FR2976757A1 - DOUBLE WINDING PASSIVE POLYPHONIC MICROPHONE FOR A STRING MUSIC INSTRUMENT - Google Patents

Abstract

The invention relates to a passive polyphonic double-coil stranded musical instrument microphone (10) comprising: - a support (11), - a set of coil pairs, - in which for each pair of coils, the two coils are electrically connected in series and in magnetic connection (LC) with each other. The microphone according to the invention is essentially characterized in that it further comprises - an assembly of at least one internal dipole magnet (40), the poles of which are in magnetic connection with the respective core of a coil of a pair of coils, - a set of magnetic shields, integral with the support (11), - each coil being surrounded by a respective magnetic shielding, in which - For each pair of coils, one of the coils is connected to a ground, and the other is equipped to carry an output signal to an amplifier.

Description

PASSIVE DOUBLE COIL POLYPHONIC MICROPHONE FOR STRING MUSICAL INSTRUMENT.

The present invention relates to the field of amplification of a stringed instrument. The microphones for stringed instruments, hereinafter "micro (s)", are well known, they are classically integrated into the body of the musical instrument and there are many documents of the prior art on this subject. Unlike piezoelectric microphones whose output signal depends on the mechanical tension of the string, conventional magnetic pickups include coils (solenoids) whose output signal depends on the movement of the string. A solenoid produces a magnetic field in its vicinity when it is traversed by a current. According to this principle, but conversely, a microphone generates an output current in response to the disturbance of the magnetic field of its coils. The disturbance of the magnetic field is in fact due to the vibration of the string (or strings) played by the musician. When a metallic rope vibrates near the microphone, the variation of the magnetic field creates an induced current, of the same frequency as the vibrating cord, which then needs to be amplified.

There are two types of microphones: single or double coil.

A single coil magnetic microphone is composed of a magnet, a coil traversed by the magnetic field of the magnet and a movable diaphragm. Variations in the moving diaphragm modify the magnetic field induced by the magnet which generates a counter-electromotive force in the coils. In the case of a stringed musical instrument, the movable diaphragm is constituted by the strings.

A double-coil magnetic pickup works on the same principle as a single-coil pickup but with two coils electrically connected to each other. An example of these so-called humbuckers microphones is illustrated in Figure 1. In these microphones, two coils are fused that is to say, mounted in series (at the electrical level) and with a reversed magnetic polarity, to cancel the electromagnetic disturbances exterior. These microphones are characterized by a rich sound in bass and midrange and a level of output generally higher than on single coil pickups.

However, especially as part of an instrument played with a distortion effect, the notes played acquire a diffuse sound (the grain or "crunch") that makes them less slamming. The more we increase the distortion and the natural sound of the instrument (especially an electric guitar) is substituted for the benefit of the crunch and "sustain" (ability of the instrument to preserve, maintain the sound of a note, without it being replayed) which increases. This effect, obtained by saturation of a conventional amplifier or using an ad hoc effect module (or pedal), proceeds by clipping, compresses the attack of the note played while increasing its harmonics. In practice, the signal from a single string is perfectly distinct. Beyond this, for a two-string chord, the signal is still audible but for chords with three or more strings, the output signal is then an unusable noise.

Thus conventional microphones single or double coil are not applicable to polyphonic sounds.

In this spirit, the Applicant has filed the patent application FR9607937. The present invention aims to improve the solution proposed in the application FR9607937 by providing an audible analog solution allowing polyphony for any type of string instrument, including distortion.

With this objective in view, according to a first of its objects, the invention relates to a passive polyphonic double-coil microphone for a stringed musical instrument comprising: - a support, - a set of pairs of coils each pair of coils comprising a first a coil and a second coil, each coil comprising a magnetic core and a coil around said core, an upper face and a lower face, - in which for each pair of coils, the two coils are electrically connected in series and in magnetic connection; one with the other. According to the invention, the microphone is essentially characterized in that it further comprises: - an assembly of at least one internal dipole magnet, one pole of which is in magnetic connection with the core of a coil of a pair of coils and the other pole is in magnetic connection with the core of the other coil of said pair, 20 - a set of magnetic shields, integral with the support, - each coil being surrounded by a respective magnetic shielding, and 25 - for each pair of coils, one of the coils is equipped with an electrical wire to be connected to a ground, and the other coil is equipped with another electrical wire for the transport of an output signal to an amplifier.

Preferably, the distance separating two coils of the same pair is identical for each pair of coils.

