EP2139266A1 - New bass transducer with excitation motor for loudspeakers of acoustic chambers allowing an adjustment of the coupling between the loudspeaker and the listening room - Google Patents

Abstract

The motor has a power supply for adjusting electrical power supplied to an electro-magnet from 0.4 to 90 watts or from 1.75 to 30 volts, where the motor presents an air gap (2) of 2 mm, backplate thickness of 28 mm and cross-sectional area of 20 mm. A coil comprises two copper layers with 1500 turns for electrical resistor of 8.2 ohms. The power supply has an electrical signal detector for detecting the presence of sound and automatically exciting the power supply. Independent claims are also included for the following: (1) a bass transducer for acoustic enclosures (2) a mode for utilizing a bass transducer.

Description

Technical sector of the invention:

The present invention relates to the technical field of loudspeakers, in particular high and very high-end speakers and in particular their component type bass transducer for loudspeakers speakers.

Technical problem posed:

In the field of loudspeakers, especially high or very high range, it is always inevitable to achieve very difficult compromises between often conflicting features.

In general, the "serious" transducer is a very important element in the design of any acoustic reproduction system.

In an acoustic reproduction system, the role of the bass is to cover the frequency band in which we find the first harmonics between 20 and 250 Hz.

This point is important because these harmonics will give the full size and size of the instrument returned.

Indeed, the human ear being a "transient type" sensor, it is the perception of all harmonics that will give sound restored all its finesse, its definition, without dragging or "coloring".

As can be seen, few loudspeakers can faithfully reproduce frequencies below 35 Hz.

This bass transducer indeed is particularly sensitive to high-level dynamic compression, dragging, and can present very strong colorations if it is poorly studied.

In 1995, the applicant created the Grande Utopia ^™ reference chamber, which will have a worldwide impact. For the first time, a loudspeaker can reproduce the entire audible band by the human ear (from 20 to 20 kHz) with a particularly low level of distortion while maintaining high performance.

To obtain these performances, the bass was distributed between two speakers, one of very large diameter loaded in a large volume to reproduce the extreme-bass (frequency lower than 70 Hz) and a second speaker smaller for the high-bass (70 Hz to 250 Hz).

This is mainly responsible for the measurements of the enclosure since it weighs about 220 kg for 1.80 m in height.

The bass reproduction quality of this FOCAL JMLAB ™ speaker series has set a new standard in performance and musicality for audiophiles.

• l'appui d'un bon amplificateur assurant le bon contrôle du transducteur;
• un auditorium conçu pour recevoir cette grande enceinte et un emplacement éloigné des murs.

But such performances impose a large number of constraints since a serious quality can only be obtained by:

• the support of a good amplifier ensuring good control of the transducer;
• an auditorium designed to accommodate this large enclosure and a location far from the walls.

Indeed, the bass is very sensitive to the listening room, because the sound generated by the bass transducer has wavelengths fairly close to the dimensions of the room. This generates nodes and pressure bellies degrading very seriously the quality of bass.

• à la dimension de la pièce,
• à la position des enceintes,
• à la position d'écoute,
• à l'emplacement de diffuseur ou absorbant,
• à la forme de la pièce,
• au passage d'une écoute en 4 Pi stéradians soit un rayonnement sphérique, à une écoute en pression si cette pièce est petite.

These elements are directly linked:

• to the size of the room,
• at the position of the speakers,
• at the listening position,
• at the diffuser or absorbent location,
• to the shape of the room,
• at the passage of a listening in 4 Pi steradians is a spherical radiation, to a pressure listening if this piece is small.

• coefficient d'amortissement,
• puissance,
• capacité à fournir le courant nécessaire,
• bande passante, ...

The amplifier too can affect the bass with these characteristics:

• damping coefficient,
• power,
• ability to provide the necessary current,
• bandwidth, ...

Measurement campaigns on existing systems have been carried out: they have notably shown that these effects could in very unfavorable cases vary the level of bass up to +/- 6 dB on frequencies below 70 Hz.

In order to go further in the control of the low register and to offer more flexibility to the user, FOCAL ^™ decided to engage more recently a centered approach this time on the possibility of adjusting the level of the transducer. serious to reproduce the frequencies lower than 70 Hz to adapt the speaker to these two external factors which are the room and the amplifier.

