WO2012001419A1

WO2012001419A1 - Apparatus for radiating an audio signal

Info

Publication number: WO2012001419A1
Application number: PCT/GB2011/051240
Authority: WO
Inventors: Kamlesh Prajapati; Brian Douglas Smith
Original assignee: Feonic PLC
Current assignee: Feonic PLC
Priority date: 2010-07-02
Filing date: 2011-06-30
Publication date: 2012-01-05
Anticipated expiration: 2013-01-02
Also published as: GB201019838D0; GB201011183D0; CN103190159A; GB2481662A

Abstract

Apparatus for radiating an audio signal comprises an elongate metal rail (6), mounted relative to a structural surface on mountings (5, 26) adapted to minimise transmission of vibration from the rail to the surface, the rail having an audiofrequency actuator (8) coupled thereto so as to induce vibrations in the rail in a direction normal to the said surface, and means for supplying audiofrequency driving signals to the actuator.

Description

APPARATUS FOR RADIATING AN AUDIO SIGNAL

Field of the Invention

[0001] This invention relates to apparatus for radiating an audio signal, for example as a public address or announcement system or to provide background music.

Background to the Invention

[0002] Audio reproduction in large spaces such as public buildings, railway and bus stations, airports, and sports stadia is traditionally achieved using multiple cone speakers working from a centralised audio control system. As the audio signal originates from a point source, and often has to be loud to cover a large area, the physical characteristics of the building often affect the acoustic performance of the audio system, and echoes or reverberations from the loud generated signals lead to compromised levels of acoustic clarity (intelligibility). Additionally the speed of sound through air (330m/s) means that the audio signals from loudspeakers over certain distances apart can be heard at different times and are thus slightly out of phase. This is common on station platforms, particularly open platforms where wind can blow strong audio signals large distances. As a consequence of these two points, poor intelligibility is particularly noticeable in many of today's larger public buildings. A further problem that arises is noise pollution to the surrounding areas.

[0003] Traditional cone-based directional speakers are well known for reproducing audio signals for public announcements (PA), background audio, and voice alarms (VA), which are increasingly now preferred to tonal emergency alarms, as it is known that people respond better to a VA signal than a tone alert.

[0004] Flat panel loudspeakers are also well-known for reproducing localised audio, normally music, and typically consist of a rigid panel of laminated plastics, card or wood with an acoustic transducer (exciter) attached to one face of the panel. Typical transducers are moving coil electromagnetic devices or piezoelectric devices. Sound produced by a flat panel driven in this way is commonly referred to as distributed mode loudspeaker (DML for short). A DML ex- hibits a different acoustic output from a traditional speaker in that the signal strength is distributed through the entire flat surface such that the output although of the same acoustic power does not have the strength or distance throw that a point source speaker exhibits. This in turn mans that the penetration of the audio signal is not as strong, but covers a wider area local to the driven surface, making them ideally suited to delivering PA/VA.

[0005] Magnetostrictive devices are also known, for example the type disclosed in WO 02076141 . These devices have the ability to deliver considerably more excitation power and frequency response than traditional electromagnetic devices or piezoelectric devices described above, and can be used particularly when the acoustic excitation of larger, heavier, panels is required. The importance of broad acoustic bandwidth is relevant to the issue of intelligibility.

[0006] Although large panels can be excited by various actuators, including magnetostrictive actuators, a multiplicity of such discrete devices in large public spaces can still give rise to phasing problems, as well as involving a high cost.

Summary of the Invention

[0007] The invention provides apparatus for radiating an audio signal, comprising an elongate metal rail, mounted relative to a structural surface on mountings adapted to minimise transmission of vibration from the rail to the surface, the rail having an audiofrequency actuator coupled thereto so as to induce vibrations in the rail in a direction normal to said surface, and means for supplying audiofrequency driving signals to the actuator.

[0008] The rail is preferably rigid, which in the context of this invention means that it is capable of at most only a very small degree of flexure in a plane normal to the surface.

[0009] The driving signals may be supplied to the actuator from a audio source such as a public address system through cables or via a radio link, the actuator comprising part of a unit incorporating a radio receiver.

