EP1621044A1

EP1621044A1 - Headphone for spatial sound reproduction

Info

Publication number: EP1621044A1
Application number: EP04742599A
Authority: EP
Inventors: Hong Cong Tuyên Pham; Ambroise Recht
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-04-29
Filing date: 2004-04-28
Publication date: 2006-02-01
Anticipated expiration: 2024-04-28
Also published as: EP1621044B1; DK1621044T3; JP2006525708A; AU2004234906B2; KR20060003902A; KR101116081B1; WO2004098235A1; ATE477684T1; US7532734B2; CN1781336A; CA2523074C; CN1781336B; US20060204016A1; AU2004234906A1; ES2350692T3; DE602004028594D1; FR2854537A1; CA2523074A1

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

TITLE: Acoustic headphones for the spatial reproduction of a sound.

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.

By spatialization of a sound is meant the restitution 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, the aim of which is to solve such a technical problem. However, in most cases they only offer 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 provided with speakers, or using an acoustic headset, each earpiece of the headset comprising a speaker.

According to a first method, called stereophony on two channels, to simulate the movement of a sound source, two speakers are used, one channel per speaker, and the intensity of the sound is weighted on the two corresponding channels, 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. In addition, the sound sources can only be moved on one dimension instead of the whole space.

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

However, such a system does not make it possible to precisely locate the sound sources since the central speaker focuses them whatever the listening position. Furthermore, it is not possible, in such a room, to make separate sounds for the two ears.

According to another method for simulating a spatialization effect, a series of loudspeakers oriented regularly towards a listening point is regularly distributed in a circle, each loudspeaker broadcasting a particular sound channel. It is therefore an extension of the stereophonic process on two channels. However, the spatialization effect is really only obtained at a particular point in the room, called the focal point. Listeners who are somewhere other than this focal point also hear the sounds, but they suffer from acoustic illusions, which one could compare to optical illusions. However, a perceived sound can be reduced to a presumed uniform sound pressure at the level of the eardrums. Thus, at the level of one ear, the only variable of interest is the sound pressure at the level of the eardrum, which itself depends on the sound pressure at the entrance to the ear canal, on the morphology of the ear of the ear. 'auditor. In an acoustic helmet, the goal is to reproduce this pressure, in order to reconstitute a sound.

However, for two different listeners, the sound pressure at the eardrum, and even at the entrance to the ear canal, resulting from the same sound source, will be different. This will not prevent them, except hearing loss, from locating the sound source correctly. These differences between individuals and between the ears of the same individual, come from morphological differences. Indeed, the spacing of the listener's ears and the presence of an obstacle, the head, on the trajectory of the acoustic wave, introduce a phase shift and a difference in intensity in an acoustic wave coming from the same sound source. Thus, the sound pressure at the eardrum is different between the right ear and the left ear, for the same sound source, depending on the position of this source versus the listener.

Various devices attempt to spatialize a sound by taking into account these differences in perception between the two ears. It is simply a matter of diffusing 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 binaural principle.

However, binaural techniques are based on a database gathering experimental measurements, corresponding to “average” morphologies. It is not possible to model the human hearing system, in particular the pavilion of the ear, whose shape is too complex to take into account all the physical phenomena necessary for a computational approach. Thus, the techniques used correspond to medium ears and the measurements are carried out on mannequins. These techniques therefore have the drawback of not being suitable for everyone. Also known from US Pat. No. 6,038,330 is an acoustic headset for the spatialization of sound. The headphones have, for each earpiece, loudspeakers regularly placed on a cap surface.

Each of said speakers is combined with a waveguide to orient and concentrate the sound emitted on the listener's horn. However, the spectral representation of the sound emitted by each of said speakers is modified by said waveguides. Such headphones do not then allow spatial reproduction of sounds according to the Huygens-Fresnel principle.

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 on the individual characteristics of the hearing aid. In other words, such headphones must allow the spatialization of sound for the vast majority of listeners.

Another object of the present invention is to provide a dynamic system, which can take account of the movements of the head in the acoustic field reconstructed using such a headset.

Another object of the invention is to propose a space-saving acoustic helmet, simple to use and allowing good mobility of the head, in particular for easily adapting it to a dynamic system.

An object of the invention is also to propose a helmet making it possible to reproduce a sound in a precise manner, 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 propose an inexpensive helmet.

