WO2006013311A1

WO2006013311A1 - Devices for displaying modal patterns

Info

Publication number: WO2006013311A1
Application number: PCT/GB2005/000404
Authority: WO
Inventors: John Reid
Original assignee: Sonic Age Ltd
Priority date: 2004-08-06
Filing date: 2005-02-07
Publication date: 2006-02-09

Abstract

Digital images of modal patterns, initially derived by digitising and storing the modal phenomena of a wide range of audio signals can be viewed in real time on, for example, a cathode ray tube, computer monitor, LCD screen, plasma monitor, video projector or band-held display device. Sound from a live or recorded source can be converted by a microphone into a representative electrical audio signal. The signal is suitably fed to an analogue-to-digital converter, whereupon fit is processed by a computer at a sampling rate of, typically, not less than 25 times per second. The wave form of the round sample is analysed for its harmonic content and the modal pattern image corresponding most closely to the harmonic content is released from the device's memory. Thus, a moving set of patterns is seen by the viewer in synchronism with the recorded or live round source.

Description

DEVICES FOR DISPLAYING MODAL PATTERNS

This invention relates to an electro-acoustic device for creating patterns of particulate matter, the patterns being indicative of the harmonic structure of the particular audio signal fed to the device.

This invention also relates to an electronic device for displaying patterns indicative of the harmonic structure of an audio signal fed to the electronic device.

It is well-established theory that the inherent harmonic structure of an audio signal can be rendered visible by exciting particulate matter to create a pattern associated with that signal.

For example, in 1785, E. F. P. Chladni demonstrated this modal phenomenon by exciting a brass plate carrying sand using a violin bow, resulting in the formation of sand patterns caused by the various modal flexions of the plate at the plate' s natural frequencies (modal patterns) .

Inspired by Chladni, In 1831, Michael Faraday repeated Chladni' s experiments and went further to explore, in depth, what he called ^λcrispations' . These were modal patterns which formed using a variety of media, including sand, water, lycopodium and mercury, on glass plates, wooden planks etc.

It is known that sound propagates spherically in air, whether it originates from a person' s vocal folds or from a loudspeaker. For example, when a person sings or speaks the outer leading edge of the expanding sphere of sound leaves the mouth and some of its energy is refracted backwards, thus completing an expanding sphere which is centred on the person's head. A greater proportion of the acoustic energy is measured in the direction of propagation but at every point on the surface of the expanding sphere all the acoustic data arrives in the form of compressions and rarefactions of the local air molecules.

When the spherical wave front from a persons voice is incident with a microphone diaphragm the compressions cause the diaphragm to vibrate in sympathy and the vibrations are converted into an analogue electrical signal. If this signal is then amplified to a level which is able to drive a full range transducer, the transducer's cone will generate a spherical wave front with very similar properties to that which was created by the person's vocal folds.

If the spherical wave front from the transducer is arranged to be incident with a flat flexible membrane, the membrane will vibrate in sympathy. If particulate a matter is sprinkled on the membrane the particles will follow the modal forms of the membrane, thus manifesting some of the structure in the incident wave front.

The present inventor has recognised that the extent to which the membrane is able to display the structures inherent in the wave front is dependent upon the physical characteristics of the membrane. The present inventor has found that no single membrane can display all the structure present in the wave front. For example, a membrane of 300 mm diameter may display bass and mid range audio structure but it cannot display high frequency structure, for example due to its inherent mass and inertia.

US3407897 describes a device having a single membrane onto which finely granulated sand is dispersed for visualising sound.

To date, the value of being able to create patterns of particulate matter indicative of the full range of an associated audio signal has not been fully appreciated, and the present inventor considers that there would be advantages in providing an electro-acoustic device capable of creating such patterns, there being a variety of potential practical applications.

The first aspect of the invention, described below, seeks to address the drawbacks associated with known electro- acoustic devices.

The present inventor has also found that an electro- acoustic device may not always be an appropriate or convenient way of visualising sound wave structure, for example because of the difficulties of working with loose particulates and because generally the membrane in such devices must be perfectly horizontal to function properly. The second to sixth aspects of the invention seek to address these drawbacks and are discussed below, after the first aspect.

In a first aspect of the invention there is provided an electro-acoustic device for creating patterns of particulate matter, the device having a housing; a first diaphragm extending across the housing; and, within the housing, an electro-acoustic transducer unit, the arrangement being such that, in use with the first diaphragm extending horizontally and on actuation of the transducer unit by an audio signal, the acoustic output of the transducer unit excites the first diaphragm such that when particulate matter is located on the diaphragm it creates a pattern indicative of the audio signal; wherein the device includes a second diaphragm associated with the housing, the second diaphragm being responsive to sound frequencies different to those to which the first diaphragm is responsive.

The term "responsive" as used herein is intended to mean that for a given sound frequency the diaphragm will vibrate as a result of the acoustic output. Certain responses give rise to modal patterns created in particulate matter located on the diaphragm, being indicative of properties the sound (e.g. frequency, frequency distribution, harmonics, harmonic content, etc) .

Preferably the second diaphragm is responsive to sound frequencies different to those to which the first diaphragm is responsive.

So, for example, a diaphragm that is non-responsive to sound at a particular frequency will not vibrate sufficiently for patterns indicative of the harmonic structure of the sound (modal patterns) to be created in particulate matter located on the diaphragm. The term "modal pattern" as used herein is intended to mean the patterns indicative of the harmonic structure of the particular audio signals that are created by particulate matter on a diaphragm, or a digitised image of such patterns. These patterns are also known as ^NXChladni figures".

Suitably, one of the first diaphragm and second diaphragm is responsive to relatively high frequency sound and the other is responsive to a lower frequency sound, e.g. a relatively low frequency sound. In this way the electro- acoustic device can be responsive to a wider range of sound frequencies than a single diaphragm device.

Typically the first diaphragm is responsive to (i.e. is capable of producing modal patterns) low and/or mid range frequencies, for example 40 Hz to 1 kHz.

Typically the second diaphragm is responsive to (i.e. is capable of producing modal patterns) high frequency sounds, for example frequencies in the range 1 kHz to 5 kHz.

Suitably the second diaphragm is smaller than the first diaphragm, for example it may have a smaller diameter. Preferably the second diaphragm is lighter than the first diaphragm, for example it may be thinner or made from a lighter (less dense) material. A smaller and/or lighter diaphragm may be more responsive to higher frequencies.

Similarly, the tension applied to the two diaphragms may be different. For example the tension applied to the second diaphragm may be higher than the tension of the first diaphragm. A tauter diaphragm may be more responsive to higher frequencies.

The second diaphragm may be located within the housing or external to the housing. Preferably the second diaphragm is located within the housing.

Preferably the second diaphragm is located coaxially with the first diaphragm. This allows a viewer to see the modal patterns created on the second diaphragm as if they were superimposed on the first diaphragm. Suitably, the second diaphragm is located above the first diaphragm. Thus, when the first diaphragm and second diaphragm are viewed from above in use the viewer will see them as a single diaphragm.

Preferably the device includes a second transducer unit for producing sound to excite the second diaphragm. An advantage of providing a second transducer unit is that the acoustic output from the main transducer unit can be used to excite the first diaphragm and the acoustic output from the second transducer unit can be used to excite the second diaphragm.

Preferably the second transducer unit is capable of producing sound at frequencies different from those which can be produced by the main transducer unit. Suitably, the second transducer unit is capable of producing sound at higher frequencies than the main transducer unit. In this way, the second diaphragm, which is preferably responsive to high frequencies, can be excited by the second transducer unit which is capable of producing such frequencies, whereas the first diaphragm, which is preferably responsive to low and/or mid-range frequencies, can be excited by the main transducer unit, which is capable of producing such frequencies. By tailoring the excitation of each diaphragm in this way, the performance of the device may be improved, e.g. by increasing the range of sound frequencies for which the device can produce modal patterns.

