EP1621044B1 - Headphone for spatial sound reproduction - Google Patents

Abstract

The invention concerns a headphone and a compatible recording device for spatial sound reproduction provided with two earphones, each earphone having a support defining at least partly a cap-like surface comprehensively covering the listener's ear. Each earphone includes at least five speakers arranged on said support. The speakers are adapted to reproduce an acoustic field, such that it is perceived as being continuous by the human ear, for acoustic frequencies lower than a given maximum frequency.

Description

The present invention relates to a device, in particular an acoustic headset, for the spatialization of a sound. The invention also relates to a recording device compatible with such a spatialization device.

Spatialization of a sound is the rendering of the three-dimensional characteristics - azimuth, elevation and distance - of a sound source emitting a sound having a given frequency and intensity.

Many systems and devices are known whose purpose is to solve such a technical problem. However, they most often offer only a simple immersion in a sound environment, without really restoring the three-dimensional characteristics of a sound. These systems can be implemented either in a room, in which case the room is equipped with several speakers equipped with speakers, or with the aid of an acoustic headset, each earphone of the headset including a speaker.

According to a first method, called two-channel stereophony, to simulate the movement of a sound source, two loudspeakers, one channel per loudspeaker, are used, and the intensity of the sound is weighted on the two corresponding channels, in distributing the power to be emitted between the two speakers. It is therefore possible to move the sound source by adjusting the weighting coefficient.

However, this technique has the disadvantage of placing the sound sources inside the listener's head. Moreover, sound sources can only be moved on one dimension instead of all space.

In order to improve the impression of immersion in a sound environment, it has been proposed to use four or five loudspeakers in a room. These include the "Dolby Surround" device. Such a system comprises three frontal acoustic channels and a rear acoustic channel. A central loudspeaker and two left and right loudspeakers broadcast said front channels. The center speaker focuses the sound sources regardless of the listening position. The fourth channel is broadcast by two rear speakers and corresponds to ambient information and reverb effects.

However, such a system does not locate the sound sources precisely since the central speaker focuses them regardless of the listening position. Moreover, it is not possible, in such a room, to emit distinct sounds for both ears.

According to another method for simulating a spatialization effect, a series of loudspeakers oriented towards a listening point is regularly distributed in a circle, each speaker diffusing a particular sound channel. It is therefore an extension of the stereophonic process on two channels. However, the spatialization effect is actually obtained only at a particular point of the room, called focal point. Auditors outside this focal point also hear the sounds, but they experience acoustic illusions, which could be compared to optical illusions.

However, a perceived sound can be reduced to an acoustic pressure, supposedly uniform, at the level of the eardrums. Thus, at the level of an ear, the only variable of interest is the acoustic pressure at the level of the eardrum, which itself depends on the acoustic pressure at the entrance of the ear canal, the morphology of the ear of the ear. 'auditor. In an acoustic headphone, the goal is to reproduce this pressure, to reconstruct a sound.

However, for two different listeners, the sound pressure level of the eardrum, and even the entrance of the ear canal, resulting from the same sound source, will be different. This will not prevent them, except hearing impairment, from locating the sound source properly.

These differences between individuals and between the ears of the same individual come from morphological differences. Indeed, the spacing of the ears of the listener and the presence of an obstacle, the head, on the trajectory of the acoustic wave, introduce a phase shift and a difference of intensity in an acoustic wave coming from the same sound source. Thus, the sound pressure level of the eardrum is different between the right ear and the left ear, for the same sound source, depending on the position of this ear. source compared to the listener.

Various devices attempt to spatialize a sound by taking into account these differences in perception between the two ears. It is simply to broadcast the same sound, taking into account the physical phenomena leading to the phase shift and the difference in intensity, in both ears. This is the main binaural.

However, binaural techniques rely on a database of experimental measurements, corresponding to "average" morphologies. It is not possible to model the human hearing instrument, especially the ear flag, whose form is too complex to take into account all the physical phenomena necessary for a computational approach. Thus, the techniques used correspond to average ears and the measurements are made on mannequins. These techniques therefore have the disadvantage of not being suitable for all.

