FIELD OF THE INVENTION
[0001] This invention relates to acoustic devices of the type that use members that support
bending wave action over the surface of the member, the bending waves in turn coupling
to the ambient. Such devices may be used, for example, as loudspeakers or microphones.
BACKGROUND TO THE INVENTION
[0002] The International patent application WO97/09842 and related applications describe
speakers and other acoustic devices having an acoustic member and a transducer coupled
to the acoustic member. In these devices, the various parameters of the member may
be adjusted so that resonant bending wave modes in the member are distributed evenly
in frequency. The resonant bending wave modes may also be distributed over the surface
of the member. Preferential locations for mounting the transducer on the member are
also disclosed. A typical preferential mounting location is at a near-centre location,
but not at the centre. However, other preferential locations may also be available
depending on the shape of member.
[0003] US-A-4,989,254 describes an electro-acoustic transducer having a spherically shaped
diaphragm for the generation of sound in an omni-directional capacity.
[0004] It is not always easy to provide sufficient modal density, especially at lower frequencies.
Accordingly, it would be advantageous if improved modal density or other enhancement
could be provided, especially to the lower or mid frequency response.
SUMMARY OF THE INVENTION
[0005] According to a first aspect of the invention, there is provided an acoustic device,
comprising a substantially continuous outer shell bent to at least partially enclose
an air volume and a transducer coupled to the shell, characterised in that said shell
supports evenly distributed bending wave modes, wherein said bending waves couple
to the air volume to provide coupled resonant modes, thereby coupling an electrical
signal in the transducer with the coupled modes and hence in turn to ambient sound.
[0006] In the device according to the invention, in addition to the resonant bending wave
modes available in conventional distributed mode devices, additional modes are present.
Calculations will be presented later showing the increased number of modes with air
coupled to the outer shell. Accordingly, the device according to the invention may
increase the number of modes present in a predetermined frequency range.
[0007] Preferably, the coupled resonant modes are evenly distributed in frequency over a
predetermined frequency range. Usefully, this frequency range is around 1 to 2 or
3 octaves above the fundamental resonant frequency. It is in this range that the resonant
bending wave modes are most sparse and in which distributing the bending and in-plane
modes gives the greatest benefit.
[0008] The outer shell may be fully closed to totally surround the volume. Alternatively,
ports or vents may be provided in the outer shell. The ports or vents may be designed
to provide specific resonance effects, and in particular enhance or control the output
in the lower acoustic frequency range.
[0009] Although it is not necessary that the outer shell fully surrounds the enclosed volume
the outer shell must be substantially continuous so that it may demonstrate effective
acoustic action. In other words, the outer shell must not have too many perforations
or windows. Highly perforate members may not be suitable as acoustic radiators, since
radiation from the front of the member will destructively interfere with radiation
from the rear that is emitted in antiphase to radiation from the front. Moreover,
the shell should be sufficiently continuous for coupling of the shell to the enclosed
volume to be significant.
[0010] Tests on panels have shown very low coupling of perforate members with ambient air.
Accordingly, the outer shell may define holes in its surface of total area no greater
than 20% of the surface area, preferably no greater than 10% and further preferably
no greater than 5%.
[0011] Air inside the volume may also exhibit cavity resonances.
[0012] The acoustic device according to the invention supports resonant bending wave modes
over the surface of a three-dimensional shell and coupling to a volume at least partially
enclosed by the shell. In contrast, conventional distributed mode loudspeakers have
resonant bending wave modes distributed over a single panel.
[0013] In the aforementioned WO97/09842 it is suggested to mount a distributed mode panel
to the front of a frame. In such prior art devices any resonant bending wave modes
are substantially restricted to the panel area, not the frame. Accordingly, such devices
do not provide the improved modal density and hence acoustic performance offered by
devices according to the invention.
[0014] Another prior publication, WO 98/31188, describes a flat panel mounted in a tray.
The tray is highly perforate, with more window area than solid area, and accordingly
not substantially continuous. The tray will therefore not couple effectively to the
ambient nor to the air within the tray.
[0015] The outer shell may be of constant thickness. Alternatively, the thickness of the
outer shell may be varied, either slowly or continuously or more rapidly.
[0016] Ribs or other extensions may be provided on the outer shell.
[0017] The shell may be a single integral shell. Alternatively, the outer shell may comprise
a combination of members mechanically coupled to create the desired acoustical radiator
structure. The boundary condition at the joins between the members may usefully be
specified.
