WO2007020409A1 - Method of making an acoustic device - Google Patents

Method of making an acoustic device Download PDF

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Publication number
WO2007020409A1
WO2007020409A1 PCT/GB2006/003019 GB2006003019W WO2007020409A1 WO 2007020409 A1 WO2007020409 A1 WO 2007020409A1 GB 2006003019 W GB2006003019 W GB 2006003019W WO 2007020409 A1 WO2007020409 A1 WO 2007020409A1
Authority
WO
WIPO (PCT)
Prior art keywords
transducer
bending wave
width
bending
wave member
Prior art date
Application number
PCT/GB2006/003019
Other languages
French (fr)
Inventor
Mark Starnes
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
Publication of WO2007020409A1 publication Critical patent/WO2007020409A1/en

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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
    • H04R31/00—Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor
    • H04R31/006—Interconnection of transducer parts
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R17/00—Piezoelectric transducers; Electrostrictive transducers
    • 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
    • H04R2440/05—Aspects relating to the positioning and way or means of mounting of exciters to resonant bending wave panels
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2499/00—Aspects covered by H04R or H04S not otherwise provided for in their subgroups
    • H04R2499/10—General applications
    • H04R2499/11—Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's

Definitions

  • the present invention relates to acoustic devices, i.e. loudspeakers or microphones and the like, in particular those utilising bending inertial vibration transducers, e.g. an inertial piezoelectric vibration transducer.
  • Such bending inertial vibration transducers are discussed in WO01/54450 and may employ a plate-like piezoelectric member that resonates in bending.
  • a mass may be provided on the piezoelectric member.
  • Coupling means typically a stub, are provided for mounting the transducer to a site to which force is to be applied from or to the member.
  • the member is free to bend and so generate a force via the inertia associated with accelerating and decelerating its own mass during vibration.
  • the bending of the member can either be in response to an electrical signal, in which case the transducer acts as a vibration exciter, or can generate an electrical signal, in which case the transducer acts as a vibration sensor.
  • an acoustic device comprising a bending wave member and a plate-like bending inertial vibration transducer, the method comprising mounting the transducer with its plane normal to the plane of the bending wave member, analysing the power output of the acoustic device which varies as the square of the linear increase in width of the transducer and selecting the width which achieves a desired power output.
  • bending inertial vibration transducers are mounted with their planes parallel to the plane of the bending wave member, see for example, WO01/54450.
  • bending wave vibration is excited in the bending wave member by presenting forces normal to the plane of the bending wave member.
  • the transducer is mounted with its plane at right angles to the plane of the bending wave member. In this way, complex modes may be generated in the bending wave member due to the coupling because additional degrees of freedom may be brought into action.
  • the transducer may be attached to the bending wave member over a small proportion of its length, e.g. via a stub, so as to leave the majority of the transducer free to vibrate in bending.
  • the transducer may be coupled to the bending wave member at a non-central location on the transducer. In this way, in addition to producing a force normal to the plane of the bending wave member, the transducer provides extra rotational components.
  • the stub may be mounted to a short edge of the transducer.
  • the transducer may be a distributed mode actuator, e.g. as described in WO01/54450 which is incorporated herein by reference.
  • the transducer may be in the shape of a beam, i.e. an elongate rectangle.
  • the transducer may be a bi-morph, a bi-morph with a central vane or substrate or a uni-morph .
  • the bending wave member may be a panel-form member.
  • the acoustic device may be a resonant bending wave loudspeaker wherein the transducer excites resonant bending wave modes in the bending wave member.
  • a loudspeaker is described in International Patent Application WO97/09842 which is incorporated by reference and other patent applications and publications, and may be referred to as a distributed mode loudspeaker.
  • the bending wave member may be transparent.