As will be seen below, FOCAL ^™ did not wish to use a globally known solution, that is to say an active electronics (besides with sometimes dubious qualities, much criticized by the audiophiles), but rather of to act in his research with a radically original approach directly at the level of the bass transducer using an excitation motor (that is to say motor employing an electromagnet).

Nevertheless, the inventors have noticed a defect known elsewhere on the excitation motor which resides in the heating of the motor when it is fed continuously.

This is a significant disadvantage and even very serious for the powers and parameters targeted by the Applicant, since this increase in temperature modifies the parameters of the transducer by increasing the electrical resistance of the coil. This increase in temperature also reduces the power handling of the transducer.

One of the objectives of the present invention is to achieve the creation of a bass transducer capable of providing a level-adjustable bass level, employing an excitation motor while maintaining a high quality level, and solving the known problems of such an engine, and while achieving extreme simplicity of use.

One of the merits of the inventors is to have persisted in this original approach, despite the severe and known defects of such an engine, and another merit is to have reached a solution.

Prior art:

• Le filtre actif analogique ;
• La source en dipôle à rayonnement cardioïde soit un rayonnement contrôlé en forme de double coeur ;
• Le filtre actif numérique;
• Event réglable sur des charges de type bass-réflex ;
• Filtre passif ;
• Moteur utilisant un électro-aimant dit à « excitation ».

There are many solutions to get a serious adjustable:

• Active analog filter
• The cardioid radiation dipole source is a dual-core controlled radiation;
• Digital active filter;
• Adjustable event on bass-reflex type loads;
• Passive filter;
• Motor using an electromagnet said to "excitation".

Outside the active speakers, no manufacturer offers a real bass level adjustment.

Some bypass the problem by proposing a setting to lower the level of the medium and that of the "tweeter" ("acute" transducer).

The speakers equipped with an active analog filter thus offer the possibility of modifying the level of bass or correcting defects of the speaker. But the signal is then degraded by the passage in a multitude of electronic correction circuits, sources of loss of information and therefore of transparency.

In addition, the power amplifier modules used for each of the transducers are very often of a very average quality.

The digital active filter reduces the number of circuits traversed by the signal by processing the corrections numerically. The accuracy of the calculation comes into play and comes to limit the system with a defined number of decimals. The signal is then converted from digital to analog.

Listening, the level of transparency does not reach the level of a single very good amplifier connected to an enclosure with a passive filter equipped with very good transducers.

It is recalled that "transparency" is a well-known concept that resides in the ability of a system to faithfully reproduce a sound without distortion, "coloration" or so-called "veil" effect, the coloring being, because of a reproduction not perfect, a very slight modification of the sound reproduced compared to the sound emitted, which, for an audiophile, gives an instrument a certain "coloration" different from the original.

Some manufacturers offer the possibility to modify the parameters of the vent on "bass-reflex" type loads (that is to say that the back wave is recovered and is sent back in phase to the wave before, which can substantially double the yield), either by changing the length of the vent or by plugging or clogging with a foam.

By changing its length, you can change the resonance frequency of the vent. This results in a "boost" (amplitude boost on a particular frequency area) on the resonant frequency (ie, an increase in the bass level) but sounds below this frequency tend rapidly to an acoustic short circuit (low level of bass). This results in an imbalance of the bass response.

While plugging the vent the level of severe declines of a few decibels but this only partially solves the problem.

The passive filters are positioned between the amplifier and the speaker. They offer adjustment possibilities to lower the level, but do not allow to gain level.

By the 1930s, the first speakers did not use a permanent magnet (which was then not powerful enough) but an electromagnet . It offered, among other things, a lot of flexibility for the development of speakers because the parameters "Thiele and Small" were not yet known at that time. These speakers were not studied to reproduce the 20 Hz but rather the high-bass and the medium.

The Applicant offers on its speakers the possibility of use in "passive biamping". This consists in feeding the bass speaker with a second amplifier. This provides excellent features but requires the customer to purchase another amplifier with among other things the need for a gain adjustment. Filtering is always done by the speaker filter.

Recently, the Applicant has decided to direct his research towards a gravitational transducer equipped with an excitation motor.

The well-known disadvantages of the motor excitation, including its very intense heating, have ruled out its use for decades and it is no longer used except for some very special productions and with exorbitant cooling means. It will be understood that liquid nitrogen or an agent of this refrigerating power, or any ultra-complex or bulky system, can not be used as coolant, for a production of very high-end speakers but which remain "large". public "that is to say can be reasonably produced industrially and not only in the laboratory. Faced with the difficulties encountered, the Applicant was also on the point, after the launch of the research, to abandon this way too.

