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WO2002013575A1 - Haut-parleur a ondes de flexion - Google Patents

Haut-parleur a ondes de flexion Download PDF

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Publication number
WO2002013575A1
WO2002013575A1 PCT/GB2001/003353 GB0103353W WO0213575A1 WO 2002013575 A1 WO2002013575 A1 WO 2002013575A1 GB 0103353 W GB0103353 W GB 0103353W WO 0213575 A1 WO0213575 A1 WO 0213575A1
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WO
WIPO (PCT)
Prior art keywords
panel
frequency
damping
bending
boundary
Prior art date
Application number
PCT/GB2001/003353
Other languages
English (en)
Other versions
WO2002013575A8 (fr
Inventor
Henry Azima
Original Assignee
New Transducers Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by New Transducers Limited filed Critical New Transducers Limited
Priority to JP2002518122A priority Critical patent/JP2004506360A/ja
Priority to AU2001275706A priority patent/AU2001275706A1/en
Priority to EP01953210A priority patent/EP1305976A1/fr
Publication of WO2002013575A1 publication Critical patent/WO2002013575A1/fr
Publication of WO2002013575A8 publication Critical patent/WO2002013575A8/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R7/00—Diaphragms for electromechanical transducers; Cones
    • H04R7/02—Diaphragms for electromechanical transducers; Cones characterised by the construction
    • H04R7/04—Plane diaphragms
    • H04R7/045—Plane diaphragms using the distributed mode principle, i.e. whereby the acoustic radiation is emanated from uniformly distributed free bending wave vibration induced in a stiff panel and not from pistonic motion
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R7/00—Diaphragms for electromechanical transducers; Cones
    • H04R7/16—Mounting or tensioning of diaphragms or cones
    • H04R7/18—Mounting or tensioning of diaphragms or cones at the periphery
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2440/00—Bending wave transducers covered by H04R, not provided for in its groups
    • H04R2440/01—Acoustic transducers using travelling bending waves to generate or detect sound
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R7/00—Diaphragms for electromechanical transducers; Cones
    • H04R7/16—Mounting or tensioning of diaphragms or cones
    • H04R7/18—Mounting or tensioning of diaphragms or cones at the periphery
    • H04R7/20—Securing diaphragm or cone resiliently to support by flexible material, springs, cords, or strands

