EP1405545A2 - Sound transmitter and speaker - Google Patents

Abstract

The invention concerns a sound transmitter comprising at least a vibrating membrane mounted on the wall of an enclosure so that one surface of the speaker membrane radiates in the enclosure, the enclosure being provided with a vent forming a conduit between an outlet inside the enclosure and an outlet outside the enclosure. The invention is characterised in that the vent comprises aerodynamic turbulence attenuating means at least at one of the outlets, said turbulence resulting from an air stream caused by the large amplitude displacements of the membrane. The invention also concerns a sound transmitter wherein air moves in a conduit (33) extending from the membrane to an outlet (35) of the conduit (33) on the outside. The invention further concerns a speaker whereof the members have an aerodynamic shape.

Description

 Sound transmitter and speaker.

The invention relates to a sound transmitter of the type converting an electrical signal into an audible signal, that is to say into a pressure wave radiating in the atmosphere. Transmitters of the type are known comprising at least one loudspeaker mounted on the wall of an enclosure, one face of the membrane radiating in the outside air, while the other face radiates in the enclosure.

The enclosure is generally provided with a vent putting the interior of the enclosure in communication with the outside and allowing the radiation towards the outside of pressure waves generated by the radiating membrane in the enclosure.

The vent forms the neck of a Helmholtz resonator, the reservoir of which is formed by the enclosure. According to a well-known property of this type of resonator, the pressure wave radiated at the outlet of the vent is in phase opposition with the pressure wave radiated by the membrane in the enclosure. The pressure wave radiated at the outlet of 1 ′ (vent is therefore in phase with the pressure wave radiated by the face of the membrane turned towards the outside of the enclosure, so that the effects of the two waves of pressure are added to increase the sound power restored. We know that such a resonator has a characteristic frequency representing a low limit for the frequency of the sounds transmitted by the resonator. This characteristic frequency varies due to the cross section of the vent and inversely due to the volume of the enclosure and the length of the vent

To lower the characteristic frequency of the resonator and thus allow the transmission of sounds of very low frequency, it would be necessary to increase the volume of the enclosure, which turns out to be bulky, or to increase the length of the vent, which makes it difficult to position it. - ment in the enclosure, or reduce the section of the vent. In the latter case, it can be seen that the sound power of the transmitter decreases.

An object of one invention is to provide a sound transmitter having better performance than known sound transmitters, especially in the low frequencies.

To this end, a sound transmitter is proposed comprising at least one speaker provided with a vibrating membrane and mounted on the wall of an enclosure so that one face of the speaker membrane radiates into the enclosure. , the enclosure being provided with a vent forming a conduit between an outlet inside the enclosure and an outlet outside the enclosure, the vent according to the invention comprising means for attenuating turbulence aerodynamics at at least one of the outlets, this turbulence being consecutive to an air flow in one vent caused by displacements of the membrane of great amplitude.

By large amplitude is meant a displacement of the membrane sufficient to cause a displacement of the air in the vent which is not insignificant with respect to the dimensions of the vent.

Under such conditions, and in the absence of the adaptations provided by the invention, the flow out of the vent at the level of the outlets is essentially turbulent, which on the one hand unnecessarily dissipates energy and on the other hand deteriorates the performance of the sound transmitter.

The vent according to the invention makes it possible to minimize the production of turbulence at the level of outlets, so that the efficiency of the sound emitter is thereby improved.

It has thus been found that the vent according to the invention allows a spectacular improvement in the reproduction of sound in the low frequencies, even allowing one to go against what is usually experienced. in acoustics, to obtain an excellent efficiency for frequencies lower than the characteristic frequency of the Helmholtz resonator formed by the enclosure and the vent.

Careful analysis of this phenomenon has led the inventor to hypothesize that the pressure wave obtained at the outlet of the vent under these conditions is no longer a wave obtained in a conventional manner, that is to say by putting in vibration the spring formed by the air in the enclosure and the mass formed by the air in the vent. At low frequencies, the air in the resonator rather behaves like an incompressible fluid. It then seems that the pressure wave generated by a transmitter according to the invention is the result of macroscopic displacements of the air almost incompressible in the vent which creates radiation in the outside air.

