U.S. patent application number 09/011832 was filed with the patent office on 2001-08-30 for loudspeakers with panel-form acoustic radiating elements.
Invention is credited to AZIMA, HENRY, COLLOMS, MARTIN, HARRIS, NEIL JOHN.
Application Number | 20010017924 09/011832 |
Document ID | / |
Family ID | 46256097 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010017924 |
Kind Code |
A1 |
AZIMA, HENRY ; et
al. |
August 30, 2001 |
LOUDSPEAKERS WITH PANEL-FORM ACOUSTIC RADIATING ELEMENTS
Abstract
A loudspeaker (81) comprising an enclosure, an acoustic radiator
(2) in the enclosure, a compliant suspension (3) mounting the
radiator in the enclosure for pistonic movement relative thereto,
and transducer means (9) for driving the radiator pistonically,
characterized 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 (11) for varying the air pressure in the
enclosure to cause the radiator to move pistonically.
Inventors: |
AZIMA, HENRY; (CAMBRIDGE,
GB) ; COLLOMS, MARTIN; (LONDON, GB) ; HARRIS,
NEIL JOHN; (CAMBRIDGE, GB) |
Correspondence
Address: |
ALAN I. CANTOR
FOLEY & LARDNER
3000 K STREET N.W.
WASHINGTON
DC
20007-5109
US
|
Family ID: |
46256097 |
Appl. No.: |
09/011832 |
Filed: |
September 21, 1998 |
PCT Filed: |
September 2, 1996 |
PCT NO: |
PCT/GB96/02166 |
Current U.S.
Class: |
381/165 ;
381/162; 381/431; 712/E9.002 |
Current CPC
Class: |
H04R 3/04 20130101; H04R
1/2811 20130101; H04R 2307/029 20130101; B60R 11/0217 20130101;
H04R 2499/15 20130101; H04R 2499/13 20130101; G07F 9/02 20130101;
B42D 15/022 20130101; G06F 1/1605 20130101; G06F 1/1616 20130101;
G06F 1/1688 20130101; H04R 2440/07 20130101; H04R 2201/021
20130101; H04R 1/24 20130101; G06F 9/02 20130101; H04R 17/00
20130101; H04R 1/021 20130101; H04R 7/08 20130101; H04R 7/045
20130101; H04R 5/027 20130101; H04R 7/06 20130101; H04R 9/066
20130101; H04R 1/025 20130101; H04R 1/26 20130101; H04R 9/045
20130101; H04R 5/02 20130101; H04R 1/028 20130101; H04R 9/025
20130101 |
Class at
Publication: |
381/165 ;
381/431; 381/162 |
International
Class: |
H04R 001/00; H04R
011/02 |
Claims
1. A loudspeaker comprising an enclosure, an acoustic radiator in
the enclosure, a compliant suspension mounting the radiator in the
enclosure for pistonic movement relative thereto, and transducer
means for driving the radiator pistonically, 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.
2. A loudspeaker according to claim 1, characterised in the air
pressure varying means comprises an air pump.
3. A loudspeaker according to claim 2, characterised in that the
air pump comprises 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.
4. A loudspeaker according to claim 3, characterised by
acoustically absorbent means in the said enclosure and/or in the
subsidiary enclosure.
5. A loudspeaker according to any preceding claim, characterised in
that the distributed mode acoustic radiator comprises a panel
having a lightweight cellular core sandwiching a pair of high
modulus lightweight skins.
Description
TECHNICAL FIELD
[0001] The invention relates to loudspeakers and more particularly
to loudspeakers comprising panel-form acoustic radiating
elements.
BACKGROUND ART
[0002] It is known from GB-A-2262861 to suggest a panel-form
loudspeaker comprising:
[0003] 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 (.mu.) of at least
10;
[0004] a mounting means which supports the panel or attaches to it
a supporting body, in a free undamped manner;
[0005] and an electromechanical 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.
DISCLOSURE OF INVENTION
[0006] 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. Uses are envisaged in co-pending International
application No. (our file P.5711) of even date herewith for such
members as or in "passive" acoustic devices without transducer
means, such as for reverberation or for acoustic filtering or for
acoustically "voicing" a space or room; and as or in "active"
acoustic devices with transducer means, such as in a remarkably
wide range of sources of sound or loudspeakers when supplied with
input signals to be converted to said sound, or in such as
microphones when exposed to sound to be converted into other
signals.
[0007] This invention is particularly concerned with active
acoustic devices in the form of loudspeakers.
[0008] Members as above are herein called distributed mode acoustic
radiators and are intended to be characterised as in the above PCT
application and/or otherwise as specifically provided herein.
[0009] 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.
[0010] Acoustically absorbent means, e.g. wadding, may be provided
in the said enclosure and/or in the subsidiary enclosure.
[0011] The distributed mode acoustic radiator may comprise a panel
having a lightweight cellular core sandwiching a pair of high
modulus lightweight skins.
