EP1186203B1 - Bending wave acoustic device - Google Patents
Bending wave acoustic device Download PDFInfo
- Publication number
- EP1186203B1 EP1186203B1 EP00935350A EP00935350A EP1186203B1 EP 1186203 B1 EP1186203 B1 EP 1186203B1 EP 00935350 A EP00935350 A EP 00935350A EP 00935350 A EP00935350 A EP 00935350A EP 1186203 B1 EP1186203 B1 EP 1186203B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- panel
- axis
- along
- modal
- acoustic device
- Prior art date
- Legal status (The legal status 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 status listed.)
- Expired - Lifetime
Links
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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
- H04R1/00—Details of transducers, loudspeakers or microphones
- H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
- H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
- H04R1/40—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers
- H04R1/403—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers loud-speakers
-
- 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
- H04R7/06—Plane diaphragms comprising a plurality of sections or layers
Definitions
- the invention relates to an acoustic device, and in particular to an acoustic device of the type that uses resonant bending wave modes.
- a prior resonant bending wave device is described in WO97/09842.
- This document describes a panel having resonant bending wave modes in the area of the panel.
- a transducer may be provided at a preferential location on the panel for exciting the resonant modes, to produce a loudspeaker or microphone.
- Such a device is known as a distributed mode loudspeaker.
- US 3 347 335 describes a loudspeaker in which bending waves are sent along a beam.
- the bending waves are excited at one end of the beam and a non-reflecting termination is provided at the other. Since the termination is non-reflecting, the bending waves will travel down the beam, be abscrbed and will not reflect back to form resonant modes.
- an acoustic device comprising a member having a modal axis along which axis there are a plurality of resonant bending wave modes, and non-modal axes perpendicular to the modal axis, wherein the fundamental frequency of the resonant modes along each non-modal axis is at least five times the fundamental frequency of the resonant modes along the modal axis.
- the fundamental frequency of the resonant modes along each non-modal axis is at least ten times the fundamental frequency along the modal axis.
- the member may be a panel with the modal axis along the length of the panel and a non-modal axis along the width of the panel.
- the panel need not be flat.
- the fundamental frequency along a particular axis is the frequency of the lowest bending wave mode along that axis.
- the density of modes along an axis is related to the fundamental frequency along that axis: in a broad frequency range there will be more resonant modes along an axis with a low fundamental frequency than along an axis with a higher fundamental frequency.
- the fundamental frequency f o along an axis of a panel may be related to the panel bending stiffness B (about a perpendicular axis) and the panel length L along the axis by the proportional relationship (which assumes constant mass per unit area) (f o ) 2 ⁇ B/L 4 .
- the width may be less than half, preferably less than a third of the length.
- the sound emitted from a panel is anisotropic at frequencies where resonant bending wave modes along the modal axis, but not the non-modal axis, are excited.
- sound is preferentially emitted into a plane perpendicular to the panel through the modal axis, and reduced in a plane perpendicular to the modal axis through the non-modal axis.
- This can give rise to enhancement of the sound into the plane through the modal axis at these frequencies.
- the panel may be particularly suitable for use with piezoelectric transducers, which have a frequency response which tails off at low frequencies. The increased low frequency sound output can compensate for this tailing off of excitation to provide a more even sound overall.
- the preferential sound radiation into a single plane can also be useful in some specific applications, for example to direct sound into a horizontal plane in a room and avoid sending too much sound to a ceiling or floor of the room.
- the panel may be stiffer to bend about the modal axis than about the non-modal axis.
- the bending stiffness of the panel about the modal axis panel may be at least 1.5 times that about the non-modal axis, further preferably at least twice as stiff. Since the resonant bending wave modes along an axis cause bending about a perpendicular axis, if the panel is stiffer to bend about the modal axis this will reduce the number of modes along the non-modal axis.
- a panel having anisotropic bending stiffness may be made of a material having a corrugated or cellular structure, with the cells or corrugations running in the plane of the panel along the non-modal axis.
- a transducer may be provided to excite the resonant bending wave modes.
- the transducer may preferably be placed at a location at which spaced away from the nodes of the lower modes along the modal direction.
- the transducer may be placed at a preferred location along the length of the member, for example at substantially 4/9, 3/7 or 5/13 of the length along the modal axis. These locations are similar to those taught in WO97/09842, except that in that document the preferred locations have these coordinate values in both directions.
- the transducer need not be placed on the modal axis, but may be placed laterally thereof.
- a plurality of transducers may be provided. To provide multiple transducers at one preferred location a plurality of transducers may be placed side by side across the width of the panel. This can provide increased output. Alternatively, a single transducer may extend across the width of the panel at a preferred location. Such a transducer can be effective even if it only causes bending along one axis.