Suitably the main transducer unit is a moving coil loudspeaker. Suitably the second transducer unit is either a moving coil tweeter or a piezo electric tweeter.

The main transducer unit is typically capable of producing sound in the frequency range 40 Hz to 1 kHz. For example, the main transducer unit may be a bass or mid-range loudspeaker.

The second transducer unit is preferably capable of producing sound in the frequency range 1 kHz to 5 kHz.

For example the second transducer unit may be a tweeter.

The second diaphragm is preferably attached to the housing and/or second transducer unit, directly or indirectly, by second transducer fixing means. Any suitable fixing means known to the skilled worker can be used. For example, the fixing means may be one or more of wires, brackets, fasteners (e.g. screws, nuts and bolts) adhesive or gripping or clamping annuli (e.g. two diaphragm rings, suitably one above and one below the diaphragm) . In a preferred e^'mbodiment the second diaphragm is held by gripping annuli which are in turn attached to the housing with steel wires. Preferably the second transducer unit is attached to the housing, directly or indirectly, by second transducer unit fixing means. Any suitable fixing means known to the skilled worker can be used. For example, the fixing means may be one or more of wires, brackets, fasteners (e.g. screws, nuts and bolts) or adhesive or a transparent plastic disc which is edge fixed to the housing. In a preferred embodiment the second transducer unit is attached to the housing with steel wires.

Suitably the main transducer unit and first diaphragm are arranged coaxially. Suitably the second transducer unit and second diaphragm are arranged coaxially.

In a particularly preferred embodiment the second diaphragm and second transducer unit are suspended coaxially above the first diaphragm by fine steel wires.

In embodiments where the second transducer unit is fixed to the housing and/or fixed to the second diaphragm by wires, preferably at least some of the wires carry the audio signal used to drive the second transducer unit.

In a preferred embodiment the invention provides an electro-acoustic device for creating patterns of particulate matter, the device having a housing; a first diaphragm extending across the housing; a second diaphragm, smaller than the first diaphragm and responsive to sound frequencies higher than those to which the first diaphragm is responsive, said second diaphragm being associated with the housing and located coaxially with respect to the first diaphragm; a main electro-acoustic transducer unit, located within the housing, and a second transducer unit associated with the housing and arranged coaxially with the second diaphragm, the arrangement being such that, in use with the diaphragms extending horizontally and on actuation of the transducer unit by an audio signal, the acoustic output from the transducer units excites the diaphragms such that particulate matter located on the diaphragms creates a pattern indicative of the audio signal.

In preferred embodiments the second diaphragm and second transducer unit are attached to one another, directly or indirectly, e.g. by steel wires, brackets, fasteners (e.g._. screws, nuts and bolts) or other fixing means. In other embodiments the second diaphragm and second transducer unit are located in a second housing. Preferably the second housing is fixed, directly or indirectly, to the main housing by second housing fixing means. For example, the fixing means may be one or more of wires, brackets, fasteners (e.g. screws, nuts and bolts) or adhesive.

In a particularly preferred embodiment the second diaphragm is held between gripping annuli, e.g. two diaphragm rings, and the second transducer unit is attached to the gripping annuli, e.g. one of the two diaphragm rings (suitably the lower ring) . Attachment is preferably by fasteners (e.g. screw, nut and bolts) .

In an alternative embodiment of the invention, the device may include one or more waveguides arranged to direct the acoustic output from the main transducer unit to be incident upon the upper or lower surface of the first diaphragm.

The diaphragms may be made of the same material, or different material. Preferably one or both of the diaphragms is a membrane. For example, one or both the diaphragms may comprise a tensioned sheet of flexible, preferably elastic, material such as PVC or latex. The tension in the diaphragm may be pre-set and/or may be adjustable.

The first and/or second diaphragm is/are preferably circular. Preferably the diameter of the first diaphragm is at least about 20cm, more preferably at least about 30cm. Most preferably the diameter is in the range 30cm to 60cm. Preferably the diameter of the second diaphragm is no more than about 10cm, more preferably no more than about 6cm.

The electro-acoustic device may include 3 or more diaphragms, for example 3, 4, 5 or 6 diaphragms. Suitably, each diaphragm is responsive to a range of sound frequencies that is different to the range of sound frequencies to which the other diaphragms are responsive. For example, the device may include a bass diaphragm, responsive to low frequencies, a mid-range diaphragm responsive to mid-range frequencies and a high-range diaphragm responsive to high frequencies. In such embodiments it is preferred that there are a corresponding number of transducer units. Suitably each diaphragm has a transducer unit associated therewith. In multi-diaphragm arrangements the diaphragms are preferably arranged side by side rather than coaxially with respect to each other to facilitate unobstructed viewing of their surfaces.

Preferably the housing has an open end and a closed end and the first diaphragm extends across the housing at or adjacent the open end to define and close a hollow interior to the housing. An advantage of such a closed interior is that the vibrations of the first diaphragm can be dampened. This may help to prevent tonal colouring associated with e.g. unwanted resonances which may otherwise result in distortions of the archetypal modal patterns. Preferably the main electro-acoustic transducer unit is located within the hollow interior defined by the housing and first diaphragm.

Preferably the main transducer unit is fixed to a baffle (e.g. a wall extending across the housing) . Suitably, the baffle together with one or more sidewalls and/or an endwall of the housing forms a main transducer unit enclosure. Preferably the main transducer unit is enclosed in an ^λinfinite baffle' . An advantage of such an enclosure is that the movement of the transducer unit may be dampened, e.g. to help reduce unwanted resonances.

In a preferred embodiment of the invention, the upper end of the housing is closed by a transparent window overlying the first diaphragm and/or second diaphragm (and/or further diaphragms) through which the patterns in the particulate matter can be viewed.

Such a window reduces the escape of sound from the housing and reduces acoustic feedback whereby a wider range of sources, including ^λlive' microphones, can be used to activate the main transducer unit and/or the second transducer unit.

Problems associated with acoustic feedback can be further reduced or eliminated by mounting the housing in an outer enclosure. The volume of air between the housing and the outer enclosure may be totally or partially evacuated.

In such an embodiment, it is preferred that elasticated suspension means are provided to assist in mechanically decoupling the housing and the outer enclosure, thereby suspending the housing within the outer enclosure so that direct conduction of acoustic energy between the housing and the outer enclosure is reduced.

Suitably the device includes particulate matter located on the first diaphragm and/or on the second diaphragm.

The particulate matter is typically sized between 250 and 1000 microns, and may be, for example, crushed quartz crystal or proprietary micro glass spheres or table salt or sugar. Preferably the particulate matter on the second diaphragm is smaller than the particulate matter on the first diaphragm, e.g. sized between 100 and 250 microns.

Preferably, one or more of the diaphragms has a tuning system. Suitably each diaphragm has a tuning system associated therewith. Preferably each tuning system is integral with the corresponding diaphragm. Preferably the tuning system(s) includes tensioning means for adjusting the tension of the diaphragm. The present inventor has found that the tuning of a diaphragm may be critical to the performance of the diaphragm in terms of its ability to produce modal patterns in particulate matter located on the diaphragm. In particular tuning of a diaphragm responsive to low and/or mid range frequencies is important to get the best response from the diaphragm.

In preferred embodiments the first diaphragm has tuning means, more preferably tensioning means.

