EP0331566B1 - Cylindrical acoustic wave guide - Google Patents

Description

The present invention relates to the optimization of acoustic couplings between neighboring electroacoustic transducers, over the whole extent of their frequency spectrum, by means of a particular waveguide. The purpose of this waveguide is to transform an isophase circular plane wave surface (loudspeaker membrane or compression chamber outlet) into an isophase rectangular plane wave surface. The alignment of several rectangular surfaces thus formed constitutes an isophase flat ribbon from which a coherent cylindrical progressive wave can emerge. Several transducers thus coupled generate a coherent cylindrical wave while these same transducers without the waveguide of the invention generate as many spherical traveling waves interfering with each other.

Document US-A-4,718,517 discloses a loudspeaker having a coupling device with a rectangular output and further comprising a phase part. This system is incapable of generating a coherent cylindrical wave.

Document US-A-3,980,829 discloses a waveguide comprising a plurality of outlet orifices and intended to be placed in front of an electrostatic panel used in high fidelity to reduce the directivity thereof. The waveguide inlet is rectangular. This guide cannot be used with loudspeakers or compression chambers of circular or annular shape and is unsuitable for high power sound systems.

In general, the invention is defined in claims 1 to 3. Thus, the sound waveguide has a circular or annular input and a rectangular output so that the propagation time of the wave between input and output is constant, whatever the acoustic path taken.

The other claims define characteristics specific to an exemplary embodiment.

According to a characteristic of this example, the conduit between the inlet orifice and the outlet area has a passage evoking the general shape of a sheet.

The so-called sheet form is obtained by deformation of the walls of the conduit or by incorporation of one or more bodies internal to the conduit, or both by deformation of the walls of the conduit and by incorporation of one or more bodies internal to said conduit.

The small internal body has various shapes and is made up of several elements. This body may have the general appearance of a flattened pyramid, or of a flattened cone, the point of which penetrates into the entry orifice, and the other end of which is bevelled so that its edge is flush with the outlet area of the conduit along the axis of said outlet.

The diffuser is designed to work with several speakers and several waveguides. In this case, the oblong areas of the outlet orifices are all in one plane and in line with one another.

• Fig. 1 est une vue en perspective d'un diffuseur,
• Fig. 2 est une coupe axiale horizontale
• Fig. 3 est une coupe axiale verticale
• Fig. 4 est une vue arrière du guide pour haut-parleur à chambre de compression,
• Fig. 5 est une vue arrière pour haut-parleur à diaphragme annulaire,
• Fig. 6 est une vue avant,
• Fig. 7 est une coupe suivant VII-VII de la Fig. 5,
• Fig. 8 est une coupe suivant VIII-VIII de la Fig. 5,
• Fig. 9 montre la forme du corps interne,
• Fig. 10 est une vue de côté du corps interne,
• Fig. 11 est une vue de dessus du corps interne,
• Fig. 12 est une vue de face du corps interne.

To better understand the invention, there is given below an exemplary embodiment of a waveguide represented by the accompanying drawings in which

• Fig. 1 is a perspective view of a diffuser,
• Fig. 2 is a horizontal axial section
• Fig. 3 is a vertical axial section
• Fig. 4 is a rear view of the guide for speaker with compression chamber,
• Fig. 5 is a rear view for an annular diaphragm speaker,
• Fig. 6 is a front view,
• Fig. 7 is a section along VII-VII of FIG. 5,
• Fig. 8 is a section along VIII-VIII of FIG. 5,
• Fig. 9 shows the shape of the internal body,
• Fig. 10 is a side view of the internal body,
• Fig. 11 is a top view of the internal body,
• Fig. 12 is a front view of the internal body.

The waveguide shown "in Fig. 1 is made up of three elements 1, 2, 3.

Elements 1 and 2 are symmetrical along a vertical plane and constitute shells between which the internal body 3 is fixed. Each shell has a rear flange 4 or 4 ′ and a front flange 6 or 6 ′ joined by a spacer plate 5 or 5 ′, The flanges 4-4 ′ coming in extension of one another, and it is the same for the flanges 6, 6 ′ which leave between them a slot 9 formed by the notches 8, 8 ′. The hollow parts 7 and 7 ′ form a housing for the element 3.

The rear flanges 4,4 ′ have a small circular notch 10 10 ′ facing each other after assembly to determine the inlet orifice 11.

Fig. 4 shows the case of a guide provided for loudspeaker with compression chamber, and the orifice 11, of a relatively small surface area, reveals the tip 12 of the internal body 3 which will be described later in detail.

Fig. 5 shows the case of a waveguide provided for a speaker with an annular diaphragm. The orifice 11 ′ has a larger surface area than in the previous case. We see at 13 the end of another internal body. Fig. 6 shows the front flange 6 and 6 ′ with their notch 8, 8 ′ determining the slot 9 leaving the body 3 ending on this side with an edge 14.

In Figs. 2 and 3 we see a waveguide fixed on a loudspeaker 15 and provided with a horn 16. We see that between the body 3 and a housing 7, 7 ′ remains a continuous passage bearing the references 16 to 18 ′. This passage surrounds the body 3 on all sides, and has an almost constant width.

O =

35mm, diamètre de l'orifice de sortie de la chambre de compression,

a =

50°, angle du cône (entrée) et du biseau (sortie),

I =

30mm, largeur de l'orifice rectangulaire de sortie,

L =

220mm, hauteur de l'orifice rectangulaire de sortie,

A =

112mm, demi-longueur du dispositif.