The interest of being able to modify the magnetic power of the transducer to vary the level of bass and also to modify the alignment (form of the frequency response to the high or low cut, here low, and which is related to the overvoltage of the coupled system (or QF quality factor)) was of great importance for the invention. The magnetic field can also be more powerful than motors with permanent magnets.

The concepts of transducer, midrange, treble, bass, bass-bass, harmonic, harmonic range, bass-reflex, boost, power, power handling, performance, resonance, distortion, dragging, membrane, coloration (modifying the the exact sound of a given instrument by giving it, when passing through the transducer, a very slightly different "acoustic coloration", that the music lover detects), bandwidth, acoustic connection, coupling, alignment, transparency (ability to make the sound with perfection and no detectable effect of sail), point source, cutoff, "waterfall" (response curve (in symbolic form of "waterfall") in frequency in time: the extinction of a given frequency - and all the frequencies of the band - must be as fast as possible, not "dragging", and must be ideally instantaneous, that is to say without "extinction accidents" and thus without bringing "coloration to a given instrument ) and analogs are well known to those skilled in the art and will not be otherwise defined herein. This is general knowledge of the skilled person.

• extension en fréquence jusqu'à 20 - 30 Hz ;
• rendement élevé supérieur à 95 dB ;
• facteur de force (BL) élevé ;
• QTS ( qualité globale des paramètres qui permet d'ajuster le couplage du haut-parleur au local ou pièce d'écoute) ajustable et réglable.

The objective of the present invention is the creation of an excitation motor driven bass transducer which meets the highest quality requirements, such as:

• frequency extension up to 20 - 30 Hz;
• high efficiency greater than 95 dB;
• high force factor (BL);
• QTS (overall quality of the parameters which makes it possible to adjust the coupling of the loudspeaker to the local or listening room) adjustable and adjustable.

Another objective to be achieved in the chosen route of research has been to design a motor excitation no longer has the known drawbacks, including intense heating incompatible with a mainstream production.

As will be seen below, the invention relates to both a new bass driver, a new excitation motor and also a new use (or mode of use) of this transducer with a "force factor" BL very much higher (at least doubled in general) compared to what is known to achieve in the prior art, in particular of the order of 25 to 35 , in particular 27 and 34 with a prototype made, against a maximum of 25 in the prior art (this value of 25 only being achieved in the laboratory and at an exorbitant production cost and by achievements that are technically very complex and incompatible with "reasonable" high-end industrial production).

• Avoir la possibilité de modifier le niveau de grave de +3 dB - 3 dB par rapport au niveau actuel de 20 à 70 Hz - le haut-parleur étant filtré ;
• Maintenir le faible taux de distorsion sur la plage de fréquence utile ;
• Avoir une courbe de réponse linéaire de 20 Hz à 70 Hz, avec un amortissement rapide ;
• L'impédance minimale ne doit pas descendre en dessous de 2,5 ohms ;
• La mise en oeuvre du réglage doit être facile ;
• Maintenir le niveau de performance du transducteur y compris en échauffement/dilatation, même après plusieurs heures de fonctionnement du moteur à excitation ;
• Résoudre le problème très ardu de l'échauffement ;
• Le tout avec un encombrement et une complexité, et à un coût, accessibles pour une enceinte très haut ou haut de gamme mais qui doit rester « grand public ».

Objectives of the present invention are to make it easier to integrate Grande Utopia-type loudspeakers into different listening rooms and different amplifiers, the subwoofer transducer must be able to have an adjustable level and meet the following performance levels:

• Have the possibility to change the bass level of +3 dB - 3 dB from the current level of 20 to 70 Hz - the speaker being filtered;
• Maintain the low distortion rate over the useful frequency range;
• Have a linear response curve from 20 Hz to 70 Hz, with fast damping;
• The minimum impedance must not fall below 2.5 ohms;
• The implementation of the adjustment must be easy;
• Maintain the performance level of the transducer including heating / dilatation, even after several hours of operation of the excitation motor;
• Solve the very difficult problem of warming up;
• All with a size and complexity, and at a cost, accessible for a speaker very high or high-end but must remain "mainstream".