Thus, the electro-acoustic device preferably includes tensioning means for adjusting the tension of one or both (or all) of the diaphragms. Suitably, the tensioning means includes a plurality of tensioning devices so that the diaphragms can be tensioned evenly. For example, at least four, preferably at least six or eight tensioning devices are provided for each diaphragm that has tensioning means. In a preferred embodiment, twelve tensioning devices are provided.

Preferably, the tensioning means are integral with the diaphragm.

Typically, the tensioning devices are associated with a particular diaphragm around the circumference of the diaphragm. The tensioning devices may be attachable directly to the diaphragm, for example the tensioning device may include a tensioning wire and the wire is connected to the diaphragm via an eyelet or other fixing point, or indirectly, for example via gripping annuli (e.g. two diaphragm rings, or offset gripping annuli) . Preferably the tensioning devices are spaced equally around the circumference of the diaphragm to ensure even tensioning.

The tensioning devices suitably include a tensioning member and an adjustment device. The tensioning member can be a wire, e.g. a steel wire, or a strap or webbing connectable to a diaphragm, and the adjustment device acts on the tensioning member so as to transmit a selected tension to the diaphragm.

The tensioning member may be connected to the diaphragm via apertures in the diaphragm, e.g. eyelets, or for example, by adhesives or stitching.

The adjustment device applies tension to the tensioning members. The adjustment device is typically fixed with respect to the housing of the electro-acoustic device. Tension can be applied to the tensioning members by, for example, shortening the length of the tensioning member between the diaphragm and the adjustment device. For example, the adjustment device may include winding gear for winding the tensioning member to adjust its length. The adjustment device may include a tuning wheel or a tuning screw to operate the winding gear.

In order that the user can accurately monitor the tension of the diaphragm, the tensioning means preferably includes a tension gauge. Suitably, each of the plurality of tensioning devices includes a tension gauge. The tension gauge can be a spring gauge or other mechanical gauge. In this way it is possible to quantify the tension in each tensioning device. In an embodiment, the tensioning means may include a plurality of tensioning rods attached to two gripping annuli (e.g. offset gripping annuli) , which sandwich the periphery of a diaphragm. The tensioning rods are preferably connected to a central adjustment device that can apply tension to all the tensioning rods. For example, the adjustment device may include a threaded rod and a tuning wheel wherein rotation of the tuning wheel causes the threaded rods to move with respect to the tensioning rods so that tension is applied to the rods and hence the annuli. The variation in force applied to the annuli by the rods causes a change in tension in the diaphragm. For example, an increased gripping force between the annuli can tighten the diaphragm.

Preferably, the tensioning rods are spaced equally around the circumference of the diaphragm.

This arrangement is similar to the mechanical tuning apparatus used on orchestral drums.

Alternatively or additionally the tuning means may include one or more fixed weights attached, directly or indirectly, to the diaphragm so as to stretch the diaphragm. In preferred embodiments the diaphragm is sandwiched between gripping annuli and one or more weights are attached to the upper gripping annulus (e.g. an upper diaphragm ring) so as to increase the gripping force applied to the diaphragm and thereby increase the tension in the diaphragm. Suitably the gripping annuli are offset gripping annuli. Preferably there are four or more weights spaced equally around the circumference of the diaphragm (e.g. at 90°) . It is also possible to use only 2 or 3 weights, or more than 4 weights, e.g. 5, 6, 7, 8, 9 or 10 or more weights.

Alternatively or additionally there may be only one weight and the weight is attached to the upper gripping annulus at a plurality of locations around the circumference of the diaphragm. For example, attachment may be by wires, e.g. steel wires. Suitably the attachment points are equally spaced around the circumference of the diaphragm.

Alternatively or additionally the tuning means may include a tuning bezel which is in threaded engagement with gripping annuli, e.g. in threaded engagement with one of two diaphragm rings which grip the diaphragm, preferably the diaphragm ring located above the diaphragm. Rotation of the tuning bezel in a first direction causes the bezel to move towards the diaphragm held by the gripping annuli, e.g. between the two diaphragm rings. Continued rotation of the tuning bezel causes a diaphragm engaging part of the bezel to contact the diaphragm and stretch the diaphragm. Further rotation causes increased stretching of the diaphragm, thus tensioning it. Rotation in a second direction, opposite to the first direction, causes the bezel to move away from the diaphragm, thereby reducing the tension in the diaphragm. Rotation of the bezel can therefore control the tension of the diaphragm. Preferably the diaphragm engaging part is rounded to prevent damage to the diaphragm. Preferably the bezel is arranged coaxially with the gripping annuli, e.g. coaxially with two diaphragm rings. Preferably the tuning bezel, or at least the diaphragm engaging part of the bezel, is located within the gripping annuli, e.g. within the circumference of an upper diaphragm ring. Preferably an upper gripping annulus (e.g. upper diaphragm ring) is threaded on an inner surface and the tuning bezel is threaded on an outer surface.

In a further aspect the present invention provides a diaphragm tuning apparatus, the apparatus including an annular member to which a diaphragm can be attached, the annular member having a threaded inner surface; and a tuning bezel having a threaded outer surface, wherein the outer threaded surface of the tuning bezel and the inner threaded surface of the annular member are in threaded engagement such that in use rotation of the tuning bezel in first direction causes the bezel to move towards the diaphragm so that a diaphragm engaging part of the tuning bezel contacts the diaphragm and continued rotation causes stretching of the diaphragm thereby tensioning it, and rotation in a second direction, opposite the first direction, causes the bezel to move away from the diaphragm.

Preferably the diaphragm engaging part of the bezel has a rounded surface, to prevent damage to the diaphragm. The optional and preferred features of the tuning bezel described above in relation to the first aspect also apply to this aspect. Returning to the first aspect of the invention, the device may include means for projecting the patterns in the particulate matter on one or more of the diaphragms on to a viewing panel external to the housing.

The means for projecting the pattern may comprise a source of light within the hollow interior of the housing, a lens, preferably a flat fresnel lens, below the diaphragm, and a focusing lens above the diaphragm, the diaphragm being transparent.

In a further embodiment of the invention, the device includes a video camera located above one or more of the diaphragm and arranged to transmit signals to a remote viewing location whereby the patterns in the particulate matter can be viewed at said location.

Although this apparatus may be capable of displaying full range audio structure, its electromechanical nature makes it less convenient to use and view than, say, a television. The present inventor has noted potential drawbacks associated with an electro mechanical device wherein the diaphragm(s) must be horizontal in use.

In a second aspect the present invention provides an electronic device for displaying digital images of modal patterns in response to an audio signal, the device including sound analysis means for analysing a property of the audio signal, sound comparing means for comparing the measured property of the audio signal with the same property of excitation sound signals used to generate stored modal pattern images, to identify a stored modal pattern image that corresponds to the excitation sound signal, which excitation sound signal has the property that most closely matches the measured property of the audio signal; and display means for displaying the selected modal pattern image.

Preferably the property or properties of the audio signal that are analysed include one or more of the frequency, fundamental frequency, frequency distribution, harmonic frequencies and harmonic content. References below in any of the aspects to "harmonic content" include references to one or more of the above properties.

Preferably the sound comparing means comprises sound code generating means for generating a sound code for the audio signal on the basis of the harmonic analysis.

Preferably the sound comparing means also includes code comparing means for comparing the sound code with modal image codes associated with stored modal pattern images and identifying the closest match.

Preferably the modal image codes reflect the harmonic content of the excitation sound signals used to produce the modal pattern images. Preferably there is therefore no need to directly compare the audio signal with the excitation sound signals. Suitably, the modal image codes are generated prior to the user operating the electronic device by analysing the harmonic content of the excitation sound signals and ascribing a code indicative of the harmonic contents to the associated modal pattern image.

