EP1728409B1 - Sound device provided with a geometric and electronic radiation control - Google Patents

Description

1- Indication of the domain

The device which is the subject of the present invention concerns the sound reinforcement of acoustically reverberant premises. To obtain a good clarity of the sound and a good intelligibility of the voice in such premises, the loudspeakers must radiate directionally towards the listeners, so that the direct sound perceived by them (sound propagating directly from the speaker to the listeners) is of important energy compared to that of the sound reaching him after reverberation by the walls of the local. The sound system must also provide the most homogeneous sound coverage of the area to sound. The listeners being generally located on a horizontal plane of large surface area, it is necessary to consider a speaker column type, the directivity is marked in the vertical plane, and little marked in the horizontal plane.

2- State of the art

The figure 1 describes a typical configuration. The enclosure (11) must produce a sound level as homogeneous as possible over an entire area (12) where the audience is located, and this on a band of the widest possible frequency. It must moreover, as we have seen, minimize the sound energy radiated elsewhere than towards the audience, in order to minimize the energy reverberated by the local and reaching the listeners.

Two types of approaches have been developed to achieve this goal: geometrically controlled networks, and electronically controlled networks.

2.1- The geometrically controlled network

Knowing the objective of sound coverage, we can deduce the shape of the acoustic wavefront that the speaker must radiate. Licences FR 2626886 and derivatives describe a device for generating a wavefront close to this objective. The principle uses a cylindrical waveguide excited at one end by a loudspeaker, and radiating at the other end by an elongated rectangular opening. The shape of the waveguide is such that the radiated acoustic field is similar to that radiated by a rectangular piston of elongated shape. By superimposing several of these waveguides, and tilting them relative to each other, we can approach the shape of the desired wavefront, and thus approach the objective of sound coverage sought. The figure 2 illustrates this principle with a superposition of eight waveguides (22) such as that described in the patent FR 2626886 , associated with eight loudspeakers (21), generating a wavefront (23). Licences FR 2813986 and associates describe another waveguide to achieve the same goal.

But this principle of geometric synthesis of the wavefront inevitably leads to a curved form of enclosure. It is therefore difficult to apply if the enclosure is intended to be mounted vertically, for example applied to a wall or a pillar.

The patent US5590214 entitled "Vertical Array Type Speaker" presents a device consisting of two columns of speakers mounted face-to-face, radiating through a vertical slot. But this device is not able to generate a wave front ensuring a homogeneous sound coverage.

2.2- The electronically controlled network

In order to generate the desired wavefront, it is also possible to use a network of traditional loudspeakers, and conventional filtering techniques derived from radars. The figure 3 illustrates the principle of using delays (31), denoted R _n in the figure, associated with loudspeakers (34) via filters (32) and power amplifiers (33) to approach the wavefront (35). ) desired. Thus, for example, a rectilinear and regular network of loudspeakers spaced a distance noted a generates a wavefront oriented along the direction φ when R _n = (n-1) .a / c.sin is selected. (φ), where c is the speed of sound, where n is the index of the loudspeaker. The proper use of the filters (32) makes it possible to minimize the frequency variations of the structure of the radiated acoustic field. The patent WO 03034780 describes a device of this type. Unfortunately, the fact of using a limited number of loudspeakers (a discrete network, and not continuous) induces high amplitude secondary lobes, which degrade the acoustic quality. These secondary lobes are magnitudes all the more important that the direction of the main lobe deviates from the normal to the network.

Licences EP0791279 and associated have a device of this type, and claim a principle of positioning of the speakers, which are spaced regularly on a portion of the enclosure, and then spaced logarithmically. This principle makes it possible to limit the number of necessary loudspeakers, but leads to an unequal power distribution on all the loudspeakers, and therefore to a smaller maximum radiated sound level than if the power were equally distributed over all the loudspeakers. speakers as is the case in geometric networks.

The electronically controlled network has the advantage of being able to control to a certain extent the structure of the radiated field without mechanical alteration of the device, by simply playing on the filtering parameters. On the other hand, it has the disadvantage of generating high frequency high frequency side lobes, ie when the wavelength is less than or equal to the distance separating the loudspeakers (spatial sampling criterion). .

The Wave Field Synthesis (WFS) technique also uses an electronically controlled speaker array of delays, filters, and power amplifiers. By application of the Huygens principle, an adequate adjustment of the delays and filters makes it possible to generate a wavefront corresponding to a virtual source situated at a given place of space. This is called "spatialization". By extension, this technique has been used for recording and sound reproduction, as well as acoustic rooms to simulate in a room or in the open air the acoustics of another room (see, for example, patents EP0335468 , US5452360 and associates). Curved loudspeaker networks have been implemented as part of the WFS (see Evert W. Start "Application of Curved Arrays in Wave Field Synthesis", preprint No. 4143, 100th Convention of the ESA, 1996 ). Licences EP12099498 and associates describe an implementation of the WFS with a particular type of loudspeakers. The article of Mark S. Ureda "Wave Field Synthesis with Hom Arrays" (preprint No. 4144, 100th AES Convention, Copenhagen, May 1996 ) describes the implementation of the WFS with flush loudspeakers.

