, and the overall coupled mass of the exciter as mounted, which forms a lower frequency resonance with the compliance of the glass window panel to incite drumming and thus to restrict the lower frequency output. The consequently limited frequency range and problematic and severe resonance m the working range has found little favour with the market and the prior art proposals have not proved successful . Nevertheless the concept of employing viable window panels capable of supporting bending waves for sound reproduction remains of interest on grounds of utility and the large area of a typical window has advantages for loudspeaker use m that the device may be modelled as an area drive to a given room volume defined as an acoustic duct .

This model shows that the loudness m the room is relatively constant with position m contrast to a relatively smaller cone type driver of typically 100th the area and which performs according to the point source rule, with the output falling as the inverse square of distance. Thus the loudness coverage of a large bending wave window is substantially superior to an ordinary speaker. A successful window speaker device must address the dominant issue, namely that glass is a physically tough medium and that for safety and constructional reasons window glass has a thickness m the range 4 to 8mm. Such is the very high stiffness coupled with high density that glass plate presents a very high mechanical impedance and is thus difficult for mechanico-acoustic exciter to drive.

Complementary exciter technology is required to obtain an effective result.

It is among the ob ects of the invention to provide a window e.g. for a vehicle or m a building or m other apparatus formed with a window or viewing port which can be driven as a loudspeaker, e.g. to reproduce speech or music.

The present invention is based on the surprising discovery that very high stiffness and very dense materials such as window glass can be successfully driven by mertial vibration exciters intended to drive stiff light weight panels, e.g. mertial vibration exciters as described m O97/09842, provided that certain conditions are met, as described below.

DISCLOSURE OF INVENTION According to the invention, there is provided a window loudspeaker combination comprising a pane of glass or other transparent material adapted to be supported at its periphery m a surround and a vibration exciter coupled to the pane to cause bending wave vibration therein to produce an acoustic output, characterised m that the vibration exciter is an electrodynamic mertial device having a low mass voice coil, a magnet system associated with the voice coil, and a suspension for mounting voice coil m the magnet system for movement relative thereto, the vibration exciter being mounted on the pane, e.g. via the voice coil . Preferably the exciter is positioned on the pane to maximise the interleaving of resonant modes of bending wave vibration. The window may comprise superposed spaced inner and outer panes defining between them a fluid gap, and the vibration exciter may be disposed on the inner pane .

The or each pane may be supported at its periphery m a rubber or rubber-like glazing seal.

The window loudspeaker combination may comprise electrical leads on the pane for connecting the vibration exciter to a signal source, the leads being substantially invisible . The window or other member may be of plastics or may be of glass or other transparent material, e.g. transparent plastics, and may form part of a vehicle such as an automobile, aircraft railway tram or boat or may form part of a building or other fixed structure or other device having a window or viewing port.

More than one vibration exciter may be provided to apply bending wave energy to the pane to cause it to resonate to produce an acoustic output. The drive means may be mounted to an edge or marginal portion of the panel- form member as taught 099/37121 or to a portion of the pane outside its transparent portion or at least outside a portion thereof used as a window.

From another aspect the invention is a vehicle or other structure incorporating one or more loudspeaker windows as defined above.

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

Figure 1 is a perspective view of part of an omnibus coach or railway tram carriage incorporating window loudspeakers of the present invention; Figure 2 is a perspective view of part of the passenger cabin of an aircraft incorporating window loudspeakers of the present invention;

Figure 3 is a face view of an automobile or the like motor vehicle windscreen or windshield incorporating window loudspeakers of the present invention;

Figure 4 is a perspective view of the rear windshield or screen or an automobile incorporating window loudspeakers of the present invention;

Figure 5 is a perspective view of a door for an automobile incorporating window loudspeakers of the present invention;

Figure 6 is a perspective view of a fixed side window of an automobile incorporating window loudspeakers of the present invention; Figure 7 shows a window m a building incorporating window loudspeakers of the present invention;

Figure 8 is a perspective view of a bay window m a building incorporating window loudspeakers of the present invention;

Figure 9 is a face view of a door m a building incorporating window loudspeakers of the present invention; Figure 10 is a face view of a pair of glass doors a building incorporating window loudspeakers of the present invention;

Figure 11 is a face view of a double glazed window m a building incorporating window loudspeakers of the present invention;

Figure 12 is a partial cross-sectional view of the double glazed window/loudspeaker combination of Figure 11;

Figure 13 is a frequency response graph of an example of window loudspeaker; Figure 14 is a graph of double glazed window attenuation;

Figure 15 is a graph of m-room sound pressures at 1M and 2M from the window loudspeaker;

Figure 16 is a mathematical model of a double glazed window of the kind as shown m Figure 12;

Figure 17 is a graph of a mathematical simulation corresponding to Figure 14 ; and

Figure 18 is a graph of a mathematical simulation of the velocities of the passive and driven panes the model of Figure 16.