BRIEF DESCRIPTION OF DRAWINGS
[0012] The invention is diagrammatically illustrated, by way of
example, in the accompanying drawings, in which:
[0013] FIG. 1 is a diagram showing a distributed-mode loudspeaker
as described and claimed in our co-pending International
application No. (our case P.5711);
[0014] FIG. 2a is a partial section on the line A-A of FIG. 1;
[0015] FIG. 2b is an enlarged cross-section through a distributed
mode radiator of the kind shown in FIG. 2a and showing two
alternative constructions, and
[0016] FIG. 3 is a diagram of an embodiment of distributed-mode
loudspeaker according to the present invention.
BEST MODES FOR CARRYING OUT THE INVENTION
[0017] Referring to FIG. 1 of the drawings, there is shown 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.
[0018] The transducer (9) is driven by a signal amplifier (10),
e.g. an audio amplifier, connected to the transducer by conductors
(28). Amplifier loading and power requirements can be entirely
normal, similar to conventional cone type speakers, sensitivity
being of the order of 86-88 dB/watt under room loaded conditions.
Amplifier load impedance is largely resistive at 6 ohms, power
handling 20-80 watts. Where 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.
[0019] FIGS. 2a and 2b are partial typical cross-sections through
the loudspeaker (81) of FIG. 1. FIG. 2a shows that the frame (1),
surround (3) and panel (2) are connected together by respective
adhesive-bonded joints (20). 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.
[0020] FIG. 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. Where 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.
[0021] Envisaged skin layer materials and reinforcements thus
include carbon, glass, Kevlar (RTM), Nomex (RTM) i.e. aramid etc.
fibres in various lays and weaves, as well as paper, bonded paper
laminates, melamine, and various synthetic plastics films of high
modulus, such as Mylar (RTM), Kaptan (RTM), polycarbonate,
phenolic, polyester or related plastics, and fibre reinforced
plastics, etc. and metal sheet or foil. Investigation of the Vectra
grade of liquid crystal polymer thermoplastics shows that they may
be useful for the injection moulding of ultra thin skins or shells
of smaller size, say up to around 30 cm diameter. This material
self forms an orientated crystal structure in the direction of
injection, a preferred orientation for the good propagation of
treble energy from the driving point to the panel perimeter.
[0022] Additional such moulding for this and other thermoplastics
allows 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.
[0023] 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.
[0024] Several of the preferred formulations for the panel employ
metal and metal alloy skins, or alternatively a carbon fibre
reinforcement. Both of these, and also designs with an alloy
Aerogel or metal honeycomb core, will have substantial radio
frequency screening properties which should be important in several
EMC applications. Conventional panel or cone type speakers have no
inherent EMC screening capability.
[0025] In addition the preferred form of piezo and electro dynamic
transducers have negligible electromagnetic radiation or stray
magnet fields. Conventional speakers have a large magnetic field,
up to 1 meter distant unless specific compensation counter measures
are taken.
[0026] Where it is important to maintain the screening in an
application, 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.
[0027] The suspension (3) may damp the edges of the panel (2) to
prevent excessive edge movement of the panel. Additionally or
alternatively, further damping may be applied, e.g. as patches,
bonded to the panel in selected positions to damp excessive
movement to distribute resonance equally over the panel. The
patches may be of bitumen-based material, as commonly used in
conventional loudspeaker enclosures or may be of a resilient or
rigid polymeric sheet material. Some materials, notably paper and
card, and some cores may be self-damping. Where desired, the
damping may be increased in the construction of the panels by
employing resiliently setting, rather than rigid setting
adhesives.
[0028] 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.
[0029] 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.
[0030] While the radiation from the acoustic panel is largely
non-directional, the percentage of phase related information
increases off axis. For improved focus for the phantom stereo
image, placement of the speakers, like pictures, at the usual
standing person height, confers the benefit of a moderate off-axis
placement for the normally seated listener optimising the stereo
effect. Likewise the triangular left/right geometry with respect to
the listener provides a further angular component. Good stereo is
thus obtainable.
[0031] There is a further advantage for a group of listeners
compared with conventional speaker reproduction. The intrinsically
dispersed nature of acoustic panel sound radiation gives it a sound
volume which does not obey the inverse square law for distance for
an equivalent point source. Because the intensity fall-off with
distance is much less than predicted by inverse square law then
consequently for off-centre and poorly placed listeners the
intensity field for the panel speaker promotes a superior stereo
effect compared to conventional speakers. This is because the
off-centre placed listener does not suffer the doubled problem due
to proximity to the nearer speaker; firstly the excessive increase
in loudness from the nearer speaker, and then the corresponding
decrease in loudness from the further loudspeaker.
[0032] There is also the advantage of a flat, lightweight
panel-form speaker, visually attractive, of good sound quality and
requiring only one transducer and no crossover for a full range
sound from each panel diaphragm.
[0033] FIG. 3 illustrates another way of combining pistonic and
distributed mode resonant behaviour in a loudspeaker (81). In the
drawing a lightweight, rigid distributed mode sound radiator panel
(2) of the kind shown in FIGS. 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. to emulate the roll surround of a conventional
pistonic cone loudspeaker and carries a transducer (9) of the kind
described with reference to our co-pending International
application Nos. (our files (P5683/4/5) of even date herewith
mounted wholly and exclusively on the panel (2) at a predetermined
location as described in our said co-pending International
application No. (our file P.5711) of even date herewith to launch
bending waves into the panel.
[0034] 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. In addition 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.
* * * * *