Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Driven diverse static structure
Reexamination Certificate
2002-04-05
2004-11-02
Le, Huyen (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Driven diverse static structure
C381S423000, C381S186000
Reexamination Certificate
active
06813362
ABSTRACT:
BACKGROUND
1. Technical Field
The invention relates to loudspeakers, and more particularly to resonant bending wave speakers of the general kind described in U.S. Pat. No. 6,332,029 (incorporated by reference herein in its entirety). This patent describes a new class of speaker known as a distributed mode loudspeaker (DML).
2. Background Art
It is known from International Application WO97/09846 to provide a loudspeaker comprising two separately driven panels. The first panel is small and designed to operate at higher frequencies than the large second panel in which it is suspended. The frequency ranges of each panel may overlap in the mid-range and a cross-over network may be added to control output in any overlapping frequency range.
It is known from International Application WO98/52381 to have a loudspeaker comprising a larger low frequency panel and a smaller higher frequency panel which are both excited by a common driver. The smaller and larger panels may be attached together by a material forming a controlling compliant coupling whereby differentiation of the high and lower frequency parts of the loudspeaker is achieved.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a loudspeaker comprising an assembly of at least two bending wave panel-form acoustic members each having a set of modes which are distributed in frequency, the parameters of at least two of the acoustic members being selected so that the modal distributions of each acoustic member are substantially different and the arrangement being such that the modal distributions of the assembly of acoustic members are interleaved constructively in frequency. The loudspeaker further includes a transducer to apply bending wave energy to the acoustic members to cause them to resonate to produce an acoustic output.
By constructively interleaving the modal distributions of the acoustic members, the overall modal distribution of the loudspeaker is more dense, i.e. has more modes in a given frequency range, than the modal distribution of any individual acoustic member. Thus in contrast to the prior art, the acoustic members are designed to cover substantially overlapping or substantially the same frequency ranges rather than different frequency ranges which may have some overlap in the mid-range (i.e. around 1 to 2 kHz).
In particular the modal distributions may be constructively interleaved whereby the modes in the overall modal distribution of the assembly are more evenly distributed in frequency than the modes of any individual acoustic member. Thus, any “bunching” or clustering of the modes which may be present in an individual acoustic member may be significantly reduced in the overall distribution. The modes in the modal distribution of the assembly may be substantially evenly distributed in frequency. In these ways, the overall output of the loudspeaker may be enhanced and a smoother frequency response may be achieved.
The acoustic members may have different areas and or shapes so that each acoustic member has a different modal distribution as required. Alternatively, different modal distributions may be achieved by using acoustic members which differ in their mechanical parameters, i.e. parameters such as bending stiffness, damping, mass per unit area or Young's modulus etc.
At least two of the acoustic members may be coupled together by a coupling such that bending wave energy is transmissible between the acoustic members. Thus, the acoustic members may be both mechanically and acoustically coupled by the coupling. In this way, a transducer need only be attached to one face and adjacent faces may be driven by bending wave energy which is transmitted across the coupling. Complex interactions between acoustic members in the assembly, both mechanical and acoustic, may thus be encouraged to increase the excitation of the available modes in each member, particularly if some of the acoustic members are not actively excited.
The assembly of acoustic members may comprise a single piece of stiff lightweight sheet material which should greatly simplify manufacture and assembly. Alternatively, the assembly may comprise a plurality of discrete acoustic members made from stiff lightweight sheet material. A stiff material is one which is self-supporting. The coupling may be sufficiently flexible to allow flat-packing of the assembly. The coupling may be continuous or discontinuous.
For an assembly formed from a single sheet, the coupling may be formed by at least one fold or a parallel pair of folds in the sheet material. A double fold may provide extra compliance and more decoupling between faces. Each fold may be formed by grooving the sheet material and the grooving may comprise local compression of the sheet material.
For an assembly made of discrete members, the coupling may comprise coupling members. The coupling members may comprise hinge portions whereby the acoustic members are moveable relative to one another.
The assembly of acoustic members may form a three-dimensional or box-form loudspeaker which defines a volume, may be of any suitable geometrical shape, e.g. tetrahedron and may be open or closed with different orientations of members. The assembly may comprise a front face and side faces and may be arranged to define a rear opening for example between an opposed pair of rear faces. At least one or two of the acoustic members may be substantially triangular. The assembly may form a truncated pyramid and the plane of the truncation may be angled, for example at 20°, with respect to the plane of the base of the pyramid.
Alternatively, the acoustic members may be arranged to lie substantially in the same plane. The acoustic members may be in the form of panels which may be flat or curved in one or more planes. For curved panels, the panels may be arranged on the same surface of a volume of rotation.
Each acoustic member may act as a baffle for an adjacent acoustic member. The baffling effect may be improved by partially or completely filling the volume defined by the assembly, e.g. with foam or other known acoustic treatments.
The transducer may comprise an inertial or grounded vibration transducer which may be a moving coil inertial exciter comprising a magnet assembly and a voice coil assembly, a piezoelectric transducer, a magnetostrictive transducer, a bender or torsional transducer (e.g. of the type taught in U.S. patent application Ser. No. 09/384,419 (filed on Aug. 27, 1999)) or a distributed mode transducer (e.g. of the type taught in U.S. patent application Ser. No. 09/768,002 (filed on Jan. 24, 2001)) (each of which is incorporated by reference herein in their entirety). Particularly for folding speakers, the transducers are preferably inertial. The transducers may be mounted to the acoustic members for example as taught in U.S. Pat. No. 6,192,136, U.S. patent application Ser. No. 09/341,295 (filed on Jan. 5, 1998) or U.S. patent application Ser. No. 09/437,792 (filed on Nov. 10, 1999) (each of which is incorporated by reference herein in their entirety) The transducers, particularly low frequency transducers, may be designed to have a fundamental suspension resonance below that of the desired low frequency range of the speaker and a filter may be used to prevent bottoming of the transducers below their fundamental resonance.
The transducer may be a moving coil inertial exciter comprising a magnet assembly and a voice coil assembly. If the transducer is mounted on a sloping face, there is uneven weight loading which may lead to unwanted non-axial movement of the magnet assembly. The magnet assembly may thus be supported in a transducer housing mounted to the acoustic member. The housing may be in the form of a plastic spider which decouples the mass of the transducer from the acoustic member. The transducer housing discourages unwanted non-axial movement of the magnet assembly and hence voice coil damage may be alleviated and the transducer excursion may be limited.
The transducers may comprise respective vibration transducers attached to respective acou
Bank Andrew D.
Burton Paul
Harris Neil
Hills Keith D.
MacFarlane Ian D.
Le Huyen
New Transducers Limited
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