EP2433432A1

EP2433432A1 - Acoustic device

Info

Publication number: EP2433432A1
Application number: EP10728797A
Authority: EP
Inventors: Patrick Robuchon; Khaled Ben Hellal; Laurent Humen
Original assignee: Elno Societe Nouvelle SAS
Current assignee: Safran Electronics and Defense SAS; Elno SAS
Priority date: 2009-05-20
Filing date: 2010-05-20
Publication date: 2012-03-28
Also published as: FR2945904B1; WO2010133812A1; FR2945904A1

Abstract

The invention relates to an acoustic device including an acoustic contact microphone (4), an arch (10) for maintaining the microphone (4) against a side of the skull, said microphone (4) including a transducer for mechanically stimulating bone, wherein the transducer can receive a sound signal from the vocal cords by bone conduction and convert said sound signal into an electric signal. The acoustic device is characterized in that it comprises, connected to the transducer output, an electronic corrective filtering circuit for applying, depending on the frequency, a correction coefficient to the electric signal generated by the transducer in order to obtain a corrected signal that differs by only 10 decibels from the electric signal of an aerial acoustic microphone detecting variations in air pressure.

Description

Acoustic device

The present invention relates to an acoustic device of the type comprising an acoustic contact microphone, a microphone holding bar resting on a lateral side of the skull, said microphone comprising a bone mechanical excitation transducer able to receive by bone conduction a sound signal from vocal cords and transforming the sound signal into an electrical signal.

The invention also relates to an operator head equipment comprising a protective helmet and such an acoustic device. With a microphone of the acoustic device of the state of the art, the reception of the sound waves of the voice is not done by air, as is the case with the aerial acoustic microphone, but by solidarity, particularly through the mandible bone of the skull of an operator.

The microphone transducer converts a mechanical excitation received by bone conduction into an electrical signal.

However, the voice propagating through the air, this type of transduction does not allow the restitution of all the information contained in the sound signal.

The object of the invention is therefore to allow a better reproduction of the information contained in the solidly transmitted sound signal.

The invention therefore relates to an acoustic device of the aforementioned type, characterized in that it comprises connected at the output of the transducer, an electronic correction filter circuit adapted to apply a correction coefficient, depending on the frequency, the electrical signal derived from the transducer, so as to obtain a corrected signal close to 15 decibels, preferably close to 10 decibels, an electrical signal from an aerial acoustic microphone capable of detecting variations in air pressure.

According to other embodiments, the acoustic device comprises one or more of the following characteristics, taken separately or in any technically possible combination:

- The correction filtering electronic circuit is adapted to apply the correction coefficient to the electrical signal from the transducer for a predetermined frequency range, called the correction band; the lower frequency of the correction band is between 100 and 500 Hertz, and in that the upper frequency of the correction band is between 2000 and 8000 Hertz;

the correction filtering electronic circuit reduces the amplitude of the electric signal coming from the transducer for the frequencies of the correction band substantially lower than a switching frequency, and the correction filtering electronic circuit increases the amplitude of the electrical signal coming from the transducer for the frequencies of the correction band substantially greater than the tilt frequency; the electronic correction filter circuit has a substantially linear shape in the correction band;

the slope of the correction filtering electronic circuit is between 13 and 43 decibels per decade, preferably equal to 25 decibels per decade;

- The correction filtering electronic circuit is disposed in a housing located near the contact microphone and connected to the hoop, the distance between said housing and the contact microphone being less than 30 cm;

the device comprises an amplifier of the electrical signal;

the gain of the amplifier is between 13 and 43 decibels, preferably equal to 25 decibels; the acoustic microphone is able to bear on the mandibular bone, also called the lower jawbone;

the device comprises two lateral acoustic modules resting on the lateral flanks of the skull and capable of transmitting a sound signal to the auditory nerve;

- The lateral acoustic modules each comprise a bone mechanical excitation transducer adapted to transmit a sound signal to the auditory nerve by bone conduction, and are interconnected by at least one connecting arch;

the device is, by its dimensions, suitable for use with a heavy infantryman's helmet or with a chemical bacteriological nuclear mask. The invention also relates to a head gear for operator comprising a protective helmet, characterized in that it comprises an acoustic device as defined above. The invention and its advantages will be better understood on reading the description which will follow, given solely by way of example, with reference to the appended drawings, in which:

FIG. 1 is an overall perspective view of an acoustic device according to the invention,

FIG. 2 is a partial exploded view of the device of FIG. 1,

FIG. 3 is a schematic representation of an electronic card of the acoustic device according to the invention,

FIG. 4 is an asymptotic representation of the Bode diagram of an electronic correction filter circuit of the acoustic device according to the invention, and

FIG. 5 is a set of curves representing the amplitude of electrical signals respectively derived from a conventional overhead acoustic microphone and an acoustic contact microphone according to the invention, as a function of frequency and for a sound signal coming from a real voice.

In FIG. 1, an acoustic device 2 comprises an acoustic contact microphone 4 and two lateral acoustic modules 6. The acoustic device 2 also comprises an upper arch 8, a rear arch 10 connecting the acoustic modules 6, and a connection cable 12. The acoustic microphone 4 comprises a bone mechanical excitation transducer, not shown, disposed in a protective casing 14. The housing 14 is connected to one of the two acoustic modules 6 by two link arms 15. The transducer of the microphone is a clean accelerometer to receive bone conduction, especially through the mandible bone of the skull, the vibratory waves of a sound signal from the vocal cords and transform it into an electrical signal.

The microphone 4 also comprises at the output of the transducer, a filter for electromagnetic compatibility (EMC), not shown, able to protect the transducer against electromagnetic interference. The upper arch 8, also called headband 8, is of adjustable length and adapted to be positioned on the top of the head.

The rear arch 10, made of a rigid material, is a mechanical support bar of the microphone 4 resting on the mandible bone and of each module 6 resting on a lateral flank of the skull. The support bar 10 is of adjustable length, and able to be positioned under the bone of the rock behind the head, near the neck.

Each acoustic module 6 comprises a support plate 16 on a side flank of the skull and a transducer 17 for mechanical bone excitation.

A hinge 18 is provided between the support plate 16 and the transducer 17. A spring, not shown, equips the hinge 18 and is adapted to ensure a return in rotation about the hinge axis 18, the transducer 17 relative to the plate 16 to a rest position. Each plate 16 comprises a support plate 20 to bear on the skull above an ear. A clearance passage of the ear is provided in the lower part of each plate 20. Each plate 16 comprises in the rear part of the plate 20 a housing 22 formed of two half-shells 24, 26, fixed together by means of fixing means 28 such as screws 28 with countersunk head. The housing 22 is located near the contact microphone 4, the distance between the housing 22 and the microphone 4 being less than 30 cm.

The support plate 20 and the half-shells 24, 26 of the housing 22 are, for example, plastic and injection molded.

An electronic card 30, visible in FIG. 2, is fixed in the housing 22 of the plate 16 which is connected to the microphone 4. The electronic card 30 is connected on the one hand to the output of the transducer of the microphone 4 by a cable 32 link, and the other 12 connection cable. The connection cable 12 and the connecting cable 32 each comprise a plurality of wires.

In FIG. 3, the electronic card 30 comprises an electronic correction filter circuit 34, an amplifier 36 and an electronic control circuit 38 for level adjustment. The electronic card 30 also comprises an electronic circuit 40 for filtering power, and a first 42 and a second 44 electronic filter circuits for electromagnetic compatibility (EMC).

The correction filtering electronic circuit 34, also called correction filter, is intended to apply a correction coefficient, as a function of frequency, to the electrical signal from the transducer. The corrected signal from the electronic correction filter circuit 34 is close to an electrical signal from an overhead acoustic microphone capable of detecting variations in air pressure.

The correction coefficient is applied by the electronic correction correction circuit 34 to the electrical signal coming from the transducer for a predetermined frequency range, called the correction band, as represented in FIG. 4.

The lower frequency Finf of the correction band is, for example, between 100 and 500 hertz (Hz), preferably equal to 300 hertz. The upper frequency Fsup of the correction band is, for example, between 2000 and 8000 hertz, preferably equal to 3400 hertz.

The correction coefficient is, for example, substantially equal to -15 decibels for the lower frequency Finf and substantially equal to 11 decibels for the higher frequency Fsup.