[0018] The outer shell may be in the form of a polyhedron or part thereof having a plurality
of individual faces.
[0019] Each face may have a natural resonant frequency and the natural resonance frequencies
may be selected to have different values. This can increase the modal density of the
outer shell as a whole. Further, the different natural resonant frequencies may be
selected so that the resonant modes on different faces are at interleaved frequencies.
This approach may be particularly useful to increase the modal density for the lower
10 to 20 resonant modes.
[0020] The individual faces or separate panel members need not have uniform mechanical properties
and they may vary in stiffness, isotropy of stiffness, damping, or thickness.
[0021] The acoustic device may be a loudspeaker, the transducer being an exciter.
[0022] The acoustic device may comprise front and rear faces in the form of panels together
with at least one further panel providing a path for resonant modes from front to
rear and so coupling the front and rear panels. The front and rear panels may be substantially
planar. The front and rear panels may be driven by separate discrete exciters, or
a single exciter may be coupled to both the front and the rear panel.
[0023] In embodiments, the voice coil of an exciter may be coupled to one of the panels
and the magnet assembly of the exciter to the other of the panels. Since the magnet
assembly is heavy, the coupling of it to the panel will result in high frequency roll-off.
This may enhance the bass response of the acoustic device. A plurality of exciters
may be provided. The exciters may be driven in-phase, out of phase or in any suitable
phase relationship to one another.
[0024] In a conventional flat panel loudspeaker any in-plane compression waves produce little
or no acoustic output. This is because in-plane compression and expansion of a flat
panel does not couple to ambient air. In contrast, in a device according to the invention
the outer shell is bent, so in-plane compression and expansion causes shrinking and
expansion of the shell, locally or globally, which acts as a mechanism to couple the
compression waves to the enclosed volume and to the ambient. Accordingly, in-plane
compression waves may usefully contribute to the coupled modes. In fact, the resonant
modes may in some embodiments couple bending waves, in-plane modes and the enclosed
volume. The modal density may accordingly be improved.
[0025] According to a second aspect of the invention, there is a provided an acoustic device,
comprising a substantially continuous shell enclosing a volume, supporting a plurality
of resonant modes coupling the shell and the enclosed volume, the resonant modes spanning
the shell, and a transducer coupled to the shell for coupling an electrical signal
in the transducer with the resonant modes and hence in turn to ambient sound.
[0026] In the device according to the second aspect of the invention, the resonant modes
span the surface, from front to back, side to side and top to bottom. This allows
good coupling of the modes over the whole surface with the enclosed volume. It is
not necessary that the modes cover the whole surface; the shell may for example have
ports or areas that do not resonate.
[0027] According to a further aspect of the invention there is provided a method of driving
an acoustic device comprising a substantially continuous outer shell supporting bending
waves, the shell being bent to at least partially enclose an air volume so that the
bending waves couple to the volume to provide coupled resonant modes, and two transducers
coupled to the shell, including driving the two transducers in phase with a common
electrical signal, so that the transducers drive the coupled modes of the shell and
volume in a monopole configuration, and radiating sound energy from the coupled modes
into the ambient air.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Specific embodiments of the invention will now be described, purely by way of example,
with reference to the accompanying drawings in which:-
Figure 1 shows sections through a loudspeaker according to a first embodiment of the
invention having an ellipsoidal shell;
Figure 2 shows a section through a loudspeaker according to a second embodiment;
Figure 3 shows a section through a loudspeaker according to a third embodiment having
a port;
Figure 4 shows a section through a modification of the port;
Figure 5 shows a view of a loudspeaker according a fourth embodiment to the invention
in the form of an open box;
Figure 6 shows a view of a fifth embodiment of the invention having a closed box;
Figure 7 illustrates various excitation techniques that can be used with the loudspeaker
shown in Figure 6;
Figure 8 illustrates the response to excitation in an open box without air;
Figure 9 illustrates the response to excitation in the open box shown in Figure 8,
including the effects of air coupling;
Figure 10A shows the velocity response at the exciter as a function of frequency for
the box modelled in Figure 8, without air;
Figure 10B shows the velocity response at the exciter as a function of frequency for
the box modelled in Figure 9, including the effects of air;
Figure 11 shows the pressure inside the box of Figure 9B
Figure 12 shows the modes in a loudspeaker having a closed box with two exciters driven
in antiphase;
Figure 13 shows the modes in the loudspeaker modelled in Figure 12 with two exciters
driven in phase;
Figure 14 shows the velocity response of the device modelled for Figures 12 and 13;
Figure 15 shows the velocity response of a six sided closed box in which the bending
stiffness of the front face does not match that of the rear face;
Figure 16 shows views of a loudspeaker according to the invention in the form of a
truncated pyramid;
Figure 17 shows a view of a loudspeaker according to the invention in the form of
a tetrahedron;
Figure 18 shows a view of a loudspeaker according to the invention in the form of
a dodecahedron;
Figure 19 shows a view of a loudspeaker according to the invention in the form of
a cylinder;
Figure 20 shows a view of a loudspeaker according to the invention in the form of
a cone section;
Figure 21 shows the root mean square (rms) central difference of mode frequency as
a function of aspect ratio of the front face of the device of Figure 5,
Figure 22 shows velocity profiles for three exciter positions of the device of Figure
5 having a front face aspect ratio of 2:1; and
Figure 23 shows a figure of merit for exciter location as a function of exciter position
on the device used in the model for Figure 22.