We know the helmet of the document US 6038330 a headset whose speakers are directed by waveguides.

The article "Wellenfeldsynthese" of the magazine FERNSEH UND KINOTECHNIK n ° 57 concerns a technique for the reconstruction of a free-field wavefront from several loudspeakers. This technique does not take the listener into account. The listener naturally plunges into the reconstituted acoustic field.

The object of the present invention is to provide an acoustic headset for the spatial reproduction of a sound, which overcomes the aforementioned drawbacks.

In particular, such a headset must allow the emission of distinct sounds for the two ears, without dependence vis-à-vis the individual characteristics of the hearing aid. In other words, such a headset must allow the spatialization of a sound for the vast majority of listeners.

Another object of the present invention is to propose a dynamic system that can take account of the movements of the head in the acoustic field reconstituted using such a helmet.

Another object of the invention is to provide an acoustic headset compact, easy to use and for good mobility of the head, in particular to adapt easily in a dynamic system.

An object of the invention is also to provide a helmet for reproducing a sound accurately, avoiding the sensations of jerks during the movement of a sound source, giving the impression of a continuous acoustic field.

Yet another object of the invention is to provide a helmet adaptable to any head.

Another object of the invention is to provide an inexpensive headphone.

Yet another object of the invention is to provide a recording device compatible with such an acoustic headset.

Other aims and advantages of the invention will become apparent from the description which follows, which is given for information only and which is not intended to limit it.

The invention relates to a method for the spatial reproduction of a sound with an acoustic headset having two earphones, each earpiece comprising a support defining a cap surface completely encompassing the ear of the listener, each earpiece comprising at least five high speakers, arranged on said hemispherical surface.

According to the process according to the invention, each of said at least five loudspeakers is ideally assimilated to an omnidirectional source, said method consisting in restoring the spatiality of a sound by applying the Huygens-Fresnel principle by reconstituting, for each ear and a horn of the listener, a sound surface corresponding to the addition of spherical waves emitted by said at least five loudspeakers.

The invention also relates to an acoustic headset, suitable for implementing the method for the spatial reproduction of a son, according to the invention, provided with two earphones, each earpiece comprising a support at least partially defining a cap surface completely encompassing the ear of the listener, each earpiece comprising at least five speakers disposed on said hemispherical surface and capable of reconstructing the acoustic field, each speaker being assimilated ideally to an omnidirectional source, two contiguous loudspeakers being spaced apart by a distance less than half the smallest wavelength corresponding to a given maximum frequency of in such a way as to reconstitute an acoustic field perceived as continuous by the human ear for acoustic frequencies lower than said given maximum frequency, said maximum frequency being a frequency audible to the human ear.

The invention relates to a device for recording a sound intended for a subsequent spatial reproduction, in accordance with the spatial spatial reproduction method of a sound according to the invention, consisting of a headset as defined above and in which said loudspeakers are replaced by omnidirectional or cardioid microphones, the recording cap surface corresponding to said recording device being merged with the cap area (acoustic emission) of said headphone.

• la figure 1 représente schématiquement la tête d'une personne coiffée d'un casque acoustique conforme à l'invention,
• les figures 2a, 2b, 2c sont des vues en perspective de l'écouteur gauche d'un casque conforme à l'invention, avant, intérieur et arrière respectivement,
• les figures 3a et 3b sont des vues en coupe d'un écouteur d'un casque conforme à l'invention, selon un plan vertical et un plan horizontal respectivement,
• les figures 4 et 5 sont deux variantes de répartition de huit haut-parleurs, ou microphones, dans un écouteur, illustrées en plan et en coupe,
• la figure 6 est une variante de répartition de six haut-parleurs, ou microphones, dans un écouteur, illustrées en plan et en coupe.