In all these works, the objective is to be able to generate wave fronts of various shapes, and the orientations of the emission axes of the loudspeakers are perpendicular to the network. The radiation control of the network is therefore done exclusively through the electronic parameters (delays and filters essentially), and not by acting on the orientations of the speakers as is the case for the geometrically controlled networks of which we spoke.

3- Presentation of the invention

The advantage of the device that is the object of the present invention is to combine the advantages of the geometrical network with those of the electronically controlled network: it allows an excellent control of the radiated acoustic field, minimizing the secondary lobes, optimizing the maximum power emissible thanks to a homogeneous distribution on all the speakers, while having a rectilinear shape allowing easy integration, for example applied to a wall.

For this purpose, the subject of the invention is a sound device allowing a homogeneous sound coverage over an area to be sounded, comprising a network of electroacoustic sources, each electroacoustic source diffusing a delayed version by a delay, filtered by a filter, and amplified by an amplifier of the input signal of the device, characterized in that said network is essentially rectilinear and vertical, in that the angles θ formed by the emission axes of the electroacoustic sources and the normal to the network are such that θ _n > θ _n-1 , where n is the index of the electroacoustic sources numbered in ascending order from the top to the bottom of the device, and in that the delays cooperate with the angles θ so that the device generates a wavefront of the form corresponding to the desired sound coverage of the zone to be sounded.

Preferably, the angles of inclination θ of the electroacoustic sources are chosen so that for each of the electroacoustic sources, the distance d separating the center of said electroacoustic source from the point of intersection between the emission axis of said electroacoustic source and the desired wavefront is minimal. The delays are essentially R _n = R _n-1 + (d _n-1 -d _n ) / c for n> 1, R _n being the delay (in seconds) associated with the n ^th electroacoustic source, R ₁ being any, where c is the velocity of the sound in m / s, the distances d being expressed in meters.

In the case where the electroacoustic sources are all of the same height, the definition of the delays given above essentially corresponds to R _n = R _n-1 + a _{n-1 /} csin ₍ (θ _n + θ _n-1 ) / 2) for n> 1, where R ₁ is arbitrary, where _n is the distance (in meters) separating the center of the n ^th electroacoustic source from the center of the (n + 1) ^th , and the angles θ being expressed in radians .

• la figure 1 représente une configuration de sonorisation traditionnelle ;
• la figure 2 représente le principe d'un réseau contrôlé géométriquement conforme à l'état de la technique ;
• la figure 3 représente le principe d'un réseau contrôlé électroniquement conforme à l'état de la technique ;
• la figure 4 représente le principe de l'invention, vu en coupe longitudinale ;
• la figure 5 représente une vue de face du réseau de haut-parleurs monté dans une enceinte ;
• la figure 6 représente une vue de face d'un haut parleur à membrane essentiellement rectangulaire ;
• la figure 7 représente, sous forme de vues de face, l'assemblage de haut-parleurs à membranes rectangulaires et circulaires ;
• la figure 8 représente un mode de réalisation de l'invention vu en coupe longitudinale, dans lequel les sources électroacoustiques sont constituées de groupes de haut-parleurs ;
• la figure 9 représente un mode de réalisation de l'invention vu en coupe longitudinale, dans lequel les sources électroacoustiques sont de hauteurs différentes.

The invention will be better understood on reading the following description of exemplary embodiments, with reference to the appended drawings in which:

• the figure 1 represents a traditional sound configuration;
• the figure 2 represents the principle of a geometrically controlled network according to the state of the art;
• the figure 3 represents the principle of an electronically controlled network according to the state of the art;
• the figure 4 represents the principle of the invention, seen in longitudinal section;
• the figure 5 represents a front view of the loudspeaker network mounted in an enclosure;
• the figure 6 represents a front view of a substantially rectangular membrane loudspeaker;
• the figure 7 represents, in the form of front views, the assembly of rectangular and circular diaphragm loudspeakers;
• the figure 8 represents an embodiment of the invention seen in longitudinal section, in which the electroacoustic sources consist of groups of loudspeakers;
• the figure 9 represents an embodiment of the invention seen in longitudinal section, in which the electroacoustic sources are of different heights.