- a bending transducer extending across the width of the panel may be able to provide greater power than a single point-like transducer for use on a two-dimensional panel which cannot have a significant spatial extent.
- the panel may also be possible to excite the panel at a less-preferred location, for example a location nearer one end than the preferred location. It is possible to vary the bending stiffness along the modal axis so that other positions than those mentioned above become preferred. Alternatively, it may be possible to damp or clamp the panel in some way to improve the efficiency of the panel even when excited at a less preferred location.
- a rectangular panel 1 is substantially flat extending in the x (length) and y (width) directions as shown.
- the panel is anisotropic in bending stiffness and is much narrower than it is long. It is also much stiffer about the x axis than the y axis. Accordingly, the fundamental frequency is much less along the x axis, the modal axis, than along the non-modal y- axis. Therefore, there are many more resonant bending wave modes along the x axis than along the y axis.
- a plurality of transducers 5 are arranged spaced apart from one another in the y direction along a line 3 extending across the width of the panel.
- the line 3 is spaced from one end of the panel along the length of the panel at a distance of four ninths of the length of the panel in the x direction.
- the plurality of transducers can input more power into the panel than would be possible with a single transducer.
- the transducers 5 are connected to a conventional amplifier by leads 7; they are conventional bending wave transducers. They can be piezoelectric transducers.
- the sound pressure level in dB produced by such a panel has been measured as a function of frequency.
- Figure 2 shows the sound pressure level "on axis", i.e. perpendicular to the plane of the panel, and at two further directions offset by 45° and 60° from that axis towards the x direction.
- Figure 3 shows the sound pressure level "on axis", i.e. perpendicular to the plane of the panel, and at two further directions offset by 45° and 80° from that axis towards the y direction.
- Figure 3 shows sound pressure levels emitted sideways and
- Figure 2 shows sound pressure levels emitted along the length of the panel. The sound pressure levels are measured at a distance of 1m from the panel.
- the panel measured is made from a corrugated polymer sold under the trade mark "Correx". It is about 2.83 times stiffer about the modal axis than about the non-modal axis.
- the sound energy is not very directional in the plane of the modal axis (see Figure 2).
- the high frequencies are radiated to a very wide angle, and the mid frequencies are only slightly reduced off axis.
- This curve is similar to the curve obtained from a classic distributed mode panel as taught, for example, by WO97/09842.
- the width of the panel can be increased.
- the wavefronts become cylindrical and the low frequency output rises at 3dB per octave as the frequency is lowered. This can compensate for a falling output from a piezoelectric driver at these frequency ranges.
- the width of the panel in order that the fundamental frequencies remain different enough for effective one-dimensional behaviour.
Landscapes
- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Signal Processing (AREA)
- Piezo-Electric Transducers For Audible Bands (AREA)
- Diaphragms For Electromechanical Transducers (AREA)
Description
(fo)2 α B/L4.
Claims (12)
- An acoustic device for operation in a predetermined frequency range comprising a member (1) having a modal axis, whereby the member (1) can support a plurality of resonant bending wave modes in the predetermined frequency range along the modal axis characterised in that the member (1) further comprises a non-modal axis orthogonal to the modal axis and the fundamental frequency of resonant bending wave modes along the non-modal axis is at least five times the fundamental frequency of the resonant bending wave modes along the modal axis whereby sound emitted from the member is anisotropic at frequencies where resonant bending wave modes along the modal axis, but not the non-modal axis, are excited.
- An acoustic device according to claim 1, wherein the fundamental frequency of the resonant modes along the non-modal axis is at least ten times the fundamental frequency along the modal axis.
- An acoustic device according to claim 1 or 2, wherein the member (1) is in the form of a panel having a length and a width wherein the modal axis is along the length of the panel and the non-modal axis across the width of the panel.
- An acoustic device according to claim 3, wherein the width of the panel is less than half the length of the panel.
- An acoustic device according to claims 3 or 4, wherein the bending stiffness of the panel about the modal axis is at least 1.5 times the bending stiffness of the panel about the non-modal axis.
- An acoustic device according to claim 5, wherein the panel has a corrugated or cellular structure, with the corrugations or cells running along the non-modal axis.
- An acoustic device according to any preceding claim, further comprising a transducer (5) coupled to the member (1) for exciting the resonant bending wave modes.
- An acoustic device according to claim 6, wherein the transducer (5) is placed at a location spaced away from the nodes of a predetermined plurality of lower frequency resonant bending wave modes.
- An acoustic device according to claim 8, wherein the transducer (5) is placed at or laterally of a position substantially 4/9, 3/7 or 5/13 along the modal axis of the member (1) from either end of the member (1).