  • the transducer may be mounted at the edge of the bending wave member.
  • the acoustic device may be incorporated in a mobile phone, PDA (personal data assistant) or similar small electronic devices.
  • the acoustic device may also be incorporated in other devices.
  • an acoustic device comprising a bending wave member capable of sustaining bending wave vibration, and a plate-like bending inertial vibration transducer mounted to the bending wave member with the plane of the bending inertial vibration transducer at an angle to the plane of the bending wave member.
  • the transducer is preferably mounted with its plane normal to the plane of the bending wave member. Nevertheless, the principle of exciting complex modes is applicable over a range of angles with the strength of excitation changing as the angle changes.
  • a method for designing an acoustic device comprising a bending wave member and a plate-like bending inertial vibration transducer, analysing the performance of the acoustic device with the transducer mounted to the bending wave member with its plane at an angle to the plane of the bending wave member, varying the width of the transducer and selecting the width which achieves a desired acoustic output.
  • Figures Ia, Ib, Ic and Id are schematic isometric, plan, end and side views, respectively of an acoustic device according to the invention
  • Figures 2a, 2b, 2c and 2d are schematic isometric, plan, end and side views, respectively of an acoustic device which is driven in accordance with known techniques
  • Figure 3 is graph of sound pressure against frequency for the device of Figure 2a and a similar device with a transducer of increased width
  • Figure 4 is graph of sound pressure against frequency for the device of Figure Ia and a similar device with a transducer of increased width.
  • Figures Ia to Id show an acoustic device, i.e. loudspeaker, comprising a generally rectangular bending wave panel 10 driven by two piezoelectric transducers 12, each mounted close to a short edge of the panel 10.
  • Each transducer 12 is a bi-morph and comprises two piezoelectric beams 20,22 which are mounted with the beam plane perpendicular to the panel plane.
  • the beams have width (w) .
  • the panel is made from solid polycarbonate but may be made from any other suitable materials.
  • the beams 20,22 are both attached at one end to a stub 24 which inputs a force normal to the plane of the transducer into the panel to excite bending wave vibration in the panel.
  • the stubs are made from a material which is solid, stiff and has low mass.
  • the stubs are located along the long axis of the panel.
  • the transducers 12 are mounted within an enclosure 16 which is mounted to a face of the panel 10.
  • the transducers 12 and enclosure 16 are shown on opposite sides of the panel for clarity.
  • the enclosure 16 is shaped so as to define a thin air gap 14 behind the majority of the panel 12. In the edge regions of the panel 12 where the transducers 12 are located, the enclosure defines deeper air pockets into which the transducers 12 extend.
  • FIGS 2a to 2d show an acoustic device which is identical to that of Figures Ia to Id except for the orientation of the transducers.
  • the acoustic device comprises a rectangular bending wave panel 30 driven by two piezoelectric transducers 32, each mounted close to a short edge of the panel 30.
  • Each transducer 32 comprises two piezoelectric beams 40,42 but in this embodiment, the beam planes are parallel to the panel plane, i.e. mounted in accordance with standard known technology.
  • the beams 40,42 are both attached at one end to a stub 44 which inputs a force normal to the panel plane into the panel to excite bending wave vibration in the panel.
  • the transducers 32 are mounted in an enclosure 36 which defines a layer of trapped air behind the panel and two air-pockets into which the transducers are mounted.
  • the transducers 32 are shown on the opposite side of the panel for clarity.
  • the material from which the stubs and panel are made is the same as that in Figure Ia.
  • Figure 3 shows the far field acoustic pressure for the device of Figure 2a (dotted line) and a similar device (solid line) in which the width of each piezoelectric beam is doubled. A 6dB increase occurs when the width is doubled.
  • the far field acoustic pressure may be predicted and observed for different width increase as set out in the table below.
  • Figure 4 shows the far field acoustic pressure for the device of Figure Ia (dotted line) and a similar device
  • the far field acoustic pressure may be predicted and observed for different width increase as set out in the table below.