The adaptation of the shapes of the vent according to the invention has thus made it possible to update a new mode of creation of acoustic waves not dependent on the elasticity of the air, this new mode being particularly suitable for transmission of low frequencies. For the rest, we will give this phenomenon the name of convective radiation.

The means for reducing turbulence advantageously consist of internal shapes of the pipe and / or outlets, arranged to allow a regular flow of air in the vent.

By regular, it is meant that the flow tends towards a flow of one-dimensional type in the outlet section of the flow. We will endeavor to make this discharge as laminar as possible, by providing passage sections that progressively evolve, without roughness.

According to a preferred version of the invention, at least one of the outlets has a shape which widens towards its end. Thus, in the case of a flow going from the interior of the enclosure towards the exterior, the outlet tieur presents a convergent shape which allows the progressive setting in speed of the air of the enclosure in the vicinity of the vent so that it can flow there in a regular way, without formation of turbulence, and thus by minimizing the losses energy.

For the same flow direction, a flaring external outlet makes it possible to slow down the air escaping from the vent, and therefore to reduce turbulence at the outlet. It is thus possible to throttle the conduit in order to reduce the characteristic frequency of the resonator while providing at the output an appreciable radiation surface to the pressure wave, not limited to the section of the conduit

This possibility of throttling makes it possible, for the same characteristic frequency, to give the volume of the enclosure dimensions that are much more compact than that of current transmitters.

Furthermore, according to a phenomenon well known in fluid mechanics, the slowing down of the air obtained by the divergent form of the external outlet makes it possible to convert the corresponding kinetic energy variation of the air into an additional pressure. A kinetic energy which has no acoustic utility is thus transformed into a pressure which has an acoustic effect, which makes it possible to further improve the performance of the sound emitter. Throughout this document, interior and exterior relate to the enclosure, while converging and diverging relate to a direction of air flow from the interior to the exterior of the enclosure, it being understood that the 'air flows alternately in one direction then' in the other at the rate of the alternating movements of the membrane.

According to an advantageous aspect of the invention, the flaring outlet has a sectional profile having a terminal concavity turned towards the interior of the outlet.

Thus, the outlet forms a nozzle allowing an outlet of the channeled air, without detaching the threads air from the outlet wall.

According to a particular arrangement, the vent is equipped between the interior and exterior outlets with a tranquilization chamber. This chamber makes it possible to further decrease the turbulence of the flow, and thus further increase the efficiency of the sound emitter.

According to an advantageous aspect, the stilling chamber forms a bevel gear between the interior outlet and the exterior outlet. This arrangement allows for compact vents.

Preferably, at least one of the outlets has a diameter suitable for making the flow of laminar air at the outlet. To make the most of these newly highlighted phenomena, the inventor came to the conclusion that instead of trying to channel the flow only in the vent, it would be much more profitable to channel the flow from the immediate start. of the membrane. The invention therefore also relates to a new type of sound emitter comprising at least one vibrating membrane mounted in a body comprising a conduit in communication with the outside by an end portion and in which one face of the membrane radiates, the duct comprising means for attenuating aerodynamic turbulence at the level of the terminal part during an air flow in the duct caused by displacements of the membrane of great amplitude.

Thus, contrary to the universally established habits in the field of acoustics, the inventor no longer seeks only to create pressure waves by playing on the elasticity of the air in the body, but also to guide a flow of air set in motion by the membrane towards the outside with as little turbulence as possible so that this flow acts as a piston at the outlet of the body and creates a pressure wave in the ambient air under the effect of the macroscopic displacements of this air piston, by the phenomenon of convective radiation.

Preferably, the means for attenuating the turbulence are constituted by internal shapes of the duct, these shapes being arranged to allow a regular flow of air in the duct.

According to a first alternative embodiment, the conduit has a flaring end portion. This divergent part makes it possible, like what has been explained for the vent, to transform into pressure a month part of the kinetic energy of the air set in motion by the membrane.

According to a preferred arrangement, the sound transmitter comprises two speakers each having a vibrating membrane, and mounted in a body so that the membranes face each other and are electrically connected in phase opposition, the faces of the membranes being radiating face in the internal duct. The membranes combine their effect on the movement of air in the duct. For a displacement of air and therefore for a given acoustic power, the membranes have a reduced displacement, which makes it possible to move back the power threshold beyond which the membranes or the associated mobile organs come into abutment.