Definitions

  • the invention relates to bending wave loudspeakers which are often flat panel loudspeakers .
  • cone type loudspeakers suffer from a variety of shortcomings including limited bandwidth and beaming at the higher range of their operative bandwidth a phenomenon which is diaphragm size dependant.
  • bending wave loudspeakers have been developed, see for example EP 0541,646 of Heron and EP0847661 of Azima et al , which rely on either a multi- modal or a distributed-mode operation.
  • DML which substantially defines the basis of a new form of wide-band loudspeaker using natural plate resonance to reproduce acoustic output
  • the modality is caused by the finite panel size and the ensuing build-up of modes primarily due to the dimensions of the panel, bending stiffness, and areal mass density of the material. It has been shown that this type of loudspeaker can exhibit desirable acoustic properties that were not possible to achieve in the prior art.
  • the ⁇ lower frequency range can in some circumstances suffer from sparse modality which limits, at least for high-fidelity purposes, the speaker in its lower frequency range of operation.
  • the intention of the present invention to achieve a more effective use of bending waves for reproduction of sound especially in the lower operating range of the loudspeaker. It is an objective of this invention to avoid altogether or at least reduce the modal behaviour of the panel, either throughout the operating range or at least in the lower frequency range of operation. Ideally, the panel should behave as if it were infinite in size - that is no energy is reflected from the boundaries, despite its finite physical size.
  • the core idea of the present invention is that the imposition of an acoustic aperture onto a conceptually infinite panel results in a net acoustic power available in the far field of the panel at below the coincidence frequency, and also above it .
  • the present invention stipulates substantially terminating the panel structure at the panel boundaries, ideally to absorb incident bending wave energy. This is tantamount to an infinite panel with a fini te acoustic aperture imposed on it. This is a significant departure from the prior art and in fact an antithesis to a modal object.
  • a loudspeaker comprising a panel which is sufficiently stiff to support bending waves, the panel having a boundary, a transducer mounted to the panel to apply bending wave energy in the form of dispersive travelling waves thereto at a first location in response to an electrical signal applied to the transducer to cause the panel to vibrate and radiate an acoustic output, the loudspeaker having a frequency range extending from a lower frequency to a higher frequency and the panel having a stiffness giving a coincidence frequency above the lower frequency, and comprising means on or associated with the panel at a second location to attenuate travelling bending waves in the panel to prevent or at least substantially to moderate panel resonance, the attenuating means acting in the manner of an acoustic aperture over an infinite bending plate .
  • the attenuating means may comprise mechanical impedance means at a panel boundary and matched to the mechanical impedance of the panel to provide absorption of bending wave energy reaching the panel boundary.
  • the attenuating means may be located on or in the panel to attenuate bending wave energy before it reaches the panel boundary.
  • the attenuating means may be frequency dependent . The frequency dependence may be such that higher frequencies of bending wave energy are reflected from the panel boundary.
  • the mechanical impedance means may extend round substantially the entire panel boundary.
  • the attenuating means may comprise a predetermined stiffness or structural mechanical impedance profile across the panel .
  • the mechanical impedance means may increase bending wave energy absorption at, or bending wave energy transfer across, at least a portion of a boundary of the panel.
  • the attenuating means may provide a non-uniform or varying mechanical impedance profile across at least a portion of the panel .
  • the attenuating means may provide an increase in attenuation towards a boundary of the panel .
  • the attenuating means may provide a reduction in attenuation towards the centre of the panel.
  • the attenuating means may have a mechanical impedance which is substantially matched to a mechanical impedance at an interface between at least a portion of the panel and a frame for the panel .
  • the attenuating means may comprise a variation in panel thickness or density across at least a portion of the panel .
  • the attenuating means may comprise a layer over one or both surfaces of the panel and/or incorporated within the panel .
  • the bending wave panel may comprise a termination provided at or towards at least a portion of a panel boundary .
  • the termination may have a predetermined mechanical impedance for substantially terminating a mechanical impedance of at least a portion of the panel to an impedance of a portion of a frame for the panel .
  • the termination may have a predetermined mechanical resistance for reducing the energy of a bending wave moving towards a panel boundary.
  • the first location may be at the panel centre.
  • the invention is a microphone comprising a panel which is 'sufficiently stiff to support bending waves, the panel having a boundary, a transducer mounted to the panel to produce an electrical signal in response to bending wave energy in the form of dispersive travelling waves in the panel caused by incident acoustic radiation, the microphone having a frequency range extending from a lower frequency to a higher frequency and the panel having a stiffness giving a coincidence frequency above the lower frequency, and comprising means on or associated with the panel to attenuate travelling bending waves in the panel to prevent or at least substantially to moderate panel resonance, the attenuating means acting in the manner of an acoustic aperture over an infinite bending plate.
  • the invention is an acoustic device comprising a panel which is sufficiently stiff to support bending waves, the panel having a boundary, the device having a frequency range extending from a lower frequency to a higher frequency and the panel having a stiffness giving a coincidence frequency above the lower frequency and comprising means on or associated with the panel to attenuate travelling bending waves in the panel to prevent or at least substantially to moderate panel resonance, the attenuating means acting in the manner of an acoustic aperture over an infinite bending plate.
