Note: Descriptions are shown in the official language in which they were submitted.
CA 02349856 2001-05-04
WO 00/28780 PCT/GB99%03613
LOUDSPEAKERS COMPRISING A PHASE UNCORRELATED DIFFUSE SOUND SOURCE
DESCRIPTION
TECHNICAL FIELD
The invention relates to loudspeakers.
It is an object of the invention to provide means
whereby sound from a loudspeaker can be channelled to one
or more remote locations.
BACKGROUND ART
It is known from W098/43464 of New Transducers
Limited to provide a personal computing device of the kind
having a body comprising a keyboard and a lid hinged to
15 the body and comprising a display screen, characterised by
a resonant panel loudspeaker in or attached to the lid and
an acoustic waveguide or horn directing acoustic output
from the loudspeaker in a desired direction.
DISCLOSURE OF INVENTION
According to the invention, there is provided a
loudspeaker comprising a phase uncorrelated diffuse sound
source and a duct or wave guide coupled to the sound
source to direct acoustic energy from the source, the duct
25 or wave guide having a substantially parallel section
extending from the vicinity of the sound source and a
termination positioned remotely from the panel.
The sound source may comprise a bending wave mode
CA 02349856 2001-05-04
WO 00/28780 PCTIGB99I03613
2
acoustic radiator panel. A transducer may be fixed to the
panel to excite resonant bending waves therein, the
resonant bending wave modes associated with each of the
axes of the panel being arranged to be interleaved in
5 frequency and the transducer location being chosen
preferentially to couple to the resonant bending wave
modes.
The duct may be shaped as a narrow slot in cross
section, or may be of any other desired cross-sectional
10 shape.
The duct may be terminated by a horn section.
The panel may be located in the duct to couple
acoustic radiation from both sides of the panel.
An acoustic reflector may be coupled to the duct and
15 to the sound source to direct acoustic radiation into the
duct.
The duct may have a plurality of terminations and
these may be spaced along the duct.
A plurality of the panels may be coupled to the duct.
20 The duct may be folded.
The loudspeaker may comprise an attenuator
controlling sound output from a duct termination.
Means may be provided for subdividing the duct into a
plurality of wave guides extending along the duct. The
25 duct may be subdivided in two directions, i.e. laterally
and vertically.
An acoustic reflector may be disposed to direct the
acoustic output from a duct termination.
CA 02349856 2001-05-04
- PCT/GB99/03613
WO OOI28780
3
Enclosure means may enclose one face of the panel.
The plane of the panel may be parallel to the axis of
the duct.
Although the invention has_been described in terms of
a loudspeaker, it will be appreciated that it may find
other applications, e.g. as a microphone or as an acoustic
absorber, whether passive or active.
BRIEF DESCRIPTION OF DRAWINGS
The invention is diagrammatically illustrated, by way
of example, in the accompanying drawings in which:-
Figure 1 is a front cross-sectional view of a first
embodiment of loudspeaker of the invention;
Figure 2 is a cross-sectional side view of the
loudspeaker of Figure 1;
Figure 3 is a front cross-sectional view of a second
embodiment of loudspeaker of the invention;
Figure 4 is a cross-sectional side view of a third
embodiment of loudspeaker of the invention;
Figure 5 is a cross-sectional side view of a fourth
embodiment of loudspeaker of the invention;
Figure 6 is a cross-sectional side view of a fifth
embodiment of loudspeaker of the invention;
Figure 7 is a cross-sectional side view of a sixth
embodiment of loudspeaker of the invention;
Figure 8 is a cross-sectional side view of a seventh
embodiment of loudspeaker of the invention, and
Figure 9 is a detail of a modification.
f
CA 02349856 2001-05-04
WO 00/28780 PCT/GB99/03613
4
BEST MODES FOR CARRYING OUT THE INVENTION
The invention relies on largely phase uncorrelated,
diffuse radiation properties of a sound source or
generator e.g. a flat resonant bending wave panel, for
5 example of the kind described in W097/09842 to allow
coupling to an acoustic fluid, normally air, contained in
a shallow volume well coupled to the source of sound
energy. In contrast to the coupling aspects of correlated
e.g. pistonic devices which suffer problems due to path
10 length differences, phase cancellations and subsequent
power irregularities, a diffuse source allows for good
integration of acoustic power over its radiating surface
and that power may be conducted via fluid coupling to a
remote point via a duct. Modal resonance which are
15 normally severe in such a duct are mitigated due to
diffuse uncorrelated nature of the acoustic energy
entering the duct.