DETAILED DESCRIPTION
[0029] Referring to Figure 1, a closed ellipsoid shell (1) encloses a volume (2) and has
transducers (3), (5) mounted on the interior of the shell at opposed positions on
the minor axis of the ellipsoid. The shell (1) supports resonant modes formed from
resonant bending wave components coupled to the enclosed volume.
[0030] The transducers couple an electrical signal to the coupled resonant modes of the
shell and the volume. In the present embodiment, the transducers are exciters than
can, in use, be driven to excite coupled modes to produce an acoustic output. The
transducer may be of conventional type in which a voice coil moves relative to a grounded
magnet assembly when electrical current is passed through the voice coil. The transducer
may be inertial, in which case the magnet assembly is free and the force of the voice
coil acts against the inertia of the magnet assembly. Alternatively, a grounded transducer
may be used in which case the magnet assembly is supported. In the present embodiment,
commercially available exciters normally used to drive distributed mode panels are
used in an inertial configuration.
[0031] By driving the transducers in a known polarity it is possible to produce a desired
polar behaviour in emitted sound. For a monopole source, the transducers can be driven
in phase, whereas to produce a dipole the transducers can be driven in antiphase.
Alternatively, the exciters can be driven at any suitable phase relation.
[0032] The invention allows a loudspeaker to be used unbaffled. In a conventional pistonic
or distributed mode loudspeaker using a single diaphragm or panel the sound radiated
from the rear is in antiphase with the sound radiated from the front. Accordingly,
to avoid interference effects the sound radiated from the rear has to be prevented
from reaching the front, by enclosing the diaphragm in a box or providing a baffle
around the loudspeaker. By driving the loudspeaker according to the present invention
as a monopole with two transducers operating in phase it is possible to avoid the
need for such baffles.
[0033] The coupled modes may be made up of two types of shell vibrations coupled to the
enclosed volume. One of these types is bending waves that bend the shell out of the
local plane of the shell. The other type is an expansion or contraction in the plane
of the shell.
[0034] A totally flat plate would not provide such coupled expansion-contraction modes with
the resonant bending wave modes. Although a flat plate can have oscillation modes
of expansion and contraction, these simply move the plate in its own plane and do
not affect the motion of ambient air molecules. Accordingly, such modes in a flat
plate have little or no acoustic effect. In contrast, if the plate is sufficiently
bent back in on itself, or even forms a completely closed body, the in-plane compression
wave modes cause a global expansion and contraction of the body, which can couple
to air and hence have an acoustic effect.
[0035] The actual modes of vibration of the shell need not be pure bending wave modes, nor
pure compression wave modes. Rather, the modes may interfere and couple with one another
to provide coupled modes. These modes may still however retain a predominant bending
wave character. These waves in the shell then couple to the included volume to produce
coupled resonant modes.
[0036] It is not essential that the transducers are mounted on the minor axis. It may be
convenient to mount them off axis, as illustrated in Figure 2, or indeed at any suitable
location. It is preferred to mount the transducers at a position that is selected
for optimum or desired response. The use of a regular geometry, such as an ellipsoid,
makes this easier. Alternatively, approaches such as finite element analysis can be
used to investigate suitable transducer locations. In general, approaches similar
to those used for distributed mode loudspeakers may be suitable; in particular asymmetric
transducer locations may prove suitable. An example of this will be discussed later
with reference to Figures 21 to 23.
