FR2676321A1 - Acoustic filtering device for a sound emitter in general and an acoustic enclosure in particular - Google Patents

Abstract

The invention relates to an acoustic filtering device for a sound emitter consisting of at least one loudspeaker (1) mounted in its enclosure (2). This device consists of a passive loudspeaker (3) identical to the first one, but having no moving coil, no magnet, and no electrical connection. It is placed behind the loudspeaker (1), and it separates the latter from the main volume (P) of the enclosure (2). The space which separates these two loudspeakers should be as small as possible.

Description

 The sound emitters using speakers of small and large dimensions, are in most cases constituted by an enclosure, with or without vents, pierced in its front part with an opening in which the loudspeaker is mounted. loudspeaker; such speakers are necessary to ensure the correct functioning of the loudspeaker; but on the other hand, they create disturbances in hearing, especially in the low register, mainly due to the resonance of the loudspeaker's own volume, and to reflections parasites and randomness of its internal wall on the rear emission of the speaker; such speakers do not allow a favorable damping to the diaphragm of the speaker.

 Many solutions have been proposed to try to solve these drawbacks; it has in particular been provided for this purpose to create vents in the enclosure, to replace them with a passive speaker, without any electrical connection, to line the interior with sound absorbing materials, to divide the enclosure by an intermediate partition breakthrough of one or more vents, to mount a second speaker similar or different from the first, arranged in file, one behind the other in a common support, and electrically connected in series or in parallel, in phase with the first or out of phase, and to transmit in one direction or the other; some improvements have been obtained in this way, but none of these solutions have been entirely satisfactory.

 The device according to the present invention eliminates the aforementioned drawbacks; it comprises a passive loudspeaker (3) going to fix and close the anterior opening (5) of the enclosure (2); the loudspeaker (1) is fixed thereafter, its front face against that of the passive loudspeaker (3). see figure 1.

The loudspeaker (1) is supplied by an electric source of energy in acoustic phase; the latter being mounted upside down, it will be connected in electrical phase opposition; the sound signal is transmitted through the rear face of the loudspeaker (1).

Except that it has no magnet, voice coil, and electrical connection, the passive speaker (3) must be identical to the speaker (1) used. The passive speaker (3) produces no sound.

The volume (V) which separates the two speakers must be as low as possible.

 For a more conventional position of the loudspeaker (1), the latter is placed together with the passive loudspeaker (3), in a common support (4); they are arranged in a line, one behind the other; they are coaxial. see figure 2.

The support (4) has an internal section, equal to the diameter of the diaphragm of the speakers used; the volume (V) which separates them, must be as small as possible; the sound is transmitted through the front face of the speaker (i), which is supplied by an electric source of energy, in acoustic and electric phase.

 The appended drawing shows by way of example, in FIGS. 1 and 2 in section, the different possibilities for producing the system in enclosures with or without vents (6).

 The main volume (P) of the enclosure (2) is calculated identically to that of a conventional enclosure, in a manner known per se.

 The operation of this device is comparable to that of a sound transmitter, composed of a loudspeaker, mounted in its enclosure provided with at least one vent; vented acoustic enclosure.

 Basic principle of operation: the loudspeaker (1) under the effect of an electrical source of energy in phase, has a forward impulse; automatically a depression is created between the two membranes; at the same time, the second diaphragm of the passive speaker (3) has an impultion, created by depression, in the opposite direction and in turn creates an overpressure in the main volume (P) of the enclosure (2) .

 We thus obtain an effective pneumatic braking of the diaphragm of the loudspeaker (1); the damping is optimal, at low frequencies where the loudspeaker membrane works like a piston, or at higher frequencies where the diaphragm vibrates on itself by radiating sound directly.

 It is understood that the embodiment of the invention which has been described above with reference to the appended drawing, has been given for purely indicative and in no way limiting; many modifications can be made, without departing from the scope of the present invention.

Claims (2)

 1) Acoustic filtering device for a sound transmitter consisting of at least one loudspeaker (1) mounted in its enclosure (2), whether or not provided with vents, characterized in that in the front opening (5) of this enclosure is fixed at least one passive speaker (3) without electrical part, but identical for the rest to the speaker (1) used. The loudspeaker (1) is placed in front of the passive loudspeaker (3); they are face to face; the front face of the passive speaker (3) is closed by the front face of the speaker (1); the rear face of the passive speaker (3) closed off the front opening (5) of the enclosure (2); the loudspeaker (1) is supplied by an electric source of energy in acoustic phase.  2) Device according to claim 1 characterized in that, in the front opening (5) of the enclosure (2), are placed the two speakers, in a common support (4), coaxially; the loudspeaker (1) and the passive loudspeaker (3) are arranged in a line, one behind the other; The front end of the support (4) is closed off by the most forward speaker (1) and the rear end by the rearmost passive speaker (3). The volume (V) that separates the two speakers should be as low as possible.