In particularly preferred embodiments the present invention provides an electronic device for displaying digital images of modal patterns in response to an audio signal, the device including sound analysis means for analysing the harmonic content of the audio signal, sound code generating means for generating a sound code on the basis of the harmonic analysis; code comparing means for comparing the sound code with modal image codes associated with stored modal pattern images and identifying the closest matching modal images code; and display means for displaying the modal pattern image.

In use, the electronic device preferably compares an audio signal with stored modal pattern images by comparing codes associated with the audio signal and the modal pattern images. The device then displays digital images of modal patterns that are associated with the closest matching code. This process is preferably repeated in real time, so that moving digital modal patterns are displayed in response to an audio signal.

In further embodiments of the invention, computer accessed versions of modal patterns, initially derived by digitising and storing the modal phenomena of a wide range of audio signals, for example as displayed on an embodiment of the first aspect of the invention, can be viewed in real time on, for example, a cathode ray tube, computer monitor, LCD screen, plasma monitor, video projector or hand-held display device. Sound from a live or recorded source can be converted by a microphone into a representative electrical audio signal. The signal is suitably fed to an analogue-to-digital converter, whereupon it is processed by a computer at a sampling rate of, typically, not less than 25 times per second. The wave form of the sound sample is analysed for its harmonic content and the modal pattern image corresponding most closely to the harmonic content is released from the device's memory. Thus, a moving set of patterns is seen by the viewer in synchronism with the recorded or live sound source.

Alternatively or additionally, a pre-recorded digital source is used to generate a waveform that is analysed as discussed above and compared to stored modal image codes, e.g. stored in the device's memory.

The electronic device preferably includes modal pattern storage means for storing digital images of modal patterns, for example memory and/or a hard disk. Solid state memory is preferred. The memory can be integral with the device or removable, e.g. a memory card or memory stick) .

Preferably the modal pattern storage means contains a library of digital images of modal patterns. Preferably the modal pattern storage means contains at least 100, more preferably at least 1000 and most preferably at least 5000 images. Suitably the number of images corresponds to the number of modal image codes stored in the sound file storage means.

Preferably each image has an associated modal image code, by which it can be identified. Suitably, the modal image codes are stored with their corresponding modal pattern image. Alternatively or additionally the modal image codes may be stored in a separate library. Accordingly, the device may include a modal image code storage means. Suitably the modal image code storage means contains a library of modal image codes, preferably the number of modal image codes corresponds to the number of modal image patterns.

Preferably the display means is a display screen, for example, an LCD screen. Preferably the display means include a colour screen. Preferably the display means is an integral part of the device. Alternatively or additionally the device may include a video output, e.g. a video output socket, for connection to a separate display device.

Preferably the device includes colour-enhancing means, for example a colour-enhancing processor, for enhancing the colour of the modal patterns. One such method is to employ a computer algorithm which acts to convert the primary sound frequencies, contained in each sound sample, to light frequencies. In this way, as the primary notes of, for example, a piece of music are heard, the corresponding colours are seen on-screen.

Preferably the audio signal is derived from a pre¬ recorded sound source (e.g. CD, DVD or memory (including a memory card or memory stick) containing an audio sound file, for example MP3, WMA or other compressed audio formats) or a live sound event.

Preferably the device includes one or both of (1) reproduction means for reproducing a pre-recorded sound source, and (2) live sound processing means for converting live sound in real time to a digitised signal, Suitably the reproduction means for reproducing a pre¬ recorded sound source is selected from a CD player, DVD player, cassette player, MiniDisc player, MP3 (or other digital sound file) player (e.g. hard-disc and/or memory such as a memory card for storing the MP3 files) .

Preferably, the device includes memory for storing and reproducing pre-recorded digital sound files.

Suitably, the device includes a pre-recorded sound processor for processing audio signals derived from the pre-recorded sound source e.g. a signal decoder such as an MP3 processor, or an analogue to digital converter.

Alternatively or additionally the device may include connecting means for connection to a pre-recorded sound source.

Suitably the live sound means for converting live sound in real time to a digital signal includes a microphone, preferably an integral microphone.

Suitably the electronic device includes audio output means for relaying the pre-recorded sound or live sound event to the user, e.g. headphones, an integral loudspeaker or an audio output connector for delivering an audio output signal, e.g. a headphone socket.

Preferably the device includes sound sampling means, e.g. a sound sampling processor, for sampling the audio signal (e.g. audio signal from a pre-recorded sound source such as a CD, or an audio signal from a live sound source) . Suitably the audio signal is sampled at least 25 times per second. Preferably, the sound analysis means, e.g. a sound analysis processor, analyses samples of the audio signal produced by the sound sampling means. Preferably the sound analysis means analyses the harmonic content of the samples .

Preferably the sound code generating means generates a code associated with the samples based on the harmonic content of each sample. Suitably the results of the harmonic analysis by the sound analysis means are used to generate the sound code.

The sound analysis means may include Fourier Transform analysis means, for example a software-implemented FT algorithm. Such analysis could be carried out by a person skilled in the art of sound signal analysis.

Preferably the code comparing means compares the sound code with the stored modal image codes. Preferably the code comparing means identifies a stored modal image code that most closely matches the sound code associated with the audio signal (e.g. a sample of the audio signal) . A software or hardware implemented protocol may form the basis for deciding which of the stored modal image codes is the most similar to the sound code.

Preferably the code comparing means compares a sound code with the stored modal image codes at least 25 times per second. Suitably, the number of comparisons corresponds to the number of samples generated by the sound sampling means . Preferably the device includes image retrieval means, e.g. an image retrieval processor, for retrieving the modal pattern image associated with the modal image code identified by the code comparing means . Preferably the modal pattern image retrieves the desired image from the modal pattern storage means. Suitably the desired image is stored with its associated modal image code. In the case where the modal image codes are stored in a separate library from the modal pattern images, the image retrieval means retrieves the associated modal pattern image from the dedicated modal pattern image storage means .

In preferred embodiments the device is a handheld device. This allows the user to enjoy modal patterns on the move, preferably in conjunction with listening to the audio signal giving rise to the modal patterns. Alternatively the device may be a discrete device suitable for inclusion in a hi-fi rack.

The device may include a battery, preferably a rechargeable battery, so that it can be used on the move. Alternatively or additionally the device may be operable by mains supply.

Preferably the device includes morphing means for morphing a first modal pattern image into a second modal pattern image. This may provide a more pleasing visual effect.

In a particularly preferred embodiment the electronic device for displaying digital images of modal patterns includes modal pattern storage means for storing a library of digital images of modal patterns, each modal pattern image having an associated modal image code; reproduction means for reproducing a pre-recorded sound source; sound sampling means for sampling the audio signal from the pre-recorded sound sample; sound analysis means for analysing the harmonic content of the sampled audio signal; sound code generating means for generating a sound code for each sample of audio signal; code comparing means for comparing the sound code with modal image codes in the modal pattern storage means and identifying the closest matching modal image code; image retrieval means for retrieving the modal pattern image associated with the modal image code identified by the code comparing means from the modal pattern storage means; and display means for displaying the selected image.

In preferred embodiments, the device accesses modal pattern storage means in which is held a library of modal pattern images, stored, for example, as bit maps, each modal image being representative of the sound that made the image. The bit maps are put on-screen in a sequence determined by the sound comparing means of the device, which selection is made in accordance with a system in which the real time sound signal (e.g. from a pre¬ recorded sound source or a live sound event) is sampled at discrete intervals (preferably by the sound sampling means) . Each analysis results in creation of a code which relates to the harmonic content of that sample and which is used, e.g. by a processor, to select the bit map from the library that has the nearest code attached to it. Thus, morphing modal patterns preferably appear on screen, which follow the real time audio signal. One or more of the various functional steps for displaying a digital modal image described herein may be carried out by a computer programme. Alternatively or additionally the means for carrying out the steps may include one or more processors.