Preferably, each shield has the same magnetic polarity as that of the coil it contains. Preferably, the coil pairs are arranged so that all of the first coils are aligned along a first straight line, and all of the second coils are aligned along a second straight line. It can be provided that the set of at least one inner dipole magnet comprises: a respective internal dipole magnet per pair of coils, 10 - an internal dipole magnet for all the pairs of coils, or - a respective internal dipole magnet for each couple of adjacent pairs of coils.

Preferably, the set of pairs of coils has an upper face, intended to be positioned opposite the ropes, and a lower face; said set of at least one inner dipole magnet being positioned on the side of the lower face. In addition, an assembly of at least one magnetic shunt, arranged between the assembly of at least one internal dipolar magnet and the cores of at least one pair of coils, can be provided to attenuate the intensity of the magnetic field of said internal dipolar magnet 25 at said nuclei. Alternatively, one can not implement magnetic shunt, provided that the power of the internal magnet, for example alnico, is appropriate.

In addition, a set of at least one external dipolar magnet can be provided, in magnetic connection with at least one core and having a reverse magnetic polarity of said core.

It can be provided that said assembly of at least one external dipole magnet is secured to at least one magnetic shielding via an electrical and magnetic insulator.

In one embodiment, the microphone comprises a first external dipolar magnet common to all the first coils, and a second external dipolar magnet common to all of the second coils.

In one embodiment, each magnetic shield has a first recess at the top face to facilitate the establishment of field lines between the core of the first coil and the core of the second coil of a given coil pair. .

It can be provided that each magnetic shield has a second recess at the upper face, to facilitate the establishment of field lines between the core of the coil contained in the shield and the outer dipole magnet in magnetic connection with said core.

It can be provided that each magnetic shield has a recess at the lower face, so as to allow the penetration of an end of the inner dipole magnet within the volume that said shield without said recess.

It can be provided that all the cores of the first coils have the same magnetic polarity between them, and all the cores of the second coils have the same magnetic polarity between them, inverted with respect to the magnetic polarity of all the cores first coils.

According to another of its objects, the invention relates to a stringed musical instrument equipped with a microphone according to the invention.

Finally, the invention also relates to a system for amplifying a stringed musical instrument, the system comprising a stringed musical instrument equipped with a microphone according to the invention, and an electrically connectable electrical amplifier device. at the output of said microphone.

Other features and advantages of the present invention will emerge more clearly on reading the following description given by way of illustrative and nonlimiting example and with reference to the appended figures in which: FIG. 1 illustrates an embodiment of FIG. a humbucker microphone according to the prior art, Figure 2 illustrates a partial three-quarter view of an embodiment of the microphone according to the invention, Figure 3 illustrates a cross-section at the cores of a coil pair of an embodiment of the microphone according to the invention, Figure 4 illustrates a top view of an embodiment of the microphone according to the invention, and Figure 5 illustrates a cross section of a shield according to the invention.

For brevity, reference is made here to a musical instrument of the six-string electric guitar type. Of course, the microphone can be adapted to acoustic guitars, bass guitars, or other string instruments. Whatever the number of strings of the instrument, it is enough to adapt the number of pairs of coils to the number of strings.

The passive polyphonic double-coil microphone for a stringed musical instrument comprises a support. The support 11 is substantially planar, i.e. it can have a slight curvature, for example the curvature of the guitar neck, so that it can be more easily integrated into the instrument. Preferably, the support 11 has a central recess 12, in the plane of the support 11, to facilitate the establishment of the inner magnet (see below).

10 Pairs of Coils Microphone 10 comprises a set of pairs of coils 20, 21, 22, 23, 24, 25 etc. whose number of pairs is equal to the number of strings. Each pair of coils is intended to be positioned facing a respective rope 13, so that each pair of spools faces a respective rope.

Each pair of coils comprises a first coil 20A, 21A, 22A, 23A, 24A, 25A ... and second coil 20B, 21B, 22B, 23B, 24B, 25B ... Preferably, the distance separating two coils of a The same pair is identical for each pair of coils.

Preferably, the pairs of coils are arranged so that the first coils 20A, 21A, 22A, 23A, 24A, 25A ... are aligned along a first straight line, and the second coils 20B, 21B, 22B, 23B, 24B , 25B ... are aligned along a second line. Preferably, the first line and the second line are parallel. Preferably at least one of the first and second straight lines is perpendicular to the strings, which limits the influence of the vibration of a string on a pair of coils other than the one facing it.