The principle of the invention, presented on the figure 4 in longitudinal section for the case of eight electroacoustic sources, is inspired by Fresnel lenses used in optics. A network of N electroacoustic sources (1) is associated with delays (3), filters (4), and power amplifiers (5). The electroacoustic sources (1) are aligned vertically, and oriented so that, combined with a set of delays (3) appropriately selected, they generate the front wave (6) of the desired shape, corresponding to a desired sound coverage on an area to sound. The filters and delays can of course be switched, and other elements (eg limiters) can be inserted upstream of the power amplifiers. The input signal to be broadcast is applied to all electroacoustic sources via delays (3), filters (4), and amplifiers (5).

The originality of the present invention therefore consists in generating the desired wavefront (6) by playing both on a geometrical aspect thanks to the orientations and positioning of the electroacoustic sources (1) of the network, and on an electronic aspect by compensating in particular by delays (3) the spatial shifts between the electroacoustic sources (1).

By reference to the figure 4 the angle of inclination θ _n of the n ^th electroacoustic source is such that the distance d _n separating the center of said electroacoustic source from the point of intersection between the emission axis of said electroacoustic source and the front of the electroacoustic source; wanted wave is minimal, and this for all electroacoustic sources.

Since electroacoustic sources (1) are numbered from top to bottom, the delay R _n associated with the ^nth electroacoustic source must then be worth R _n = R _n-1 + (d _n-1 -d _n ) / c for n = 2 to N, where c is the speed of sound (in m / s) and N is the number of electroacoustic sources (R _n in seconds, d _n in meters). We can take R ₁ = 0 or any other value. Note that it is the differences d _n-1 -d _n that occur, and therefore that the above definition does not depend on the propagation of the wavefront.

The height of an electroacoustic source (1) is the distance separating the lower end of the upper end of said source. According to the principle explained above, and in the case where the electroacoustic sources are all of the same height, the values of the delays (3) can still be expressed as a function of the angles of inclination θ (in radians) of the electroacoustic sources ( 1) according to the formula R _n = R _n-1 + (a _{n-1 /} c ).sin ₍ (θ _n + θ _n-1 ) / 2) for n = 2 to N, where R _n is the delay (in seconds) associated with the n ^th electroacoustic source, R ₁ being arbitrary, where _n is the distance (in meters) separating the center of the n ^th electroacoustic source from the center of the (n + 1) ^th , and c being again the sound speed (in m / s).

In the usual situation where the device is placed above the area to be sound, this principle leads to a set of angles θ such that θ _n > θ _n-1 .

Thus, to a shape of the wavefront (6) and a given type of electroacoustic source corresponds a set of angles θ and values of the delays (3). However, by assigning the delays (3) slightly different values from those resulting from the formulas given above, and possibly playing on the gains and frequency responses of the filters (4), it is possible to generate a different wavefront of the one corresponding to the set of angles θ. This allows, for example, to partially correct the effect of a positioning of the column at a height different from that for which it was designed (angles of inclination θ), or to correct an inadequate sound level in a certain area resulting from an acoustic phenomenon of the local area.

If the electroacoustic sources are not all identical, then the filters (4) will also be used to correct the differences that may exist between their frequency and / or time response characteristics.

The filters (4) and delays (3) can be realized by a digital signal processor (DSP) equipped with appropriate software.

The length of the network is an important parameter of the invention, as it is for all other types of networks. The larger it is, the larger is the area that the network can cover, and the better is the homogeneity of coverage at low frequencies.

In a first embodiment of the invention, the electroacoustic sources (1) are direct-radiation loudspeakers, these loudspeakers preferably being equipped with essentially rectangular membranes. Optimum performance in terms of side lobe rejection is achieved when each speaker radiates in the manner of a rectangular piston as high as the gap between loudspeakers allows. The figure 5 shows a front view of the loudspeaker array (51) mounted in an enclosure (52), whose radiating faces are preferably substantially rectangular, possibly slightly curved in the vertical plane to better match the shape of the wavefront to return. The figure 6 shows a substantially rectangular diaphragm loudspeaker (61) seen from the front.

In a second embodiment of the invention, the electroacoustic sources (1) are loudspeakers radiating through waveguides. Each waveguide radiates through a substantially rectangular orifice and such that the particle acoustic velocity is at all times substantially the same at any point of the radiation orifice. Indeed, optimal performance in terms of secondary lobe rejection are obtained when the waveguides radiate through a rectangular opening as would a rectangular piston (for example those described in the patents FR 2626886 and FR 2813986 already mentioned), and that their height is as great as the gap between the waveguides allows.

