FR2505125A1 - Loudspeaker casing with baffles holding two units - has closed, common cavity and open tuned cavity transmitting low frequency tones - Google Patents

Abstract

The assembly includes two loudspeakers operating acoustically in phase, mounted in a housing comprising two resonant cavities. The upper cavity (3) is enclosed and is common to the two loudspeakers (1,2), one (1) being directed out from the front vertical surface, and one (2) being directed down from the lower horizontal surface. The second cavity (4) is open and has the lower speaker facing down into it, with an opening (5) directed forward. The second loudspeaker provides the low frequency notes. The ratio between the volumes of the cavities is between one and two and a half. The housing is made of reconstituted wood with two layers of polyester resin material forming a lining inside. Crossover networks are included using inductors of at most 0.3 ohm resistance and up to 15 mH inductance, having therefore, high Q factor.

Description

 The subject of the present invention is a system for coupling baffled electro-acoustic transducers, the principle of which is known, consisting of one or more loudspeakers, the assembly of which constitutes a hell transducer.

 For such a system to transform electrical energy into acoustic energy under the best possible conditions, this acoustic energy must remain practically constant and of a high level for a determined electrical energy, in a very wide frequency bandwidth, useful for reproduction in high quality acoustics.

 Many solutions exist, which tend to obtain this result, but none, until now, proved to be completely effective.

 The present invention presents a box with two cavities, (fig.l) resonating at two different natural frequencies (fig.l).

 The volumes (3 and 4) of these cavities are in a ratio between one and two and a half.

 In addition, a vent (5) is provided, allowing the front wave of the loudspeaker (2), located inside the cabinet, to be transmitted, without coloring or parasitic drag, with an appropriate resulting sound pressure, this vent being granted to the resonant system of the closed cavity. To this reproduction system is provided the addition of an electro-acoustic transducer, of high frequency, completing the bandwidth. The transducer, in this case, has no effect on the behavior of the resonant system specific to the coupling of the cavities.

 Indeed, the box is made using high density chipboard (1) like some existing systems. However, this material, in the context of the present invention, is treated on all the internal parts, using two successive layers of polyester resin (fig. 2).

 The first layer (2) penetrates into the wood, while the second (3) layer of highly charged polyester resin, after stabilization of the mechanical characteristics of the first, forms a "laminate" on the surface of the walls.

 These treatments provide the baffle wood with specific mechanical characteristics and a specific stiffness for better reproduction of low frequencies.

 Some sides of the box are made up of several thicknesses of wood, a feature which allows, for example, to maintain the PVC vent in order to eliminate certain problems of parasitic resonances.

 It also makes it possible to give additional stiffness to the open cavity, the latter being, furthermore clamped by a crosspiece of cleats, situated at a suitable location for the best possible distribution of the intensity of the resulting vibrations over the entire useful bandwidth medium-low cabinet.

 Similarly, the use of different materials placed inside the cabinet allows better damping for the respective acoustic loads of the cavities. To ensure better sealing and vibration isolation between the speakers and the cavities, a closed cell rubber seal has been inserted.

 The loudspeaker 1 of FIG. 1 has been the subject of a special treatment based on Epoxy resin with very high mechanical characteristic and low density. In addition, a modification was made on this speaker at the level of the fixing of the membrane on the external edges of the salad bowl (suppression of the traditional cork joint, from where improved sticking).

 The combination of the two aforementioned elements (treatment of the loudspeaker and modification of the bonding) gives a new result in the form of the elimination of small sensitive irregularities on a very specific part of the response curve. In addition, the loudspeaker thus modified, goes up in frequency much more easily without a deformation noted during the restitution of the high frequencies by conventional loudspeakers (not having the denomination tweeter).

 The transient response in this part of the spectrum is improved.

 The loudspeaker (1 in fig. 1) has undergone these treatments to compensate for the imperfections resulting from the resonant system. (closed cavity containing the treated speaker (1) and the traditional speaker (2).

 The two speakers making up the cabinet do not work in the same frequency range.

 The frequency distributing filters of such a system also include original arrangements giving a new result in the sense that the filters are outside the resonant system and, moreover, they are removable (FIG. 3).

 These arrangements consist of mounting the main printed circuit (1) on a wooden counter-plate (2), the assembly being fixed with the aid of shock absorbers (3 and 4) on the upper and external parts of the box, according to figure three.

 The removability of the filters allows them to be placed as close as possible to the power amplifier of the Hi-Fi system, which reduces the length of the connections between the amplifier and the general input of the filters, the connection of loudspeakers to filters therefore requiring longer connecting cables.

 The various components of the filters are isolated from each other by a systematic Rubson glaze, which makes it possible to avoid all forms of parasitic vibration between the components which could have harmful consequences on certain frequencies, it being understood that the filters are mounted on the cabinet .

 The inductors used are of a particular technology, never used in the application of loudspeakers. They have internal resistances less than or equal to 0.3 Ohm for inductive values up to 15 mH, therefore very high Qs. In addition, these chokes are unsaturable.

 The curve in solid line represents the use of a special inductor with very low internal resistance (fig. 4).

 The dotted line represents the use of a conventional self with a lower Q.

Claims (5)

- CLAIMS  1.- Acoustic system characterized by a coupling of two dissimilar transducers mounted in the acoustic phase in a box consisting of two resonant cavities, one closed common to the two transducers and the other open on a vent tuned to the resonant system of the closed cavity this same vent transmitting the front wave of the internal bass transducer. The ratio of the internal volumes of the cavities must be between one and two and a half in relation to the resultant of elasticity generated by the combination of the different electro-mechanical characteristics of the transducers used.  2. Acoustic system according to claim 1, characterized in that the box produced by means of agglomerated wood is treated on all the internal parts using two successive layers of polyester resin, one of which is loaded very strongly.  3. Acoustic system according to claim 1 and 2 characterized by the fact that the front loudspeaker is dissimilar from the internal loudspeaker, whether they are of the same diameter or of different diameter, by a difference in membrane treatment to using epoxy resin to improve the acoustico-mechanical coupling of the two transducers used.  4. Acoustic system according to any one of claims 1 to 3, characterized in that the distributing filters are not in an active zone of the resonant systems.  In addition, the printed circuits of these filters are mounted on a wooden counter-plate fixed with shock absorbers to the external parts of the cabinet.  5. Acoustic system according to any one of claims 1 to 4, characterized in that the inductors used have very low internal resistances less than or equal to 0.3 ohm for inductive values up to 15 mH.