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
  • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
  • H04R1/26—Spatial arrangements of separate transducers responsive to two or more frequency ranges
• • 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
  • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
  • H04R1/28—Transducer mountings or enclosures modified by provision of mechanical or acoustic impedances, e.g. resonator, damping means
  • H04R1/2807—Enclosures comprising vibrating or resonating arrangements
  • H04R1/2838—Enclosures comprising vibrating or resonating arrangements of the bandpass type
  • H04R1/2842—Enclosures comprising vibrating or resonating arrangements of the bandpass type for loudspeaker 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
  • H04R2440/07—Loudspeakers using bending wave resonance and pistonic motion to generate sound

Definitions

• the invention relates to loudspeakers and more particularly to loudspeakers comprising panel-form acoustic radiating elements.
• a panel-form loudspeaker comprising:- a resonant multi-mode radiator element being a unitary sandwich panel formed of two skins of material with a spacing core of transverse cellular construction, wherein the panel is such as to have ratio of bending stiffness (B) , in all orientations, to the cube power of panel mass per unit surface area ( ⁇ ) of at least 10; a mounting means which supports the panel or attaches to it a supporting body, in a free undamped manner; and an electro-mechanical drive means coupled to the panel which serves to excite a multi-modal resonance in the radiator panel in response to an electrical input within a working frequency band for the loudspeaker.
• B bending stiffness
• ⁇ cube power of panel mass per unit surface area
• Embodiments of the present invention use members of nature, structure and configuration achievable generally and/or specifically by implementing teachings of our co- pending PCT application no. (our case P.5711) of even date herewith.
• Such members thus have capability to sustain and propagate input vibrational energy by bending waves in operative area(s) extending transversely of thickness often but not necessarily to edges of the member(s); are configured with or without anisotropy of bending stiffness to have resonant mode vibration components distributed over said area(s) beneficially for acoustic coupling with ambient air; and have predetermined preferential locations or sites within said area for transducer means, particularly operationally active or moving part(s) thereof effective in relation to acoustic vibrational activity in said area(s) and signals, usually electrical, corresponding to acoustic content of such vibrational activity.
• This invention is particularly concerned with active acoustic devices in the form of loudspeakers.
• the invention provides a loudspeaker comprising an enclosure, an acoustic radiator in the enclosure, a compliant suspension mounting the radiator in the enclosure for limited pistonic movement relative thereto, and transducer means for driving the radiator, characterised in that the radiator is a panel-form distributed mode acoustic radiator, by a first transducer mounted wholly and exclusively on the radiator to vibrate the radiator to cause it to resonate, and by means for varying the air pressure in the enclosure to cause the radiator to move pistonically.
• the air pressure varying means may comprise an air pump.
• the air pump may comprise a subsidiary enclosure, a pistonic driver mounted in the subsidiary enclosure and means coupling the interiors of the respective enclosures such that air pressure waves produced by motion of the pistonic driver are transmitted to the said enclosure.
• Acoustically absorbent means e.g. wadding, may be provided in the said enclosure and/or in the subsidiary enclosure.
• the distributed mode acoustic radiator may comprise a panel having a lightweight cellular core sandwiching a pair of high modulus lightweight skins.
• Figure 2a is a partial section on the line A-A of Figure 1;
• Figure 2b is an enlarged cross-section through a distributed mode radiator of the kind shown in Figure 2a_ and showing two alternative constructions, and
• Figure 3 is a diagram of an embodiment of distributed- mode loudspeaker according to the present invention.
• a panel-form loudspeaker (81) of the kind described and claimed in our co-pending International application No. (our case P.5711) of even date herewith comprising a rectangular frame (1) carrying a resilient suspension (3) round its inner periphery which supports a distributed mode sound radiating panel (2).
• a transducer (9) e.g as described in detail with reference to our co-pending International applications Nos. (our cases P.5683/4/5) of even date herewith, is mounted wholly and exclusively on or in the panel (2) at a predetermined location defined by dimensions x and y_, the position of which location is calculated as described in our co-pending International application No. (our case P.5711) of even date herewith, to launch bending waves into the panel to cause the panel to resonate to radiate an acoustic output.
• the transducer (9) is driven by a signal amplifier (10), e.g. an audio amplifier, connected to the transducer by conductors (28) .
• a signal amplifier (10) e.g. an audio amplifier
• Amplifier loading and power requirements can be entirely normal, similar to conventional cone type speakers, sensitivity being of the order of 86 - 88dB/watt under room loaded conditions.
• Amplifier load impedance is largely resistive at 6 ohms, power handling 20-80 watts.
• the panel core and/or skins are of metal, they may be made to act as a heat sink for the transducer to remove heat from the motor coil of the transducer and thus improve power handling.
• Figures 2a. and 2b are partial typical cross-sections through the loudspeaker (81) of Figure 1.
• Suitable materials for the frame include lightweight framing, e.g. picture framing of extruded metal e.g. aluminium alloy or plastics.
• Suitable surround materials include resilient materials such as foam rubber and foam plastics.
• Suitable adhesives for the joints (20) include epoxy, acrylic and cyano-acrylate etc. adhesives.
• Figure 2b illustrates, to an enlarged scale, that the panel (2) is a rigid lightweight panel having a core (22) e.g. of a rigid plastics foam (97) e.g. cross linked polyvinylchloride or a cellular matrix (98) i.e. a honeycomb matrix of metal foil, plastics or the like, with the cells extending transversely to the plane of the panel, and enclosed by opposed skins (21) e.g. of paper, card, plastics or metal foil or sheet.
• the skins are of plastics, they may be reinforced with fibres e.g. of carbon, glass, Kevlar (RTM) or the like in a manner known per se to increase their modulus.
• RTM Kevlar
• thermoplastics allow for the mould tooling to carry location and registration features such as grooves or rings for the accurate location of transducer parts e.g. the motor coil, and the magnet suspension. Additional with some weaker core materials it is calculated that it would be advantageous to increase the skin thickness locally e.g. in an area or annulus up to 150% of the transducer diameter, to reinforce that area and beneficially couple vibration energy into the panel. High frequency response will be improved with the softer foam materials by this means.
• Envisaged core layer materials include fabricated honeycombs or corrugations of aluminium alloy sheet or foil, or Kevlar (RTM), Nomex (RTM), plain or bonded papers, and various synthetic plastics films, as well as expanded or foamed plastics or pulp materials, even aerogel metals if of suitably low density.
• Some suitable core layer materials effectively exhibit usable self-skinning in their manufacture and/or otherwise have enough inherent stiffness for use without lamination between skin layers.
• a high performance cellular core material is known under the trade name 'Rohacell' which may be suitable as a radiator panel and which is without skins. In practical terms, the aim is for an overall lightness and stiffness suited to a particular purpose, specifically including optimising contributions from core and skin layers and transitions between them.
• electrical connection can be made to the conductive parts of an appropriate DML panel or an electrically conductive foam or similar interface may be used for the edge mounting.
• Effective said selective damping includes specific application to the panel including its sheet material of means permanently associated therewith. Edges and corners can be particularly significant for dominant and less dispersed low frequency vibration modes of panels hereof. Edge-wise fixing of damping means can usefully lead to a panel with its said sheet material fully framed, though their corners can often be relatively free, say for desired extension to lower frequency operation. Attachment can be by adhesive or self-adhesive materials. Other forms of useful damping, particularly in terms of more subtle effects and/or mid- and higher frequencies can be by way of suitable mass or masses affixed to the sheet material at predetermined effective medial localised positions of said area.
• An acoustic panel as described above is bi ⁇ directional.
• the sound energy from the back is not strongly phase related to that from the front. Consequently there is the benefit of overall summation of acoustic power in the room, sound energy of uniform frequency distribution, reduced reflective and standing wave effects and with the advantage of superior reproduction of the natural space and ambience in the reproduced sound recordings.
• FIG 3 illustrates another way of combining pistonic and distributed mode resonant behaviour in a loudspeaker (81) .
• a lightweight, rigid distributed mode sound radiator panel (2) of the kind shown in Figures 1 and 2 forms a front wall of a box-like enclosure (8) having sides (135) and a rear wall (12) e.g. of medium density fibreboard, together defining a cavity (155).
• a panel (51) of acoustic absorption material is provided in the cavity (155) .
• a panel (51) of acoustic absorption material is provided in the cavity to damp standing waves.
• the radiator panel (2) is mounted in the enclosure (8) by means of a compliant suspension (7) e.g.
• the interior cavity (155) of the enclosure (8) is coupled to a bass pump (11), that is to say to the interior of a box-like enclosure (185) containing a pistonic bass loudspeaker drive unit (42), by means of a pipe-like conduit (90), whereby air pressure waves of acoustic frequency in the bass region are applied to the interior (155) of the enclosure to cause the panel (2) to move pistonically on its compliant suspension (7) to produce a low frequency acoustic output.
• the panel is caused to resonate by the transducer (9) to cause the panel to radiate an acoustic output at higher frequencies.
• An amplifier (1) is arranged to feed an acoustic signal to the bass pump (11) and to the transducer (9) to drive the loudspeaker.