  • a bending wave object of the present invention may use a combination of the two techniques.
  • the panel system should have a structure with a mechanical impedance all around its boundaries designed to terminate the mechanical impedance of the panel. This will result in the full absorption of the bending wave energy reaching the boundaries.
  • the damping can be incorporated in or around the panel so as to significantly reduce the energy of the bending waves at, or as the waves approach, the periphery of the panel.
  • Damping of a desired kind can be achieved by having a predetermined stiffness or structural impedance profile across the panel or by the inclusion of forms of edge termination.
  • a bending wave panel is provided with a medium for reducing the reflection of bending wave energy from at least a portion of a boundary of the panel .
  • a bending wave panel of the present invention there is a gradual reduction or increase in damping or impedance across a panel .
  • a reduction or increase in damping or impedance across a panel is substantially linear.
  • a reduction or increase in damping across a panel is substantially non-linear and can be, for example, exponential.
  • a bending wave panel comprises a medium which presents an impedance to a bending wave in the panel .
  • references herein to impedance include references to reactance and/or resistance. References herein, both explicit and implicit, to acoustics or sound include references to infrasound and ultrasound.
  • the present invention is not limited to application in loudspeakers but can also be applied to other acoustic transducers such as microphones, couplers and the like.
  • Figures la to Ik are cross-sectional side views of various embodiments of bending wave panel
  • Figure 11 is a perspective view of part of an embodiment of bending wave panel ;
  • Figures 2a to 2n are partial cross sectional side views of embodiments of the edges of bending wave panels;
  • Figure 3a is a cross-sectional edge view of a moulded interior trim panel, e.g. for an automobile, incorporating a loudspeaker of the present invention;
  • Figures 3b to 3f are front views of embodiments of trim panel of the kind generally shown in Figure 3a;
  • Figure 4 is a schematic view of damping bending waves at a panel edge
  • Figure 5 is a graph plotting material with opposite damping properties against frequency
  • Figure 6 is a graph plotting a bending wave in an edge damped panel ;
  • Figure 7 is a graph plotting a bending wave in a damped panel
  • Figure 8 is a diagram of an end damped beam
  • Figure 9 is a graph of edge reflection coefficient as a function of frequency
  • Figure 10 is a graph comparing absorption maximum;
  • Figures 11a and lib are graphs of termination impedance and beam impedance;
  • Figure 12a is a graph showing the amplitude of the reflection coefficient
  • Figure 12b is a graph showing the phase of the reflection coefficient
  • Figure 13a is a graph showing the amplitude of the reflection coefficient
  • Figure 13b is a graph showing the phase of the reflection coefficient
  • Figure 14a is a graph showing the amplitude of the reflection coefficient
  • Figure 14b is a graph showing the phase of the reflection coefficient
  • Figure 15a is a graph showing the amplitude of the reflection coefficient
  • Figure 15b is a graph showing the phase of the reflection coefficient
  • Figure 16 is a graph comparing the damping factor versus frequency of an untreated and surface treated beam
  • Figure 17 is a graph showing the damping factor for a beam with a damping strip applied
  • Figure 18 is a graph showing the damping factor for a beam with two damping strips applied
  • Figure 19 is a graph showing the damping factor for a beam with three damping strips applied.
  • Figure 20 is a diagram of an edge terminated bending wave beam
  • Figure 21 is a graph showing the reflection coefficient amplitude of the beam of Figure 20;
  • Figure 22a is a rear view of an experimental panel
  • Figure 22b is a front view of the panel of Figure 22a and showing an arrangement of damping strips;
  • Figures 23 to 26 are graphs showing the drive point velocity for the panel of Figure 22a at its different drive points;
  • Figure 27 is a graph showing the acoustic pressure of the panel of Figure 22a;
  • Figures 28a to f show various configurations of edge termination of a beam;
  • Figures 29a to f are graphs showing the reflection coefficient amplitude for the configurations of edge terminations of Figures 28a to f respectively;
  • Figures 30a to c show various configurations of compressed edge termination of a beam
  • Figures 31a to c are graphs showing the reflection coefficient amplitude for the configurations of edge termination of Figures 30a to c respectively.
  • edge termination may be achieved in many ways, however, in all the various schemes useful performance may be reached by the application of gradual damping obeying either a simple linear function or more ideally an exponential law. The latter can provide a smaller area of panel treated with damping material .
  • damping material onto the panel for better consistency and lesser cost, if the design lends itself to injection moulding processes.
  • Materials that allow control of damping with frequency may be found very useful in configuring the optimum behaviour of the panel to suit the application. For example, it may be desirable to allow the panel to behave in a DM fashion for acoustical reasons in part of the frequency range .
  • damping is applied to the panel remote from the panel edge.
  • a variety of methods can be applied in the construction of the panel in order to add the required damping.
  • the idea here is for the bending waves to be attenuated sufficiently by the time they reach the extremities of the panel in order to avoid reflection from the edges.
  • These may take many forms including: a) Using a monolithic panel with high inherent damping. b) Adding a layer of damping material to the panel, which may be a composite or monolith panel: this may be a simple layer of damping foam or applied as a coating. c) Using the damping layer as a layer in the construction of the panel, e.g.
  • Figures lb, lc, If and lg show a damping layer of uniform thickness provided on one or both surfaces of a panel 1.