The inventor noticed that the present loudspeakers have a shape which is hardly adapted to allow a laminar flow of air, especially on the side of the diaphragm cooperating with the motor. Thus, in order to better control the air flows generated by the vibrating membrane, the invention also relates to a loudspeaker comprising a vibrating membrane mounted on a support and actuated by a motor linked to the support, the motor and the support having aerodynamic shapes capable of causing the least tur- possible bubbles in the air flow generated by the displacement of the membrane and bathing the motor and the support.

Finally, the subject of the invention is a method for producing sound, consisting in causing an internal and convective displacement of air contained in a duct having an outlet to the outside and at least partially transforming the kinetic energy thus communicated to pressurized air at the outlet of the duct.

By convective displacement is meant an overall displacement of the air of non-negligible amplitude relative to the dimensions of the duct. By alternating, we mean a displacement in one direction then in the other, at the rhythm imposed by the organ causing the displacement of air.

Other characteristics and advantages of the invention will appear more clearly in the light of the following description of particular non-limiting embodiments of the invention with reference to the appended figures among which:

- Figure 1 is a sectional view of a sound transmitter according to the invention.

- Figure 2 is an enlarged partial view of Figure 1 illustrating a vent fitted to the sound transmitter according to the invention;

- Figure 3 is a view similar to Figure 2 of a second embodiment of the invention;

- Figure 4 is a view similar to Figure 2 of a variant of the embodiment illustrated in Figure 3;

- Figure 5 is a view similar to Figure 2 of a third embodiment of the invention;

- Figure 6 is an axial sectional view of a sound transmitter 1 according to the invention;

- Figure 7 is an axial sectional view of a sound transmitter according to the invention; - Figure 8 is an axial sectional view of a sound transmitter according to the invention;

- Figure 9 is an axial sectional view of a loudspeaker according to the invention.

With reference to FIGS. 1 and 2, a sound transmitter according to the invention comprises, in a manner known per se, a loudspeaker 1, here of the electrodynamic type with a vibrating membrane mounted on the wall of an enclosure 2 so that a face of its membrane radiates to the outside, while another face radiates to the interior of the enclosure 2. The enclosure comprises a vent 3 of tubular shape with an axis X and having an outlet 4 inside of the enclosure 2, a conduit 5 here reduced to a simple neck or constriction, and an outlet 6 outside the enclosure 2.

The interior outlet 4 forms a converging manifold guiding the air from the enclosure 2 forced to escape from the latter due to the displacement of the diaphragm of the speaker 1 towards the interior of the enclosure 2. The conduit 5 forms a neck limiting the passage section of the vent 3 and playing the role of the neck of a Helmholtz resonator whose enclosure 2 constitutes the reservoir. The external outlet 6 constitutes a divergent diffuser.

The operation of the sound transmitter is as follows.

For medium or high frequency sounds, the pressure waves are generated mainly due to the compressibility of the air in the enclosure. The movement of the air in the vent 3 is not significant with respect to the internal dimensions of the vent 3. The assembly behaves like a conventional resonator. For powers causing large displacements of the membrane, the pressure in the enclosure varies in great proportions and the air then undergoes displacements in the vent 3 which are no longer negligible compared to the dimensions of the vent 3. The internal forms of the vent 3 allow a setting in motion of the air in a regular flow substantially one-dimensional. The air is first set in speed by the internal outlet 4, then passes through the central duct 5 in a regular flow, and is channeled in a jet towards the outside by the external outlet 6.

The regular flow thus produced makes it possible on the one hand to minimize the energy losses in the form of turbulence and internal friction. It also makes it possible to avoid excessive turbulence at the outlet of the external outlet 6, which in conventional vents is responsible for background noise deteriorating the reproduction of sounds. It can thus be seen that the presence of a vent 3 according to the invention has a regularizing effect over the entire operating frequency range of the sound transmitter, and thus overall increases the performance of the sound transmitter. In this regard, the internal shapes of the vent 3 will follow a slowly evolving profile, the wall of the vent 3 being as free of asperities as possible which can cause turbulence. The inlet edges of the outlets will have a softened profile, to avoid whistle effects.