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

Other objects and advantages of the invention will appear during the description which follows, which is given only for information and which is not intended to limit it.

The invention relates to an acoustic headset for the spatial reproduction of sound, 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 loudspeakers, arranged on said support and able to reconstruct an acoustic field. The invention also relates to a device for recording a sound intended for subsequent spatial reproduction, consisting of a headset as defined above and in which the loudspeakers are replaced by omnidirectional or cardioid microphones, the surface in a recording cap corresponding to said recording device being merged with the surface in a cap (of acoustic emission) of a said hearing helmet. The invention will be better understood on reading the description, accompanied by the appended figures, among which:

- Figure 1 shows schematically the head of a person wearing an acoustic helmet according to the invention, - Figures 2a, 2b, 2c are perspective views of the left earpiece of a helmet according to invention, front, interior and rear respectively,

FIGS. 3a and 3b are sectional views of a headset earpiece according to the invention, in a vertical plane and a horizontal plane respectively,

FIGS. 4 and 5 are two variants of the distribution of eight speakers, or microphones, in a listener, illustrated in plan and in section,

- Figure 6 is a variant of distribution of six speakers, or microphones, in an earphone, illustrated in plan and in section.

The invention was born from the observation of the nonexistence of a simple device for spatializing sound, requiring little computing power, and suitable for all. Indeed, the devices based on the binaural principle are specific to the listener - or the mannequin - on which the measurements were carried out while the stereophonic rooms allow a spatialization of the sound only 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 came up with the invention by modifying the point of view used to tackle the problem of the spatialization of a sound. Instead of trying to reproduce the sound pressure at the eardrum or the entrance to the ear canal, as has been the case until now, they have sought to reconstruct the sound wave as it can be measured at a given distance from the ear, before transformation by the pinna and the ear canal.

The inventors therefore decided to create a sound surface transmitter surrounding the pavilion of the ear. The fact that this surface surrounds the pinna is not trivial. Indeed, this makes it possible to get rid of the individual morphological characteristics of the pavilion since the wave emitted will be transformed by the pavilion of the ear, just like any sound.

The use of a helmet also makes it possible to overcome problems with the geometry of a room. This also makes it possible to develop, for example, dynamic systems taking into account the movements of the head in space, to move, virtually, the sound environment reconstructed as a function of these movements of the head.

According to the Huygens-Fresnel principle, any point in 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 it is 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, you cannot produce an infinite number of sound sources. It was therefore necessary to determine a finite number of sound sources which, diffusing sounds at the same time, would be equivalent to said emitting sound surface.

For this, we use information theory, and more particularly Shanon's theorem. According to this theorem, the sampling pulse of a sinusoidal signal must be at least twice greater than the pulsation of said sinusoidal signal, if one wishes to avoid a loss of coherence between the continuous sinusoidal signal and the sampling. In other words, the sampling period must be twice as small as 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 twice the wavelength of this signal. If we consider that the limiting wavelength is the shortest wavelength of the signal, i.e. the limiting frequency is the highest frequency of the signal, we obtain: Δl <2.λ, where I is the distance between two speakers (or microphones) and λ is the shortest wavelength of the signal. Thus, the sampling - emission or recording - preserves all the information of the sampled signal for the frequencies lower or equal to half of the sampling frequency.

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

As illustrated in the different figures, we end up with a helmet

1 comprising two earphones 2, each earpiece comprising at least five speakers arranged on a support 3, 4. Said support 3, 4 at least partially defines a cap surface, capable of completely encompassing the ear of the listener 6.

The expression “in a cap” means that the earpiece completely encompasses the pavilion of the ear, without there being any contact between the surface “in a cap” and the pavilion. Advantageously, this surface is in the form of a hemisphere or a portion of a hemisphere. It can also be ovoid, even possibly polyhedral. The main thing is that the cap surface includes the listener's ear, and is a skeleton support for the speakers.

In the various figures, said earpiece has a hemispherical cap surface. Said earpiece 2 can be opened 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 materializes said hemispherical surface. Advantageously, said at least five speakers can 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 bands 4, a horizontal band 42 and a vertical band 43. Said curved bands 4 form a cross. In addition, they are pierced with orifices 41 capable of receiving said speakers 44.

The orifices 41 are distributed regularly, 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 curved strip 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 strip 42 includes four orifices 41 spaced at an angle of 36 ° between them; the vertical strip 43 comprises three orifices 41 spaced at an angle of 45 ° between them. Thus, the earpiece 2 can receive six speakers, one of which is at the intersection of the two support strips 42, 43. For example, the hemispherical surface has a radius r of 4 cm.