The duct termination may radiate directly, which if
in the form of a narrow slot or similar aperture has wide
20 directivity and is not frequency controlling or frequency
selective. If modified directive properties are required
then various sizes shapes and combinations of acoustic
horn known to the art may be added to the open end of the
duct.
25 The principle of diffuse coupling may extend to
simple single reflective elements acting as vestigial
horns or part ducts, and the length of the duct may be
varied to a point where the horn section is almost
CA 02349856 2001-05-04
WO 00/28780 PCT/GB9~/03613
directly presented to the diffuse source.
A notable feature of the invention is that the duct
can be presented in the plane of the radiator and achieve
effective action. Also the sound energy on the surface of
5 the source can be divided and directed down more than one
duct or wave guide, and these may be of unequal lengths
and if required the several outputs may be recombined
smoothly after passage down the ducts or wave guides.
Twin ducts may be used to utilise the energy from
both sides of the diffuse source. The preferred source is
one or more bending wave panels but other such sources
include an array of small conventional pistonic speakers
fed phase randomised signals or an array of digital
speaker elements driven by signals suitably processed to
provide a diffuse acoustic function. The duct provides a
beneficial integrating function which may be designed as a
low pass acoustic filter to complete the desired response
from an array element digital speaker.
The twin ducts may be laterally disposed to provide
sound at two separated locations e.g. across the passenger
compartment of a vehicle benefiting from a single
centrally or near centrally located sound generator.
The duct may be straight, curved or folded to allow a
slim assembly to be fitted into difficult locations where
conventional speaker could not be placed.
Wide range sound may ducted to substantially small
radiating apertures, for example the slots (normally
disguised behind an acoustically transparent grille) at
r
CA 02349856 2001-05-04
WO 00/28780 PCT/GB99/03613
6
the sides of a television monitor. Duct performance may
be further enhanced by cellular subdivision to inhibit
cross standing waves.
The duct and/or horn has a low frequency loading
function which may be simply calculated using lumped
parameters. This may beneficially load' the sound source
to enhance the low range performance by added/matched air
mass and by a baffle effect due to extended path length
between the front and rear of the sound generators where
relevant.
The rear of the panel or multiple panel (with same or
frequency selective/differential area drive/form) or
multiple cone type sound generators may have a partially
or wholly enclosed rear chambers) for additional resonant
enhancement and control of the low frequency acoustic path
between front and rear.
Duct height and/or cross sectional area is
influential in determining the higher frequency point for
smooth transmission of sound energy. Thus a rectangular
duct of 30mm height will show some frequency dependency
above lOkHz, whereas a lOmm section will perform well to
beyond 25kHz.
In addition to lateral subdivisions of the duct, the
sub division of the duct may be extended to the vertical
direction to subdivide the duct still further for
maintained transmission performance at higher frequencies.
The exit area of duct driven by a diffuse source has
an influence on loudness and relative to the intrinsic
CA 02349856 2001-05-04
- WO 00/28780 PC'fIGB99~036I3
7
area of the exit a variable area mechanism such as a
moveable blanking plate over the duct termination may
provide a convenient and effective form of loudness
control without a significant loss in sound quality. A
5 horn directive element may be applied after the mechanical
,loudness control device. Thus a user volume control may be
remote from the sound generator. Alternatively a duct
control device may be provided at any convenient location
along the duct.
10 A horn termination is driven well by the duct of the
invention, and the horn can provide an effective and
calculable control of directivity for a diffuse source.
The duct termination alone provides uniform wide angle
radiation, an almost perfect slot or near point source.
15 In respect of coincidence effects which may result in
off axis lobes of power at discrete frequencies for
particular designs of bending wave panel, the fluid
coupling and duct integration action reconfigures the
sound energy such that the directive effects of
20 coincidence are no longer a feature of the resultant
acoustic output.