[0037] A single transducer may be sufficient for some applications; others may require several
transducers spaced over the shell. The placement of transducers may influence the
directivity of coupling of the outer shell to the ambient.
[0038] The provision of an enclosed volume allows the use of ports to control the resonance
inside the volume. Figure 3 illustrates a port (7) in the form of a simple hole in
one end of the ellipsoid. Alternatively, a ducted port (9) may be provided as illustrated
in Figure 4.
[0039] The port may result in effects analogous to effects that such ports produce in conventional
pistonic-type loudspeakers, or pipes. The ports may have an asymmetric cross-section.
[0040] As indicated above, it is not necessary that the volume is wholly enclosed by the
shell. Rather, all that is required is that the shell is sufficiently bent back on
itself that resonant modes in the shell couple to the air in the enclosed volume so
as to produce an acoustic effect. Figure 5 illustrates an open box comprising a large
front face (11) surrounded by a frame (13) comprising four side faces (15) at right
angles to the front face (11). A single transducer (3) is provided, connected to an
amplifier via audio connections (9). The side faces (15) are all acoustically coupled
to the front face (11). Resonant bending wave modes in the front face (11) do not
simply remain in the front face but couple round to the side faces (15).
[0041] A box can also be implemented in the form of a sealed enclosure (Figure 6), with
front and rear faces (11), (17) and four side faces (13) joining the front (11) to
the rear (17) face to form a sealed enclosure containing a volume. Two transducers
(3), (5) are provided, one on each face (11), (17).
[0042] Also shown in Figure 6 is an electrical circuit (19) that can switch between inverting
and non-inverting drive of the two transducers. A double pole double throw switch
(21) switches between a parallel drive of the transducers and an anti-parallel drive.
[0043] The transducers or front and rear faces can be uncoupled, as shown in Figure 7A.
Alternatively, the magnet assemblies of two conventional moving coil transducers can
be coupled together as shown in Figure 7B. As a further alternative, a single transducer
can have its voice coils connected to the front face (11) and the magnet assembly
connected to the rear face, (17). The magnet assembly is much heavier than the voice
coil, and so this assembly will preferentially couple low frequencies to the rear
face. Accordingly, this arrangement can be used to increase the bass response of a
loudspeaker. Front and rear faces may be reversed.
[0044] Finite element calculation of the response of an acoustic device has been performed
for a five-sided device similar to that shown in Figure 5. For convenience, this configuration
will be referred to as an open box. Figure 8 shows the behaviour of the box in response
to excitation, in the absence of air, at 178Hz (Figure 8A), at 348Hz (Figure 8B) and
at 1000Hz (Figure 8C). Figure 9 shows the behaviour in the presence of air at the
same frequencies, i.e. at 178Hz (Figure 9A), at 348Hz (Figure 9B) and at 1000Hz (Figure
9C). As can be seen, the responses are not restricted to any one of the planar surfaces,
but instead couple over the whole of the five surfaces of the box. Moreover, the presence
of air beneficially adds to the complexity of the shapes.
[0045] The velocity response at the transducer as a function of frequency is shown in Figure
10: Figure 10A shows the results without air and Figure 10B shows the results with
air. A large value indicates a high velocity achieved by excitation at that frequency.
Particularly large velocities occur at resonance. As can be seen, the response with
no air shows a smaller number of larger peaks. This is characteristic of a smaller
number of resonant modes. The response when there is air enclosed shows a larger number
of peaks, each of which is smaller. This is characteristic of a larger number of weaker
modes. As can be seen, the coupling of the modes in the panel to the enclosed volume
increases the number of resonant modes and so improves the acoustic device. What is
surprising is that this effect is so marked even in an open box.
[0046] The air pressure inside the box at 348 Hz is shown in Figure 11. The asymmetric air
pressure pattern can clearly be seen. It is this air pressure distribution that causes
the complex mode shapes of the air coupled resonant modes.
[0047] Similar calculations have been carried out for an acoustic device similar to that
shown in Figure 6, i.e. a closed six-sided box having a front, a rear and four side
faces. Some of these results are shown in Figure 12 and 13. All the calculations include
air. Again, the coupled modes couple over all of the surfaces of the box, front and
back, left and right sides together with the top and bottom.