The Applicant has deliberately avoided the use of mechanical resonances which nevertheless artificially increase the sound level (especially using a high resonance frequency and "break up" (deformation of the membrane and possibly rupture) at 20 kHz not damped) but which generate a lot of dragging (the drag is the frequency response to the extinction of a sound: the extinction of the frequencies concerned should ideally be instantaneous, but we can note "extinction accidents" that is to say frequencies that are slow a little too much to go out; the corresponding frequency / time curve is called "waterfall").

The examples below, and the above, show not only a powerful and continuous research effort on the part of the Applicant, while allowing to understand that progress is difficult and innovations more and more problematic because it is acts of advanced technologies. In such areas, often, even a "weak" improvement of a property can be a significant inventive effort and struggle against many technical or "historical" prejudices, and the difficulty of always allowing conflicting or inconsistent factors to work, ultimately, within the same innovation.

As will be seen below, the invention manages in this difficult context to achieve a "quantum leap".

Summary of the invention

• A un nouveau transducteur de graves caractérisé en ce qu'il comporte un moteur à excitation (c'est-à-dire comportant un électro-aimant), ce moteur étant lui même caractérisé par des optimisations difficiles des matériaux ferromagnétiques et des flux magnétiques et des capacités de réglages jusqu'alors inconnues ;
• B l'utilisation du transducteur de graves tel que ci-dessus dans des enceintes acoustiques ;
• C lesdites enceintes.

The invention relates to

• A new bass transducer characterized in that it comprises a motor excitation (that is to say comprising an electromagnet), the engine being itself characterized by difficult optimizations of ferromagnetic materials and magnetic fluxes and previously unknown adjustment capabilities;
• B the use of the bass transducer as above in loudspeakers;
• C said speakers.

Detailed description of the invention

The invention will be better understood on reading the description which follows, and non-limiting examples below.

Description of studies, tests, prototypes, synthesis of tests, information from tests and prototypes.

The Applicant has noted that when the excitation motor is supplied with 60 W continuously inside an enclosure, its temperature can rise very high in temperature, for example 97 ° C.

This is a very important disadvantage even crippling since this increase in temperature increases the electrical resistance of the speaker (+ 33%). In addition, this reduces the power handling of the transducer, another serious disadvantage.

These problems had to be solved, among other things.

Development of the excitation motor according to the invention. (with use of magnetic simulations) Point with the best performance of the prototype:

• The gap has been reduced to a minimum: (it goes from 3.6 mm to 2 mm)

• La forme de la bobine du moteur a été étudiée :

This was possible using a 2-layer copper speaker coil (ie 1500 turns for an 8.2 ohm electrical resistance) instead of 4.

• The shape of the motor coil has been studied:

• L'augmentation de l'épaisseur du métal dans les zones susceptibles de saturer a été étudiée :

A square section of the coil provides the smallest loopback length (i.e., the length of the magnetic loop). This modification reduces magnetic leakage.

• The increase of the thickness of the metal in the zones likely to saturate was studied:

When we increase the power supply of the engine, we noticed that zones were saturated: the thickness of the base plate thus passes according to the invention of 10 mm to 20 mm, and the section of the core passes of 22 mm at 28 mm.

Cf. Figures 1 to 4 attached.

Figure 1 :

Lines of the magnetic flux induced by the excitation coil. In the air gap, the lines of magnetic fields are well parallel and symmetrical.

Square section coil example

Note that other coil sections are possible, and that the square section is only the very preferred solution because one allows a short loop length; all sections meeting this criterion are eligible and the person skilled in the art will be able to extrapolate them from the teaching of the square section.

Figure 2:

Magnetic field intensity curve in the air gap of the motor obtained with an excitation power supply power of 90 W.

The magnetic field reaches 1.75 Tesla and 2.37e-5 Webers

(Performance almost doubled compared to a motor using a permanent magnet with the same gap).

Figure 3:

• 1 - Le trait noir épais représente la bobine du haut-parleur positionnée dans l'entrefer ;
• 2 - entrefer du moteur ;
• 3 - La plaque de champ (fer doux) ;
• 4 - cerclage de rebouclage magnétique (en fer doux) ;
• 5 - La zone repérée par des cercles représente l'orientation des fils de la bobine d'excitation (cuivre) ;
• 6 - plaque noyau (fer doux).

