Acoustic devices

Details Acoustic devices Acoustic devices

1999-02-09

2002-07-30

Kuntz, Curtis (Department: 2643)

Electrical audio signal processing systems and devices

Electro-acoustic audio transducer

Driven diverse static structure

C381S162000, C381S386000, C381S395000, C381S398000, C381S431000, C181S171000, C181S173000

Reexamination Certificate

active

06427016

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to acoustic devices capable of acoustic action involving bending waves.
BACKGROUND TO THE INVENTION
Co-pending International Patent Application PCT/GB96/02145 (published W097/09842) includes various teaching as to nature, structure and configuration of acoustic panel members having capability to sustain and propagate input vibrational energy through bending waves in operative area(s) extending transversely of thickness usually (if not necessarily) to edges of the member(s). Detail analyses are made of various specific panel member configurations, with or without directional anisotropy of bending stiffness across said area(s), so as to have resonant mode vibration components distributed over said area(s) beneficially for acoustic coupling with ambient air. Analyses extend to predetermined preferential location(s) within said area(s) 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 also envisaged in the above PCT application for such members as or in “passive” acoustic devices, i.e. without transducer means, such as for reverberation or for acoustic filtering or for acoustically “voicing” a space or room. Other “active” acoustic devices, i.e. with bending wave transducer means, include a remarkably wide range of loudspeakers as sources of sound when supplied with input signals to be converted to said sound, and also in such as microphones when exposed to sound to be converted into other signals.
Co-pending International Patent Application PCT/GB98/00621 concerns applying to panel member(s) distribution(s) of stiffness(es) and/or mass(es) not centred coincidentally with centre(s) of mass and/or geometrical centre(s) . This is particularly (but not exclusively) useful to beneficially combining both pistonic acoustic action (as for hitherto conventional, typically cone-type, loudspeakers) with bending wave acoustic action generally as in the above published PCT application. Specifically, location(s) of transducer means for both pistonic and bending wave actions can include at centre(s) of mass and/or geometrical centre(s) (as very much suits pistonic action), but still satisfy general desiderata for bending wave action.
This invention has arisen from intuitive feeling that various approaches of the above PCT applications to design and specification of acoustically useful bending wave action members reflect some other useful concept/methodology that should be capable of yielding as good or yet better and/or as practical or more practical design/specification criteria, perhaps including other useful configurations and transducer locations not before specified or otherwise appreciated. It has been an object of this invention to investigate, and arrive at such results.
SUMMARY OF THE INVENTION
According to first general method and device aspects of this invention, panel member parameters affecting bending wave action, such as particularly configuration/geometry in relation to bending stiffness(es) and/or bending wave transducer location(s), is/are in accordance with desiderata applied to analysable characteristic(s) relevant to power transfer for the acoustic device concerned, such desiderata usefully favouring acceptable distribution and/or density and/or evenness of excitation of acoustically relevant resonant modes of surface vibration involved in bending wave action.
It has been particularly established that desirably effective resonant mode density/distribution correlates with a measure of smoothness of power transfer for the acoustic device concerned; and use and results of such correlation in terms of acoustic panel members involving bending wave action constitute various other aspects of this invention.
Underlying inventive rationale or concept involved includes appreciation that, for active acoustic devices as sources of sound, satisfactory acoustic performance of panel members concerned is more dependent on smoothness of power output than on hitherto conventionally esteemed flatness of output over whatever frequency range is concerned/desired. Deviation from flatness of output is actually readily compensated by suitable electronic signal conditioning, specifically so long as the output deviations concerned are reasonably smooth.
Energy losses within panel members and transducer means of acoustic devices concerned tend to be both relatively small and reasonably smooth in themselves. Accordingly, for the purposes hereof, effectiveness of device design and specification can be based on smoothness of input power transfer, including particularly as to geometry/configuration such as aspect ratios and as to bending wave transducer location(s) such as in terms of proportionate co-ordinates.
Whatever particular characteristic(s) is/are involved in assessing smoothness of power transfer, conveniently and preferentially input power transfer, it is practical to be concerned with deviation from some useful condition, state or value, whether of arbitrary or of relational nature. Thus, analysis relative to same or unity weighting of whatever resonant frequency modes are concerned has produced useful results, as has analysis relative to mean value(s) . However, selective adjustment of weighting etc is also seen as useful refinement, for example at least for end-most modal frequencies involved, particularly lowest; and feasibly more generally or otherwise.
The frequency modes concerned/involved in analytical assessment hereof can be as arise from making practically viable simplification, such as using analogies of one-dimensional nature, say to orthogonal beams notionally in directions parallel to pairs of opposite sides of substantially rectangular panel members. This simplification approach reflects success achieved in specific teaching of W097/09842, including first consideration relative to a number of resonant modes in each beam direction and directly related inter-active modes. Refinements of analyses relative to two-dimensional relationships should more closely reflect realities of panel members as such, including revealing and taking appropriate account of more inter-actively related resonant modal frequencies.
Preferred said characteristic(s) relevant to power transfer for the panel member include criteria for mechanical impedance, say as to standard deviation with application of a smoothing factor, say 10%.
In some particular inventive aspects hereof, criteria for mechanical impedance are used in assessing input power transfer, specifically in finding practical geometries and/or stiffness parameters/distributions of panel members for acoustic action relying on distribution of resonant modes of bending wave action. It can be of high practical value first to investigate relative to known favourable transducer locations and to present results functionally, usefully graphically, relative to variant aspect ratios of general geometrical shape concerned in looking for minima of deviation.
In other particular inventive aspects hereof, criteria for mechanical impedance is/are used to find practical transducer locations for particular desired geometries/configurations and/or stiffness distributions of panel members for acoustic action involving bending waves, specifically and advantageously without limitation to panel members having favourable geometry/configuration such as available from said some inventive aspects. It can be of high practical value to investigate variable one relative to fixed other of co-operative areal locators such as co-ordinates of transducer location and present results functionally, usefully graphically, in looking for minimum deviation of preferably smoothed mechanical impedance. It can also be of high practical value to present results of this investigation of panel members as areal distribution of mechanical impedance or deviation thereof, conveniently in contoured manner to indicate extremes and gradations betw

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