In a third aspect the present invention provides a computer programme for use on an electronic device to display digital images of modal patterns in response to an audio signal, the computer programme, when implemented on the device, carries out the steps of analysing the harmonic content of the audio signal, comparing the harmonic content of the audio signal with the harmonic content of excitation sound signals used to generate stored modal pattern images and identifying a stored modal pattern image that represents the harmonic content of an excitation sound signal that most closely matches the harmonic content of the audio signal; and displaying the selected modal pattern image.

Preferably, the computer programme, when implemented on the device, carries out the steps of analysing the harmonic content of the audio signal, generating a sound code on the basis of the harmonic analysis; comparing the sound code with modal image codes associated with stored modal pattern images; identifying the closest matching modal images code; and displaying the modal pattern image. As noted above, the modal image codes suitably reflect the harmonic content of the excitation sound signals used to produce the modal pattern images. The optional and preferred features described in relation to the second and fourth to sixth aspects may also apply to this aspect.

A fourth aspect of the invention provides a method of displaying digital images of modal patterns, the method including the steps of analysing the harmonic content of the audio signal, comparing the harmonic content of the audio signal with the harmonic content of excitation sound signals used to generate stored modal pattern images and identifying a stored modal pattern image that represents the harmonic content of an excitation sound signal that most closely matches the harmonic content of the audio signal; and displaying the selected modal pattern image.

Preferably the step of comparing the harmonic content of the audio signal with the harmonic content of excitation sound signals used to generate stored modal pattern images includes the steps of generating a sound code on the basis of the harmonic analysis of the audio signal; comparing the sound code with modal image codes associated with stored modal pattern images wherein the modal image codes reflect the harmonic content of the excitation sound signals used to produce the modal pattern images; identifying the closest matching modal images code; and displaying the modal pattern image.

The optional and preferred features of the second, third and sixth aspect may also apply to this aspect. A fifth aspect in the invention provides a use of an electronic device to display digital images of modal patterns in response to an audio signal.

The optional and preferred features of the second to fourth and sixth aspects may also apply to this aspect.

A sixth aspect of the invention provides a method of producing digital images of modal patterns created by particulate matter on a diaphragm, the method including the steps of producing modal patterns in the particulate matter by exciting the diaphragm with the audio output of an electro-acoustic transducer unit, capturing images of the modal patterns and storing the images as digital image files.

The step of capturing images of the modal patterns may include photographing (e.g. using a digital or conventional camera) and/or filming (e.g. using a digital video camera or a conventional video camera) the modal patterns.

Alternatively or additionally the step of capturing images may include using laser holography to generate hologram data. In some embodiments the method includes the step of generating interference patterns that are then captured (e.g. by photograph or filming as discussed above) . The images of the interference patterns are then stored as digital 2D image files.

In embodiments where the step of capturing images of modal patterns includes photographing or filming an electro-acoustic device of the sort described in the first aspect, the step of producing modal patterns in particulate matter includes such patterns on two diaphragms. The diaphragms of the device are preferably coaxial membranes . Suitably they are excited by respective transducer units, as driven by sound signals of known length, amplitude and complexity.

Thus, the stored digital images of modal patterns referred to in the second aspect may be generated by filming or photographing a mechanical device that generates modal patterns. For example, a device that uses a membrane and particulate matter to create moving modal patterns. For example, by sampling a recorded sound track, typically every 1/25 second, then time stretching the samples, for example to 5 seconds, the modal patterns representing such samples may be created, for example by employing an embodiment of the first aspect of the invention and video recording or cinematographically filming the patterns sequentially, frame by frame. Such a procedure creates a moving pattern for the eye when replayed e.g. at not less than 25 frames per second. In particular, when viewed in synchronism with the recorded sound track, this can enhance the pleasure of listening, the visual element being indicative of the harmonic structure of the recorded sounds.

In the process of building a library of bit maps (or other format of digital image) a wide variety of sound signals are split up into sample lengths each of, for example, a 25th of a second. Similarly, each 25th of a second sound signal sample is electronically looped so that it repeats over a-time period which is long enough to cause the particulate matter to form patterns on the twin membranes. A composite modal pattern is thus formed by one such 25th of a second sample and the pattern is photographed (e.g. digitally) . The image can then be computer enhanced e.g. to clean up the fuzzy edges of the particulate-formed patterns. If necessary the photograph is converted to a digital image. This image is held in digital memory (e.g. of a computer) . Preferably each image is coded in relation to identification protocol, which allows for its fast retrieval, e.g. when certain parameters are met. This process is preferably repeated for many types of sound signal to build a library of bit maps (or other digital image files) .

Having created the bit map (or other digital image file) it is then desirable to analyse the same signal sample for its harmonic content. In this process a number of key elements concerning the sample are preferably identified by analytical software. These elements preferably form the basis of the coding (tagging) protocol, resulting in a unique code being allocated by the processor to that specific bit map (or other digital image file) . This process is repeated for each sound sample, thus, each bit map (or other digital image file) is given a unique tag and each is associated with a sound sample of specific harmonic content. The process by which the library of bit maps and tagging is built is slow but once created it can provide a powerful tool.

As discussed above, the sample length of sound signal is typically a 25th of a second. Its amplitude may be governed by compressor circuits and the complexity of the combined signal may be analysed by Fast Fourier Transform software or other digital analytical software. Note that, as with most proprietary analysis software, the sampling rate of the frequency analysis is normally at least twice that of the bandwidth of the waveform to be analysed. In the present invention, since a high frequency transducer unit can only form useful modal patterns up to approximately 5 KHz, the bandwidth, for the purposes of analysis, is capped at that figure and the analysis software will, therefore, typically sample at 10 kHz.

When the device of the second aspect is in use, the incoming audio signal (which can originate from recordings or live music or voice, for example) is preferably repeatedly sampled and analysed by the device and a tagging code is created for each sample (e.g. by the sound comparing means as discussed above) . In a preferred embodiment it then compares each code with all those held in its library; it selects the nearest match and retrieves and displays the associated bit map (or other image file) on-screen. This results in a sequential stream of bit maps appearing on- screen and appearing, to the eye, as a moving image in the case of music, for example, or a steady state image if the sound being viewed is that of a continuous unchanging tone.

Brief Description of the Drawings The invention will now be described by way of example only with reference to the accompanying figures in which: Figure 1 shows a twin diaphragm device, being a first embodiment of the present invention; Figure 2 shows a high frequency diaphragm and transducer unit, being a further embodiment of the present invention; and

Figure 3 shows a schematic representation of the operations performed by an embodiment of the electronic device of the present invention.

Detailed Description of Embodiments of the Invention Referring to Fig. 1 there is shown a device according to the first aspect of the invention comprising a housing indicated generally at 2 which is preferably of circular transverse section and of, for example, an acrylic plastic material, which may be transparent or opaque.

The precise size and shape of the housing 2, its wall thickness and the material thereof are chosen to minimise acute natural resonances in the device on actuation thereof which may otherwise adversely affect the formation of consistent patterns in the particulate material. Curved housings generally perform better than angular housings in terms of natural resonances due to the manner in which wave fronts reflect off the internal surfaces of the housings.