Representation of the excitation motor:

• 1 - The thick black line represents the coil of the loudspeaker positioned in the gap;
• 2 - air gap of the engine;
• 3 - The field plate (soft iron);
• 4 - magnetic loop backing (made of soft iron);
• 5 - The area marked by circles represents the orientation of the son of the excitation coil (copper);
• 6 - core plate (soft iron).

Figure 4:

Representation of the zones where the magnetic field is greater than 1.75 Tesla when the power supply of the excitation coil is at 90 W. They make it possible, among other things, to visualize the areas where the soft iron saturates magnetically.

It can be seen that the modifications made it possible to obtain a magnetic field of 1.75 teslas for a power supply of 90 W

Before these changes, the field was only 1.1 Tesla.

Realization and performance of a prototype

The UNIQUE APPENDIX table summarizes the results: (temperature, magnetic field, HP performance, competing product).

We see that :

The magnetic field:

With only 9 W of power we obtained a magnetic field identical to that of the motor multiferrite (0.93 Tesla). The maximum field with 90 W reaches well 1.75 T is an increase of 88% of the field.

The efficiency is much higher than the first version (prior art) of the engine since it required 60 W to obtain the magnetic field of the multiferrite against only 9 W for this new version according to the invention.

Temperature measurement:

No change because the motor mass and the heat dissipation of the enclosure remain unchanged.

• BL (facteur de force) passe de 18,5 (art antérieur) à 34,84 (pour une résistance électrique du transducteur de 6 ohms) ;
• QTS passe de 0,42 à 0,13 ;
• Rendement passe de 92,7 à 98,6 dB (98,1 dB à 90 W.);
• Rendement du grave à 30Hz passe de 87,5 dB à 90,5 dB ;
• Fréquence de coupure à - 3 dB passe de 41,15 Hz à 33,51 Hz.

Very good HP performance (speaker) : (9 W -> 90 W)

• BL (force factor) increases from 18.5 (prior art) to 34.84 (for an electrical resistance of the transducer of 6 ohms);
• QTS goes from 0.42 to 0.13;
• Yield increased from 92.7 to 98.6 dB (98.1 dB at 90 W.);
• Performance of the bass at 30Hz goes from 87.5 dB to 90.5 dB;
• Cutoff frequency at - 3 dB changes from 41.15 Hz to 33.51 Hz.

Better engine performance than the known prior art:

This new motor provides the same magnetic field with 2 times less electrical power applied.

Distortion rate at 100 Hz, 1 W:

• Original speaker: 0.35% to 1%;
• Loudspeaker with excitation motor with 5 volts supply: 0.33%;
• Loudspeaker with excitation motor with 25 Volt power supply: 0.22%.

The measurements show that the more the magnetic field is increased, the lower the distortion rate.

All of these improvements have reduced the power supply of the engine.

Despite this significant increase in engine efficiency, it is nevertheless desirable that the engine is not powered continuously; indeed it is desirable to be able to use the new engine performance to its maximum, or 90 W.

It is therefore prudent that the motor supply is cut off after use by the Customer.

Excited motor power Creation of a power supply with automatic signal detection, timed and ultra reliable

• essai avec une régulation en courant: (sur du signal musical)
  Bizarrement il a été constaté des problèmes d'ondulation électrique sur le courant ainsi que sur la tension électrique (soit 2 000 mV). Ce défaut est audible.
  Il est probable que la forte inductance du moteur induit une importante rotation de phase du courant qui est non compatible avec une régulation électronique en courant.
  Par contre, la très grande inductance du moteur (320 mH) suffit à auto réguler le courant. Seule la tension doit être régulée.

It is extremely important to note that it is this power supply which makes it possible to regulate the electrical power supplied to the electromagnet (in particular from 0.4 W to 90 W) (ie from 1.75 Volts to 30 Volts).

• test with current regulation: (on music signal)
  Strangely, there were problems with electrical ripple on the current as well as on the electrical voltage (ie 2000 mV). This defect is audible.
  It is likely that the high inductance of the motor induces a large phase rotation of the current which is not compatible with electronic current regulation.
  On the other hand, the very large inductance of the motor (320 mH) is enough to self regulate the current. Only the voltage must be regulated.

- test with voltage regulation

A value of 100mV of ripple was noted. Which is a very good result

Temperature resistance problems of the regulator have been measured: 70 - 80 ° C despite large radiators. This represents a significant risk of destruction of electronic components, incompatible with the manufacturer's ten-year warranty.