[0010] It has surprisingly been found that the amplitude of the audio signal, when measured at a fixed distance from the rail, reduces by only a small amount with distance from the actuator, with a drop along a 6m length of less than 3dB, with as little as 1 dB having been measured in one test, and the perception of the listener is that the volume of sound is substantially the same at any point along its length.

[0011] The rail is preferably hollow and may be an extrusion comprising, in cross-section, a plurality of adjacent voids defined by metal webs. It preferably has, in cross-section, a greater overall dimension in a direction normal to the structural surface than in the direction parallel thereto.

[0012] The mountings may comprise an elastomeric material.

[0013] Preferably, a plurality of sound-radiating panel members are rigidly attached to the rail along the length thereof. The panels may be mounted on or in the structural surface and the rail is carried by the panels.

[0014] Suitable panels are honeycomb aluminium panels having a thickness of at least 10mm, and preferably between 10mm and 25mm. Such panels have been found to enhance sound quality and distribution of the signal along the rail. The panels may serve also as a support for signage and/or graphics. For example, in a railway station the panels may identify the station and carry indicators to exits and other facilities.

[0015] In one embodiment, the surface is horizontal, and opposed edges of the panels rest on a layer of acoustically-compliant material carried on or in said surface.

[0016] Alternatively, opposed edges of the panels are secured to the surface through acoustically-compliant mountings.

[0017] The audiofrequency actuator is preferably a magnetostrictive actuator, since such actuators are capable of delivering a high force at a relatively low amplitude, for example less than 10 μηι, reducing the risk of vibration damage to the surrounding structures while delivering clear audible audio in the locality of the apparatus.

[0018] A plurality of the audiofrequency actuators may be coupled to the rail at intervals along the length thereof, where the rail is of greater continuous length than, say, 3m, and the means for supplying audiofrequency driving signals is connected to all the said actuators.

[0019] Where the rail is a hollow extrusion, it may carry within it cables supplying power and driving signals for the or each actuator.

[0020] The invention provides apparatus for delivering audible speech messages or other audio output over a wide area without problems of phase difference and interference commonly associated with loudspeaker-based systems. As a result, less power may be required, and complex signal processing systems are not required. Because the audio output is delivered along a continuous rail at a substantially constant level to the surroundings, and this can be where people congregate and intelligible PA/VA is required, the volume of sound does not need to be as high as with loudspeaker systems, with a consequent reduction in the risk of sound pollution outside the target area for the sound. For example, loudspeaker-based public address systems in railway stations can give rise to complaints from the occupants of neighbouring buildings. With the apparatus of the present invention, the peak volume of sound at any given point can be reduced below the level at which problems arise.

[0021] Another possible application for the apparatus of the invention would be in providing emergency announcements guiding people out of an area. For example, in a stairwell, the handrail for the stairs could be configured to radiate sound, with the actuator being housed in a protective enclosure to ensure that it continues to operate for as long as possible. Power could be supplied by batteries, and the audio signals could be pre-recorded, or transmitted to the actuator by radio. An advantage of this is that no wiring is required in the stairwell; the sound being transmitted solely by the rail, which would suitably be continuously welded.

Brief Description of the Drawings

[0022] In the drawings, which illustrate exemplary embodiments of the invention:

Figure 1 is a cross-sectional view of apparatus according to one embodiment of the invention, at the point of mounting of an actuator; Figure 2 is a view corresponding to that of Figure 1 , but at a mounting point between the actuators;

Figure 3 is a diagrammatic view of a length of the rail of the embodiment of Figures 1 and 2 and the corresponding tiles;

Figure 4 is a cross-sectional view of apparatus according to another embodiment of the invention, again at the point of mounting of an actuator;

Figure 5 is a cross-sectional view of apparatus according to yet another embodiment of the invention; and

Figure 6 is a side elevation of a joint section of the apparatus shown in Figure 5.

