FR2474266A1 - Wide bandpass flat diaphragm loudspeaker drive - uses separate transducers distributed around diaphragm circumference and has printed circuit conductors - Google Patents

Abstract

The flat diaphragm arrangement is intended to provide a wide frequency response and is driven from several points on its circumference. The driving force may be orthodox electro-dynamic, piezoelectric, electronic, hydraulic or mechanical. In the first case each peripheral pole-piece air gap field is reinforced by setting the magnets within a soft iron 'U' element. The magnetic material consists of nine millimeter thick rods of grain orientated iron and strontium oxide. The diaphragm conducting element set within the two millimeter or less air-gap, uses a printed circuit arrangement, both faces have a surface of fine conductors. Directivity can be reduced by either having a membrane design biassed for peripheral high frequency response or response over all of the surface.

Description

 The present invention provides so-called speakers. å "high fidelity".

To date, the various studies have led to the conclusion that it was impossible to operate correctly a single speaker of this classification in the whole sound spectrum (apart from some achievements which remain marginal). Ceoi being due to the fact that the terms of the mass / frequency / speed / Displacement equation are antagonistic. technical choice was dono a splitting in several channels of the sound spectrum with consequences: loss of power in the filters - phase rotation - distortion or irregularity of the response curve us frequencies of connection - nonlinear impedance - necessity of 2 or 3 (or more) diffusers.

 New research has concluded that a flat membrane would be more effective. But the design of the motor element limited the use of this type of membrane for the following reasons i-or the motor completely obscured the rear surface of the membrane, oe which considerably unbalanced the resistance to radiation of the membrane between the crest positive and negative of the signal, also generating resonances, with the corollary of a random operation in transient control systems. In addition, an inhomogeneity of the polar flux prevented large displacements of the membrane (generator of the fondanental frequencies).

 - or we are dealing with the recent type of loudspeaker called "isophaîe" whose design recalls the electro-static principle by avoiding the need for a high voltage polarization of the armatures but again, and always because of displacements very small deWla membrane, we are dealing with a type of speaker "high-mid-weseter".

 The present invention relates essentially to the displacement of the motor element at the periphery of the membrane, thus completely releasing the front face and arriving. This motor then making an angle of 900 parmpport to the plane of the membrane, works according to Laplaoe's law.

The choice of the current conductor, its design, its location, its weight, its volume, is therefore dictated by the performance sought. So if the use of any other motor system could be envisaged, for example electro-static or even electro-dynamic b separate excitation - piezoelectric - fluidic or mechanical electronics.

 With regard to the drawing (sectional view) it clearly appears that the displacements of the membrane are in no way limited, and that it is moreover possible to choose between a small width of the conductor and a large magnetic field surface or else a large one. conductor width and small field area.

The membrane, in this case, and compared to the traditional conical system, no longer serving as a buffer element between the driving element and the suspension, no longer undergoes deformation. On the other hand, the motor is located, glow placed between two resistances to overcome.
a) - radiation resistance (through the membrane)
b) - resistance of the suspensions
We have therefore a clear reversal of the parameters which until now wanted the movement of a loudspeaker to be mainly determined by the phenomena of elasticity.

In this new arrangement, the electrical energy transforming first into mechanical energy and then being converted into acoustic energy is located at the center of the transformation resistors. Whereas in the traditional conical loudspeaker, this energy was located at the start of a chain of resistance and inertia and the membrane was then set in motion after the proper reactions of these different antagonistic phenomena.

 The directivity can be considerably reduced by the use of a membrane whose design can favor the dispersion of high frequencies either on its perimeter or on the whole of its surface or in its volume.

 A reduction in the intermodulation distortion by the "piston" operation practically possible over the whole range of the sound spectrum (this being naturally a function of the fall of the location and the number of driving elements as well as the total surface of the membrans).

In addition, the choice of a surface produced in more than one different modulus deneity material can fully resolve s - the intermodulation distortion
- the distortion of timbre.

 Furthermore, it should be noted that this new arrangement makes it possible to add, at all points on the surface of the membrane, one or more elements of this same flat motor in order to produce either a movement analysis sensor or a corrective motor. surface deformation of the membrane or alternatively a current generator for a feedback

Claims (1)

 Analysis of the drawing calls for only one remark regarding the transformation of electrical energy into mechanical energy, it being understood that the geometry, the ratio of surfaces and volumes can be modified ad infinitum according to the desired performances ; similarly, the number of driving elements, their location and their power are the same process.  The mechanical / acoustic transformation being directly dependent on the load (dono of the type of enclosure) does not come within the scope of this presentation. Note however the great ease of adaptation of this speaker to the realization of large diffusing panels.  For the presentation of this drawing, the eleotro-dynamic system with permanent magnet was chosen. For the sake of clarity, the pole pieces of C have not been drawn. The magnetic field in the air gap has been increased by encasing the magnets in a soft iron U, the magnetic material used in this case is made up 9 mm thick bars of oriented grain iron and stromtium oxide. The air gap has been opened at 2 am for convenience, but can be easily reduced. The field surface is 25 mm; the conduction width is 17 mm; in this case the elongation of the membrane is + and - 4 mm around the equilibrium position, i.e. a total displacement of 8 µs. For the current conducting element (B) bonded to the membrane, a printed circuit (2 openwork faces) of low mass in epoxy 2/10 a was chosen, the design of which consists of fine lines parallel to each other and the length of the magnetic element. The Mord / Sud field maintained in the air gap and crossed by a perpendicular current causes an alternating vibration of the plane of the membrane (Laplaoe's law). The thickness of the conductive material is to be determined as a function of t  - a) resistivity sought - b) dissipated power I1 is also possible, in order to lighten the moving part, to envisage a current conductor by printing (conductive ink, silver glues, etc.); the reciprocating motor can be of a single peripheral part (in this case use a flexible support) or else fractional, oe which makes it possible to make series / parallel connections in order to more easily obtain the desired resistivity, the connections are then made by flexible wire or flexible twist at each intersection of the magnetic elements provide in this regard a conductive circuit of length slightly greater than the magnetic element, in order to make these connections).