[0048] Figure 12A illustrates the mode at 178 Hz caused by driving the closed box with the
velocity in phase. Since the front and rear faces face the opposite directions, this
is achieved with the transducer on the front panel moves the panel outwards when the
transducer on the rear panel moves the panel inwards. This may be achieved by electrically
connecting the transducers out of phase, for example using the switch shown in Figure
6. Figure 12B shows the oscillation at 1000Hz.
[0049] Figures 13A and 13B show the same frequency modes with the box acting as a monopole
with the front and rear panel moving in antiphase, i.e. with the electrical connections
to the transducers in phase. As can be seen, a complex response is again obtained.
[0050] Figures 12C and 13C shows the air pressure inside the box driven at 1000Hz as a dipole
and a monopole respectively, corresponding to the response of the box shown in Figures
12B and 13B. Figure 12C clearly shows an asymmetric response, even though the drive
and the box are symmetric. Figure 13C shows the very different pressure response just
caused by driving the same box in a different way.
[0051] Some of the transducer velocity against frequency graphs obtained with the closed
box are presented in Figure 14. Figure 14A and 14B show that the response on the front
and rear faces (driven as a monopole) of a symmetrical closed box match, as might
have been expected. Figure 14C shows the significantly less even, and hence worse,
results obtained for a dipole drive of the same box.
[0052] Of course, all the above results are just calculations but they do show improvement
possible using a shell bent back on itself to enclose a volume.
[0053] Figure 15 shows the velocity response graph for a box in which the front face has
a different stiffness from the rear, driven by two transducers one on the front (shown
in Figure 15A) and one on the rear face (Figure 15B). As can be seen, the response
of the front face is beneficially different from that of the rear face. Accordingly,
the use of asymmetry can beneficially increase the modal density in frequency.
[0054] It should be noted that there is a difference between devices such as that illustrated
in Figure 5 with a plurality of faces, and devices such as that of Figure 1 in the
form of a continuous curve. The joins (23) between the faces act as hinges and so
resonant bending wave modes do not simply travel from one facet to the next. Rather,
a more complex coupling of the modes occurs.
[0055] Other multi-faced structures are also possible. Figures 16 to 20 illustrate various
such forms, namely a truncated square pyramid, a tetrahedron, a dodecahedron, a cylinder
and a cone section. Each of these forms may be open or closed; for example the cylinder
may be either with or without end faces, and the cone section may have a rear face,
or not. The individual faces may be formed separately, and then joined, or groups
of faces or even the whole structure may be integrally formed.
[0056] As discussed in WO97/09842, good aspect ratios for an isotropic rectangular panel
are 0.707:1 and 0.882 to 1. It is also possible to optimise acoustic devices according
to the invention to maximise the distribution of resonant modes in frequency by adjusting
the properties of the shell and to provide a good even coupling of a transducer to
the modes by correctly locating the transducer on the panel.
[0057] This may be done using the techniques discussed in various distributed mode patent
applications. In particular, the use of an orderly approach to finding optimum aspect
ratios and transducer locations to provide results that are as good as possible has
been described in WO99/41939, published 19 August 1999, in the names of New Transducers
Ltd, etc.
[0058] In order to find suitable properties for an open box, the first step that was carried
out was to model the variation of the aspect ratio of the central panel in the open
box of Figure 5. The aspect ratio was varied from 1 to 2.25, and the corresponding
frequencies of the modes were calculated by finite element analysis. The root mean
square central difference of mode frequencies plotted against aspect ratio (see Figure
21). The central difference of mode frequency is, for the nth mode, the frequency
of the (n+1)th mode plus that of the (n-1)th mode, minus twice the frequency of the
nth mode. If the modes were equally spaced, this measure would equal zero. Accordingly,
the root mean square (rms) central difference provides a Figure of merit for various
aspect ratios. The smaller the rms central difference the better.
[0059] From Figure 21 it may be seen that good results are obtained for aspect ratios between
1.6 and 2.2, with especially good results between 1.95 and 2.05. An aspect ratio of
2 was taken as a convenient value for further study.