  • one or more damping layers can be incorporated into the structure of the panel itself.
  • a panel 1 can be formed of a monolithic or composite low loss material, as is shown in Figure Id, or a high loss material, as is shown in Figure le .
  • Internal and structural damping can be designed into the panel with an appropriate choice of damping material for the application, for example in terms of panel size, i.e. the damping should be sufficient to reduce bending wave energy reflections from the boundaries to useful levels. To optimise performance over-damping should in general be avoided.
  • polyurethane in general makes for a better self damped foam core than a polyester material in a sandwich construction.
  • Figure lj shows a panel 1 having a polyurethane foam core 3 and face skins 4.
  • Two other structural damping strategies may be adopted, in which a damping material is injected in the core cavities in order to provide for suitable and adequate damping which is appropriate for the application.
  • Figure Ik shows a self skinned extruded panel 1 according to a first of the structural damping strategies while
  • Figure 11 shows a panel 1 having a honeycomb type core 5, and face skins (not shown) according to a second of the structural damping strategies and into which damping foam 6 has been injected.
  • the injected material is light and flexible, then the other properties of the panel, for example the stiffness and areal mass density, do not change appreciably as a consequence of a modification of the panel damping to suit the design requirements.
  • Edge damping can be thought of and modelled as a mass spring and dashpot system. More particularly, edge damping can be considered as a series of spring/dashpot systems which gradually increase in their magnitude.
  • the Spring and dashpot system can be applied at the edge of the panel, in the edge region, or in an area of the panel where the radiation from the panel needs to be minimised.
  • Figures 2a to 2n show means by which radiation or reflection from the edge region of a panel can be minimised.
  • the stiffness should increase as the edge termination is approached.
  • the stiffness should increase in a gradual fashion to avoid abrupt mechanical impedance changes and the consequent reflections.
  • the damping may also be increased in the same fashion. It is desired that the amplitude of the bending waves gradually reduce to zero as the waves approach the edge of the panel.
  • Figures 2a to 2j show panels 1 having edge damping 6 which forms the means by which the magnitude of bending waves can be gradually reduced as the waves approach the edge of a panel .
  • Panel stiffness in Figures 2a to 2d is increased in the panel edge regions 7 by locally increasing the panel thickness.
  • the damping material is fixed to a rigid frame 8.
  • the panel 1 is of uniform thickness but the damping material 6 at its edge is of tapering thickness.
  • the panel thickness, and therefore its stiffness is reduced gradually towards the edges, as shown at 9.
  • the absorption of the incident bending wave energy can be enhanced by the use of a damping material which is effective at low frequencies.
  • Internal moulded panel trims and structures of air and ground transportation vehicles e.g. automobiles provide a very useful application of this technique.
  • an automobile trim panel 10 is formed with an acoustically active panel area 11 excited by a vibration transducer 12 can be isolated and its performance enhanced by applying damping 6 to the panel area outside the active area.
  • This technique is also effective in many other applications where an active area of a structure functions as a loudspeaker, such as television cabinets, computer enclosures and the like.
  • Figure 4 is a schematic of a damping system 13 employed at an end or edge 14 of a beam 15 which is excited in vibration by a transducer indicated by arrow 16.
  • the damping system shown in Figure 4 can also be applied to a panel.
  • a spring 17 represents stiffness
  • a dashpot 18 represents the damping or loss.
  • the damping system is more usually a distributed structure. It may be desirable that the stiffness and damping values vary across a panel and that the values vary, in particular, towards the extremities of the panel.
  • Certain polymeric materials can be designed to provide the required stiffness and damping properties, which stiffness and damping properties are independent of each other with frequency. Such polymeric materials can be used to tailor the behaviour of the panel. For example, damping can be reduced at high frequencies in order to retain modality at these frequencies which suits the radiation characteristic of a particular application.
  • Figure 5 is a graph of the damping and stiffness properties of certain materials that can be controlled by design. Such materials can be used advantageously to achieve particular design goals for a panel loudspeaker. For example, if the material is specified to behave with 'damping factor (a) ' , then the damping will reduce with increasing frequency -and the panel will become modal at high frequencies. Since the modes are normally quite dense at a higher frequency range and provide a diffuse radiation, this may be a desired design goal.
  • Figure 6 is a graph of bending wave expansion across an edge damped panel towards the panel edge.
  • bending waves towards the edge of the panel still have high energy levels but meet a gradually increasing restraint or lossy stiffness as the edge of the panel is approached.
  • the increase in stiffness and resistance causes a damping or loss which absorbs the energy of the bending wave in a gradual fashion such that there is little or no energy reflected from the panel edge.
  • the edge damping can be achieved by providing the panel edge with a material with appropriate mechanical properties, for example as is shown in Figures 2a to 2j .
  • edge damping can be achieved by forming the panel in a tapered or flared fashion, for example as is shown in Figures 2a to 2d.
  • the tapered edge of the panel can have a linear or exponential profile on one or both sides of the panel.
  • an increase in the panel stiffness can be achieved, which increases the velocity of the bending wave.
  • the increase in stiffness and the corresponding increase in damping causes a proportion of the energy of the bending wave to be dissipated by the time the bending wave reaches the panel edge.