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Manufacturing & Machinery (AREA)
  • Multimedia (AREA)
  • Piezo-Electric Transducers For Audible Bands (AREA)

Abstract

A method of making an acoustic device comprising a bending wave member (10) and a plate-like bending inertial vibration transducer (12), the method comprising mounting the transducer with its plane normal to the plane of the bending wave member, analysing the power output of the acoustic device which varies as the square of the linear increase in width of the transducer and selecting the width which achieves a desired power output.

Description

TITLE: METHOD OF MAKING AN ACOUSTIC DEVICE
TECHNICAL FIELD
The present invention relates to acoustic devices, i.e. loudspeakers or microphones and the like, in particular those utilising bending inertial vibration transducers, e.g. an inertial piezoelectric vibration transducer.
BACKGROUND ART
Such bending inertial vibration transducers are discussed in WO01/54450 and may employ a plate-like piezoelectric member that resonates in bending. A mass may be provided on the piezoelectric member. Coupling means, typically a stub, are provided for mounting the transducer to a site to which force is to be applied from or to the member. The member is free to bend and so generate a force via the inertia associated with accelerating and decelerating its own mass during vibration. The bending of the member can either be in response to an electrical signal, in which case the transducer acts as a vibration exciter, or can generate an electrical signal, in which case the transducer acts as a vibration sensor.
DISCLOSURE OF INVENTION According to the invention, there is provided a method of making an acoustic device comprising a bending wave member and a plate-like bending inertial vibration transducer, the method comprising mounting the transducer with its plane normal to the plane of the bending wave member, analysing the power output of the acoustic device which varies as the square of the linear increase in width of the transducer and selecting the width which achieves a desired power output.
Usually, bending inertial vibration transducers are mounted with their planes parallel to the plane of the bending wave member, see for example, WO01/54450. In such cases, bending wave vibration is excited in the bending wave member by presenting forces normal to the plane of the bending wave member. In the present invention, the transducer is mounted with its plane at right angles to the plane of the bending wave member. In this way, complex modes may be generated in the bending wave member due to the coupling because additional degrees of freedom may be brought into action. In the prior art having a plate-like transducer mounted with its plane parallel to the bending wave member, increasing the width of the transducer in the plane parallel to the plane of the bending wave member increases the rate of increase of the force transmitted to the bending wave member linearly with the increasing width. Unexpectedly in the present invention, if the width in the plane of the transducer is increased, the rate of increase of force is proportional to the square of the increase. The non-linear increase may be explained by two effects acting in combination, namely an increase due to increased width, and an additional increase due to the change in coupling geometry for the system, resulting from the increase in size.
Consequently, a greater improvement in loudness and sensitivity is possible for an acoustic device made according to the invention for only a moderate increase in size and cost of the transducer. In particular, in contrast to previous designs, it may be possible to provide sufficient power input to a compact loudspeaker with a lens type diaphragm of high mechanical impedance.
The transducer may be attached to the bending wave member over a small proportion of its length, e.g. via a stub, so as to leave the majority of the transducer free to vibrate in bending. The transducer may be coupled to the bending wave member at a non-central location on the transducer. In this way, in addition to producing a force normal to the plane of the bending wave member, the transducer provides extra rotational components. The stub may be mounted to a short edge of the transducer.
The transducer may be a distributed mode actuator, e.g. as described in WO01/54450 which is incorporated herein by reference. The transducer may be in the shape of a beam, i.e. an elongate rectangle. The transducer may be a bi-morph, a bi-morph with a central vane or substrate or a uni-morph .
The bending wave member may be a panel-form member. The acoustic device may be a resonant bending wave loudspeaker wherein the transducer excites resonant bending wave modes in the bending wave member. Such a loudspeaker is described in International Patent Application WO97/09842 which is incorporated by reference and other patent applications and publications, and may be referred to as a distributed mode loudspeaker.
The bending wave member may be transparent. The transducer may be mounted at the edge of the bending wave member.
The acoustic device may be incorporated in a mobile phone, PDA (personal data assistant) or similar small electronic devices. The acoustic device may also be incorporated in other devices. According to a second aspect of the invention, there is provided an acoustic device comprising a bending wave member capable of sustaining bending wave vibration, and a plate-like bending inertial vibration transducer mounted to the bending wave member with the plane of the bending inertial vibration transducer at an angle to the plane of the bending wave member.
The transducer is preferably mounted with its plane normal to the plane of the bending wave member. Nevertheless, the principle of exciting complex modes is applicable over a range of angles with the strength of excitation changing as the angle changes.