Of course, a greater number of loudspeakers could be provided, arranged for example on the branches of a star and closer to each other, in order to obtain a maximum frequency of the sampled signal, in this case transmitted, greater than 5 kHz. For example, as illustrated in FIGS. 4 and 5, the earpiece can include eight speakers 44. A plan view of these two variants is shown at the top left of FIGS. 4 and 5 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 plan view, the loudspeakers 44 are distributed regularly 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 FIG. 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 speakers 44 are located at the vertices of two squares inscribed respectively 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 outer 31 and inner 32 circles are substantially parallel to the plane defined by the ring 3 and are at an angle of 30 ° { ^π / ₆ rad) and 60 ° (^ rad) relative to the center 33 of the hemisphere.

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

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

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

Advantageously, a headset according to the invention comprises at least six speakers per earpiece. According to a first variant of the invention, a helmet 1 is provided with open earphones, as illustrated in the different figures. In this case, the support 3, 4 consists of an open frame, capable of receiving the loudspeakers. From an acoustic point of view, this means that the listener can hear a sound not emitted by the speakers, without distortion or attenuation. According to another variant, the headphones 2 are closed. In this case, the support consists of a shell defining a hemispherical surface capable of receiving said speakers.

Although not illustrated, electrical connection means are provided between the speakers 44 and, for example, an audio output from an amplifier, a portable music player, a sound card or any other similar electronic device. It could also be wireless transmission means, thus avoiding the congestion generated by electric wires. Advantageously, said headset serves as a support for a microphone situated at the end of a branch, in front of the listener's mouth, to allow the latter to speak, in particular interactively, with another person equipped for example with '' same helmet.

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

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

As illustrated, the two headphones 2 of the headset 1 are connected by a headband 8 which passes over the head of the listener 6. It can be an adjustable headband, made of various materials known to those skilled in the art. job.

Furthermore, according to an advantageous characteristic, such an acoustic headset is equipped with a device for monitoring the movements of the head or "head-track". Thus, the movements of the listener's head 6 can be detected and the signal broadcast by the loudspeakers of each earpiece 2 can be modified as a function of these movements, in order to offer the listener 6 a real impression of auditory displacement, in particular in a virtual space. 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 oriented towards the outside of the headphones, that is to say opposite the ears 5 of a listener 6 potential.

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

With such an acoustic headset and such a recording device, it is no longer necessary to worry about the transformations undergone by the sound wave, due to the hearing aid, since the sounds are recorded and emitted before these transformations .

Such a helmet can find its application in many fields, and in particular:

- leisure and so-called “virtual reality” games, which reconstitute a virtual audiovisual space, - teleconferencing, to simulate a meeting or conference room and virtually locate the speakers in relation to each other, other than through the intermediary a simple screen,

- any other application where one may wish to couple, for example, an acoustic space with a reconstructed visual space. Naturally, other modes of implementation, within the reach of the skilled person, could still have been envisaged without departing from the scope of the invention, subject of the claims below.

Claims

1. Headphones for the spatial reproduction of sound, provided with two earphones, each earpiece comprising a support defining at least partially a skullcap surface completely encompassing the ear of the listener, each earpiece comprising at least five speakers , arranged on said hemispherical surface characterized in that two contiguous loudspeakers are spaced by a distance less than twice the smallest wavelength corresponding to a given maximum frequency so as to reconstitute a sound 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 average human ear.

2. Headphones according to claim 1 comprising at least six speakers per earpiece.

3. Headphones according to claim 1, wherein said maximum frequency is 5 kHz and wherein two contiguous speakers are spaced apart by a distance less than or equal to 3 cm.

4. Headphones according to any one of the preceding claims, in which the said earphones are open, the said support being constituted by an armature capable of receiving the said speakers.

5. Headphones according to any one of claims 1 to 3, wherein said earphones are closed, said support comprising a shell defining a cap surface capable of receiving said speakers.

6. A device for recording a sound intended for a subsequent spatial reproduction, consisting of a headset according to any one of the preceding claims in which the loudspeakers are replaced by omnidirectional or cardioid microphones, the cap surface d the recording corresponding to said recording device being merged with said cap (acoustic emission) surface of said helmet.