  • This technique can be used to make a panel with self-framing possibility.
  • Figure 7 is a graph of bending wave expansion across a surface or implicitly damped panel towards the panel edge. As is shown in Figure 7, the amplitude, and as a result the velocity, of the bending waves vary over the panel from the point of excitation to the edge of the panel.
  • the panel has sufficient damping to absorb the bending wave energy as the waves travel from the point of excitation towards the edges of the panel. It is desired that the implicit damping is sufficient to cause the bending waves to lose most or all of their energy by the time the waves reach the panel edge. However, even if some of the incident energy is reflected from the panel edge it will not normally be sufficient to set up substantial resonant modes in the panel. Thus, little or no modal frequency preference can exist as a result of the finite dimensions of the panel. Therefore, little or no energy is reflected from the edges of the panel and that the panel only radiates the energy of the original bending wave which is generated in the first instance. As can be seen from Figure 7, the amplitude of the bending wave for the 'undamped' panel reduces as the wave propagates towards the edge of the panel . It should be noted that the reduction in amplitude is due to the wave expansion and not loss of energy.
  • the provision of implicit or areal damping and of edge damping in panels provides in certain circumstances a yet further advantage over the low-loss DML panel.
  • the panel resonance so long as the panel reverberation time is generally less than substantially lOmS, is not particularly audible and can add to the spaciousness of the sound.
  • the reverberation time in the panel can exceed the audible threshold. Therefore, the sound takes an echo-type coloration which can detract from the quality of the sound and from good intelligibility.
  • the damping methods described herein can reduce or even eliminate this effect.
  • Viscoelastic materials with mechanical properties having a time-dependence, are often applied either as a liquid coating or in sheet form directly to plates or panels in order to increase the damping properties of a system in order to reduce or eliminate unwanted vibrations.
  • a viscoelastic layer is applied directly to a vibrating plate without any constraint on the viscoelastic layer, it is termed 'free layer damping' and the damping layer principally operates in extension/compression parallel to the panel surface.
  • the effects of free layers on the vibration characteristics of plates is well researched and documented.
  • the effectiveness of the damping treatment is governed by the composite loss factor as given in Equation 1 :
  • Equation 2 A general form of the equation is given in Equation 2 :
  • Equation 3 mass of free layer
  • Free layer damping applied to the whole surface of a plate provides broadband damping as described by equation 1
  • Strips or discrete pieces of free layers can be used in specific regions of the panel surface to provide energy absorption at a controlled level and over a controlled frequency range .
  • the aim of edge absorption is to absorb some or all the energy incident on an edge from an exciter.
  • the waves emitted by the exciter spread out across the bending wave plate with distance. By the time they reach the edge of the panel their curvature is greatly reduced, and they approximate to a plane wave. This plane wave approximation is valid over most of the length of the boundary, and best when furthest from the corners of the panel .
  • the plane wave approximation greatly simplifies the problem as it becomes one-dimensional i.e. a plane wave incident on a parallel boundary.
  • the problem can therefore be addressed by considering a one dimensional (ID) beam, the waves propagating along it, and the termination at the edge. It is important to note that the experiment and theory following does not mean that the analysis is restricted to beam-like panels.
  • the termination impedance only couples into the lateral velocity, ie it does not provide any torque resistance, which in turn makes the bending moment equal to zero at the edge, and
  • Z r is the termination impedance of the foam and Z B is the mechanical impedance of the end of the beam, given by:
  • the ratio of beam end impedance to the termination impedance determines the reflection coefficient
  • the beam impedance is frequency dependent, and is proportional to the square root of frequency
  • the beam impedance is both real and reactive in equal weights (i.e. 45 degree phase angle), and
  • the reflection coefficient is likely to be strongly frequency dependent . These factors help the engineer/design beam terminations .
  • Example 1 pure resistive damping.
  • a typical panel material with a pure resistive damper on the edge; the material is 5mm thick acoustic 66, which is a phenolic paper composite with a honeycomb core, with material parameters as follows:
  • Figure 9 shows the amplitude of the reflection coefficient as a function of frequency for a range of resistive dampers applied. This graph illustrates the following points of pure resistive damping: 1. The system shows a maximal absorption at a frequency that increases with the level of resistance applied;
  • Figure 10 shows the comparison of the modulus of the beam terminal impedance with the resistive impedance applied to the edge of the beam. It is clear that the absorption maximum occurs when these are equal, giving a reflection coefficient of 0.41 (41%).
  • the phase of the reflection varies from - ⁇ to - ⁇ /2 as the frequency increases .
  • Figure 11a shows the (x) that is the real part of the termination impedance versus imaginary part of the beam impedance
  • Figure lib shows the (y) that is the imaginary part of the termination impedance versus the negative of the real part of the beam impedance.
  • the parameters of the termination are :
  • a complex impedance may be used to perfectly terminate the edge. This can be achieved with an impedance that has both resistive and compliant components. 2. If the edge is perfectly terminated the reflection coefficient becomes smaller and narrower in frequency.
  • the phase of the reflection varies from ⁇ to - ⁇ /2 as the frequency increases .
  • Example 3 Termination with a resistance, compliance, and a mass
  • Termination with a complex impedance close to the matching criterion