- An acoustic device according to any of claims 7 to 9, wherein the transducer (5) is a piezoelectric transducer (5).
- An acoustic device according to any of claims 7 to 10, comprising a plurality of transducers (5).
- An acoustic device according to any of claims 3 to 6, further comprising a plurality of transducers (5) arranged across the width of the panel.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9913465 | 1999-06-10 | ||
GBGB9913465.2A GB9913465D0 (en) | 1999-06-10 | 1999-06-10 | Acoustic device |
PCT/GB2000/002054 WO2000078090A2 (en) | 1999-06-10 | 2000-06-07 | Bending wave acoustic device |
Publications (2)
Publication Number | Publication Date |
---|---|
EP1186203A2 EP1186203A2 (en) | 2002-03-13 |
EP1186203B1 true EP1186203B1 (en) | 2003-07-23 |
Family
ID=10855054
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP00935350A Expired - Lifetime EP1186203B1 (en) | 1999-06-10 | 2000-06-07 | Bending wave acoustic device |
Country Status (10)
Country | Link |
---|---|
EP (1) | EP1186203B1 (en) |
JP (1) | JP2003501982A (en) |
CN (1) | CN1261002C (en) |
AU (1) | AU5089600A (en) |
DE (1) | DE60004045T2 (en) |
GB (1) | GB9913465D0 (en) |
HK (1) | HK1040875B (en) |
NZ (1) | NZ515328A (en) |
TW (1) | TW479434B (en) |
WO (1) | WO2000078090A2 (en) |
Families Citing this family (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
AU2002238709A1 (en) * | 2001-03-23 | 2002-10-08 | New Transducers Limited | Bending wave acoustic radiator |
US7120263B2 (en) | 2001-03-23 | 2006-10-10 | New Transducers Limited | Bending wave acoustic radiator |
GB0123932D0 (en) * | 2001-10-05 | 2001-11-28 | New Transducers Ltd | Loudspeakers |
GB0317331D0 (en) * | 2003-07-24 | 2003-08-27 | New Transducers Ltd | Acoustic device |
JP5545083B2 (en) * | 2010-07-07 | 2014-07-09 | ソニー株式会社 | Speaker device |
EP3195617A1 (en) * | 2014-09-19 | 2017-07-26 | Corning Incorporated | Thin panel loudspeakers |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE1132593B (en) * | 1965-04-05 | 1962-07-05 | Bolt Beranek & Newman | Acoustically effective plate, especially for coupling to an electroacoustic transducer |
UA51671C2 (en) * | 1995-09-02 | 2002-12-16 | Нью Транзд'Юсез Лімітед | Acoustic device |
TW450011B (en) * | 1998-02-10 | 2001-08-11 | New Transducers Ltd | Acoustic devices |
-
1999
- 1999-06-10 GB GBGB9913465.2A patent/GB9913465D0/en not_active Ceased
-
2000
- 2000-06-07 NZ NZ515328A patent/NZ515328A/en not_active IP Right Cessation
- 2000-06-07 AU AU50896/00A patent/AU5089600A/en not_active Abandoned
- 2000-06-07 CN CNB008078068A patent/CN1261002C/en not_active Expired - Lifetime
- 2000-06-07 WO PCT/GB2000/002054 patent/WO2000078090A2/en active IP Right Grant
- 2000-06-07 DE DE60004045T patent/DE60004045T2/en not_active Expired - Lifetime
- 2000-06-07 JP JP2001502614A patent/JP2003501982A/en active Pending
- 2000-06-07 EP EP00935350A patent/EP1186203B1/en not_active Expired - Lifetime
- 2000-06-12 TW TW089111418A patent/TW479434B/en not_active IP Right Cessation
-
2002
- 2002-03-19 HK HK02102096.7A patent/HK1040875B/en not_active IP Right Cessation
Also Published As
Publication number | Publication date |
---|---|
DE60004045D1 (en) | 2003-08-28 |
CN1261002C (en) | 2006-06-21 |
WO2000078090A2 (en) | 2000-12-21 |
HK1040875B (en) | 2003-10-17 |
WO2000078090A3 (en) | 2001-07-12 |
CN1356015A (en) | 2002-06-26 |
NZ515328A (en) | 2002-04-26 |
JP2003501982A (en) | 2003-01-14 |
HK1040875A1 (en) | 2002-06-21 |
EP1186203A2 (en) | 2002-03-13 |
DE60004045T2 (en) | 2004-05-06 |
AU5089600A (en) | 2001-01-02 |
TW479434B (en) | 2002-03-11 |
GB9913465D0 (en) | 1999-08-11 |
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