[0060] The next stage is to find the optimised drive point on the face. The velocity response
as a function of frequency is calculated for several drive point positions. Figure
22 gives three examples, at the centre (22A), at the standard drive point for a flat
distributed mode panel (22B), and at an optimum drive point (22C). The standard deviation
for graphs such as these is plotted as a function of position on Figure 23. The best
results are those with the smallest deviation, shown in black. Note that the edges
of the panel are not shown - these are poor drive points.
[0061] As can be seen by inspecting the Figure the optimum drive point occurs in four regions,
located around 30% of the distance along the long side and 30% of the distance along
the short side, together with three other regions found by reflecting the first region
about the central symmetry axis, to locations around 70% along the long axis and 30%
along the short axis, 30% and 70% along the respective axes, and 70% and 70% along
the respective axes. These positions are different from the optimum drive point for
a simple rectangle, which occurs near centrally at coordinates around (3/7,4/9) expressed
as a ratio of the distance along the sides.
[0062] The positions are quite tolerant to variation and good results are obtained at positions
from 14% to 42% along the long side and from 22% to 34% along the short side, together
with reflections of these values.
[0063] Although the above calculations are carried out without the influence of air being
taken into account, they provide good indications of suitable aspect ratios and transducer
locations even for a real device. Of course, features such as air coupling or slight
anisotropy of the faces may move the optimum aspect ratios and drive positions slightly.
[0064] The embodiments described above relate to loudspeakers, i.e. devices that convert
electrical energy into sound. The methods of the present invention are equally applicable
to microphones, in which incident sound energy is converted by a transducer to electrical
energy.
1. An acoustic device, comprising a substantially continuous outer shell (1) bent to
at least partially enclose an air volume (2) and a transducer (3) coupled to the shell
(1), characterised in that said shell (1) supports evenly distributed bending wave modes, wherein said bending
waves couple to the air volume (2) to provide coupled resonant modes, thereby coupling
an electrical signal in the transducer (3) with the coupled modes and hence in turn
to ambient sound.
2. An acoustic device according to claim 1, wherein the resonant modes span the shell
(1).
3. An acoustic device according to any preceding claim, wherein the transducer (3) is
an exciter for exciting resonant modes so that the acoustic device functions as a
loudspeaker.
4. An acoustic device according to any preceding claims having a port (7,9) in the outer
shell.
5. An acoustic device according to claim 4, wherein the port (9) includes a duct extending
into the volume (2) from the outer shell (1).
6. An acoustic device according to any preceding claim, wherein the outer shell (1) comprises
a plurality of faces (11,13,15,17).
7. An acoustic device according to claim 6, wherein each face (11,13,15,17) has a natural
resonant frequency and the natural resonance frequencies have different values.
8. An acoustic device according to claim 7, wherein the different natural resonant frequencies
are selected so that the ten to twenty lowest frequency resonant modes are at interleaved
frequencies.
9. An acoustic device according to claim 6, wherein the outer shell (1) includes a front
face (11) and the front face (11) has an aspect ratio from 1.6 to 2.2.
10. An acoustic device according to claim 6 or claim 9, wherein the outer shell (1) includes
a rectangular front face (11) and the transducer (3) contacts the front face (11)
at a location at between 14% to 42% from one edge along the long side and a distance
of between 22% and 34% from one edge along the short side.
11. An acoustic device according to any of claims 6, 9 or 10, wherein the outer shell
(1) includes opposed front (11) and rear faces (17).
12. An acoustic device according to claim 11, wherein a first transducer (3) is provided
on the front face (11), and a second transducer (5) on the rear face (17).
13. An acoustic device according to claim 12, wherein the first and second transducers
(3,5) are mechanically coupled.
14. An acoustic device according to claim 11, wherein a single transducer (3) is coupled
to both front and rear faces (11,17).
15. An acoustic device according to claim 6, wherein the outer shell (1) has truncated
square pyramid form.
16. An acoustic device according to claim 6, wherein the outer shell (1) has tetrahedral
form.
17. A method of driving an acoustic device comprising providing a substantially continuous
outer shell (1) which is bent to at least partially enclose an air volume (2), and
two transducers (3,5) coupled to the shell, characterised by the shell (1) supporting bending waves which couple to the volume to provide coupled
resonant modes and driving the two transducers (3,5) in phase with a common electrical
signal, so that the transducers (3,5) drive the coupled modes of the shell (1) and
volume (2) in a monopole configuration, and radiating sound energy from the coupled
modes into the ambient air.