  • the system has been chosen to be Miers foam, which is a soft PVC predominantly closed cell foam, 5mm thick terminating acoustic 66, 5mm thick.
  • This system behaves as a matched termination with compliant, resistive, and mass-like components, resulting in the sharp absorption shown in Figures 13, 14a and 14b and a phase varying from ⁇ to - ⁇ . Termination with a resistance
  • the aim is to illustrate the effects of energy absorption treatments on a specific material in the form of a beam and then to extend this analysis to a full size 5 panel
  • a low damping, high stiffness beam was selected in order to illustrate the effectiveness of the energy absorbing treatments .
  • a carbon fibre skin laminated onto an aluminium honeycomb core using epoxy adhesive was 10 selected. Its mechanical properties are listed below in Table 1 :
  • Beams of this material were then subjected to the following treatments and the properties of this beam were analysed as described below :
  • a filled polymer layer applied to a panel produces a broad band damping effect.
  • a low modulus PVC foam which is predominantly closed cells, is applied, in strips of width 5mm along the length of a beam of Table 1.
  • This foam strip has a resonant frequency dependent upon the thickness, compression modulus, material damping and density of this strip.
  • Figure 17 shows the damping factor for the beam (Table 1) with a single strip of low modulus foam applied along the beam length.
  • Figure 17 indicates a resonance of the foam strip at approximately 3.3kHz which has enhanced the damping of the beam considerably around this frequency. The foam resonance has effectively increased the energy absorption for this arrangement.
  • the peak damping factor is approx. 0.058 with three strips of foam alongside each other but the absorption frequency is approx. 3.3kHz. This compares with a smaller peak damping factor of approx. 0.036 at approx. 3.3kHz for the single strip of foam.
  • Figure 22a shows the panel size and the four exciter positions used in these vibrations.
  • a single electrodynamic exciter 25mm diameter was placed in turn in each of the four positions as shown below and the drivepoint velocity and on-axis acoustic pressure were measured. These measurements were repeated with the three treatments as described above applied to this panel. These treatments are listed here :
  • the modal distribution excited in a panel is best shown by the velocity characteristic at the drive point, when the panel is excited with a constant force.
  • the degree of smoothness of the velocity is used to demonstrate success in removal of the modes in the panel.
  • Figure 27 shows the on-axis acoustic pressure for the free panel versus the damping-treated panel for exciter position 1 (panel midpoint) . From Figure 27, it is clear that the low damping modes present in the free panel have been considerably reduced in magnitude by the damping treatments applied to the panel .
  • Strips of soft low modulus PVC foam are applied to the end of a beam of Table 1 across the full width of the beam in different configurations as shown in Figures 28a to 28f.
  • a continuous block or wedge of foam is applied to the beam.
  • the beam is in the free configuration i.e. no load or compression is applied to the edge condition.
  • the corresponding Figures 29a to 29f show the reflection coefficients for those configurations.
  • Figure 28b has the same number of strips as that of the con iguration of Figure 28a but a different arrangement of three layers, the base layer and intermediate layers being of four strips and the top layer being of two strips, as shown.
  • Figure 28c is similar to that of Figure 28b, but with the arrangement of the strips of foam reversed.
  • Figure 28d comprises an opposed pair of low modulus PVC foam wedges 20 fixed to the opposed faces of the end of the beam.
  • Figure 28e is similar to that of Figure 28d, but with the direction of the foam wedges 20 reversed.
  • the configuration of Figure 28f is similar to that of Figures 28d and 28e, but with the foam wedges replaced by rectangular section low modulus PVC foam blocks 21.
  • the foam blocks used in this configuration have an identical volume and therefore mass as the wedges of foam used in the configurations of Figures 28d and 28e. Effect of Shape on Restrained Layers.
  • Figure 30a uses the same wedge blocks 20 as used in the configuration of Figure 28d but with the foam edge compressed to 10mm thickness from its original thickness of 28mm.
  • Figure 30b uses the same wedge blocks 20 as in the configuration of 28e but with the foam edge compressed to 10mm thickness from its original thickness of 28mm.
  • Figure 30c uses the same rectangular blocks 21 as in the configuration of Figure 28f but with the foam edge compressed to 10mm thickness from its original thickness of 14mm.
  • Clamping or constraining the foam blocks significantly changes the absorption characteristics of the edge compared to the free case for all foam/beam configurations.
  • the edge impedance is significantly altered by the compression of the foam and this affects the absorption characteristics.
  • the foams applied produced a useful level of broadband energy absorption above approximately 2 kHz. This is shown by the amplitude of the reflection coefficient varying between 0.6 to 0.8 above this frequency.
  • Benefits of a loudspeaker of the present invention may include the following:-
  • the panel produces all frequencies equally throughout its operating frequency range and does not suffer from sparse modality in the lower range, as is possible in the case for a DM .
  • Panel shape and geometry has little or no influence on the performance of the loudspeaker. Indeed, and unlike a DML, an axisymmetrically driven strategy can be a preferred method of excitation. In fact a circular panel excited in the middle may provide the most effective solution with uniform termination across the whole perimeter .
  • the radiation characteristic and the effective radiating area can be configured to suit the application with the choice of an appropriate damping strategy i.e. its magnitude and frequency dependence .
  • the low-frequency output level may be controlled to suit the application by moving the exciter (s) away from the centre of the panel to provide reduced LF power.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Diaphragms For Electromechanical Transducers (AREA)
  • Details Of Audible-Bandwidth Transducers (AREA)
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Abstract