It was necessary to solve this problem, which had been anticipated and had abandoned this technology for decades.

- transformer test + simple rectification

Ripples slightly higher than the regulated version have been measured (200 mV) but are acceptable. In addition, they can be further reduced by increasing the filtering capabilities.

The plays did not reveal any audible defect.

This passive power supply has the advantage of not heating up and withstanding electrical overvoltages.

The Applicant has deliberately discarded the well-known and advantageous solution of switching power supplies for the following reasons: electrical noise, less reliable power supplies than traditional power supplies.

An electrical signal detector detects the "presence" of the sound and allows the automatic switching on of the motor supply. It also stops after 15 minutes of inactivity.

It prevents the motor from being fed continuously. We can use the engine at full power without the engine heats up. This playing with the significant thermal inertia of the engine and the high efficiency of the engine.

An increase of only + 30 ° C for 2 hours of operation at full power.

• MLSSA (système de mesure acoustique - mesure de courbe réponse et d'impédance).
• DAAS (système de mesure acoustique - mesure de distorsion).
• Gaussmètre (mesure magnétique).
• KLIPPEL (mesure de la température en fonction de la puissance).
• Oscilloscope (mesure électrique).

Materials used:

• MLSSA (acoustic measurement system - measurement of response curve and impedance).
• DAAS (acoustic measurement system - distortion measurement).
• Gaussmeter (magnetic measurement).
• KLIPPEL (temperature measurement according to the power).
• Oscilloscope (electrical measurement).

• LSPCAD5,25 ^™ (simulation acoustique).
• GEMINI ^™ (simulation magnétique).

Software:

• LSPCAD5,25 ^™ (acoustic simulation).
• GEMINI ^™ (magnetic simulation).

Claims (10)

Excitation motor, that is to say having an electromagnet, for use in acoustic enclosures, characterized in that it comprises: - a minimum air gap; the loopback length, that is to say the length of the magnetic loop, the smallest; an increase in the thickness of the bottom plate; - and an increase in the section of the core; - And a power supply that adjusts the electrical power supplied to the electromagnet, including 0.4 W at 90 W, including 1.75 to 30 volts. Excitation motor according to Claim 1, characterized in that : - the air gap is 2 mm; the coil comprises only 2 layers of copper, ie 1500 revolutions for an electrical resistance of 8.2 ohms; the thickness of the bottom plate is 28 mm; - The section of the core is 20 mm. Engine according to claim 1 or 2, characterized in that the section of the coil is square in shape or similar. Motor according to any one of Claims 1 to 3, characterized in that with only 9 W of power a magnetic field of 0.93 teslas is obtained and, with 90 W, 1.75 teslas are obtained. Motor according to any one of claims 1 to 4, characterized in that its power supply comprises a transformer plus simple rectification and controls said adjustment. Motor according to Claim 5, characterized in that its power supply furthermore comprises an electrical signal detector which detects the "presence" of the sound and enables the automatic switching on of the motor power supply and also ensures the stoppage after a predetermined time, including 15 minutes, of inactivity. Loudness transducer for loudspeakers, characterized in that it is equipped with an excitation motor according to any one of claims 1 to 6. Transducer according to Claim 7, characterized in that it makes it possible to modify its magnetic power to vary the bass level and also to modify the alignment, in particular the shape of the frequency response at the low cut, this being due to a power supply that allows to change the electrical power supply of the electromagnet, for example from 0.4 W to 90 W, 1.75V to 30 V. Transducer according to claim 7 or 8, characterized by the following parameters: - frequency extension up to 20 - 30 Hz; - high efficiency greater than 95 dB; - force factor, BL, very high; - QTS, global quality of the parameters which allows to adjust the coupling of the speaker to the room or listening room, adjustable and adjustable. - possibility to change the bass level from +3 dB to -3 dB; compared to the current level of 20 to 70 Hz - the speaker being filtered; a low rate of distortion over the useful frequency range; a linear response curve from 20 Hz to 70 Hz, with rapid damping; an impedance that does not fall below 2.5 ohms. New mode of use of the transducer according to any one of claims 7 to 9 with: a "force factor" BL of the order of 25 to 35 , in particular 27 and 34 for a transducer having an electrical resistance of 6 ohms. - QTS of 0.13; - efficiency of 98.6 dB; - bass output at 30 Hz of 90.5 dB; - cutoff frequency at - 3 dB of 33.51 Hz.

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