Detailed Description of the Illustrated Embodiment

[0023] Referring first to Figures 1 to 3, the apparatus illustrated is suitable for installation along the platform of a railway station. It is a requirement, at least in Europe, that a tactile strip be installed along a railway platform at a predetermined safe distance from the platform edge as an indication to blind and partially sighted people of the proximity of the platform edge. Typically, such a strip is formed from paving tiles or slabs having a distinctive pattern of projecting formations which can be felt by the user when walking on them. In this embodiment of the invention, the tiles may conveniently serve another function as well. A channel 1 is formed in the platform, for example by cutting into the existing formation to a pre-determined depth, and then installing along the opposed edges of the trench so formed an edging strip 2 having a generally L-shape in cross-section, the lower part 2a of the L abutting the side of the trench while the longer side 2b of the L extends along the horizontal edge of the trench. A flange 2c stands up from the reverse face of the longer side 2b approximately mid-way along it to define the limit for the asphalt or other platform surfacing material 3 which is then laid over the projecting part of the strip 2 to hold it in place. The L-shape of the edging strip allows casting or pointing up to the edge of the strip, spacing the strips correctly for the tiles 4 to be located on and between them.

[0024] The tiles 4 are then located across the channel 1 between the strips 2, their edges resting on neoprene gaskets 5 located on the strips. The gaskets 5 are formed so as to be sufficiently soft to minimise the transmission of acoustic energy into the surrounding surface, which would tend to attenuate the signal, but firm enough to ensure that the tiles are firmly located.

[0025] A rail 6 is suspended from the tiles, effectively linking all the tiles together. Ideally, a single continuous length of rail will extend along the length of the platform, but where this is not possible, for example to follow the contour of curving station platforms, shorter lengths may need to be joined together. The rail 6 consists of an aluminium extrusion of generally rectangular cross-section having a central web, extending parallel to the plane of the tiles, and a plurality of webs upstanding therefrom on both ends to define compartments within the rail, formed with lengthways-extending slots to allow for the attachment of fixings, or to permit the introduction of cables 7, for example for providing power to operate audiofrequency actuators, described hereinafter, and to provide the driving audiofrequency signals thereto.

[0026] At a position intermediate the ends of the rail, an audiofrequency actuator 8 is mounted on the rail. For longer rails, a number of such actuators may be provided, for example spaced along the rail at intervals of 3m. Figure 1 shows one such actuator. This may be of the form described and claimed in our European Patent No 1576851 . The actuator 8 has its "foot", being the component which couples an acoustic signal into a surface, secured to a metal plate 9, which is in turn fastened to the rail by means of bolts and nuts 10.

[0027] The rail is secured to the tiles 4 by means of screws 1 1 passing through supporting sleeves 12 acting as spacers between the rail and the underside of the tile. The screws 1 1 then pass through countersunk holes 13 through the tile. A locking collar is screwed on to the end of the screw and engages the countersink to form a rigid hard joint to conduct the vibration from the rail 6 to the tile. The screws 1 1 are provided with asymmetrical heads to enable them to be inserted into the channel in the rail and then rotated through 90 degrees to enable the head to bear on either side of the slot within the rail. A pair of the screws 1 1 is used, one on each side of the actuator, which is positioned centrally of the tile. Figure 2 illustrates one of the screws at the centre of another tile where the actuator is not mounted.

[0028] Figure 3 shows the rail 6 suspended beneath a number of the tiles 4, and with the actuator 8 located on the rail beneath one of the tiles.

[0029] In use, the actuator 8 is provided with a driver signal from the station public announcement system, with anything from train announcements to safety announcements, and the actuator in turn couples the acoustic signal into the rail. This signal is in turn coupled into each of the tiles 4 causing the tile to radiate the signal so that it is audible in the vicinity of the signal. Because the signal is transmitted through the metal of rail at a velocity substantially greater than that through air, the tiles all radiate the local audio signal at substantially the same time, and because the signal does not need to travel further than the immediate vicinity of the tile, there are no significant interference effects ensuring maximum clarity of the announcements without the need for complex processing to attempt to avoid the interference effects experienced with conventional loudspeaker-based public address systems.

[0030] The channel 1 also provides an additional benefit in serving as a conduit for communications cables, and other services, to be laid with the minimum of disruption at a later date, for example.