According to a remarkable aspect of the invention, the external outlet 6 has a divergent shape. This shape allows a slowing down of the air at the outlet of the vent 3 in accordance with the principle of conservation of the flow rate, and therefore a reduction in jet turbulence in the outside. This characteristic makes it possible to reduce the diameter of the conduit 5 in order to tune the Helmholtz resonator at very low frequencies, while ensuring a low speed of air flow towards the outside and keeping the volume of the enclosure in reasonable dimensions. The outlet section of the external outlet 6 may thus exceed half the surface of the diaphragm of the loudspeaker 2, while the diameter of the conduit 5 may be reduced in considerable proportions. The divergent shape also makes it possible to convert the kinetic energy corresponding to the slowing down of the air into pressure. This characteristic is particularly interesting during the emission of low frequency sounds, for which it is known that a significant part of the energy supplied to the membrane of the loudspeaker is transformed into kinetic energy of the whole. air in the vent. However, this kinetic energy does not participate in any way in acoustic phenomena. Thanks to this conversion, part of the kinetic energy of the air is thus recovered to convert it into pressure which interests the acoustic phenomena.

Remarkably, the exterior outlet 6 has an end portion having a concave profile, of concavity turned towards the interior of the outlet. The outlet thus acts like a diffuser or a nozzle, channeling air without violent detachment of the air streams from the wall when leaving the vent.

It will be noted that the exponential flags sometimes used as impedance adapters at the output of the loudspeakers do not allow this conversion to be carried out. Indeed, pavilions of this type have a convex profile unsuitable for ensuring a monodimensional laminar flow. At the high flow velocities reached at low frequencies under high amplitude, the air stalls prematurely from the surface of the pavilion and leaves in vortices. The acoustic performance collapses.

It was found that the vent 3 according to the invention makes it possible to significantly improve the sound efficiency for all the frequencies beyond the characteristic frequency of the Helmholtz resonator. Dramatically, the vent also makes it possible to obtain a transmission of sounds of frequency lower than the characteristic frequency of the resonator, with excellent efficiency. This effect seems to be explained by the convective radiation, as detailed in the introductory part of the request.

FIG. 3 relates to a second embodiment of the invention, in which the sound transmitter is equipped with a vent with a stilling chamber.

The vent 13 has a converging internal outlet 14 and a divergent external outlet 16. A tranquilization chamber 15 is disposed between the outlets 14, 16 and communicates with the internal outlet 14 by a neck 17 and with the outside outlet by a neck 18.

The stilling chamber 15 allows on the one hand to regularize the air flow by slowing it down after the passage of the neck 17 in order to dampen any turbulence which could have arisen upstream from the neck 17. The air is again ac ~ celerated at the outlet of the tranquilization chamber 15 by the neck 18 then slowed down by the divergent external outlet 16. Depending on the dimensions of the tranquilization chamber 15, the air in the latter may be more or less accentuated. The stilling chamber 15 also forms with the neck 18 a second Helmholtz resonator in series with the first resonator formed by the enclosure 2 and the neck 17. It is known that a resonator of this type has the property of reverse the phase of the pressure wave with respect to the movement of the diaphragm of the loudspeaker 1. The second resonator makes it possible to reverse this phase again to make the pressure wave in phase with the movements of the membrane.

The second resonator radiates not only outwards via the neck 18, but also inside the enclosure 2 via the neck 17. This reflected radiation has the property of regulating the movements of the membrane of the loudspeaker 1, and thus makes it possible to increase the power threshold beyond which the movable members of the loudspeaker abut, which is particularly advantageous at low frequencies. In a way, the stilling chamber 15 stiffens the membrane.

Any variant may be made to the sound emitter as described above without departing from the scope fixed by the claims.

In particular, although the flow of air from the interior of the enclosure to the outside has essentially been described corresponding to a movement of the membrane towards the interior of the enclosure, it is obvious that for a movement of the membrane towards the outside of the enclosure, the flow will take place from the outside towards the inside of the enclosure. In this case, the interior outlet of the vent plays the role of the exterior outlet, and vice versa. Preferably, vents of symmetrical shape will be produced between upstream and downstream, although non-symmetrical shapes produced according to the invention also work.