The housing 2 comprises tubular member 4 the bottom end of which is closed by an acrylic disc 6 sealed in the tubular member 4 by an 0-ring 8.

A first diaphragm 10, typically of PVC sheet material 0.2mm thick is stretched across, to close, the upper end of the tubular member 4. More particularly the first diaphragm 10 is held between gripping annuli 12. The material of the first diaphragm 10, in particular the density, thickness and stiffness of the material of the first diaphragm 10, and the overall area of the diaphragm 10 are important factors in relation to the frequency range of sounds to be displayed/studied by the device. For example, smaller, stiffer diaphragms are easier to excite into higher frequency modes of resonance than larger, more elastic diaphragms, such larger, more elastic diaphragms being easier to excite into low frequency modes of resonance.

Preferably, the apparatus includes tuning means (not shown in Fig. 1) for tuning the first diaphragm.

In a simpler, more economic version of the device suitable for operation under temperature and pressure conditions within certain tolerances, the tension of the first diaphragm 10 is pre-set in the factory, the first diaphragm 10 being clamped between upper and lower bezels with no adjustment thereafter being possible.

An electro-acoustic transducer, for example a full range loudspeaker 14 is located within the housing 2 below the first diaphragm 10, the loudspeaker being mounted on a baffle plate 16 to be coaxial with the tubular member 4 and the first diaphragm 10 and to direct its acoustic output onto the underside of the first diaphragm 10.

Λ feed cable 18 from an external source to the loudspeaker extends through an air-tight gland 20 in the tubular member 4. The back pressure of the loudspeaker 14 is fully enclosed in an ^λinfinite baffle' arrangement so that: a) natural transducer resonances tend to be dampened, thus helping to flatten the transducer' s overall response. This ensures that the first diaphragm 10 is excited with the minimum of resonant peaks (such peaks, if existing, would cause disproportionate excitation of the diaphragm and disrupt the expected modal patterns); b) the escape of sound from the housing is reduced.

Although the spacing between the loudspeaker 14 and the first diaphragm 10 is not critical, a distance based on the phi ratio (1:1.618) generally produces optimal results - i.e. for a first diaphragm diameter of 10 units, the distance between the loudspeaker and the first diaphragm is set at 6.18 units.

An exception to this rule is in scientific applications where, if patterns of shorter wavelengths are being studied, better results may be achieved with shorter distances or even by direct coupling of the loudspeaker with the first diaphragm.

Particulate matter 22, for example crushed quartz crystal typically sieved to between 250 and 1000 microns, or proprietary glass spheres , or salt or sugar crystals, similarly sized, is sprinkled onto the first diaphragm 10. The mass of the particulate matter 34 is a consideration depending upon the frequencies to be studied. For example, patterns resulting from low audio frequencies (e.g. frequencies up to 500 Hz) may be formed from almost any particulate matter, whereas patterns resulting from high frequencies (in the range 500 Hz -20 KHz) generally form better with lower mass particulates. This is because modes of vibration at higher frequencies cause progressively less excursion of the first diaphragm as the frequency increases, due to their shorter wavelength. Thus only low mass particulate matter is transported to the nodal areas, and heavier particulate matter tends to remain stationery due to frictional forces.

The volume of the particulate matter is an important factor in the formation of patterns. Too great a volume may prevent their proper formation, whereas too little may provide an incomplete pattern. The optimum volume of particulate matter is a function of the diaphragm area, and 1 cubic centimetre of particulate matter for every 200 square centimetres of diaphragm area has been found to be satisfactory.

A transparent acoustic window 24 is sealingly located in an upper part of gripping annuli 12 and closes the upper end of the device to retain the particulate matter 22 on the first diaphragm 10 and to reduce the escape of sound from the housing 2. A cavity of typically 20mm between the upper surface of the first diaphragm 10 and the underside of the window 24 is generally sufficient to allow free movement of the particulate matter 22 and to provide some reduction in sound escape. Without an acoustic window, use of a ^λlive' microphone as the source of sound becomes almost impossible due to acoustic feedback. Located above the first diaphragm 10 is a second diaphragm 26 and a second transducer unit 28.

The second diaphragm and second transducer unit are fixed to the housing 2 via steel wires 30. Steel wires 30 are connected to winding posts 32 on gripping annuli 12. An example of a second diaphragm and a second transducer unit are shown in Fig. 2 and are discussed below.

In order that patterns in the particulate matter 22 can be clearly seen, the particulate matter should preferably have a high degree of colour contrast against that of the diaphragm. Colour dyed particulate matter can also be used - by sieving the particulate matter into grades and colour dying each grade in a given protocol of colours, the particulate matter becomes sorted by the exciting vibrations, causing colour fringing effects within the patterns .

Levelling of the diaphragm 10 is important, since the particulate matter 22 will gather towards one side of the diaphragm if the diaphragm is not horizontal. A spirit level of the bullseye type is generally adequate for this purpose, either as an integral feature of the device or as an accessory.

In use of the device, the loudspeaker 14 may be fed with a variety of pre-recorded audio signals, including voice, music and oscillator waveforms, all of which may be conveniently stored in e.g. solid state memory within an integrated or separate electronics section of the device. Alternatively, the device may be provided with sound bytes stored on e.g. Compact Disc or MiniDisc or other format of sound signal storage, which the user plays on an appropriate playback system, e.g. via a proprietary screened cable, or the sound bytes may be transmitted acoustically to the device and picked up via e.g. an internal microphone.

An external live microphone may also be employed with the device in order that voice sound patterns may be viewed, although care must be taken to ensure that the distance between the microphone and the housing 2 is carefully controlled in combination with the overall gain of the electronics section of the device. Otherwise acoustic feedback may occur.

It may be desirable initially to distribute the particulate matter evenly over the diaphragm by a deliberate noise pulse, in preparation for formation of a pattern. This could be achieved by typically a 1-second burst of pink noise, e.g. conveniently stored in solid state memory within the electronics section of the device and retrieved at the push of a button on a control panel of the electronics section. This burst of noise is fed to the transducer at a sufficient level to cause the particulate matter to randomise over the surface of the diaphragm.

In use, the described device creates patterns within the particulate matter 22 indicative of the harmonic structure of sound. The particulate matter 22 gathers in nodal areas on the tensioned first diaphragm 10, which is excited into modes of acoustic vibration by incident sounds emitting from the loudspeaker 14. When fed to the loudspeaker 14, simple sinusoidal waveforms create modal patterns of simple structure, while complex musical waveforms, which are rich in harmonics, produce complex patterns. The device generates patterns in a consistent manner provided the tuning of the first diaphragm is in accordance with designed parameters.

The described device has numerous applications including: Educational establishments, e.g. teaching the fundamentals of music and musicology;

Natural history museums, e.g. to display bird song patterns and land animal/aquatic mammal sound patterns;

Ancient history museums e.g. to display ancient musical instrument patterns;

Science museums e.g. helping to unravel the physical constants of the Cosmos via mathematical analysis of patterns, and displaying contemporary musical instrument patterns; Entertainment in the home e.g. viewing patterns of sound bytes stored on Compact Disc, MiniDisc etc. and viewing voice sound patterns (provided some basic precautions are taken to minimise acoustic feedback) .

Still referring to Fig. 1, the housing 2 is located in an outer enclosure 32 whereby acoustic feedback is further controlled by minimising the escape of sound from the housing 2. Such an arrangement enables the use of a 'live' microphone as the source of sound in all but the most extreme circumstances.

More particularly the enclosure 32 comprises a tubular member 34 and a base disc 36 sealed in one end thereof, the upper end of the tubular member 34 being closed by a transparent window 38. The tubular member 34 and disc 36 may be an opaque acrylic material, while the window 38 may be of glass or plastic. The enclosure 34 may be lined with an acoustically absorbent material in order further to enhance the enclosure' s sound attenuation properties by reducing internal standing waves and reflections .