[0031] Figure 4 illustrates an alternative embodiment, where the rail is mounted along a wall, for example to radiate sound at average head height. The wall is provided with vertical supports 20 for the mounting of decorative or protective cladding or the like, with horizontal struts 21 being used to space the cladding from the wall, for example to permit service cables and pipes to be run along the wall hidden behind the cladding. In this embodiment of the invention, the rail 9 has the general form, in cross-section, of an inverted L-shape and is mounted between adjacent pairs of the struts 21 by means of threaded rods 22 which pass into slots on the opposed sides of the rail 9 and are held by nuts 23 bearing against the external surface of the rail through acoustically-isolating washers. A magnetostrictive actuator unit 8 is mounted on the downwardly- depending arm of the inverted L-shape with its foot attached to a metal plate 9 which is bolted to the rail as described hereinbefore with reference to Figure 1 .

[0032] A sound-radiating tile or panel 24, which is formed in a rigid lightweight material such as ceramics or plastics, or possibly a sandwich construction of metal sheets separated by a honeycomb mesh, has a metal bracket 25 attached to the rear face 24a thereof, for example by rivets or adhesive. The bracket 25 has a flange 25a upstanding therefrom, engageable with the underside of the uppermost arm of the rail 9, and a hook formation 25b which is received in a slot in the upper side of the outwardly-extending top arm of the inverted L-shape in such a manner as to hold the panel 24a firmly against the rail 9 so as to permit acoustic energy in the rail to be coupled into the panel. Neo- prene stops 26 are located between the panel 24 and the struts 21 , stabilising the panel but limiting any acoustic damping effect that contact with the surrounding structure might otherwise cause. Separate panels 24 will be attached to the rail along its length, with only a small linear space between them to give the general appearance of a continuous surface. The actuator unit 8 is located at a position intermediate the ends of the rail, and for a long rail additional units may be included at appropriate intervals, for example 3m intervals.

[0033] The formation of the rail as an inverted L-shape, and the mounting of the actuator 8 on the downwardly-depending leg of the L-shape, mean that the actuator is contained in a space created behind the panels, so that it is easily accessible simply by removing the panels; the rails do not need to be detached to enable installation or maintenance of the actuator.

[0034] In an alternative embodiment, the threaded rods 22 are dispensed with, and the rail is simply carried by the panels 24, which are secured to the struts through neoprene or similar mountings, for example using screws passing through neoprene bushes.

[0035] In both embodiments of the invention, the outwardly facing channels are principally provided to facilitate fixing of the rail and attachment of the actuator. They will, however, serve to increase rigidity of the rail, which is beneficial in the performance in conducting and outputting sound accurately. [0036] While the invention has been particularly described with reference to railway stations, it will be appreciated that it is not limited to such use. The apparatus of the invention can be deployed in any location where the delivery of audio signals over a wide area is required, such as public buildings of all sorts.

[0037] Referring to Figures 5 and 6, the rail comprises an aluminium extrusion 30 of overall square cross-section, internally divided by longitudinal webs into a central square section 31 and four closed sections 32 separated by a central longitudinal outwardly-opening channel 33 in each face of the square extrusion 30. Each channel 33 has a longitudinal opening 34 narrower than the body of the channel, so as to provide a ledge on either side of the opening.

[0038] A sound-radiating panel 35 is attached to an outwardly-facing side of the extrusion 30 by means of socket screws 36, each engaging a specially- shaped T-bolt 37 which can be inserted into the channel 33 and then rotated through 90 degrees so that it is retained by engagement with the ledges on either side of the opening 34. The T-bolt 37 is provided with serrated faces engaging the ledges to ensure that it is held firmly in place. The panel 35 is preferably formed from opposed face sheets of aluminium sandwiching between them a honeycomb structure of slit and expanded aluminium, the structure and face sheets being held together by adhesive, providing a light weight and stiff board. A 12mm overall thickness of the panel is suitable. A cover moulding 38, which obscures the mounting of the rail, hereinafter described, from view, is also secured in place over the upper part of the panel 35 using the same socket screws. The cover moulding 38 can suitably be formed of extruded aluminium or plastics.

