EP2577989B1 - Acoustic loudspeaker - Google Patents

Description

TECHNICAL AREA

The invention relates to the field of acoustic loudspeakers. It is more particularly a loudspeaker equipped with arrangements allowing it to provide adjustment in the field of low frequencies, and more specifically bass sounds.

PRIOR TECHNIQUES

In general, it is known that the reproduction of bass sounds, that is to say located in the band 20-250 Hertz, is a major element in the assessment of the quality of an audio system. Indeed, insofar as a recording has been carried out correctly by including enough richness in the lower part of the spectrum, the quality of listening depends on one hand on the ability of an amplifier to reproduce these serious sounds, but on the other hand, performances of the speaker which themselves are, as far as the bass is concerned, dependent on the room in which the loudspeaker is located. Thus, the size and geometry of the room can have an influence, to the extent that, at the frequencies considered in the bass, the amount of air displaced by the speaker diaphragm is important. Likewise, at the corresponding frequencies, the wavelengths are such that the phenomena of reflection can cause the appearance of knots and wavelets that, depending on the location of the user, the sound quality can be very variable.

Thus, it is known that adjustments may be necessary to ensure optimal listening quality, these adjustments to take place in the room where the speaker is installed.

Various techniques have already been proposed to provide this type of adjustment, but are not really satisfactory. Thus, mechanical solutions have already been proposed, consisting in modifying the parameters of the vent on "bass-reflex " type charges, either by modifying the length of the vent or by plugging it with a foam. Such a solution modifies the resonant frequency of the vent. This results in an increase in the level at the resonant frequency, but the lower frequency sounds are on the contrary attenuated, with a feeling of imbalance of the bass response.

Electronic solutions have also been proposed by filtering the signal transmitted to the loudspeaker. In the case of passive filtering, they cause a drop in amplitude without actually providing solutions over a sufficiently wide frequency band. Active type filtering is also not satisfactory insofar as any gain in amplitude generally causes signal degradation by passing through a multitude of electronic correction circuits, which are sources of information loss and therefore of acoustic transparency. .

Another solution has been proposed by the Applicant which consists in using as a source of magnetic field, not a magnet (which generates a constant field), but a device comparable to an electromagnet. If this solution is satisfactory from an acoustic point of view, it is complex and expensive to implement, so it is limited to very high-end installations.

A particular speaker has been described in the document DE 195 28 904 . This speaker has a second coil mounted on the moving element, and in the magnetic field of the magnet of the speaker. This coil is short-circuited, and protects the speaker against over-currents and excessive vibrations.

The problem to be solved by the invention is therefore to allow adjustment in the low frequency band, without causing significant changes to the surrounding frequencies, without requiring complex or expensive installation.

SUMMARY OF THE INVENTION

• une source de champ magnétique constant ;
• un équipement mobile incluant une membrane, un bobinage apte à être parcouru par un courant électrique représentatif du signal sonore à générer, et à interagir avec ce champ magnétique constant, et un second bobinage également situé dans le champ magnétique.

The invention therefore relates to an acoustic loudspeaker which comprises:

• a constant magnetic field source;
• mobile equipment including a membrane, a coil adapted to be traversed by an electric current representative of the sound signal to be generated, and to interact with this constant magnetic field, and a second coil also located in the magnetic field.

According to the invention, this loudspeaker is characterized in that the two terminals of the second winding are connected by a substantially resistive component, selected from a set of resistive elements of distinct resistance values, by means of ensuring the connecting one of these elements to the terminals of the second winding. These means may be particularly varied, and it may for example be a set of jumpers or even multi-position buttons that connect the most appropriate resistance.

In other words, the loudspeaker is equipped with a coil in short circuit or closed circuit on a resistor, which moves in the magnetic field as the main coil, and which is therefore the seat of induced currents that dissipate by effect Joule in the resistive element connected to its terminals. In this way, the damping factor (or Qms) of the loudspeaker is adjusted so as to ensure optimum coupling between the volume of the listening room and the loudspeaker volume. Thus, the complementary winding, which is in practice associated with the main winding in which the control current flows, is the seat of a counter electromotive force which tends to prevent the coil from moving in the gap.

In practice, it should not be too heavy the mobile equipment by the presence of this complementary coil, and a good compromise can be found when the second coil has a volume of conductive material substantially identical to that of the main coil. By substantially equal volumes, it is meant that the difference between the two volumes is less than 20% relative to the smallest volume. Nevertheless, the phenomenon of damping can intervene for complementary windings which present a volume clearly different from that of the main volume, according to which one wishes to privilege the inertia of the mobile equipment, or conversely the degree of amortization.

Thus, in a preferred version, preference will be given to the use of rectangular section wires which allows winding with less space loss than a wire with a cylindrical section, although more difficult to produce.

In practice, the son of the damping coil may be made of copper, that is to say in the same material as that of the main winding, or in another material such as aluminum or the like. A compromise can be found between weight gain through the use of a less dense conductor such as aluminum, and the resistance value of the conductor, depending on its resistivity and section.