BEST MODE FOR CARRYING OUT THE INVENTION Figure 1 shows part of the interior (1) of an omnibus coach or railway tra carriage (2) having seating (3) for passengers and windows (4) associated with the seating and which are driven to resonate by vibration exciters (5) applied to the lower margins (6) of the window panes at positions hidden from view to cause the window panes to act as loudspeakers substantially as described m our International patent application W099/37121. Additional resonant panel loudspeakers (7) e.g. as taught WO97/09842 are mounted overhead, e.g. m the roof (not shown) of the carriage (2) .

Figure 2 shows part of the interior (1) of the passenger cabin (2) of an aircraft (8) and showing cabin windows (4) driven to act as loudspeakers m a manner which, m essence, is generally similar to that of Figure 1.

Figure 3 is a view of an automobile or the like motor vehicle windscreen or windshield (9) m which vibration exciters (5) have been applied to marginal portions of the screen so as to be invisible to the vehicle occupants and arranged to cause the screen to resonate to act as a loudspeaker substantially as described m our International patent application W099/37121. The vehicle dashboard is shown m dashed lines at (10) along with a steering wheel (11) and rear view mirror (12) . Figure 4 is a view generally similar to that of Figure 3 and showing the rear windshield or screen (13) of an automobile or the like driven to act as a resonant panel loudspeaker, and showing a rear parcel shelf (14) . Figure 5 is a view of a door 15) for an automobile having an openable window (16) slidable m a frame (17) with vibration exciters (5) applied to the lower marginal edge (6) of the window glass out of sight of the vehicle occupants whereby the window is driven to resonate and to act as a loudspeaker substantially as described our International patent application W099/37121.

Figure 6 is a partial view of an automobile (18) having a fixed rear side window (19) and having vibration exciters (5) applied to the lower marginal portion (6) of the glass window panel (19) out of sight of the vehicle occupants whereby the window can be driven to resonate and to act as a loudspeaker substantially as described m International patent application W099/37121. Figure 7 shows a window (20) the wall (22) of a building (21) and comprising a glass pane excited at its upper edge (23) at a position hidden from view behind the window frame by a pair of vibration exciters (5) to form a loudspeaker e.g. of the kind described m our International application W099/37121.

Figure 8 shows a bay window (24) m a building (21) and m which panes of glass (25) are driven to resonate and to act as loudspeakers e.g. of the kind described m our above application by vibration exciters (5) mounted near the lower edges of respective panes, at a position hidden from view behind the window frame.

Figure 9 shows a door (26) a building (21) incorporating a glass pane (25) which is excited to resonate to act as a loudspeaker e.g. of the kind described m our above application by vibration exciters (5) mounted at the lower edge of the pane at a position hidden from view behind the window frame . Figure 10 shows a pair of glass doors (27) m a building (21) and each of which is driven by a pair of vibration exciters (5) mounted at the upper edges of the doors to resonate the doors to act as loudspeakers e.g. of the kind described in our above application. Figures 11 and 12 show a double glazed wmαow (28) the wall (22) of a building (21) which defines a room (29) and shows that, where desired, the vibration exciter (s) (5) may be mounted inwardly of the edges of the panes of glass, i.e. m a near centre position on the pane, to act as loudspeakers e.g. of the kind described m our International application WO97/09842. The exciter (s) is of the electrodynamic mertial kind as described m WO97/09842 or m WO98/34320 and is mounted wholly on the pane either exclusively via the voice coil or via the voice coil with a resilient suspension between the pane and the magnet assembly

Figure 12 shows that the vibration exciter (5) is mounted on the inner pane (30) of the pair of glass panes

(30,31) forming a double glazed window unit (28) mounted m a frame (32) m the wall (22) of the building (21) by means of a rubber or rubber like glazing strip (33) . The two panes (30,31) define an air gap (34) .

Figure 13 shows a frequency response curve of a window as shown m Figures 11 and 12, and demonstrates a wide effective sound output m the 20Hz to 15KHz region.

Figure 14 is a graph measuring, m-room, the effect of the double pane sound attenuation of a window loudspeaker as shown m Figures 11 and 12. The lower curve is of the excitation of the external pane (31) , and the upper curve is of the inner (room) pane (30) excitation.