The invention will be better understood on reading the description, accompanied by the appended figures, among which:

• the figure 1 schematically represents the head of a person wearing an acoustic headset according to the invention,
• the Figures 2a, 2b, 2c are perspective views of the left earphone of a helmet according to the invention, front, inside and rear respectively,
• the Figures 3a and 3b are cross-sectional views of an earphone of a helmet according to the invention, in a vertical plane and a horizontal plane respectively,
• the Figures 4 and 5 are two variants of distribution of eight loudspeakers, or microphones, in an earphone, illustrated in plan and in section,
• the figure 6 is a distribution variant of six speakers, or microphones, in an earphone, shown in plan and in section.

The invention arose from the observation of the non-existence of a simple sound spatialization device, requiring little computing power, and adapted to all. Indeed, the devices based on the binaural principle are specific to the listener - or the dummy - on which the measurements were made while the stereophonic rooms only allow spatialization of the sound at the focal point of the room. In addition, indoor devices frequently depend on the geometry of the room and the relative arrangement of the speakers.

The inventors have resulted in the invention by modifying the point of view used to address the problem of the spatialization of a sound. Instead of trying to reproduce the sound pressure at the tympanum or ear canal entrance, as has been the case so far, they have sought to reconstruct the acoustic wave as it can be measured at a given distance from the ear, before transformation by the flag and the auditory canal.

The inventors have therefore decided to create a sound surface transmitter surrounding the flag of the ear. The fact that this surface surrounds the flag of the ear is not insignificant. Indeed, it makes it possible to get rid of the individual morphological characteristics of the flag since the emitted wave will be transformed by the flag of the ear, in the same way as any sound.

The use of a helmet also makes it possible to overcome the problems of geometry of a room. This also makes it possible, for example, to develop dynamic systems that take account of movements of the head in space, to virtually move the reconstituted sound environment according to these movements of the head.

According to the principle of Huygens-Fresnel, every point of the space touched by an acoustic wave becomes a secondary source and in turn re-emits a spherical wave. Thus, the contribution of an emitting sound surface as perceived by the eardrum is equivalent to the addition of all the spherical waves emitted by the infinity of points of this emitting sound surface.

However, in practice, we can not produce an infinity of sound sources. It has therefore been necessary to determine a finite number of sound sources which, broadcasting sounds at the same time, would be equivalent to said emitting sound surface.

For this, we use the theory of information, and more particularly the theorem of Shanon. According to this theorem, the sampling pulse of a sinusoidal signal must be at least twice as great as the pulsation of said sinusoidal signal, if it is desired to avoid a loss of coherence between the continuous sinusoidal signal and the sampling. In other words, the sampling period must be two times smaller than the period of the sinusoidal signal.

A sound signal can be broken down into a sum of sinusoidal signals. By a space-time analogy, the sampling distance between two loudspeakers of the sound signal must be less than half the wavelength of this signal. If we consider that limiting wavelength is the shortest wavelength of the signal, that is to say that the limiting frequency is the highest frequency of the signal, we obtain: 2 · Δl ≤ λ, where I is the distance separating two speakers (or microphones) and λ is the smallest wavelength of the signal.

Thus, the sampling - transmission or recording - retains all the information of the sampled signal for frequencies less than or equal to half the sampling frequency.

The audible frequency range is 20 Hz to 20 kHz, but the most frequently heard sound frequencies are below 5 kHz. We therefore choose a sampling frequency of 10 kHz.

As illustrated in the various figures, the result is a helmet 1 comprising two earphones 2, each earpiece comprising at least five loudspeakers arranged on a support 3, 4. Said support 3, 4 at least partially defines a cap surface adapted to completely encompass the listener's ear 6.

The expression "cap" means that the earpiece completely encompasses the flag of the ear, without there being any contact between the "cap" surface and the flag. Advantageously, this surface is in the form of a hemisphere or a portion of hemisphere. It can also be ovoid, possibly even polyhedral. The bottom line is that the cap surface encompasses the listener's ear, and is a supporting skeleton for the speakers.

In the different figures, said earpiece has a hemispherical cap surface.

Said earphone 2 can be open or closed. If it is open, said hemispherical surface is only partially materialized by the support 3, 4. If it is closed, the support 3, 4 completely embodies said hemispherical surface. Advantageously, said at least five loudspeakers may be distributed in the form of a cross, which makes it possible to obtain a satisfactory emitting acoustic surface.