The duct can be any length, and terminations may be
provided along the length of the duct to give a simple
distributed low level sound system. Multiple resonant
25 panels could feed a duct, and a multiple panel
arrangement could be made more compact by folding or
bending the region in front of the panel, before the
duct.
CA 02349856 2001-05-04
- WO 00/28780 PCT/GB9~/03613
8
In the drawings, and referring to Figures 1 and 2
there is shown a loudspeaker 1 comprising a resonant
bending-wave panel 2 generally of the kind described in
International patent application W097/09842 of New
Transducers Limited, which is driven by a vibration
exciter 3 fed with an electrical audio signal from
suitable audio amplifier (not shown). The panel 2 is
resiliently mounted by its edges on a resilient
suspension 4 in a housing 5 in the form of a parallel
sided shallow slot-like duct 6 having a closed end 7 and
an open end 8 which opens into a flared horn section 9
which ends at opening or termination 10. The housing may
be made from any suitable non resonant material such as
those materials from which loudspeaker enclosures are
normally constructed, e.g. medium density fibreboard or
plastics. Alternatively, at least the duct may be made
at a flexible material, provided that is suitably dense
as to be substantially non resonant in the frequency
range of its intended use . Thus the duct may be in the
form of a flexible pipe, e.g. of high density
polyethylene or the like.
The duct and horn sections are subdivided into wave
guides 11 by dividers 12 extending along the duct and
horn sections.
Figure 3 shows an embodiment of a loudspeaker very
similar to that of Figures 1 and 2. In this case,
however, the inner or closed end 7 of the duct 6 is
formed as a curved, e.g. parabolic, reflector to reflect
CA 02349856 2001-05-04
WO 00/28780 PCT/GB99/03613
9
acoustic radiation from the panel 2 towards the open end
of the duct. Also in this embodiment, the plane of the
panel 2 is set at right angles to the direction of the
duct whereas in Figures 1 and 2 the plane of the panel is
5 disposed in the direction of the duct. Furthermore in
this embodiment the horn section is outwardly flared or
curved, whereas in the embodiment of Figures 1 and 2, the
horn section is conical.
Figure 4 shows a loudspeaker arrangement generally
as shown in Figures 1 and 2 above and in which a housing
5 defining a parallel sided duct 6 has an open end 8
which terminates the duct, and a closed end 7. The
housing supports a resonant bending-wave panel 2 on a
resilient suspension 4 so that acoustic radiation from
15 one face 17 of the panel facing into the housing 5 is
directed along the duct to a remote location wherein the
sound radiation is emitted from the open end of the duct.
The loudspeaker shown in Figure 5 is the same as
that shown in Figure 4 except that the duct is terminated
by a horn 9.
The loudspeaker of Figure 6 is similar to that of
Figure 5, but in this case the acoustic radiation from
the side 15 of the panel facing away from the duct is
contained within a cavity 14 defined by an enclosure 13
25 fixed to our integral with the housing 5 fixed to our
integral with the having 5 to prevent radiation from the
side 15 of the panel 2 from reaching the ambient
surroundings.
CA 02349856 2001-05-04
- WO OOIZ8780 PCT/GB99/03613
The loudspeaker of Figure 7 is similar to that of
Figure 4 and in this case the housing 5 defines an
opposed pair of parallel sided ducts 6, one being
associated with each face or side 15 of the panel 2, the
5 ducts extending in opposite directions towards their open
ends 8.
Figure 8 is a modification of the loudspeaker of
Figure 7 and in which the two ducts 6 each associated
with one face of the panel 2 extend in the same direction
10 and in spaced relation.
Figure 9 shows that the termination 8 of a duct 6 of
a loudspeaker as described above may be modified by
placing an acoustic reflector 16 adjacent to the duct
termination to focus and direct the sound in the
direction shown by the arrows. Thus the reflector is in
the form of a parabolic reflector.
INDUSTRIAL APPLICABILITY
The present invention thus provides a simple
loudspeaker mechanism for ducting sound to remote
location.