1. Akustische Einrichtung mit einer im wesentlichen durchgehenden äußeren Schale (1),
die gebogen ist, um ein Luftvolumen (2) zumindest teilweise zu umschließen, und einem
an die Schale (1) gekoppelten Wandler (3), dadurch gekennzeichnet, dass die Schale (1) gleichmäßig verteilte Biegewellenmoden unterstützt, wobei die Biegewellen
zur Bereitstellung gekoppelter Resonanzmoden an das Luftvolumen (2) ankoppeln und
dadurch ein elektrisches Signal in dem Wandler (3) mit den gekoppelten Moden und folglich
des weiteren mit den Umgebungsgeräuschen koppeln.
2. Akustische Einrichtung nach Anspruch 1, bei der die Resonanzmoden die Schale (1) überspannen.
3. Akustische Einrichtung nach einem der vorhergehenden Ansprüche, bei der der Wandler
(3) ein Erreger zur Erregung von Resonanzmoden ist, so dass die akustische Einrichtung
als Lautsprecher wirkt.
4. Akustische Einrichtung nach einem der vorhergehenden Ansprüche mit einer Öffnung (7,
9) in der äußeren Schale.
5. Akustische Einrichtung nach Anspruch 4, bei der die Öffnung (9) einen Kanal umfasst,
der sich von der äußeren Schale (1) in das Volumen (2) erstreckt.
6. Akustische Einrichtung nach einem der vorhergehenden Ansprüche, bei der die äußere
Schale (1) eine Mehrzahl von Flächen (11, 13, 15, 17) umfasst.
7. Akustische Einrichtung nach Anspruch 6, bei der jede Fläche (11, 13, 15, 17) eine
natürliche Resonanzfrequenz aufweist und die natürlichen Resonanzfrequenzen unterschiedliche
Werte haben.
8. Akustische Einrichtung nach Anspruch 7, bei der die unterschiedlichen natürlichen
Resonanzfrequenzen so ausgewählt sind, dass die zehn bis zwanzig niedrigsten Frequenzresonanzmoden
bei verwobenen Frequenzen liegen.
9. Akustische Einrichtung nach Anspruch 6, bei der die äußere Schale (1) eine vordere
Fläche (11) umfasst und die vordere Fläche (11) ein Seitenverhältnis von 1,6 bis 2,2
aufweist.
10. Akustische Einrichtung nach Anspruch 6 oder Anspruch 9, bei der die äußere Schale
(1) eine rechteckige vordere Fläche (11) umfasst und der Wandler (3) die vordere Fläche
(11) an einer Position berührt, die sich zwischen 14% bis 42% von einem Rand entlang
der langen Seite und in einem Abstand von zwischen 22% und 34% von einem Rand entlang
der kurzen Seite befindet.
11. Akustische Einrichtung nach einem der Ansprüche 6, 9 oder 10, bei der die äußere Schale
(1) einander gegenüberliegende vordere (11) und hintere Flächen (17) umfasst.
12. Akustische Einrichtung nach Anspruch 11, bei der ein erster Wandler (3) auf der vorderen
Fläche (11) und ein zweiter Wandler (5) auf der hinteren Fläche (17) vorhanden ist.
13. Akustische Einrichtung nach Anspruch 12, bei der die ersten und zweiten Wandler (3,
5) mechanisch gekoppelt sind.
14. Akustische Einrichtung nach Anspruch 11, bei der ein einziger Wandler (3) mit sowohl
der vorderen als auch der hinteren Fläche (11, 17) gekoppelt ist.
15. Akustische Einrichtung nach Anspruch 6, bei der die äußere Schale (1) eine kegelstumpfförmige,
quadratische Pyramidengestalt aufweist.
16. Akustische Einrichtung nach Anspruch 6, bei der die äußere Schale (1) eine Tetraederform
aufweist.