Each coil, see FIG. 3, comprises a magnetic core 30 - for example of soft and cylindrical iron - and a coil 31 - for example copper - around said core. The shape of a coil 35 is generally cylindrical, so that it has an upper face SUP and a lower face INF. The set of pairs of coils 35 therefore has an upper face, intended to be positioned opposite the strings. In terms of magnetism, we here assimilate a coil and its core.

Preferably, two coils of the same pair are identical to each other. Preferably, it is expected that all the coils are identical to each other.

For each pair of coils, the two coils are electrically connected in series and are in magnetic connection with each other. By "magnetic bond" is meant that magnetic LC field lines exist between them (Figure 2). However, one pair of coils is not in electrical connection with another pair of coils.

Preferably, all the cores of the first coils have the same magnetic polarity between them, and all the cores of the second coils have the same magnetic polarity between them, inverted with respect to the magnetic polarity of all the cores of the coils. first coils. For example, all the upper faces of the first coils have a north pole N and all the upper faces of the second coils have a south pole S (or vice versa), see FIG. 4.

For the transport of the electrical signal generated by the vibration of a rope, it is expected that for each pair of coils, one of the coils is equipped with an electric wire intended to be connected to a ground; and the other coil is equipped with another electrical wire for carrying the output signal to an amplifier.

It can therefore be expected that each pair of coils is connected to a respective amplifier. Internal dipole magnet 10 There is also provided a set of at least one internal dipole magnet 40, for example alnico, one pole of which is in magnetic connection with the core of one coil of one pair of coils and the other pole is in magnetic connection with the core of the other coil of said pair. Preferably, the length of the inner dipole magnet is substantially equal to the distance between two cores of a pair of coils. Preferably, there is no internal dipolar magnet common to all pairs of coils (not shown). Indeed, this solution increases the crosstalk because the common magnet makes it possible to establish lines of field between pairs of coils. Preferably, there is provided a respective inner dipole magnet 40 per pair of coils (FIG. 4), so that for a given pair of coils: the core of the first coil is in magnetic connection with a pole of an inner dipole magnet And the core of the second coil is in magnetic connection with the other pole of said inner dipole magnet.

One can also provide an intermediate solution of coupling the strings by frequency, for example for a six-string guitar: the two bass strings together, the two strings medium together and the two strings treble together. For this purpose, a respective internal dipole magnet can be provided for each pair of adjacent pairs of coils.

It is also possible to provide an intermediate solution for stereophonic output by electrical coupling of the strings one in two, for example for a guitar the strings 1 3 5 and 2 4 6.

Preferably, the assembly of at least one internal dipole magnet 40 is positioned on the side of the lower face INF of the coils (FIG. 3).

To allow a polyphony including distortion, there is provided a set of magnetic shielding, preferably identical to each other, and for example soft iron. Advantageously, each magnetic shield is also electrically isolated from its neighbors.

Magnetic shielding Each coil is surrounded by a respective magnetic shield 50, preferably of substantially tubular shape, for example of soft iron.

By its shape, a shield acts as a closed coil shorting the induction variations from a neighboring coil. Thus, the core of a coil is in magnetic connection neither with its respective shielding nor another shielding.

Preferably, no shielding is in contact with an internal magnet 40.

Thanks to the magnetic shields 50A, 51A, 52A, 53A, 54A, 55A ... 50B, 51B, 52B, 53B, 54B, 55B ..., one pair of coils is not in magnetic connection with another pair of coils. , especially adjacent, which means that the vibration of a chord is detected by the pair of coils facing it but does not influence or almost not an adjacent pair of coils, which allows the polyphony of the microphone. The shield 50 thus allows the use of the instrument in distortion since it avoids the influence of a rope on the other.

The magnetic shields are integral with the support, preferably on the underside of the coils, and have a respective elongation axis XX substantially perpendicular to the support. Preferably, the elongation axes are parallel to each other. Thus, the cores of the coils contained in the shields have an axis of elongation also substantially perpendicular to the support, that is to say intended to be substantially perpendicular to the strings. The pairs of coils are advantageously parallel to each other.

Preferably, the microphone 10 structurally (not magnetically) has a plane of symmetry parallel to the axis of elongation XX and located at a distance from the pairs of coils (see FIG. 4).

Two adjacent shields are optionally in contact with each other but electrically isolated.