In a third embodiment of the invention, the electroacoustic sources (1) are groups of loudspeakers, all the loudspeakers of the same group being located in the same plane, arranged side by side and excited by the same electrical signal. The speakers of the same group are thus assembled so that the group radiates essentially as a rectangular piston in the frequency band considered. Indeed, for frequencies corresponding to wavelengths shorter than the distance between adjacent loudspeakers, the radiation of a regular assembly of small speakers in a loudspeaker group is close to the radiation of a piston the size of the assembly. The figure 7 gives two examples of speaker assembly in a group of loudspeakers for rectangular and circular diaphragm loudspeakers (71) seen from the front, on the membrane side. The figure 8 illustrates this implementation of the invention in the case of eight groups of 4 loudspeakers. This figure is identical to the figure 4 except electroacoustic sources (1) which have been replaced by groups of loudspeakers (81).

In another embodiment of the invention, the electroacoustic sources (1) are of different heights, the height of each source being essentially a function of the associated angle θ: the smaller it is, the higher the height of the source perhaps large. This is illustrated by the figure 9 , in which the indices (1), (2), (3), (4), (5), and (6) have the same meanings as on the figure 4 . This embodiment has the advantage of minimizing the depth of the column, noted p on the figure 9 . The delays (3) are essentially equal to R _n = R _n-1 + (d _n-1 d _n ) / c for n> 1, where R _n is the delay (in seconds) associated with the n ^th electroacoustic source, R ₁ being any, c being the velocity of the sound in m / s, the distances d being expressed in meters.

The electroacoustic sources (1) can be mounted or fixed on the same enclosure (2). The rear faces of the membranes of the electroacoustic sources (1) can then either radiate each in an independent volume resulting from a partitioning of the enclosure (2), or radiate all in the same volume. Indeed, for the frequencies beyond the resonant frequency of the speakers, they are mainly controlled by their moving mass, and not by the stiffness of the volume of air that charges them back.

In another embodiment of the invention, each electroacoustic source (1) is mounted on a speaker of its own, and the speakers assembled according to the positioning and orientation principle explained above with the help of a mechanical device. In other words, the electroacoustic sources (1) are fixed to the speakers mechanically connected to each other. This embodiment makes it possible to optimally adjust the orientations of the electroacoustic sources (1) for a given positioning of the device and a desired sound coverage.

The delays (3) and filters (4) can be realized by a digital signal processor (DSP) equipped with the appropriate software.

The delays (3), filters (4) and amplifiers (5) can be embedded in the enclosure (2), or stay outside the enclosure.

Claims (11)

1. A sound device allowing homogenous sound coverage over an area to be addressed, comprising a network of electroacoustic sources (1), each electroacoustic source (1) transmitting a version delayed by a delay (3), filtered by a filter (4) and amplified by an amplifier (5) of the input signal to the device,
   characterized in that the network of electroacoustic sources (1) is essentially rectilinear and vertical, in that the electroacoustic sources (1) are fixed either onto one same speaker (2) or to speakers mechanically linked together, in that the angles θ formed by the emission axes of the electroacoustic sources (1) and the normal to the network are such that θ_n>θ_n-1 where n is the index of the electroacoustic sources (1) numbered in increasing order from the top to the bottom of the device, and in that the delays (3) cooperate with the angles θ so that the device generates a wave front (6) of the shape corresponding to the desired sound coverage of the area to be addressed.
2. The device according to claim 1,
   characterized in that the tilt angles θ of the electroacoustic sources (1) are chosen so that for each of the electroacoustic sources (1) the distance d separating the centre of the said electroacoustic source from the point of intersection between the emission axis of the said electroacoustic source and the desired wave front is minimal.
3. The device according to at least one of claims 1 and 2,
   characterized in that the delays (3) essentially have a value of R_n = R_n-1 + (d_n-1 - d_n)/c n>1, R_n being the delay (in seconds) associated with the n^th electroacoustic source, R_n having any value, c being the sound velocity in m/ s, the distances d being expressed in metres.
4. The device according to at least one of claims 1 to 3,
   characterized in that the electroacoustic sources (1) are direct radiation loudspeakers.
5. The device according to claim 4, characterized in that the loudspeakers are equipped with essentially rectangular membranes.
6. The device according to at least one of claims 1 to 3,
   characterized in that the electroacoustic sources (1) are loudspeakers radiating through waveguides.
7. The device according to claim 6,
   characterized in that each waveguide radiates via an essentially rectangular orifice and such that the acoustic particle velocity is at all times essentially the same at every point of the radiation orifice.
8. The device according to at least one of claims 1 to 3,
   characterized in that the electroacoustic sources (1) are groups of loudspeakers.
9. The device according to claim 8,
   characterized in that the loudspeakers of one same group are adjacent, located in one same plane and excited by the same electric signal.
10. The device according to claim 9,
    characterized in that the loudspeakers of one same group are assembled so that the group radiates essentially as a rectangular piston would radiate in the frequency band under consideration.
11. The device according to claim 1,
    characterized in that the electroacoustic sources (1) are of different height.

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