17. Verfahren zum Antreiben einer akustischen Einrichtung mit den Schritten Bereitstellen
einer im Wesentlichen kontinuierlichen äußeren Schale (1), die gebogen ist, um ein
Luftvolumen (2) zumindest teilweise einzuschließen, und zweier an die Schale gekoppelten
Wandlern (3, 5), dadurch gekennzeichnet, dass die Schale (1) Biegewellen unterstützt, die an das Volumen ankoppeln, um gekoppelte
Resonanzmoden bereitzustellen und die zwei Wandler (3, 5) phasengleich mit einem gemeinsamen
elektrischen Signal anzutreiben, so dass die Wandler (3, 5) die gekoppelten Moden
der Schale (1) und des Volumens (2) in einer Monopolkonfiguration antreiben und Schallenergie
von den gekoppelten Moden in die Umgebungsluft abstrahlen. 1727
1. Un dispositif acoustique, comprenant une coque extérieure (1) pratiquement continue,
courbée de façon à enfermer au moins partiellement un volume d'air (2) et un transducteur
(3) couplé à la coque (1), caractérisé en ce que la coque (1) supporte des modes d'ondes de flexion uniformément répartis, ces ondes
de flexion étant couplées au volume d'air (2) pour procurer des modes résonnants couplés,
pour coupler ainsi un signal électrique dans le transducteur (3) aux modes couplés
et donc ensuite au son ambiant.
2. Un dispositif acoustique selon la revendication 1, dans lequel les modes résonnants
s'étendent sur toute la coque (1).
3. Un dispositif acoustique selon l'une quelconque des revendications précédentes, dans
lequel le transducteur (3) est un excitateur pour exciter des modes résonnants de
façon que le dispositif acoustique fonctionne comme un haut-parleur.
4. Un dispositif acoustique selon l'une quelconque des revendications précédentes, ayant
un orifice (7, 9) dans la coque extérieure.
5. Un dispositif acoustique selon la revendication 4, dans lequel l'orifice (9) comprend
un conduit s'étendant à l'intérieur du volume (2) à partir de la coque extérieure
(1).
6. Un dispositif acoustique selon l'une quelconque des revendications précédentes, dans
lequel la coque extérieure (1) comprend une multiplicité de faces (11, 13, 15, 17).
7. Un dispositif acoustique selon la revendication 6, dans lequel chaque face (11, 13,
15, 17) a une fréquence de résonance naturelle, et les fréquences de résonance naturelle
ont des valeurs différentes.
8. Un dispositif acoustique selon la revendication 7, dans lequel les fréquences de résonance
naturelle différentes sont sélectionnées de façon que les dix à vingt modes résonnants
ayant les fréquences les plus basses se trouvent à des fréquences entrelacées.
9. Un dispositif acoustique selon la revendication 6, dans lequel la coque extérieure
(1) comprend une face avant (11) et la face avant (11) a un rapport de forme de 1,6
à 2,2.
10. Un dispositif acoustique selon la revendication 6 ou la revendication 9, dans lequel
la coque extérieure (1) comprend une face avant rectangulaire (11) et le transducteur
(3) vient en contact avec la face avant (11) à un emplacement se trouvant à une distance
comprise entre 14% et 42% à partir d'un bord le long du côté long, et à une distance
comprise entre 22% et 34% à partir d'un bord le long du côté court.
11. Un dispositif acoustique selon l'une quelconque des revendications 6, 9 ou 10, dans
lequel la coque extérieure (1) comprend des faces avant (11) et arrière (17) opposées.
12. Un dispositif acoustique selon la revendication 11, dans lequel un premier transducteur
(3) est placé sur la face avant (11), et un second transducteur (5) est placé sur
la face arrière (17).
13. Un dispositif acoustique selon la revendication 12, dans lequel les premier et second
transducteurs (3, 5) sont couplés mécaniquement.
14. Un dispositif acoustique selon la revendication 11, dans lequel un seul transducteur
(3) est couplé à la fois aux faces avant et arrière (11, 17).
15. Un dispositif acoustique selon la revendication 6, dans lequel la coque extérieure
(1) a une forme de pyramide carrée tronquée.
16. Un dispositif acoustique selon la revendication 6, dans lequel la coque extérieure
(1) a une forme tétraédrique.
17. Un procédé d'excitation d'un dispositif acoustique dans lequel on fournit une coque
extérieure (1) pratiquement continue qui est courbée de façon à enfermer au moins
partiellement un volume d'air (2), et deux transducteurs (3, 5) couplés à la coque,
caractéristique par le fait que la coque (1) supporte des ondes de flexion qui sont
couplées vers le volume pour produire des modes résonnants couplés, et on excite les
deux transducteurs (3, 5) en phase avec un signal électrique commun, de façon que
les transducteurs (3, 5) excitent les modes couplés de la coque (1) et du volume (2)
en une configuration monopôle, et de l'énergie sonore soit rayonnée dans l'air ambiant
à partir des modes couplés.