Preferably, each shield 50A, 51A, 52A, 53A, 54A, 55A ... 50B, 51B, 52B, 53B, 54B, 55B ... has the same magnetic polarity N / S as that of the coil contained therein. . Advantageously, each shield 50A, 51A, 52A, 53A, 54A, 55A, 50B, 51B, 52B, 53B, 54B, 55B ... has a vector potential that is substantially equal to that of the coil which it contains; which avoids generating field lines between the shields and coils. At the structural level, it can be provided that each magnetic shield 50 has a first recess 50 El at the upper face SUP.

Preferably, for a given pair of coils, the first recess 50 E1 of one of the coils faces the first recess of one of the coils, which facilitates the establishment of field lines between the core of the coils. the first coil and the core of the second coil. It can also be provided that each magnetic shield has a second recess 50 E2 at the top face, facing the first recess.

The second recess 50 E2 faces an external dipole magnet 60 for example ceramic or alnico (described below and bearing the reference 60A and 60B with reference to the first and second coils respectively), which facilitates the establishment of lines field between the core of the coil contained in the shield and the outer dipole magnet in magnetic connection with said core.

It can also be provided that each magnetic shield has a (third) recess 50 E3, at the bottom face.

Preferably, for a given pair of coils, the recess 50A E3 at the lower face of one of the coils faces the recess 50B E3 at the lower face of the other of the coils (Fig. 2 ), which allows the penetration of one end of the inner dipole magnet 40 inside the volume that said shield would have without said recess 50 E3.

This recess 50 E3 at the lower face protects the inner magnet and limit the overall height of the microphone.

External Dipolar Magnet A set of at least one external dipole magnet 60A, 60B ... can be provided, in magnetic connection with at least one core and having a reverse magnetic polarity of said core. Each external dipole magnet has a magnetic polarity axis. Thus, each core has an N / S polarity along an axis of magnetic polarity and each external dipole magnet 60A, 60B,... Has an inverted polarity S / N along an axis of preferably substantially parallel magnetic polarity.

Preferably, there is provided a first external dipolar magnet 60A common to all the first coils (or their core), and a second external dipolar magnet 60B common to all of the second coils (or their core), see figure 4.

For example, the first 60A and second 60B external dipole magnets are identical parallelepiped magnets, for example alnico or ferrite, whose length is at least equal to the distance separating the extreme cores of a set of first coils, which allows obtain a magnetic connection for all the first / second coils. The height and width of the parallelepiped magnets depend on the nature of the magnets (the intensity of the magnetic field) and the desired sound effect.

It is also possible to provide an outer dipole magnet per core (not shown).

Preferably, each axis of magnetic polarity is parallel to the axis of polarity of the coil with which it is in magnetic connection.

Preferably, the magnetic polarity of each external dipole magnet is inverted with respect to the polarity of the coil with which it is in magnetic connection. Preferably, each external dipole magnet is disposed closer to the upper face SUP than the lower face INF, which facilitates the establishment of field lines on the side of the strings 13 of the instrument. The presence of such external dipole magnets makes it possible in particular to strengthen the medium and low frequencies of the instrument and to conserve harmonics.

Adaptation of the power of the magnets Depending on the type of magnet used, with regard to the inner dipole magnet 40, it is possible to provide an assembly of at least one shunt 41 (a shunt 41 per internal dipole magnet 40), disposed between the assembly of at least one inner dipole magnet and the cores of at least one pair of coils, to attenuate the intensity of the magnetic field of said inner dipole magnet 40 at said nuclei. Typically with an internal magnet samarium cobalt, a shunt can be implemented. With an alnico magnet of appropriate dimensions, the shunt can be optional.

Similarly, with respect to the external dipole magnet, it is possible to provide an assembly of at least one magnetic and electrical insulator 42A, 42B ... disposed between said set of at least one external dipole magnet 60 and a set of shields of first / second coils respectively. Preferably, there is provided a respective magnetic and electrical insulator 42A, 42B by external dipole magnet 60A, 60B. this magnetic and electrical insulator makes it possible to reduce the intensity of the magnetic field of the external dipole magnet 60A, 60B at the level of the first coil 20A, 21A, 22A, 23A, 24A, 25A and the second coil 20B, 21B, 22B, 23B, 24B, 25B respectively by moving the outer dipole magnet 60A, 60B away from said coils.

A magnetic and electrical insulator 42A, 42B may be common to a set of coils / shields, as shown in FIG.

For example, an external dipole magnet is common to a set of first / second coils and secured to said assembly by means of a magnetic insulator itself integral with all of the magnetic shields of said first / second coils.