The shape of the correction filter 34 is substantially linear in the correction band. The slope of the correction filter 34 is between 13 and 43 decibels per decade, preferably equal to 25 decibels per decade. More specifically, the slope of the correction filter 34 is substantially equal to 25 decibels per decade, when the lower frequencies Finf and higher Fsup are respectively 300 Hz and 3400 Hz. The slope of the correction filter 34 is substantially equal to 13 decibels per decade, when the lower frequencies Finf and higher Fsup are respectively equal to 100 hertz and 8000 hertz. The slope of the correction filter 34 is substantially equal to 43 decibels per decade, when the lower frequencies Finf and higher Fsup are respectively equal to 500 hertz and 2000 hertz. The correction filter 34 intersects the abscissa axis of the Bode diagram of FIG. 4 for a tilt frequency Fbasc.

In other words, the correction filter 34 decreases the amplitude of the electrical signal from the transducer for the frequencies of the correction band substantially lower than the switching frequency Fbasc, and increases the amplitude of the electrical signal from the transducer for the frequencies of the the correction band substantially greater than the switching frequency Fbasc. The switching frequency Fbasc is, for example, close to 1000 hertz. Outside the correction band, the correction coefficient is substantially constant and equal to 1, or else 0 decibels.

The electronic correction filter circuit 34 is optimized for extreme cases, such as receiving the sound signal from the vocal cords in a quiet environment and receiving the sound signal from the vocal cords in a noisy environment with a caterpillar vehicle.

The amplifier 36 is arranged at the input of the electronic correction filter circuit 34, as shown in FIG. 3. The gain of the amplifier 36 is high, for example between 13 and 43 decibels, preferably equal to 25 decibels . The amplifier 36 is able to provide an electrical signal compatible with the various radio wave communication systems, from an input signal from the microphone 4 whose voltage is of the order of a few microvolts.

The level adjustment circuit 38, arranged between the amplifier 36 and the correction filtering electronic circuit 34, is adapted to adapt the amplitude of the amplified signal from the amplifier 36, in order to obtain an amplitude of the signal included in a predetermined interval.

The electronic filtering circuit 40 is connected on the one hand to an external power supply, and on the other hand to the microphone 4, to the amplifier 36 and to the correction filtering electronic circuit 34. The electronic filtering circuit The power supply 40 is intended to filter the external power supplied via the connection cable 12.

The first electronic filter circuit for electromagnetic compatibility 42, also called the first EMC filter, is connected between the microphone 4 and the amplifier 36. The first EMC filter 42 is able to filter electromagnetic disturbances of the electrical signal from the microphone 4.

The second electronic filtering circuit for electromagnetic compatibility 44, also called the second EMC filter, is connected between the correction filtering electronic circuit 34 and the connection cable 12. The second EMC filter 44 is capable of filtering electromagnetic signal disturbances. electrical output on the connection cable 12.

The bone mechanical excitation transducer 17 of each acoustic module 6 comprises an emissive element, not shown, and two half-shells. 46, 48, visible in Figure 1, protecting the emissive element. The emissive element is able to transform an electrical signal received into vibratory waves representative of the sound signal and to transmit them to the auditory nerve by bone conduction.

The half-shells 46, 48 are, for example, plastic and injection molded.

In FIG. 5, a first curve 50 represents the amplitude of a first electrical signal from a conventional overhead acoustic microphone, as a function of frequency, for a sound signal coming from a real voice of an operator, the conventional overhead acoustic microphone being disposed one meter from the operator's mouth. The sound signal corresponds to the sounds emitted by the operator when reading a predefined text.

A second curve 52 represents the amplitude of a second electrical signal from an acoustic contact microphone according to the invention, as a function of frequency, for the same sound signal, the acquisition of the first and second electrical signals being performed simultaneously. The acoustic contact microphone is arranged in contact with a cheek of the operator. The second electrical signal corresponds to a corrected signal at the output of the correction filtering electronic circuit 34.

The amplitudes of the two signals are measured as a relative level with respect to a reference level common to both signals. The relative level of the two signals is expressed in decibels (dB). The two signals are represented on the respective curves 50, 52 for frequencies between 200 Hz and 5000 Hz

Note then that the difference between the first curve 50 and the second curve 52 is still substantially less than 10 decibels. The difference between the curves 50, 52 is even less than 5 decibels for certain frequency ranges, such as the range between 700 Hz and 1400 Hz, or the range between 2400 Hz and 3400 Hz.