[0039] The rail is carried by suspending wires (not shown) engaging suspension eyes 39 spaced apart along its length, the eyes being attached by threaded studs engaging tapped holes in the web defining one side of the central square section 31 . In this way, the rail can be substantially acoustically isolated from the supporting structure.

[0040] While it is envisaged that relatively long lengths of the extrusion will be used, where straight runs are possible, it will be necessary to join lengths of rail, and Figures 5 and 6 illustrate a suitable coupling arrangement for the extrusion 30. The end faces of the extrusions 30 are cut so as to present accurately butting faces, and two linking blocks 40 are attached to the respective upper and lower faces of each extrusion, adjacent to, but spaced by a small distance (a few millimetres will suffice) from the cut end face. Each block 40 is formed as a short length cut from an aluminium extrusion having a central enclosed section 41 to afford rigidity and a pair of channel sections 42 arranged either side of the central section 41 , both opening on the same face of the extrusion. The blocks 40 are secured to the extrusion 30 by means of T-bolts 37 retained within the respective channels 33 and passing through holes drilled through the central sections 41 of the blocks 40 and engaged by nuts 43. To secure two lengths of the extrusion 30 together, threaded studs 44 are placed through the channel sections 42 of adjacent blocks 40 and nuts 45 are then engaged with the studs to bear against the outward ends of the pair of blocks. Tightening of the nuts 45 draws the ends of the extrusions 30 firmly together, permitting efficient transfer of acoustic energy, induced in the rail by an actuator mounted on it as hereinbefore described with reference to Figure 4, for example, from one length to the next. It has been found that the variation in sound pressure admitted by the rail varies along the length of 6 metres by approximately 1 dB.

[0041] Where curves are to be accommodated, wedge sections of the extrusion 30 can be inserted between the square faces, or appropriately-angled cuts can be made.

[0042] It has also been found that it is desirable to place the actuator near to a joint between two rail lengths in order to get as even as possible a signal distribution on each side of the joint.

Claims

1 . Apparatus for radiating an audio signal, comprising an elongate metal rail, mounted relative to a structural surface on mountings adapted to minimise transmission of vibration from the rail to the surface, the rail having an audiofrequency actuator coupled thereto so as to induce vibrations in the rail in a direction normal to said surface, and means for supplying audiofrequency driving signals to the actuator.

2. Apparatus according to Claim 1 , wherein the rail is rigid.

3. Apparatus according to Claim 1 or 2, wherein the rail is hollow.

4. Apparatus according to Claim 3, wherein the rail is an extrusion comprising, in cross-section, a plurality of adjacent voids defined by metal webs.

5. Apparatus according to any preceding claim, wherein the rail, in cross-section, has a greater overall dimension in a direction normal to the structural surface than in the direction parallel thereto.

6. Apparatus according to any preceding claim, wherein the mountings comprise an elastomeric material.

7. Apparatus according to any preceding claim, wherein a plurality of sound-radiating panel members are rigidly attached to the rail along the length thereof.

8. Apparatus according to Claim 7, wherein the panels are mounted on or in the structural surface and the rail is carried by the panels.

9. Apparatus according to Claim 8, wherein the surface is horizontal, and opposed edges of the panels rest on a layer of acoustically-compliant material carried on or in said surface.

10. Apparatus according to Claim 8, wherein opposed edges of the panels are secured to the surface through acoustically-compliant mountings.

1 1 . Apparatus according to Claim 7, wherein the panel members are supported by and depend from the rail.

12. Apparatus according to any preceding claim, wherein the audiofrequency actuator is a magnetostrictive actuator.

13. Apparatus according to any preceding claim, wherein a plurality of the audiofrequency actuators are coupled to the rail at intervals along the length thereof, and the means for supplying audiofrequency driving signals is connected to all the said actuators.

14. Apparatus according to any preceding claim, wherein the rail carries cables supplying power and driving signals to the or each actuator.

15. Apparatus according to any preceding claim, wherein the rail has a length in excess of 3m.

16. Apparatus according to Claim 15, wherein the rail has a length in excess of 6m.