The magnetic insulator 42A, 42B is for example bakelite.

The thickness of the latter is chosen according to the desired sound effect, and the dimensions and nature of the external magnet.

Claims (15)

REVENDICATIONS1. Passive polyphonic double-coil microphone (10) for a stringed musical instrument (13) comprising: - a carrier (11); - a set of pairs of coils, each pair of coils comprising a first coil (20A, 21A, 22A, 23A, 24A, 25A) and a second coil (20B, 21B, 22B, 23B, 24B, 25B), each coil comprising a magnetic core (30) and a coil (31) around said core, an upper face (SUP), and a lower face (INF), in which for each pair of coils, the two coils are electrically connected in series and in magnetic connection (LC) with each other, characterized in that it furthermore comprises a set of at least one inner dipole magnet (40), one pole of which is in magnetic connection with the core of a coil of one pair of coils and the other pole is in magnetic connection with the core of the other coil of said pair, - a set of magnetic shields, integral with the support (II), - each coil being surrounded by respective magnetic shielding (50A, 51A, 52A, 53A, 54A, 55A, 50B, 51B, 52B, 53B, 54B, 55B), wherein - For each pair of coils, one of the coils is equipped with a wire electric to be connected to a ground, and the other coil is equipped with another electrical wire for transporting an output signal to an amplifier. 2. Microphone 10 according to claim 1, wherein each shield (50A, 51A, 52A, 53A, 54A, 55A; 50B, 51B, 52B, 53B, 54B, 55B) has the same magnetic polarity as that of the coil (20A , 21A, 22A, 23A, 24A, 25A, 20B, 21B, 22B, 23B, 24B, 25B) contained therein. 17 Microphone 10 according to any one of the preceding claims, wherein the pairs of coils are arranged so that all of the first coils (20A, 21A, 22A, 23A, 24A, 25A) are aligned along a first straight line, and the set of second coils (20B, 21B, 22B, 23B, 24B, 25B) are aligned along a second straight line. Microphone 10 according to any one of the preceding claims, wherein the set of at least one inner dipole magnet (40) comprises a respective inner dipole magnet per pair of coils. 15 5. Microphone 10 according to any one of the preceding claims, wherein the set of pairs of coils has an upper face, intended to be positioned opposite the strings, and a lower face; said set of at least one inner dipole magnet (40) being positioned on the underside side. Microphone 10 according to any of the preceding claims, further comprising an assembly of at least one magnetic shunt (41), disposed between the assembly of at least one inner dipole magnet (40) and the cores ( 30) of at least one pair of coils, for attenuating the intensity of the magnetic field of said inner dipole magnet at said cores. Microphone 10 according to any one of the preceding claims, further comprising an assembly of at least one outer dipole magnet (60A, 60B), in magnetic connection with at least one core (30) and having a reverse magnetic polarity said core. 18 Microphone 10 according to claim 7, wherein said set of at least one outer dipole magnet (60A, 60B) is integral with at least one magnetic shielding via an electrical and magnetic insulator (42A, 42B). ). 9. Microphone 10 according to any one of claims 7 or 8, comprising a first external dipolar magnet (60A) common to all of the first coils, and a second external dipolar magnet (60B) common to all second coils . A microphone as claimed in any one of the preceding claims, wherein each magnetic shield has a first recess (50 E1) at the top face to facilitate the establishment of field lines between the core of the first coil and the core of the second coil of a given coil pair. The microphone 10 according to any of claims 7 to 10, wherein each magnetic shield has a second recess (50 E2) at the top face to facilitate the establishment of field lines between the core of the coil. contained in the shield and the outer dipolar magnet (60) in magnetic connection with said core. Microphone 10 according to any one of the preceding claims, wherein each magnetic shield has a recess (50 E3) at the lower face, so as to allow penetration of an end of the inner dipole magnet (40). ) within the volume that said shield would have without said recess. 13. Microphone 10 according to any one of the preceding claims, wherein all of the cores of the first 19 coils have the same magnetic polarity between them, and all of the cores of the second coils has the same magnetic polarity between them, inverted with respect to the magnetic polarity of all the cores of the first coils. 14. Stringed musical instrument equipped with a microphone 10 according to any one of the preceding claims. 15. System for amplifying a stringed musical instrument, the system comprising a stringed musical instrument equipped with a microphone 10 according to any one of claims 1 to 13, and a connectable electrical amplifier device electrically at the output of said microphone.