Said support consists in particular of a ring 3 to which are fixed two curved strips 4, a horizontal band 42 and a vertical band 43. The said 4 curved strips form a cross. In addition, they are pierced with orifices 41 able to receive said loudspeakers 44.

The orifices 41 are regularly distributed, so that the distance separating two contiguous loudspeakers is less than or equal to 3 cm, for a maximum frequency of the sampled signal of 5 kHz. The diameter D of the ring 3 is, in this example, 8 cm.

Each bent band 42, 43 is provided with an orifice 41 at the point of intersection of the two strips, as illustrated in the various figures. For example, the horizontal band 42 comprises four orifices 41 spaced at an angle of 36 ° between them; the vertical band 43 comprises three orifices 41 spaced at an angle of 45 ° between them. Thus, the earphone 2 can receive six speakers including one at the intersection of the two support strips 42, 43.

For example, the hemispherical surface has a radius r of 4 cm.

Of course, it would be possible to provide a greater number of loudspeakers, arranged for example on the branches of a star and closer to each other, to obtain a maximum frequency of the sampled signal, in this case emitted, greater than 5 kHz.

For example, as illustrated in Figures 4 and 5 , the earphone may have eight speakers 44. Are shown, in the upper left of the Figures 4 and 5 , a plan view of these two variants and, around the plan view, sectional views along lines AA, BB, CC, A'A ', B'B', C'C '. In these examples, the headphones are hemispherical.

Thus, in plane view, the loudspeakers 44 are regularly distributed around two concentric circles, an outer circle 31 of large radius and an inner circle 32 of radius smaller than that of the outer circle 31.

In the variant illustrated in figure 4 the loudspeakers 44 are at the top of a regular pentagon inscribed in the outer circle 31 and an equilateral triangle inscribed in the inner circle 32.

In the variant illustrated in figure 5 , the loudspeakers 44 are located at the vertices of two squares respectively inscribed in the inner circle 32 and the outer circle 31, the diagonals of one of the squares being substantially parallel to the sides of the other square.

Advantageously, the circles outside 31 and inside 32 are substantially parallel to the plane defined by the ring 3 and lie at an angle of 30 ° ^(π / ₆ rad) and 60 ° ^(π / ₃ rad) relative to the center 33 of hemisphere.

According to another variant, represented in figure 6 , the earpiece comprises six speakers 44, four regularly distributed at the vertices of a square inscribed in an outer circle 31 and the other two distributed on a diagonal of said square, on an inner circle 32.

Thus, said at least five loudspeakers are capable of reconstructing an acoustic field, perceived as continuous by the human ear, for acoustic frequencies below a given maximum frequency, in particular 5 kHz.

The expression "perceived as continuous" means that the displacement of a sound source emitting a signal of frequency less than or equal to 5 kHz, restored by the acoustic headset, is perceived without jerkily or jerkily but continuously. The listener does not have the impression that the sound source passes without transition from one point of the space to the other when the displacement should have been perceived as progressive.

Advantageously, a helmet according to the invention comprises at least six loudspeakers per earpiece.

According to a first variant of the invention, a helmet 1 is provided with open earphones, as illustrated in the various figures. In this case, the support 3, 4 consists of an open armature, adapted to receive the speakers. From an acoustic point of view, this means that the listener can hear a sound not emitted by the speakers, without deformation or attenuation.

According to another variant, the headphones 2 are closed. In this case, the support consists of a shell defining a hemispherical surface adapted to receive said speakers.

Although not illustrated, electrical connection means are provided between the loudspeakers 44 and, for example, an audio output of an amplifier, a walkman, a sound card, or any other similar electronic device. It could also be wireless transmission means, thus avoiding the clutter generated by electrical son.

Advantageously, said headset serves as a support for a microphone located at the end of a branch, in front of the mouth of the listener, to enable him to speak, interactively interactively, with another person equipped for example with the same helmet.

Said earphones 2 may have various additional features. For example, the ring 3, that is to say the area of the earpiece in contact with the head of the listener, can be equipped with a ring of foam, to improve the comfort of the listener 6 when using the headset.