The correction filtering electronic circuit 34 is thus able to apply a correction coefficient, as a function of frequency, to the electrical signal coming from the transducer, so as to obtain a corrected signal close to 10 decibels close to an electrical signal derived from an overhead acoustic microphone capable of detecting variations in air pressure. Thus, a user of the acoustic device 2 begins by positioning the device 2 on his head, by placing the strap 8 on the top of his skull, the rear arch 10 behind his head, near his neck, and the plates 16 of support on the lateral flanks of his skull, above each respective ear. The clearance formed in the lower part of the support plates 20 ensures good ergonomics of the plate 16 relative to the upper part of the flag of the ear.

After positioning the device 2 on his head, the user adjusts the upper arch 8 on his head and the rear arch 10 on his neck. The adjustment of the microphone 4 on the skin of the cheek and the mandibular bone is carried out naturally and automatically by the corresponding articulation 18 and by the flexibility of the connecting arms 15.

The adjustment of the position of each bone mechanical excitation transducer 17 on the corresponding temple takes place naturally and automatically by each articulation 18.

The adjustment of the microphone 4 and transducers 17 thus produced, provides a good reception of the sound signal from the vocal cords and a good transmission of vibratory waves to the auditory nerve by bone conduction.

Due to the presence of the EMC filter in the microphone 4, the transformation by the transducer of the microphone 4 of the sound signal from the vocal cords into an electrical signal is not parasitized by electromagnetic disturbances.

The voltage amplitude of the electrical signal from the microphone 4 is of the order of a few microvolts.

The signal from the microphone 4 is first amplified by the amplifier 36 so that the amplitude of the amplified signal is compatible with the different radio wave communication systems.

The amplitude of the amplified signal is then adapted by the level adjusting circuit 38 so that the amplitude of the adapted signal is within a predetermined range. This adaptation makes it possible to obtain an electrical signal substantially independent of the initial amplitude of the sound signal emitted by the vibration of the vocal cords of the user.

The adapted sound signal is then corrected by the electronic correction filter circuit 34, so as to obtain a corrected signal close to 15 decibels near an electrical signal from an aerial acoustic microphone capable of detecting variations in air pressure. The corrected signal is preferably close to 10 decibels near the electrical signal from the aerial acoustic microphone. The electronic correction filter circuit 34 makes it possible to increase the amplitude of the electrical signal in the high frequencies relative to the low frequencies. It is indeed necessary to apply this correction since the speech is richer in energy in the bass than in the high-pitched sounds, which implies that the electric signal supplied by the microphone transducer 4 is of greater amplitude. at low frequencies, for example less than 800 Hz, than in high frequencies, for example, greater than 1000 Hz. After correction, the amplitude of the electrical signal in the low frequencies is substantially equal to the amplitude of the signal in the high frequencies.

The correction filtering electronic circuit 34 therefore applies a correction coefficient, as a function of frequency, to the electrical signal coming from the transducer, so as to obtain the corrected signal close to 15 decibels, preferably close to 10 decibels, of the signal. from the aerial acoustic microphone.

Due to the presence of the first and second EMC filters 42, 44, amplification, adaptation and correction of the electrical signal are not parasitized by electromagnetic disturbances.

The electronic correction filter circuit 34 is located near the contact microphone 4, which also makes it possible to limit the electromagnetic disturbances.

The upper bow 8 allows, because of its small thickness and its flexible material, wearing a heavy helmet without discomfort on the top of the head. The rear arch 10, being positioned under the bone of the rock behind the head, also allows the wearing of all heavy combat helmets.

The mechanical support of the microphone 4 and the two modules 6 is provided by the rear arch 10, while the upper arch 8 has a role of holding in position on the top of the head.

Advantageously, the acoustic device according to the invention allows a much better reproduction of the information contained in the sound signal coming from the vocal cords of the user and transmitted by solidary means, in particular through the mandible bone of the skull. The restitution is in particular close to that obtained in the case of a transmission of the sound signal by air.

Advantageously, the electrical signal from the acoustic device 2 according to the invention is substantially independent of the amplitude of the sound signal from the vocal cords. The device 2 thus makes it possible to obtain a good reproduction of the sound signal even though it is whispered. The device 2 is thus particularly suitable for use requiring a certain discretion.