Landscapes

• Engineering & Computer Science (AREA)
• Signal Processing (AREA)
• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Otolaryngology (AREA)
• Health & Medical Sciences (AREA)
• Multimedia (AREA)
• Diaphragms For Electromechanical Transducers (AREA)
• Details Of Audible-Bandwidth Transducers (AREA)
• Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
• Piezo-Electric Transducers For Audible Bands (AREA)
• Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
• Obtaining Desirable Characteristics In Audible-Bandwidth Transducers (AREA)

Priority Applications (14)

Applications Claiming Priority (7)

Publications (1)

Family

ID=34865252

Family Applications (1)

Country Status (13)

Cited By (24)

Families Citing this family (2)

Citations (7)

• 1996
  • 1996-09-02 JP JP9510967A patent/JPH11512261A/ja active Pending
  • 1996-09-02 EP EP96929407A patent/EP0847668B1/de not_active Expired - Lifetime
  • 1996-09-02 ES ES96929407T patent/ES2132954T3/es not_active Expired - Lifetime
  • 1996-09-02 DE DE69602100T patent/DE69602100T2/de not_active Expired - Fee Related
  • 1996-09-02 CN CN96196702.1A patent/CN1195457A/zh active Pending
  • 1996-09-02 AT AT96929407T patent/ATE179043T1/de not_active IP Right Cessation
  • 1996-09-02 EA EA199800250A patent/EA002097B1/ru not_active IP Right Cessation
  • 1996-09-02 RO RO98-00647A patent/RO119048B1/ro unknown
  • 1996-09-02 CA CA002230438A patent/CA2230438A1/en not_active Abandoned
  • 1996-09-02 AU AU68822/96A patent/AU704299B2/en not_active Ceased
  • 1996-09-02 WO PCT/GB1996/002166 patent/WO1997009849A1/en not_active Application Discontinuation
  • 1996-09-02 DK DK96929407T patent/DK0847668T3/da active
• 1998
  • 1998-07-28 HK HK98109453A patent/HK1008648A1/xx not_active IP Right Cessation

Patent Citations (8)

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