Electrodynamic-fluidic transducer element for pneumatic loudspea

Details Electrodynamic-fluidic transducer element for pneumatic loudspea Electrodynamic-fluidic transducer element for pneumatic loudspea

1991-03-13

1993-01-12

Ng, Jin F.

Electrical audio signal processing systems and devices

Electro-acoustic audio transducer

By modifying fluid flow

381156, 381114, 381194, H04R 2500

Patent

active

051795957

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a moveable assembly for the composite electrodynamic and fluidic transducer of a pneumatic loudspeaker, comprising an axially moveable tubular support, one end of which carries the coil moveable in the annular air gap of the electrodynamic stage of the transducer and the other end of which forms a nose moveable in the neck of an annular contraction of the fluidic stage of the transducer, the middle part of the said support being gripped between two concentric diaphragms separating the electrodynamic and fluidic stages of the transducer.
The Patents FR-A-2,442,565 and 2,572,615 make known a pneumatic loudspeaker, in which a moveable assembly with an electromagnetic coil is extended by a fluid modulator consisting of a nose which moves in the air flow passage. The movement, controlled by the electrodynamic transducer which receives the vocal input signal, modulates the air flow and generates a sound signal amplified in relation to the input signal.
As in any loudspeaker, the reproduction quality of the sound signal depends on the quality of the transducer, that is to say on the inertia and rigidity of the moveable assembly.
In a pneumatic loudspeaker of the above-described type, the nose has to be especially rigid in order to be capable of withstanding the pressure of the fluid which it is intended to control, whilst the moveable assembly of which the modular nose forms part must have a low inertia. These two qualities are contradictory, and therefore because of the forces generated by the air flow to be controlled it was chosen to given preference to the rigidity. The solution therefore involved using a thick coil support, a result of this being a relatively wide air gap and, for a magnet of given dimensions, a lower intensity of the magnetic flux passing through the transducer coil. The pass band and efficiency of such a transducer were unsatisfactory, and therefore the set object of the invention was to improve these characteristics.
In contrast to the first procedure, the aim was to reduce the inertia as much as possible by adopting the only possible solution, namely to minimise the thickness of the support. The result of this was a coil which was very light, but which was especially susceptible to deformation and incapable of ensuring the control of the air flow of the pneumatic circuit with the desired accuracy.
The result of the invention was, among other things, to make the moveable assembly more rigid by using the other elements of the transducer, particularly the annular elastic diaphragm, in such a way that the said diaphragm performs the function of a hoop.
The moveable assembly according to the invention is characterized in that the said support having a diameter of an order of magnitude greater than its height, itself of an order of magnitude greater than its thickness, is made rigid by means of the abovementioned diaphragms, each formed from a composite hoop which, between the support and a concentric rigid ring, includes an elastomeric collar adhering thereto and having an axial height of the same order of magnitude as its radial thickness, in order, on the one hand, to ensure the elastic return of the support in terms of its axial movement and, on the other hand, to maintain the circularity and therefore the planeness of the said support.
The explanations and figures given below by way of example will make it possible to understand how the invention can be put into practice. In these figures, the relative dimensions are not adhered to, in order to obtain greater clarity in the drawing.
FIG. 1 shows a view in diametral section of a transducer according to the invention mounted in a pneumatic loudspeaker.
FIG. 2 is a top view of the moveable assembly of the transducer.
FIG. 3 is a pseudo-diametral section through FIG. 1.
In FIG. 1, on either side of a wall 1 can be seen on the one hand the fluidic stage 2 and on the other hand the electrodynamic stage of the transducer 3.
The fluidic stage 2 as a whole comprises a nozzle 4 extended by an acoustic horn 5, this nozzle 4

REFERENCES:
patent: 3073916 (1963-01-01), Williams et al.
patent: 3674945 (1972-07-01), Hands
patent: 4055233 (1977-10-01), Huntress
patent: 4696045 (1987-09-01), Rosenthal
patent: 5054080 (1991-10-01), Julia et al.
Webster New Collegiate Dictionary, p. 808.

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