LOUDSPEAKER COMBINATION WITH PIEZO-ELECTRIC TWEETER

Abstract: This invention concerns a multiple loudspeaker with a piezo-electric "tweeter", held up by a means of support which allows the rear wave emitted by the ceramic disk and respective conical diaphragm to be fully exploited, using the main loudspeaker cone as a reflecting surface without over­ loading the moving coil of the latter. The invention is basically characterized by the fact that the piezoelectric "tweeter" is placed in front of the main loudspeaker cone, without the traditional protection and support basket, but using a different means of support which does not intercept or disturb the rear radiation from the piezoelectric "tweeter", or prevent the forward reflection of the radiation by the main loudspeaker diaphragm.

Description: This patent application for an industrial invention refers to a multiple loudspeaker with a piezoelectric "tweeter", held up by a means of support which allows the rear wave emitted by the ceramic disk and respective conical diaphragm to be fully exploited, using the main loudspeaker cone as a reflecting surface, without overloading the moving coil of the latter. For further explanation of the loudspeaker, according to the invention, we feel it is necessary to give a brief description of the current technological situation in the field of acoustic reproducers. In order to faithfully reproduce high frequencies, a loudspeaker should have a fairly small cone, while on the other hand, low frequency reproduction requires a cone of considerable dimensions; therefore when an optimum performance needs to be obtained,instead of using just one loudspeaker intended to reproduce the whole range of audiofrequencies with fidelity, an ensemble of several loudspeakers suitably arranged is usually adopted: some with large dimensions suitable for low frequency reproduction, normally called "woofers", others with small dimensions suitable for high frequency reproduction, normally called "tweeters". The multiple loudspeakers' group includes bi-phonic coaxial loudspeakers which have two reproduction appliances totally independent of each other but coaxially mounted, one equipped with a bigger cone, the other equipped with a smaller cone placed immediately in front of and on the same axis as the bigger cone. In some bi-phonic coaxial loudspeakers, a piezoelectric "tweeter" is adopted, namely using a ceramic disk generator of sound waves, situated inside a small protection and support basket, which is attached to a part of the main loudspeaker frame (i.e. the bigger loduspeaker), according to various construction solutions: in some models the basket is supported by an axial pin, while in other models a support bracket is adopted made up of one or more radial spokes the end of which is to be positioned and fixed on the main loudspeaker basket. Both construction solutions just described present some common problems and some specific problems. For example the abovementioned central support pin is not mechanically reliable; especially taking into account the economic material used for its manufacture which is mainly plastic barely resistant to the temperature, it can bend laterally until it touches the main loudspeaker coil, which results in friction between the parts which come into contact with each other and immediately causes an inadmissible crackling noise, if not at the very worst, the blockage of the bigger diaphragm. Moreover both support systems mentioned do not allow the installation of the "tweeter" completely inside the main loudspeaker diaphragm in such a way that the edges of the two maximum diameter sections of the two cones are actually coplanar. This is due to the overall dimensions of the protection and support basket of the piezoelectric "tweeter". However the most serious problem, which can occur in both systems examined so far, lies in the fact that due to the presence of the aforementioned support basket, the sound waves emitted from the rear by the ceramic disk and by the conical diaphragm of the piezoelectric tweeter cannot be fully exploited. If these sound waves could be reflected forwards, the actual radiation impedance of the sound source would be increased. Bearing this in mind, an alternative to the two abovementioned solutions has already been proposed, whereby the support of the piezoelectric tweeter is in a coaxial position in front of the main loudspeaker cone. According to this alternative solution, the piezoelectric tweeter is not situated inside a basket, but its ceramic disk is firmly joined to the mobile support of the main loudspeaker coil, the diaphragm of which can then act as a reflecting surface for the radiations emitted from the rear by the tweeter cone, but not for those radiations emitted by the ceramic disk fixed to tie mobile support of the main loudspeaker coil. In addition to the limited exploitation of the waves emitted from the rear by the piezoelectric tweeter, the last solution indicated obviously brings about an overloading of the mobile support of the main loudspeaker coil. Even if this is minimal, an increase in the size of the magnet is nevertheless necessary, which leads to a notable increase in the final production costs. In JP A-55154899 and in US A-4389548 two 2-way, coax speaker systems of the well known type are described. The patent US A-55154899 discloses a 2-way, coax speaker system which is characterized in particular by its inexpensiveness and by the simplicity of the constructive solution proposed; its working principle is, however, completely traditional. By a traditional working coax speaker system we mean a main speaker means (woofer), having a tweeter of any type placed in front of its cone, provided that the tweeter is closed from the rear side in a hermetic housing. The speaker system disclosed in the Japanese patent does observe this constructive solution, so the woofer and the tweeter employed in it can radiate sounds only forward; in particular in the japanise speaker system no sound emissions can be irradiated from the tweeter towards the woofer cone and then reflected forward. The US A-4389548 patent too, refers to a piezoelectric tweeter of the traditional type, i.e. with a dynamic structure (diaphragm + piezoelectric disk) anchored to a chassis which holds and protects the piezoelectric disk. As a matter of fact in this system too sound waves emitted from the tweeter from the rear and reflected forward by the woofer cone do not exist and neither are they exploited. In conclusion we may not certainly assert that in the above cited patents 2-way coax speaker systems are disclosed in which the piezoelectric tweeter works as an acoustic dipole. The aim of this invention is to provide a means of support for the piezoelectric "tweeter", which, without over-loading the mobile support of the main loudspeaker coil, allows the exploitation of the radiation emitted from the rear by the ceramic disk and that emitted by the cone. The diaphragm behind the main loudspeaker acts as a reflecting surface, and furthermore the overall dimensions of the piezoelectric"tweeter"are limited in such a way that the whole of the latter can fit into the main loudspeaker cone. According to this invention, the solution is based on the fact that the piezoelectric "tweeter" is placed in front of the main loudspeaker cone without the usual support and protection basket. A different means of support is used instead, which does not intercept or disturb radiation emitted from the rear by the piezoelectric "tweeter" or obstruct the forward reflection of said radiation by the main loudspeaker diaphragm. In accordance with a preferred embodiment of the invention, relating to the field of coaxial biphonic loudspeakers, the piezoelectric "tweeter', without a basket, is supported by a spider-shaped bracket with radial spokes, the ends of which are fixed to the main loudspeaker basket. In accordance with an alternative embodiment of the invention, in the field of coaxial bi-phonic loudspeakers, the piezoelectric "tweeter" is fixed on the back of the protection grille which usually covers the hole on the front of the panel on which the loudspeaker is mounted. In order to provide further explanation, the description of this invention proceeds with reference to the enclosed drawings in which two preferred embodiments of the invention at reference are schematically illustrated, to be applied in the field of bi-phonic, coaxial loudspeakers. Fig. 1 is a section with the axial plan of a bi-phonic, coaxial loudspeaker, in accordance with the invention and with its preferred embodiment. Fig. 2 is a section with an axial plan of a bi-phonic coaxial loudspeaker in accordance with the invention and with an alternative embodiment. With reference to the abovementioned figures, the loudspeaker at reference is made up of two independent reproduction devices coaxially mounted, and in conformity with traditional construction methods for bi-phonic coaxial loudspeakers. The main moving-coil loudspeaker suitable for the reproduction of medium to low frequencies is made up of a basket (1), which supports the cone diaphragm (2) internally and the centering device (3), which while allowing the coil to move longitudinally, ensures that it is always perfectly centered in the air gap and that it does not touch the two pole shoes; the external one being ring shaped (4) and the internal one cylindrical (5). Number (8) indicates an anti-dust plate which closes at the front the mobile support sleeve (9) of the coil, not shown in the figure. With reference to Fig. 1, the other smaller piezoelectric loudspeaker suitable for high frequency reproduction, is characterized by the fact that it is made up of the ceramic disk (10) and its respective cone (11) only, which are held in a position coaxial to and in front of the diaphragm (2) of the main loudspeaker, by means of a support bracket (12) which in turn is made up of a central annular flange from which one or more radial spokes branch out, level with the flange, the ends of which are linked up with the main loudspeaker support basket (1). More precisely, at the point where the diameter is greatest, the cone (11) of the piezoelectric "tweeter" is glued by its edge to a sponge ring (13), acting as a damper, which in turn is glued onto the back of the aforementioned central annular flange. With reference to figure (2), according to an alternative embodiment of the invention, it can be noted how the piezoelectric"tweeter"is supported in a coaxial position in front of the main loudspeaker diaphragm (2) by means of the protection grille (14), which usually covers the hole on the front panel on which the loudspeaker is mounted. In this alternative version, th sponge ring (13), to which the edges of the piezoelectric "tweeter" cone (11) are to be attached, is glued to a surface especially provided for the purpose, on the inside of the grille (14). Said grille, as per the example put forward by the construction solution in Fig. 2, could even have a horn(15) on the outside of the opening of which, the aforementioned sponge ring (13) may be glued. Needless to say this description refers to the enclosed drawings, reproduced for explanatory purposes only, and relating to the manufacture of bi-phonic, coaxial loudspeakers. It is, however, obvious that the invention may be applied in the field of multiple loudspeakers in general, not necessarily bi-phonic and/or coaxial, without actually deviating from the concept of this invention and the protection afforded by this industrial patent right.