SUMMARY DESCRIPTION OF THE FIGURES

• la figure 1 est une vue en coupe d'un haut-parleur conforme à l'invention ;
• la figure 2 est une vue en coupe d'un détail de la figure 1 ;
• la figure 3 est un diagramme électrique montrant la capacité de réglage du haut-parleur conforme à l'invention ;
• la figure 4 est une courbe représentant l'impédance du haut-parleur pour différentes valeurs de réglage de la résistance connectée aux bornes du second bobinage.

The manner of carrying out the invention, as well as the advantages which result therefrom, will emerge from the description of the embodiment which follows, in support of the appended figures in which:

• the figure 1 is a sectional view of a loudspeaker according to the invention;
• the figure 2 is a sectional view of a detail of the figure 1 ;
• the figure 3 is an electrical diagram showing the adjustment capacity of the loudspeaker according to the invention;
• the figure 4 is a curve representing the impedance of the loudspeaker for different setting values of the resistance connected across the second winding.

MANNER OF REALIZING THE INVENTION

As illustrated in figure 1 a loudspeaker 1 comprises, in the traditional way, a mobile unit composed of a membrane 2 to which is associated a winding 3 connected to the amplifier 10 delivering the electrical signal representative of the acoustic wave to be generated.

This coil 3 moves inside an area in which a constant magnetic field is generated, created by a field source which is generally a magnetized element 6, associated with pole pieces 7, 8, 9, so as to confining the field lines at winding 3 with a minimum air gap.

According to the invention, the loudspeaker comprises a second winding which, in the form shown, is covering the main winding, so as to be subjected to the same magnetic field.

As illustrated in figure 2 , the main winding 3 is formed by a winding son, typically copper, of round section, while the coil 20 for changing the damping factor is formed by a wire rectangular section. This arrangement makes it possible not to excessively increase the air gap while maintaining a winding resistance as low as possible and a sufficient volume of copper. However, the principle of the invention also works with the use of other types of son, for example having cylindrical section, or made of similar materials such as aluminum.

As illustrated in figure 3 the damping winding 20 can be connected to different resistive elements 21-23. One of these elements can be a resistive element of very low value to simulate a short circuit to obtain maximum damping. It can also be a resistive element of average value which limits the current and is located on an intermediate value of the mechanical overvoltage coefficient (Qms). This value is calculated on a case-by-case basis, in order to obtain an intermediate level overvoltage coefficient value. In final, this adjustment is made in the listening room, according to the user's perceptions and the level of reverberation of this place. It can also be done in the factory, as long as the geometrical parameters of the room where the loudspeaker will be installed are known. The number of connectable resistive elements may vary depending on the fineness of the adjustment that is desired. It is also possible for the damping coil 20 to be left in the air so as not to create an electromagnetic force, in which case the damping coil does not create an electromotive force so that the loudspeaker operates with these parameters. original

As already mentioned, this adjustment can be done in different ways without departing from the principle of the invention, whether it is riders 24 as shown in FIG. figure 3 , or a multi-position knob for connecting the appropriate resistor 21,22,23 .

An exemplary embodiment is illustrated in the figure 4 , in which the impedance of the loudspeaker, seen by the amplifier, is plotted on the ordinate, and the frequency on the abscissa, giving priority to the bass zone. Thus, the curve 41 which has the most marked peaks corresponds to an open circuit situation, an almost infinite resistance. The two peaks 42, 43 located in the neighborhood of 15 and 50 Hertz correspond to couplings between the loudspeaker and the vent as a function of the volume of the loudspeaker and the Thiele and Small parameters of the loudspeaker. corresponds to the position where the damping winding is almost short-circuited, ie the maximum setting position for which the original mechanical overvoltage coefficient (Qms) has been divided by more than 14, the decrease sound level between 50 and 100 Hz being -3dB compared to the initial level. Curve 45 corresponds to the intermediate current flow position in a 2.2 Ohms resistor which makes it possible to reduce the sound level between 50 and 100 Hz by -1.5 dB, the factor Qms being divided by 8.

It follows from the above that the loudspeaker according to the invention has the advantage of being able to be adjusted so as to adjust its mechanical quality factor which has a very high resolution, including in the low register, and this with an easy-to-implement solution that makes it applicable to a wide range of speakers. Thus, the invention makes it possible to adjust the response of the acoustic enclosure to the listening room.

Claims (3)

1. An acoustic loudspeaker (1) comprising:

   - a magnetic field source (6);

   - a moving part comprising a membrane (2), a coil (3) capable of conducting an electric current representative of the sound signal to be generated, and of interacting with said magnetic field and a second coil (20),

   characterized in that it comprises a set of essentially resistive elements (21, 22, 23) of different resistance values, and means (24) for connecting one of said elements across the terminals (27, 28) of said second coil (20).
2. The loudspeaker of claim 1, characterized in that the second coil (20) is formed from a wire of rectangular cross-section.
3. The loudspeaker of claim 1, characterized in that the second coil (20) has a conductor material volume substantially equal to that of the coil (3) conducting the current representative of the signal.

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