Although a tubular vent with a rectilinear mean axis has been described here, we also think of vents having a curved mean line, the curvature being nevertheless small enough to guarantee the most laminar flow possible.

If, for space constraints, a frankly bent vent has to be produced, a vent with a tranquilization chamber will preferably be used, from which the upstream and downstream parts will leave in arbitrary directions. As illustrated in FIG. 4 by way of example, the upstream 14 and downstream 16 parts come from the stilling chamber 15 in directions that are substantially normal to each other. The stilling chamber is thus used as a shock absorber allowing the angular gear while minimizing aerodynamic losses.

Although the vent has been illustrated as being placed essentially outside the enclosure, the invention still applies to a vent placed essentially in 1 enclosure.

Although the vent has been illustrated as having a tubular shape, the invention also applies to a vent having an evolving annular section, as is illustrated in FIG. 5 where the vent 23 is composed of a tubular outer part 21 and an inner core 22 connected to the outer part by connection means not shown and defining an annular channel for the flow of air. In the embodiments illustrated in relation to FIGS. 1 to 5, it will preferably be ensured that the flow is laminar at least at the level of the outlets, including for large amplitudes of membrane displacement. For this purpose, a diameter of the outlet section of the outlet large enough to obtain this laminar flow will be used.

According to another aspect of the invention, it is sought to control the air flow not only in the vent, but in the enclosure. With reference to FIG. 6, a sound transmitter according to the invention comprises a loudspeaker 30 placed in a body 31, the body 31 having internal shapes capable of conducting in a laminar manner a flow of air generated by the movement of the diaphragm of the loudspeaker 30. The body 31 comprises on one side of the diaphragm of the loudspeaker 30 a divergent conduit 32. The duct 32 guides the air pushed or sucked in by the diaphragm of the loudspeaker in a substantially one-dimensional flow, the speed of the air varying with respect to the speed of movement of the diaphragm in the inverse ratio of the sections as and as one moves away from the membrane. Correlatively, the pressure increases at the right of the outlet section in relation to the decrease in speed. Part of the kinetic energy is thus recovered from the air which is converted into pressure, while turbulence is avoided. these which generally arise at the edge of the membrane when the latter radiates directly into the air.

It would thus theoretically be possible to envisage outlet sections of the duct 32 so large that the speed of exit of the air vanishes and is entirely converted into pressure. In practice, we will use output sections of the order of at least 50% of the surface of the membrane, with which gains of several decibels at low frequencies have been measured. On the other side, the body 31 comprises a conduit 33 of the convergent / divergent type.

The duct 33 also provides a function for guiding the air flow generated by the other face of the membrane during the movement of the latter. The convergent / divergent shape with an intermediate throttle 34 makes it possible to create an internal volume delimited on the one hand by the membrane of the loudspeaker 30 and on the other hand by the throttle 34 separating the convergent part from the diverging part of the conduit 33 This volume constitutes, with the constriction 34, a Helmholtz resonator.

Two modes of operation must therefore be distinguished. When the sound emitted has a frequency higher than the characteristic frequency of the resonator thus formed, the resonator plays its role of wave generator and reverses the phase of the wave which is radiated at the outlet of the conduit 33, so that the wave radiated at the outlet of the conduit 33 is in phase with the radiated wave at the outlet of the conduit 32. Compared to a conventional enclosure, it has been found that the tapered internal shape of the body allows a gain greater than 7 decibels.

When the frequency of the sound emitted is lower than the characteristic frequency of the resonator, the conduit 33 acts as a guide for the air flow. The pressure wave is then not created by the resonator, but by the alternating movement of the air present in the duct so as to create a convective radiation in the ambient air. In order to limit turbulence at the end part 35 of the conduit 33, it will preferably be given a form of diffuser or nozzle, that is to say with a sectional profile having a concavity facing inward. of the duct. Similarly, the edge of the terminal part of the duct 33 will be softened to avoid any turbulence generating noises during a flow of incoming air. The phase of the pressure wave thus created is no longer reversed, so that the wave leaving the conduit 33 is in phase opposition to that leaving the conduit 32. We can then think that the two waves thus see their effect cancel. But compared to a wave created by a membrane radiating in the ambient air, it has been observed that the wave generated at the outlet of the conduit 33 is spectacularly stronger by several decibels. It therefore matters little that the two outgoing waves are in phase opposition, the difference in sound level preventing one from canceling the other.