Claims: Multiple loudspeaker with piezoelectric "tweeter" supported in such a way as to allow complete exploitation of the main loudspeaker diaphragm, the surface of which reflects the radiation emitted from the rear by the ceramic disk and by the piezoelectric "tweeter" diaphragm, characterized by the fact that the piezoelectric "tweeter" is made up of a ceramic disk (10) and a diaphragm (11) only and is held in position in front of the main loudspeaker diaphragm (2) by means of a support bracket (12) which in turn is made up of an annular flange, from which one or more spokes branch out towards the outside, the ends of which are to be fixed to the main loudspeaker basket (1). At the point where the diameter is at its greatest, the edge of the diaphragm (11) is fixed on the inside to the aforementioned annular flange, where a sponge ring (13) to act as a damper, has previously been applied. Multiple loudspeaker, with piezoelectric "tweeter", supported in such a way as to allow complete exploitation of the main loudspeaker diaphragm, the surface of which reflects the radiation emitted from the rear by the ceramic disk and by the piezoelectric "tweeter" diaphragm, characterized by the fact that the piezoelectric tweeter is made up of a ceramic disk (10) and a diaphragm (11) only and according to an alternative version of the invention is held in position in front of the main loudspeaker diaphragm (2) by means of a protection grille (14), which usually covers the hole on the front of the panel on which the loudspeaker is mounted. At the point where the diameter is at its greatest, the edge of the cone (11) is glued to a sponge ring (13) which is in turn attached to a flange provided for this purpose on the inside of the grille (14).

Inventors: SANCISI, CARLO, TONTINI, FRANCO
Applicants: "S.I.P.E. SOCIETA ITALIANA PRODOTTI ELETTROMECCANINI" -S.P.A.
Application year: 1985
Main classification: H04R1
IPC codes: H04R1, H04R23