According to a third aspect of the invention, there is provided a method for designing an acoustic device comprising a bending wave member and a plate-like bending inertial vibration transducer, analysing the performance of the acoustic device with the transducer mounted to the bending wave member with its plane at an angle to the plane of the bending wave member, varying the width of the transducer and selecting the width which achieves a desired acoustic output.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by way of example by reference to the following diagrams, of which:
Figures Ia, Ib, Ic and Id are schematic isometric, plan, end and side views, respectively of an acoustic device according to the invention; Figures 2a, 2b, 2c and 2d are schematic isometric, plan, end and side views, respectively of an acoustic device which is driven in accordance with known techniques;
Figure 3 is graph of sound pressure against frequency for the device of Figure 2a and a similar device with a transducer of increased width, and
Figure 4 is graph of sound pressure against frequency for the device of Figure Ia and a similar device with a transducer of increased width. DETAILED DESCRIPTION OF THE DRAWINGS
Figures Ia to Id show an acoustic device, i.e. loudspeaker, comprising a generally rectangular bending wave panel 10 driven by two piezoelectric transducers 12, each mounted close to a short edge of the panel 10. Each transducer 12 is a bi-morph and comprises two piezoelectric beams 20,22 which are mounted with the beam plane perpendicular to the panel plane. The beams have width (w) . The panel is made from solid polycarbonate but may be made from any other suitable materials.
The beams 20,22 are both attached at one end to a stub 24 which inputs a force normal to the plane of the transducer into the panel to excite bending wave vibration in the panel. The stubs are made from a material which is solid, stiff and has low mass. The stubs are located along the long axis of the panel.
The transducers 12 are mounted within an enclosure 16 which is mounted to a face of the panel 10. In Figures Ia to Id the transducers 12 and enclosure 16 are shown on opposite sides of the panel for clarity. The enclosure 16 is shaped so as to define a thin air gap 14 behind the majority of the panel 12. In the edge regions of the panel 12 where the transducers 12 are located, the enclosure defines deeper air pockets into which the transducers 12 extend.
Figures 2a to 2d show an acoustic device which is identical to that of Figures Ia to Id except for the orientation of the transducers. The acoustic device comprises a rectangular bending wave panel 30 driven by two piezoelectric transducers 32, each mounted close to a short edge of the panel 30. Each transducer 32 comprises two piezoelectric beams 40,42 but in this embodiment, the beam planes are parallel to the panel plane, i.e. mounted in accordance with standard known technology. The beams 40,42 are both attached at one end to a stub 44 which inputs a force normal to the panel plane into the panel to excite bending wave vibration in the panel.
As in the device of Figure Ia, the transducers 32 are mounted in an enclosure 36 which defines a layer of trapped air behind the panel and two air-pockets into which the transducers are mounted. The transducers 32 are shown on the opposite side of the panel for clarity. The material from which the stubs and panel are made is the same as that in Figure Ia.
Figure 3 shows the far field acoustic pressure for the device of Figure 2a (dotted line) and a similar device (solid line) in which the width of each piezoelectric beam is doubled. A 6dB increase occurs when the width is doubled.
In addition to the results shown in Figure 3, the far field acoustic pressure may be predicted and observed for different width increase as set out in the table below.
Predicted level
Width Observed level change assuming
(W) change at 200Hz linear width- (dB) pressure relationship
Ref 0 20*log(1.0)=0
Ref*1.2 1.735 20*log(1.2)=1.584 Ref*1.4 2.804 20*log(1.4)=2.93 Ref*1.6 3.612 20*log(1.6)=4.082 Ref*1.8 4.638 20*log(1.8)=5.105 Ref*2.0 5.542 20*log(2.0)=6.021
There is good agreement between the predicted and observed values. The discrepancies may be due to the changing stub dimensions and changing drivepoint . It can be concluded from this results set that the relationship between the level of the far field acoustic pressure and the transducer width is linear for the device of Figure Ia.
Figure 4 shows the far field acoustic pressure for the device of Figure Ia (dotted line) and a similar device
(solid line) in which the width of each piezoelectric beam is doubled. In this case, a 12dB increase occurs when the width is doubled.
In addition to the results shown in Figure 4, the far field acoustic pressure may be predicted and observed for different width increase as set out in the table below.
Predicted level
Width Observed level change assuming
(W) change at 200Hz linear widthΛ2- (dB) pressure relationship
Ref 0 20*log(1.0)=0
Ref*1.2 3 . 070 20*log(1.2Λ2)=3.167 Ref*1.4 5 . 750 20*log(1.4Λ2)=5.845 Ref*1.6 7 . 916 20*log(1.6Λ2)=8.165 Ref*1.8 9.958 20*log(1.8Λ2)=10.211 Ref*2.0 11.834 20*log(2.0Λ2)=12.041
Once again there is good agreement between the predicted and observed results. It can be concluded from this results set that the relationship between the level of the far field acoustic pressure is proportional to square of the transducer width for the device of Figure Ia.
The width squared relation occurs due to each piezoelectric beam acting as a lever when it is rotated. An equivalent system would be a force source increasing linearly with beam width applied to the end of a very stiff lever, the length of which increases proportionally to the beam width.