The housing 2 is suspended in the outer enclosure 34 in such a way that direct conduction of acoustic energy between the housing 2 and the outer enclosure 34 is minimised.

More particularly silicone rubber suspension members 40 circumferentially spaced about the upper regions of the housing 2 react between the housing 2 and the outer enclosure 34, with upper and lower sets of, typically, three foam rubber buffers 42 being circumferentially spaced about the housing 2, and an acoustic foam support cone 44 being provided on the disc 6 to seat in an associated indent in the disc 36.

The annular cavity between the tubular members 4,34 is typically about 50 mm wide, while the spacing between the windows 24 and 38 is kept to a minimum to maximise vision of the first diaphragm 10 and second diaphragm 26. This spacing between the windows 24 and 38 is not critical to the sound attenuation properties of the device, as the windows 24,38 are each of substantial thicknesses, typically 12 mm. The outer enclosure 32 of the device of Fig. 1 thus acts as an acoustic screen whereby, when the loudspeaker 14 and/or second loudspeaker 28 is fed with live microphone signals, acoustic feedback may be reduced. Voice sound patterns are thus easily formed without the necessity to take particular care over the proximity of microphone and transducer.

Further applications for the device of Fig. 1 include: Speech therapy practitioners, for example as a teaching aid for stroke victims, the deaf and partially deaf; patients are able to ^Λsee' the sounds they make with almost no interference from acoustic feedback; Vocal coaching, either self taught or teacher taught, where it is desirable for a vocalist to perfect, for example, vowel sound annunciation;

Overtoning practitioners, i.e. the art of creating vocal harmonics; the device of Fig. 1 permits the creation and study of such harmonics in a visual form.

If the volume of air between the housing 2 and the outer enclosure 32 of the device of Fig. 1 is partially or totally evacuated, the attenuating properties of the outer enclosure 32 are further increased whereby voice sound patterns can be created from whispers or very quiet sounds.

Even partial evacuation has a • significant effect in reducing sound leakage, the higher the evacuation the greater become the attenuation properties of the enclosure 32. For any given device, there will be an optimum value to the evacuation dependent upon the precise properties of the materials employed and the constructional method adopted in the manufacture of the device.

Referring to Fig. 2, there is shown the second diaphragm

26 and second loudspeaker 28.

Second diaphragm 26 is a PVC membrane having a diameter of about 60mm. The diaphragm is sandwiched or clamped between upper and lower gripping annuli 50, 52. The two gripping annuli are held firmly together by screws 54 spaced around the circumference of the gripping annuli.

Spaced around the outer facing surface of the lower gripping annuli (lower diaphragm ring) 52 are three suspension members 56 to which are attached steel wires

30 (not shown) . The steel wires suspend the second diaphragm and second loudspeaker, or tweeter, coaxially above the first diaphragm and main loudspeaker.

Attached to the lower side of the bottom gripping annulus 52 is second loudspeaker, or tweeter, 28. The second loudspeaker includes around its periphery holes 58 through which screws 54 can pass. Nuts 60 are secured to the screws 54 on the underside of the second loudspeaker 26 so as to secure the gripping annuli, second diaphragm and second loudspeaker together.

The apparatus includes tuning bezel 62 which is located coaxially within the upper gripping annulus 50. The tuning bezel has an outer threaded surface 64 which in use is engagable with a corresponding threaded inner surface 66 on the upper gripping annulus .

The tuning bezel 62 has a diaphragm engaging part 68 which can be brought into contact with the diaphragm by rotating the tuning bezel in a first direction (e.g. clockwise) . The diaphragm engaging part 68 then contacts the diaphragm 26 and continued rotation causes it to stretch the diaphragm, thereby changing the tension of the diaphragm 26. Rotation in the opposite direction (e.g. counter-clockwise) causes the diaphragm engaging part 68 to move away from the diaphragm 26, thereby reducing the tension in the diaphragm 26.

Figure 3 is a schematic flow diagram showing the operative steps that occur within an embodiment of the electronic device of the invention.

Step 1 loading an MP3 file into the device, for example loading the MP3 file into memory or a hard disk in the device. Other digital audio formats may also be used. This step may also involve inserting a removable storage medium, such as a memory card, into the device, with the digital audio file stored on the removable device. The digital audio file may be uploaded from the removable storage medium into the device.

Step 2 includes reproducing or replaying the MP3 file in the device. This step is performed by the pre-recoded sound source means, which in this embodiment is an MP3 decoder. The decoder includes a processor but it could also include software. The reproduction of the MP3 file includes decoding the MP3 file (or other digital audio file) and producing an audio signal.

Step 3 includes sampling the audio signal from Step 2. The audio signal could also be produced by replaying or reproducing a pre-recorded sound from a CD, DVD, MiniDisc or hard disk. Sound sampling means sample the audio signal 25 times per second. The sampling frequency could be more or less than this, for example 15 times per second or 40 times per second.

Step 4 includes analysing a sound sample produced in Step 3. Sound analysis means, in one embodiment a sound analysis software, analyses the harmonic content of the sample.

Step 5 includes generating a code that is assigned to the sound sample on the basis of the results of the harmonic analysis in Step 4. Sound code generating means in the device generate the code. In this embodiment the sound code generating means include code generating software.

Step 6 involves comparing the sound code generated in Step 5 with a library of modal image codes stored in the device. The modal image codes are stored in modal pattern storage means. In this embodiment the modal pattern storage means is memory in the device. Each modal image code is associated with a modal pattern image, also stored in the modal pattern storage means.

Step 7 includes identifying the modal image code that matches most closely the sound code, following the comparison of codes that occurred in Step 6. In this embodiment this step is carried out by code comparison means that are software implemented. This step could also be carried out by hardware, e.g. a processor.

Having identified the most relevant modal image code in Step 7, the nest step, Step 8, is to retrieve the modal pattern image that corresponds to the identified modal image code. In this embodiment Step 8 is carried out by software. It could also be carried out by hardware, e.g. a processor.

In Step 9 the modal pattern image retrieved in Step 8 is displayed on a display screen of the device. In this embodiment the display screen is a colour screen.

Steps 3 to 9 are repeated so that a modal pattern image is displayed for each sample of the audio signal and the viewer perceives continuously varying modal pattern images on the device.

In this embodiment, the modal pattern images are morphed so that a first modal pattern image morphs into a second modal pattern image, to provide a smoother transition.

These preferred embodiments have been described by way of example and it will be apparent to those skilled in the art that many alterations can be made that are still within the scope of the invention.

Claims

CLAIMS :

1. An electronic device for displaying digital images of modal patterns in response to an audio signal, the device including sound analysis means for analysing a property of the audio signal, sound comparing means for comparing the measured property of the audio signal with the same property of excitation sound signals used to generate stored modal pattern images, to identify a stored modal pattern image that corresponds to the excitation sound signal, which excitation sound signal has the property that most closely matches the measured property of the audio signal; and display means for displaying the selected modal pattern image.

2. An electronic device according to Claim 1, wherein the sound comparing means includes sound code generating means for generating a sound code for the audio signal on the basis of the measured property; and code comparing means for comparing the sound code with modal image codes associated with stored modal pattern images to identify the closest match, wherein the modal image codes reflect the property of the excitation sound signals used to produce the modal pattern images.

3. An electronic device according to Claim 1 or Claim 2, wherein the device includes an integral display screen.

4. An electronic device according to any one of claims 1 to 3 , wherein the device includes a video output socket to which may be connected a separate display device.