Advantageously, the device 2 is little dependent on external noise disturbances and thus allows good sound reproduction in noisy environment.

According to another embodiment, the acoustic device 2 comprises two separate electronic cards, the first electronic card comprising the electronic correction filter circuit 34 and the second card comprising the amplifier 36. According to another embodiment, the acoustic device 2 does not include an acoustic module.

According to another embodiment, the amplifier 36 is disposed at the output of the electronic correction filter circuit 34.

According to other embodiments, the acoustic device 2 is suitable for use with a motorcycle helmet, a helmet for a motor vehicle driver, a helmet for an armored vehicle, a fireman's helmet, a helmet for a safety officer, a helmet construction helmet, a helmet for an aircraft pilot.

According to other embodiments, the acoustic device 2 is a headphone for a switchboard operator.

Claims

1.- Acoustic device (2) of the type comprising an acoustic microphone (4) contact, a bow (10) for holding the microphone (4) resting on a lateral side of the skull, said microphone (4) having a transducer to bone mechanical excitation capable of receiving by bone conduction a sound signal from the vocal cords and transforming said sound signal into an electrical signal, characterized in that it comprises connected at the output of the transducer, an electronic circuit (34) correction filtering adapted to apply a correction coefficient, as a function of frequency, to the electrical signal coming from the transducer, so as to obtain a corrected signal close to 15 decibels, preferably close to 10 decibels, of an electrical signal coming from a aerial acoustic microphone capable of detecting variations in air pressure.

2.- acoustic device (2) according to claim 1, characterized in that the electronic circuit (34) correction filter is adapted to apply the correction coefficient to the electrical signal from the transducer for a predetermined frequency range, called band of correction.

3.- acoustic device (2) according to claim 2, characterized in that the lower frequency (Finf) of the correction band is between 100 and 500 Hertz, and in that the upper frequency (Fsup) of the band of correction is between 2000 and 8000 Hertz.

4.- acoustic device (2) according to claim 2 or 3, characterized in that the correction filtering electronic circuit (34) decreases the amplitude of the electrical signal from the transducer for the frequencies of the correction band significantly lower than a switching frequency (Fbasc), and in that the correction filtering electronic circuit (34) increases the amplitude of the electrical signal from the transducer for the frequencies of the correction band substantially greater than the switching frequency (Fbasc) .

5.- acoustic device (2) according to any one of claims 2 to 4, characterized in that the electronic circuit (34) of correction filtering has a substantially linear shape in the correction band.

6.- acoustic device (2) according to claim 5, characterized in that the slope of the correction filtering electronic circuit (34) is between 13 and 43 decibels per decade, preferably equal to 25 decibels per decade.

7. Acoustic device (2) according to any one of the preceding claims, characterized in that the electronic circuit (34) for correction filtering is disposed in a housing (22) located near the microphone (4) of contact and connected to the hoop (10), the distance between said housing (22) and the microphone

(4) contact is less than 30 cm.

8. Acoustic device (2) according to any one of the preceding claims, characterized in that it comprises an amplifier (36) of the electrical signal.

9.- acoustic device (2) according to claim 8, characterized in that the gain of the amplifier (36) is between 13 and 43 decibels, preferably equal to 25 decibels.

10.- acoustic device (2) according to any one of the preceding claims, characterized in that the acoustic microphone (4) is adapted to bear on the mandibular bone, also called lower jaw bone.

11. Acoustic device (2) according to any one of the preceding claims, characterized in that it comprises two acoustic modules (6) lateral support on the lateral flanks of the skull and adapted to transmit a sound signal to the auditory nerve.

12. Acoustic device (2) according to claim 11, characterized in that the acoustic modules (6) side each comprise a transducer (17) mechanical bone excitation capable of transmitting a sound signal to the auditory nerve by bone conduction, and are interconnected by at least one connecting arch

(8, 10).

13. Acoustic device (2) according to any one of the preceding claims, characterized in that it is, by its dimensions, suitable for use with a heavy infantryman's helmet or with a chemical bacteriological nuclear mask.

14.- Operator head equipment comprising a protective helmet, characterized in that it comprises an acoustic device (2) according to any one of the preceding claims.