Claims

1. A method of making an acoustic device comprising a bending wave member and a plate-like bending inertial vibration transducer, the method comprising mounting the transducer with its plane normal to the plane of the bending wave member, analysing the power output of the acoustic device which varies as the square of the linear increase in width of the transducer and selecting the width which achieves a desired power output.
2. A method according to claim 1, comprising mounting the transducer to the bending wave member over a small proportion of its length so as to leave the majority of the transducer free to vibrate in bending.
3. A method according to claim 1 or claim 2, comprising coupling the transducer to the bending wave member at a non-central location on the transducer.
4. A method according to claim 3, comprising coupling the transducer at one end of the transducer.
PCT/GB2006/003019 2005-08-16 2006-08-11 Method of making an acoustic device WO2007020409A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0516784A GB0516784D0 (en) 2005-08-16 2005-08-16 Acoustic device
GB0516784.6 2005-08-16

Publications (1)

Publication Number Publication Date
WO2007020409A1 true WO2007020409A1 (en) 2007-02-22

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ID=35098388

Family Applications (1)

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PCT/GB2006/003019 WO2007020409A1 (en) 2005-08-16 2006-08-11 Method of making an acoustic device

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GB (1) GB0516784D0 (en)
WO (1) WO2007020409A1 (en)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1108345B1 (en) * 1998-08-28 2003-09-24 New Transducers Limited Loudspeakers comprising a resonant panel-form member
US20040240687A1 (en) * 2003-05-30 2004-12-02 Graetz Michael L. Flat panel speaker
WO2005067344A1 (en) * 2004-01-08 2005-07-21 New Transducers Limited Bending wave panel loudspeaker

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1108345B1 (en) * 1998-08-28 2003-09-24 New Transducers Limited Loudspeakers comprising a resonant panel-form member
US20040240687A1 (en) * 2003-05-30 2004-12-02 Graetz Michael L. Flat panel speaker
WO2005067344A1 (en) * 2004-01-08 2005-07-21 New Transducers Limited Bending wave panel loudspeaker

Also Published As

Publication number Publication date
GB0516784D0 (en) 2005-09-21

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