La présente invention concerne un haut-parleur comprenant un panneau qui est suffisamment rigide pour supporter des ondes de flexion. Ce panneau présente une bordure et un transducteur, qui est monté sur le panneau et permet d'appliquer sur ce panneau une énergie d'onde de flexion se présentant sous forme d'ondes progressives dispersives, à un premier emplacement, en réponse à un signal électrique appliqué au transducteur, permettant au panneau de vibrer et de produire une sortie acoustique. Ce haut-parleur présente une gamme de fréquences qui va d'une basse fréquence à une haute fréquence et une rigidité qui fournit une fréquence de coïncidence supérieure à la basse fréquence. Ledit haut-parleur comprend des systèmes qui sont fixés ou associés au panneau, à un second emplacement, et permettent d'atténuer les ondes de flexion progressives dans le panneau, afin d'empêcher ou de réduire au moins sensiblement la résonance du panneau.
PCT/GB2001/003353 2000-08-03 2001-07-27 Haut-parleur a ondes de flexion WO2002013575A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
JP2002518122A JP2004506360A (ja) 2000-08-03 2001-07-27 撓み波ラウドスピーカ
AU2001275706A AU2001275706A1 (en) 2000-08-03 2001-07-27 Bending wave loudspeaker
EP01953210A EP1305976A1 (fr) 2000-08-03 2001-07-27 Recuperation de metaux par incineration de resine echangeuse d'ions basique metallifere