According to a second embodiment illustrated in Figure 7, the sound transmitter this time comprises an exciter consisting of two speakers 40.1 and 40.2 mounted so that their membranes face each other, the speakers being preferably electrically connected in phase opposition to impose on the membranes an alternating movement of distance and reconciliation.

The sound transmitter comprises a first conduit 41 of axisymmetric shape extending around an axis X normal to the membranes in which radiates the rear face of the membrane of the speaker 40.2, and having two successive throttles 42 and 43 as well as 'a divergent outlet 44. The portion of conduit located between the throttles 42 and 43 forms a tranquilization chamber, like the chamber 15 fitted to the vent according to the invention. The sound emitter also comprises a second duct 45 of annular shape extending around the first duct 41 and in which the facing faces of the two membranes radiate. The duct 45 has a throttle 46 and a divergent outlet 47.

The rear face of the diaphragm of the speaker 40.1 radiates in the air, but the power that it radiates is negligible compared to that radiated via the conduits 41 and 45. In operation at medium and high frequency, the line 41 forms a double Helmholtz resonator, while line 45 forms a single Helmhotlz resonator. By virtue of the phase opposition excitation, the pressure waves leaving the conduits 41 and 45 are in phase. In a low frequency operation, below the characteristic frequencies of the resonators thus formed, two macroscopic air flows are created which generate pressure waves at the output of the divergent parts 44 and 47. These pressure waves are in phase opposition, but it seems that one of the flows, in this case that of the conduit 45, has a greater effect than the other, so that the wave leaving the conduit 45 is predominant. The air contained in the other flow rather has a feedback effect which regulates the movements of the two members.

It has thus been observed that the transmissible power before saturation of the loudspeakers (that is to say before reaching the mechanical stop of the moving parts of the loudspeakers) is significantly increased compared to an operation. outdoors. Furthermore, the gain of the transmitter is significantly improved compared to a conventional transmitter, and dramatically increased in the low frequencies.

According to a third embodiment illustrated in FIG. 8, the sound transmitter comprises two speakers 50.1 and 50.2 mounted similarly to loudspeakers 40.1 and 40.2 of the previous embodiment. The faces of the membranes radiating outwards are each associated with a divergent duct in the form of a diffuser 51.1 and 51.2 extending along an axis X normal to the membranes, the faces of the membranes facing each other being associated with a duct of the convergent type. / divergent 52 remarkable in that it has a symmetry of revolution around the axis X. The duct 52 thus has an annular constriction 53 forming the neck of a Helmholtz resonator.

In the embodiments illustrated in relation to FIGS. 6 to 8, it will preferably be ensured that the flow is laminar at least at the outlet section of the conduit, including for large amplitudes. membrane displacement. For this purpose, we will retain a diameter of the outlet section large enough to obtain this laminar flow.

The invention finally relates to a loudspeaker, which, with reference to FIG. 9, comprises a membrane 60 mounted on a support 61 of tubular shape with a smooth internal wall, the support comprising arms 62 for retaining an installed motor in a streamlined 63 fairing. The motor has an actuating member 64 cooperating with the membrane to impose alternating movements on it, and thus cause the macroscopic movement of the air located on either side of the membrane. As shown in dotted lines in FIG. 9, the internal face is intended to be connected to a tapered body in order to channel the air flow thus produced. The shapes of the sections 62 and of the fairing 63 are chosen to cause the minimum of turbulence in the air flow bathing them.

In a variant that is not shown, it will be possible to separate the engine into two parts installed on either side of the membrane in tapered fairings. The invention is not limited to particular modes of realization which have just been described, but on the contrary intends to cover any variant which by the use of equivalent means, falls within the scope of the invention as defined by the claims. Although the exciter of the sound emitter has been illustrated as being constituted by the membrane of a loudspeaker, the invention can be applied more generally to any exciter which can create a macroscopic movement of air, such as a piston moving in a cylinder.

Although the means for attenuating turbulence has been described as being essentially constituted by aerodynamic internal shapes allowing a smooth flow, any device allowing for example a bonding of the boundary layer such as a flap or a parietal suction device, or still a device for damping turbulence such as a powerful wall form attenuation means according to the invention. Finally, the invention encompasses any means of adapting the shape of the conduit or the vent according to the operating regime of the sound transmitter (power, frequency), and / or the ambient conditions (temperature, noise of background...).