5. An electronic device according to any one of the preceding claims, wherein the device includes modal pattern storage means for storing digital images of modal patterns .

6. An electronic device according to Claim 5, wherein the modal pattern storage means contains a library of digital images of modal patterns .

7. An electronic device according to any one of the preceding claims, wherein the device includes reproduction means for reproducing a pre-recorded sound source.

8. An electronic device according to Claim 7, wherein the reproduction means is selected from a CD player, DVD player and digital sound file player.

9. An electronic device according to any one of the preceding claims, wherein the device includes live sound processing means for converting live sound in real time to a digital audio signal .

10. An electronic device according to Claim 9, wherein the live sound processing means includes an integral microphone.

11. An electronic device according to any one of the preceding claims, wherein the device includes audio output means for relaying pre-recorded sound or live sound to a user.

12. An electronic device according to Claim 11, wherein the audio output means include a connector to which headphones can be attached.

13. An electronic device according to any one of the preceding claims, wherein the device includes sound sampling means for sampling the audio signal at least 25 times per second.

14. An electronic device according to any one of the preceding claims, wherein the device includes image retrieval means for retrieving a desired modal pattern image.

15. An electronic device according to any one of the preceding claims, wherein the device is a handheld device.

16. An electronic device according to any one of the preceding claims, wherein the device includes a battery.

17. An electronic device according to any one of the preceding claims, wherein the device includes morphing means for morphing a first modal pattern into a second modal pattern.

18. An electronic device for displaying digital images of modal patterns in response to an audio signal, wherein the device is programmed to analyse a property of the audio signal, compare the measured property of the audio signal with the same property of excitation sound signals used to generate stored modal pattern images and identify a stored modal pattern image that corresponds to an excitation sound signal, which excitation sound signal has a property that most closely matches the measured property of the audio signal; and display the selected modal pattern image.

19. An electronic device according to Claim 18, wherein the device is programmed to analyse a property of the audio signal, generate a sound code on the basis of the measured property; compare the sound code with modal image codes associated with stored modal pattern images wherein the modal image codes reflect the same property of the excitation sound signals used to produce the modal pattern images; identify the closest matching modal image code; and display the modal pattern image.

20. A method of displaying digital images of modal patterns, the method including the steps of analysing a property of the audio signal, comparing the measured property of the audio signal with the same property of excitation sound signals used to generate stored modal pattern images and identifying a stored modal pattern image that corresponds to an excitation sound signal, which excitation sound signal has a property that most closely matches the measured property of the audio signal; and displaying the selected modal pattern image.

21. A method according to Claim 20, wherein the step of comparing the measured property of the audio signal with the same property of excitation sound signals used to generate stored modal pattern images includes the steps of generating a sound code on the basis of the measured property of the audio signal; comparing the sound code with modal image codes associated with stored modal pattern images wherein the modal image codes reflect the property of the excitation sound signals used to produce the modal pattern images; identifying the closest matching modal images code,- and displaying the modal pattern image.

22. Use of an electronic device to display digital images of modal patterns in response to an audio signal .

23. Use according to Claim 22, wherein the electronic device used to display the digital images of modal patterns is as defined in any one of claims 1 to 19.

24. A computer programme for use on an electronic device to display digital images of modal patterns in response to an audio signal, the computer programme, when implemented on the device, carries out the steps of analysing a property of the audio signal, comparing the measured property of the audio signal with the same property of excitation sound signals used to generate stored modal pattern images and identifying a stored modal pattern image that corresponds to an excitation sound signal that has a property that most closely matches the measured property of the audio signal; and displaying the selected modal pattern image.

25. A computer programme according to Claim 24 wherein the step of comparing the measured property of the audio signal with the property of excitation sound signals used to generate stored modal pattern images includes the steps of generating a sound code on the basis of the measured property of the audio signal; comparing the sound code with modal image codes associated with stored modal pattern images wherein the modal image codes reflect the property of the excitation sound signals used to produce the modal pattern images; identifying the closest matching modal images code; and displaying the modal pattern image.

26. A method of producing digital images of modal patterns created by particulate matter on a diaphragm, the method including the steps of producing modal patterns in the particulate matter by exciting the diaphragm with the audio output of an electro-acoustic transducer unit, capturing images of the modal patterns and storing the images as digital image files .

27. A method according to Claim 26, wherein the step of capturing images includes using laser holography to generate hologram data.

28. A method according to Claim 26 or Claim 27, wherein the step of producing modal patterns in particulate matter includes producing such patterns on two coaxial diaphragms .

29. An electro-acoustic device for creating patterns of particulate matter, the device having a housing; a first diaphragm extending, across the housing; and, within the housing, an electro-acoustic transducer unit, the arrangement being such that, in use with the first diaphragm extending horizontally and on actuation of the transducer unit by an audio signal, the acoustic output of the transducer unit excites the first diaphragm such that when particulate matter is located on the diaphragm it creates a pattern indicative of the audio signal; wherein the device includes a second diaphragm associated with the housing, the second diaphragm being responsive in a different manner to the first diaphragm at a given frequency or frequencies.

30. An electro-acoustic device according to Claim 29, wherein the first and second diaphragms are arranged coaxially.

31. An electro-acoustic device according to Claim 29 or Claim 30, wherein the first diaphragm is responsive to sound frequencies in the range 50Hz to IkHz.

32. An electro-acoustic device according to any one of Claims 29 to 31, wherein the second diaphragm is responsive to sound frequencies in the range 3kHz to 20kHz.

33. An electro-acoustic device according to any one of claims 29 to 32, wherein the device includes a second transducer unit for exciting the second diaphragm.

34. An electro-acoustic device according to Claim 33, wherein the second transducer unit is located coaxially with respect to the second diaphragm.

35. An electro-acoustic device according to Claim 33 or Claim 34, wherein the second diaphragm and the second transducer unit are located above the first diaphragm.

36. An electro-acoustic device according to Claim 35, wherein the second diaphragm and second transducer unit are suspended from the housing by steel wires.

37. An electro-acoustic device according to any one of claims 29 to 36, wherein an upper end of the housing is closed by a transparent window overlying the first diaphragm and/or second diaphragm.

38. An electro-acoustic device according to any one of claims 29 to 37, wherein the housing is mounted in an outer enclosure.

39. An electro-acoustic device according to any one of claims 29 to 38, wherein the housing has an open end and a closed end and the first diaphragm extends across the housing at or adjacent the open end to define and close a hollow interior to the housing.

40. An electro-acoustic device according to any one of claims 29 to 39, wherein the first and/or second diaphragm includes tuning means .

41. An electro-acoustic device according to claim 40, wherein the first and/or second diaphragm is held by gripping annuli and the tuning means comprise a tuning bezel in threaded engagement with the gripping annuli, the tuning bezel having a diaphragm engaging part which is brought into contact with the diaphragm by rotating the bezel in a first direction, thereby stretching and tensioning the diaphragm, and moved away from the diaphragm by rotating in a second direction, opposite to the first direction.

42. A diaphragm tuning apparatus, the apparatus including an annular member to which a diaphragm can be attached, the annular member having a threaded inner surface; and a tuning bezel having a threaded outer surface, wherein the outer threaded surface of the tuning bezel and the inner threaded surface of the annular member are in threaded engagement such that in use rotation of the tuning bezel in first direction causes the bezel to move towards the diaphragm so that a diaphragm engaging part of the tuning bezel contacts the diaphragm and continued rotation causes stretching of the diaphragm thereby tensioning it, and rotation in a second direction, opposite the first direction, causes the bezel to move away from the diaphragm.