Figure 15 is a graph of the m-room sound pressure of an example of window loudspeaker as shown m Figures 11 and 12, and showing m the heavy line curve the measurement at 1M and m the light line curve the measurement at 2M. This demonstrates large area room volume drive behaviour with little fall -off with distance. Sound from windows m domestic or commercial premises may be used for announcements, for background music, for noise cancellation and or noise masking, e.g. where low level pink or similarly weighted noise is employed to reduce the annoying effect of other, more periodic noise sources. A consideration is the dipolar bi-directional nature of sound radiating windows now proposed, for example a window m an outside wall. The sound radiated to the outside may be a disadvantage m a domestic setting or an advantage m the case of shop window display disposed to the street with the exciter located m a protected position on the mside.

Modern double and triple glazed window units provide new opportunities for effective window speakers since useful attenuation may be obtained to the environment furthest from the driven pane of the assembly. Each air layer, m con unction with the window elements, may provide an attenuation of around 8 to 12 dB according to the pane and air space thickness. For an exterior open space the far field sound intensity will predominantly follow the inverse square law and the sound pressure falls rapidly with distance. This plus the option of multiple glazing means that the exterior leakage may be successfully controlled.

Factors which have encourage a renewed interest m the subject include the multiple glazing integer and the availability of wide band essentially non resonant, low driving mass exciters such as those described m WO98/34320 and suitable for driving distributed mode loudspeakers of the kind described m WO97/09842. In addition for the first time m the speaker field the mechanical characteristics of the glass panel have been analysed to determine effective methods of excitation as a worthwhile loudspeaker.

Self supporting exciters may be placed at a number of effective positions including near the edge, for unobtrusiveness, as taught m W099/37121 or at optimal near centre locations as taught m WO97/09842. Since these exciters may be very compact and thm wire or even transparent tin oxide wiring may be used, the small exciters may be acceptably placed at the more optimum locations protected and enhanced by small lightweight covers .

For example a window of 1.25 by 1.1 m size of 4 mm thickness was analysed for essentially free edge conditions approximating to a typical moulded rubber support/glazing seal at the edge of the pane. The high mass of even this relatively thm grade of glass is evident, 8.8kg/square m. which is vastly higher than typical diaphragm material for a bending panel speaker. The mechanical impedance is also very high at 468.7 Ns/m. Despite the high stiffness the large area and high mass results m a low fundamental resonance of 15 Hz so that low frequency output is partially available from a frequency about an octave higher, e.g. 30 Hz. A double glazed window/loudspeaker was built using a 25mm coil mertial electrodynamic exciter of the kind described m WO98/34320 at a near central position and the attenuation measured from the front to the rear (undriven) side see Fig.14. Note that for this measurement the sound power was measured m-room for both readings while m practice the external leakage would be significantly lower due to the near free space radiation condition.

INDUSTRIAL APPLICABILITY The computer simulation of Figures 16 and 18 is based on a window loudspeaker as shown m Figure 16 which m turn is similar to that of Figures 11 to 15. Thus the window is double glazed, with glass of 4mm thickness with a 10mm air gap between the panes. The vibration exciter is at a rear centre position as taught m WO97/09842.

The graph of Figure 17 is a simplified two dimensional model showing mean external (free field) sound pressure levels at lm (heavy curve) at 2m (light curve) . The graph of Figure 18 is a computer two dimensional analysis of the velocities of the driven and passive panes m the double glazing. This indicates that the two panes are quite well coupled at low frequencies but are advantageously de-coupled at higher frequencies.

The present invention enables the ready manufacture of bending wave loudspeaker/wmdow combinations which avoid the severe practical problems encountered m the prior art .

Claims

1. A window loudspeaker combination comprising a pane of glass or other transparent material adapted to be supported at its periphery in a surround and a vibration exciter coupled to the pane to cause bending wave vibration therein to ^'produce an acoustic output, characterised that the vibration exciter is an electrodynamic mertial device having a low mass voice coil a magnet system associated with the voice coil, and a suspension for mounting the voice coil the magnet system for movement relative thereto, the vibration exciter being mounted wholly on the pane .

2. The combination of claim 1, characterised m that the exciter is positioned on the pane to maximise the interleaving of resonant modes of bending wave vibration.

3. The combination of claim 1 or claim 2, characterised m that the window comprises a superposed spaced inner and outer defining between them a fluid gap, and m that the vibration exciter is disposed on the inner pane.

4. The combination of any preceding claim, characterised in that the or each pane is supported at its periphery m a rubber or rubber-like glazing seal.

5. The combination of any proceeding claim, characterised by electrical leads on the pane for connecting the vibration exciter to a signal source, the leads being substantially invisible.

6. A vehicle characterised by a window/loudspeaker combination as claimed m any one of claims 1 to 5.

7. A building or other structure characterised by a window/loudspeaker combination as claimed m any one of claims 1 to 5.