Claims

1. Sound emitter comprising at least one vibrating membrane mounted on the wall of an enclosure (2) so that one face of the membrane radiates into the enclosure (2), the enclosure (2) being provided with a vent (3; 13; 23) forming a conduit (5; 15) between an outlet (4; 14) in the interior of the enclosure and an outlet (6; 16) outside the enclosure, characterized in that the vent (3; 13; 23) includes means for attenuating aerodynamic turbulence at at least one of the outlets during an air flow in the vent (3; 13; 23) caused by large amplitude displacements of the membrane. 2. A sound transmitter according to claim 1, characterized in that the means for attenuating the turbulence consist of internal shapes of the duct (5; 15) and / or outlets (4; 14.6; 16 ), these forms being arranged to allow a regular flow of air in the vent (3; 13; 23). 3. Sound transmitter according to claim 1 or claim 2, characterized in that at least one of the outlets (4; 14.6; 16) has a shape flaring towards its end. 4. A sound transmitter according to claim 3, characterized in that the outlet (4; 14,6; 16) flaring has an end portion having a profile in concave section of concavity turned towards 1 inside the outlet. 5. Sound transmitter according to one of the preceding claims, characterized in that it is equipped between the interior (14) and exterior (16) outlets with a stilling chamber (15). 6. Sound transmitter according to claim 5, characterized in that the stilling chamber (15) forms a bevel gear between the internal outlet (14) and the external outlet (16). 7. Sound emitter according to one of the preceding claims, characterized in that the external outlet (6; 16) has an outlet section at least equal to half the surface of the vibrating membrane. 8. Sound transmitter according to one of the preceding claims, characterized in that at least one of the outlets (4,6; 14,16) has a diameter suitable for making the flow of laminar air at the outlet ( 4.6; 14.16). 9. Sound emitter comprising at least one vibrating membrane mounted in a body, characterized in that the body comprises a conduit (32; 33; 1; 45; 51.1, -51.2; 52) in communication with the outside by a part terminal (35; 44; 47) and in which one face of the membrane radiates, the duct comprising means for attenuating aerodynamic turbulence at the level of the terminal part (35,44,47) during an air flow in the duct (3; 13; 23) caused by large amplitude displacements of the membrane. 10. Sound transmitter according to claim 9, characterized in that the means for attenuating turbulence are constituted by internal shapes of the duct (3; 13; 23), these shapes being arranged to allow a regular flow of air in the duct (3; 13; 23). 11. Sound transmitter according to claim 9 or claim 10, characterized in that the terminal part (35; 44; 47) has a flared shape. 12. Sound transmitter according to claim 11, characterized in that the terminal part (35; 44; 47) has an end portion having a profile in concave section of concavity turned towards the inside of the outlet. 13. Sound transmitter according to one of claims 9 to 12, characterized in that the transmitter comprises two speakers (40.1,40.2, -50.1,50.2) each having a membrane and mounted on the body so that the members face each other and are electrically connected in opposition phase, the faces of the membranes facing each other radiating into the internal duct (45; 52). 14. A sound transmitter according to claim 13, characterized in that the internal conduit (45; 52) has a throttle (46; 53). 15. A sound transmitter according to claim 13 or claim 14, characterized in that the conduit (52) has a shape of revolution about an axis normal to the membranes. 16. Loudspeaker comprising at least one vibrating membrane (60) mounted on a support (61) and actuated by at least one motor linked to the support (61), characterized in that the motor and the support (61) have aerodynamic shapes capable of causing the least possible turbulence in the air flow generated by the displacement of the diaphragm (60) and bathing the engine and the support (61). 17. Loudspeaker according to claim 16, characterized in that the motor is integrated in a tapered fairing (63). 18. Loudspeaker according to claim 16 or claim 17, characterized in that the support (61) is connected to the motor by profiled arms (62). 19. A method of producing sound, consisting in causing an alternating and convective displacement of air contained in a duct having an outlet to the outside, and at least partially transforming the kinetic energy thus communicated to the air into pressure at level of the outlet of the conduit.