Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Driven diverse static structure
Reexamination Certificate
1999-03-30
2003-04-08
Kuntz, Curtis (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Driven diverse static structure
C381S388000, C381S423000
Reexamination Certificate
active
06546106
ABSTRACT:
FIELD OF INVENTION
The invention relates to acoustic devices of the kind comprising a sound radiating member relying on bending wave action and resulting surface vibration to produce acoustic output.
BACKGROUND TO INVENTION
It is known from U.S. Pat. No. 3,247,925 of WARNAKA to suggest a low frequency loudspeaker consisting of an extremely rigid resonant panel, the peripheral edges of which are bolted or cemented to a rigid frame, which frame supports a conventional voice coil transducer which imparts bending wave energy to the centre of the panel. This low frequency loudspeaker device is said to operate entirely above wave coincidence frequency.
It is also known from U.S. Pat. No. 3,596,733 of BERTAGNI to propose a loudspeaker having a diaphragm formed by an expanded polystyrene plate-like member having a pre-tensioned front face and a rear face of or including an irregular shape.
Revelatory teaching concerning bending wave action acoustic devices, conveniently considered as generally of resonant panel type, is given in International Patent Application W097/09842, including as to improvement or optimisation of acoustic performance according to panel parameters including geometry and bending stiffness; particularly including operation usefully at and below coincidence frequency. Geometrical parameters of interest include proportions or aspect ratios of panels as such, including for use as passive acoustic devices. Parameters of bending stiffness(es) can usefully interact with geometric parameters, including anisotropy thereof, say as to different bending stiffnesses of or resolvable to substantial constancy along axes of geometric shapes involved for viable variation of proportions of such shapes. Preferential in-board locations for transducers of active acoustic devices usefully have proportional defining coordinates. Other areal distributions of bending stiffness can usefully contribute to affording other useful locations for transducers, for example substantially at geometric centres and/or at centres of mass, see International Patent Application WO98/00621 including for combining aforesaid bending wave action with further acoustically relevant pistonic action. Acoustic operation is described and claimed in at least W097/09842 for both of whole panels and only parts thereof being acoustically active.
On an intuitive basis, our specific analysis and design methodology to date for such resonant mode bending wave action acoustic devices has been mainly concentrated upon whole panels where edges are wholly or substantially free to vibrate when in acoustically relevant desired bending wave action, including where subject to light edge damping. This invention arises from surprising results of counter-intuitive further consideration, research and experimentation.
SUMMARY OF THE INVENTION
Certain under-lying requirements continue to apply and be of profound technological/inventive significance, specifically for an acoustic device member extending transversely of its thickness and capable of sustaining bending waves through its consequentially acoustically active area, i.e. basic requirement for what is herein called a resonant acoustic member or panel; and for parameters such as geometric and for bending stiffness to be of values consonant with resulting distribution of natural bending wave vibration of said member that is effective in or beneficial to achieving desired or acceptable acoustic operation of the device over a frequency range of interest, i.e. further requirement for a resonant acoustic member or panel hereof. Specific embodiments of this invention additionally provide for means affording substantial restraint of bending wave vibration typically at edge, periphery or other boundary of such member or panel or acoustically active area thereof, and further typically to be at least capable of operating at least partly below coincidence frequency. The wording ‘substantial restraint’ as used herein intentionally involves greater constraining of at least part(s) of edge(s) of the member than specifically disclosed in W097/09842, preferably as to both of edge extent(s) and effective loading, grip or effective grounding effect.
There are two views, effects or inventive aspects that it is seen as useful to consider relative to such substantial edge/areally bounding/peripheral restraint.
One is that limitation/reduction of available bending wave vibrational edge/peripheral/boundary movement of the member (compared with specific disclosure of WO97/09842) can produce useful compounding of achieved acoustic output from vibrational bending wave energy back in the acoustically active area. The other is that the acoustically relevant and effective natural modes of resonant bending wave action will be different (compared with specific disclosure of WO97/09842) by reason of limiting/suppressing bending wave vibration movement at edge(s)/periphery/boundary of the member, thus effectively reducing/eliminating contributions(s) from lowest resonant mode(s) that would be active if edge(s)/periphery/boundary of the acoustically effective area of the member were as free to have bending wave distribution as specifically disclosed in WO97/09842; and reduction/substantial suppression of resonant modes involving twisting.
Resulting nominally less populous or less rich content of acoustically active/relevant resonant bending wave modes can be exemplified for simplified analogy and analysis based on equivalent simple beams with account taken of interactions, in terms of involving resonant plate modes that relative to each beam start at resonant mode frequency f
1
rather than f
0
, and further ‘losing’ combinational modes involving f
0
frequencies, but with interesting and useful effects available with respect to even-ness of spacings of directly and combinationally related natural resonant modes involving f
1
frequencies.
Ramifications are extensive and can be advantageous, including attainability of improved acoustic efficiency of energy conversion and/or often very usefully increased extents of candidate sub-areas for viable/optimal transducer location(s), at least as identified by mechanical impedance analysis as taught in co-pending International patent application PCT/GB99/00404; and/or typically much greater range of viability of areal shapes/proportions of said members as exemplified for isotropic bending stiffness, even at about 1:1 through to about 1:3 and more for aspect ratio(s); and/or viability of acoustic performance for panel member materials of lower intrinsic bending stiffness at least as effectively stiffened overall by contribution from edge(s)/peripheral/boundary restraint hereof; and/or capabilities in relation to high power input transducer means for loudspeaker embodiments, all including where such restraint can afford substantial loading whether on an inertial grounding basis or as is further practical by actual fixing in a more rigid/massive carrier or other heavy loading manner.
It is a significant advantage of this invention that novel and useful resonant panel acoustic devices are provided, including active acoustic devices as loudspeakers, with significant facilitation of manufacture as robust readily-mounted panel-type devices, particularly enhanced relative to acoustic devices specifically illustrated and described in International Patent Application W097/09842.
According to one aspect of the present invention there is provided an acoustic device relying on bending wave action and capable of operating below coincidence, comprising a member affording said acoustic operation by reason of beneficial distribution of resonant modes of bending wave action therein, wherein the member has its acoustically active area at least partly bounded by means having a substantially restraining nature in relation to bending wave vibration.
According to another aspect of the present invention there is provided an active acoustic device comprising a member relying on bending wave action with beneficial distribution of resonant modes thereof and beneficial location of bending wave transd
Dabney P.
Kuntz Curtis
New Transducers Limited
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