The elements of the support 3, 4 consist for example of aluminum or another light metal, or plastic.

As illustrated, the two earphones 2 of the helmet 1 are connected by a band 8 which passes over the head of the listener 6. It may be an adjustable band, various materials known to the man of the job.

Moreover, according to an advantageous characteristic, such an acoustic headset is equipped with a device for tracking the movements of the head or "head-track". Thus, the movements of the head of the listener 6 can be detected and the signal diffused by the loudspeakers of each earphone 2 can be modified according to these movements, in order to offer the listener 6 a real impression of auditory displacement, in a virtual space in particular. This type of device is particularly useful when coupled with a three-dimensional vision helmet.

The invention also relates to a recording device for the subsequent spatial reproduction of a sound, consisting of a headset as described above. However, in such a recording device, the loudspeakers are replaced by omnidirectional or cardioid microphones facing the outside of the earphones, that is to say the opposite of the ears of a listener 6 potential.

For a good compatibility between such a recording device and an acoustic headset 1 according to the invention, the recording cap surface corresponding to the recording device is merged with the acoustic emission cap surface of such a device. acoustic headphones.

With such an acoustic headphone and such a recording device, it is no longer necessary to be concerned about the transformations experienced by the sound wave, due to the auditory apparatus, since the sounds are recorded and transmitted before these transformations. .

• les loisirs et jeux dits de « réalité virtuelle », qui reconstituent un espace audiovisuel virtuel,
• la téléconférence, pour simuler une salle de réunion ou de conférence et localiser virtuellement les intervenants les uns par rapport aux autres, autrement que par l'intermédiaire d'un simple écran,
• toute autre application où l'on peut souhaiter coupler, par exemple, un espace acoustique à un espace visuel reconstitués.

Such a helmet can find application in many areas, including:

• leisure and games called "virtual reality", which reconstitute a virtual audiovisual space,
• teleconferencing, to simulate a meeting or conference room and virtually locate stakeholders relative to each other, other than through a simple screen,
• any other application where one may wish to couple, for example, an acoustic space to a reconstructed visual space.

Naturally, other modes of implementation, within the reach of the skilled person, could still be envisaged without departing from the scope of the invention, object of the claims below.

Claims (6)

1. A method for spatial restitution of a sound with a sound helmet (1) fitted with two earpieces (2), wherein each earpiece comprises a support (3,4) defining a cap-shaped area enclosing totally the listener's ear, each earpiece (2) including at least five loudspeakers arranged on said hemispherical surface, characterised in that said method consists in reproducing the spatiality of a sound by application of the Huygens Fresnel principle by reconstructing, for each ear and auricle of the listener, a sound surface corresponding to the addition of the spherical waves transmitted by said at least five loudspeakers (44), two adjoining loudspeakers (44) being spaced apart by a distance smaller than half the shortest wavelength corresponding to a given maximal frequency so as to reconstruct an acoustic field perceived as continuous by the human ear for acoustic frequencies smaller than said given maximal frequency, said maximal frequency being a frequency audible to the human ear.
2. A method according to claim 1, including at least six loudspeakers (44) per earpiece (2).
3. A method according to claim 1 or 2, wherein said maximal frequency equals 5kHz and wherein two adjoining loudspeakers are spaced apart by a distance smaller than or equal to 3 cm.
4. A method according to one of the claims 1 to 3, wherein said earpieces are open, said support (3, 4) being formed of an armature capable of receiving said loudspeakers.
5. A method according to one of the claims 1 to 3, wherein said earpieces are closed, said support (3, 4) comprising a shell defining a cap-shaped area capable of receiving said loudspeakers.
6. A device for recording a sound intended for later spatial restitution, according to the spatial sound reproduction method according to claim 1, formed of a helmet as implemented in claim 1, wherein said loudspeakers of said helmet are replaced with omnidirectional or cardioid microphones, oriented to the outside of the earpieces, the cap-shaped recording area corresponding to said recording device being blended with said cap-shaped area of one said helmet.

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