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0018996A GB0018996D0 (en) 2000-08-03 2000-08-03 Bending wave loudspeaker
GB0018996.9 2000-08-03

Publications (2)

Publication Number Publication Date
WO2002013575A1 true WO2002013575A1 (fr) 2002-02-14
WO2002013575A8 WO2002013575A8 (fr) 2004-12-29

Family

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PCT/GB2001/003353 WO2002013575A1 (fr) 2000-08-03 2001-07-27 Haut-parleur a ondes de flexion

Country Status (7)

Country Link
EP (1) EP1305976A1 (fr)
JP (1) JP2004506360A (fr)
CN (1) CN1470148A (fr)
AU (1) AU2001275706A1 (fr)
GB (1) GB0018996D0 (fr)
TW (1) TW530518B (fr)
WO (1) WO2002013575A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003090496A1 (fr) * 2002-04-17 2003-10-30 New Transducers Limited Dispositif acoustique
WO2007065909A1 (fr) * 2005-12-07 2007-06-14 Agc Flat Glass Europe Sa Vitrage generateur de sons
US8107667B2 (en) 2004-12-20 2012-01-31 Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung E.V. Loudspeaker diaphragm and method for manufacturing a loudspeaker diaphragm
US8389120B2 (en) 2005-12-07 2013-03-05 Agc Glass Europe Sound-generating glazing

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TWI384890B (zh) * 2008-11-05 2013-02-01 Univ Nat Chiao Tung 微型揚聲器性能評估方法及系統
CH704062A2 (fr) * 2010-11-09 2012-05-15 Montres Breguet Sa Dispositif antichoc magnétique pour la protection d'un composant horloger.
CN108337621B (zh) * 2018-02-26 2024-01-02 浙江中科电声研发中心 扬声器振动部件材料粘弹性测量方法及系统
JP7434571B2 (ja) * 2020-01-17 2024-02-20 シェンツェン・ショックス・カンパニー・リミテッド マイクロフォン及びそれを有する電子機器

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0541646A1 (fr) 1990-08-04 1993-05-19 Secr Defence Brit Haut-parleur sous forme de panneau.
WO1997009842A2 (fr) * 1995-09-02 1997-03-13 New Transducers Limited Dispositif acoustique
EP0924960A2 (fr) * 1997-12-20 1999-06-23 NOKIA TECHNOLOGY GmbH Suspension pour des arrangements de reproduction sonore selon le principe des ondes de flexion
WO1999052324A1 (fr) * 1998-04-02 1999-10-14 New Transducers Limited Dispositif acoustique ayant recours a l'action d'une onde de flexion
DE19821855A1 (de) 1998-05-15 1999-11-18 Nokia Deutschland Gmbh Plattenlautsprecher
WO2000007409A1 (fr) * 1998-07-29 2000-02-10 New Transducers Limited Unite d'entrainement pour haut-parleur avec element resonant en forme de panneau

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0541646A1 (fr) 1990-08-04 1993-05-19 Secr Defence Brit Haut-parleur sous forme de panneau.
WO1997009842A2 (fr) * 1995-09-02 1997-03-13 New Transducers Limited Dispositif acoustique
EP0847661A2 (fr) 1995-09-02 1998-06-17 Verity Group Plc Dispositif acoustique
EP0924960A2 (fr) * 1997-12-20 1999-06-23 NOKIA TECHNOLOGY GmbH Suspension pour des arrangements de reproduction sonore selon le principe des ondes de flexion
WO1999052324A1 (fr) * 1998-04-02 1999-10-14 New Transducers Limited Dispositif acoustique ayant recours a l'action d'une onde de flexion
DE19821855A1 (de) 1998-05-15 1999-11-18 Nokia Deutschland Gmbh Plattenlautsprecher
WO2000007409A1 (fr) * 1998-07-29 2000-02-10 New Transducers Limited Unite d'entrainement pour haut-parleur avec element resonant en forme de panneau

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003090496A1 (fr) * 2002-04-17 2003-10-30 New Transducers Limited Dispositif acoustique
GB2400264A (en) * 2002-04-17 2004-10-06 New Transducers Ltd Acoustic device
GB2400264B (en) * 2002-04-17 2005-09-28 New Transducers Ltd Acoustic device
US8107667B2 (en) 2004-12-20 2012-01-31 Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung E.V. Loudspeaker diaphragm and method for manufacturing a loudspeaker diaphragm
WO2007065909A1 (fr) * 2005-12-07 2007-06-14 Agc Flat Glass Europe Sa Vitrage generateur de sons
US8389120B2 (en) 2005-12-07 2013-03-05 Agc Glass Europe Sound-generating glazing

Also Published As

Publication number Publication date
WO2002013575A8 (fr) 2004-12-29
JP2004506360A (ja) 2004-02-26
EP1305976A1 (fr) 2003-05-02
CN1470148A (zh) 2004-01-21
GB0018996D0 (en) 2000-09-20
AU2001275706A1 (en) 2002-02-18
TW530518B (en) 2003-05-01

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