The body 3 and the wall of the housing 7, 7 ′ have compatible shapes and dimensions to allow a fluid sheet to pass between them in the conduit provided for this purpose. In the example of embodiment presented:

O =

35mm, diameter of the outlet of the compression chamber,

a =

50 °, angle of the cone (inlet) and the bevel (outlet),

I =

30mm, width of the rectangular outlet,

L =

220mm, height of the rectangular outlet,

A =

112mm, half length of the device.

It is understood that these dimensions are not limiting, but given simply for documentary purposes to illustrate the example given.

The internal body 3 has the general shape of a cone 19, the base of which is bevelled to half its height to determine two areas 20, 21 determining the edge 14. The body 3 is fixed by any known means. In Fig. 9 we see a single tongue 22, but there is a symmetrical tongue, and during assembly the two tongues are sandwiched between the plates 5 and 5 ′.

The waveguide is made of rigid material (metal, plastic, resin) by molding. As explained above, it consists of three parts, the central part is sandwiched between two identical external parts which determine the walls of the waveguide and include the flanges for fixing to the loudspeaker at the entrance, at flag at the exit. These three parts are assembled by gluing, welding or screwing.

The shapes of the internal body and of the housing are such that all the shortest paths from the inlet to the outlet are all the same length, or very similar lengths. During operation, the propagation time of the sound wave is constant through the guide.

Thus the said waveguide makes it possible to transform the circular isophase wave plane generated by the membrane of a loudspeaker or the orifice of a compression chamber into a rectangular isophase wave plane. The dimensions of the rectangular plane in question are calibrated so that the emerging sound wave propagates in quasi-cylindrical mode.

• soit (f1, f2) avec f2 > f1, l'intervalle de fréquence sur lequel le guide doit être efficace et (λ₁, λ₂) les longueurs d'ondes associées,
• soit 1 et L respectivement les largeur et longueur du rectangle de sortie du guide, L étant le côté vertical, 1 le côté horizontal.

The optimization parameters of a guide are as follows:

• either (f1, f2) with f2> f1, the frequency interval over which the guide must be effective and (λ₁, λ₂) the associated wavelengths,
• either 1 and L respectively the width and length of the guide exit rectangle, L being the vertical side, 1 the horizontal side.

i =

largeur du conduit <λ₂

ii =

a≦30°

iii =

soit δ l'écart maximal entre les différents chemins acoustiques possibles dans le guide, il faut δ ≦ λ_2/4

   Pour que la propagation soit effectivement cylindrique le long de l'axe vertical, il faut que :

iv :

L> quelques λ₁

v :

l ≦ λ₂

   Le domaine de prédilection d'utilisation des diffuseurs selon l'invention est celui de la sonorisation professionnelle des salles ou des espaces en plein air qui requièrent un grand nombre de haut-parleurs juxtaposés.In a propagation in cylindrical mode, the axis of the cylinder being vertical, so that the exit rectangle is an isophase plane, it is necessary that the following conditions are fulfilled:

i =

duct width <λ₂

ii =

a ≦ 30 °

iii =

or δ the maximum difference between the different possible acoustic paths in the guide, you need δ ≦ λ _2/4

For the propagation to be effectively cylindrical along the vertical axis, it is necessary that:

iv:

L> some λ₁

v:

l ≦ λ₂

The preferred field of use of the diffusers according to the invention is that of professional sound reinforcement in rooms or open-air spaces which require a large number of juxtaposed loudspeakers.

The stacking of several loudspeakers with waveguides in the height direction, the L side being vertical has the effect of generating a flat isophase ribbon from which a coherent cylindrical wave can emerge. Optimal coupling between the speakers is thus achieved.

Claims (11)

1. Waveguide for the transmission of sound waves of a predetermined minimum length (λ₂), fitting on the output of an electroacoustic transducer, having a continuous passage connecting an upstream inlet, constituting the end of the waveguide closer to the said transducer, to a downstream outlet, constituting the opposite end of the waveguide, characterized in that the inlet orifice (11, 11') has a circular or annular shape, the outlet orifice consists of a plane oblong rectangular orifice (9), the passage (16, 17, 18, 18') connecting them guiding the waves emitted by the said transducer, and in that, in three dimensions, the wave paths in the passage between any point on the upstream inlet orifice and any point on the downstream outlet orifice are of practically equal lengths, so that the waveguide transforms a plane circular isophase wave surface at the inlet into a plane rectangular isophase wave surface at the outlet.
2. Waveguide according to Claim 1, characterized in that the maximum distance (δ) between the different acoustic paths possible between the inlet orifice and outlet orifice in the guide is such that: δ ≦ λ₂/4, λ₂ being the minimum wavelength transmitted.
3. Waveguide according to either one of Claims 1 or 2, characterized in that the width of the plane oblong outlet orifice is less than or equal to the minimum wavelength transmitted (λ₂).
4. Waveguide according to any one of Claims 1 to 3, characterized in that it has an outer shell (1, 2), inside which an inner body (3) is arranged, the inner body being arranged so as to leave clear, between its external surface and the internal surface of the outer shell, the said continuous passage for the propagation of the waves.
5. Waveguide according to Claim 4, characterized by the fact that is formed by three members, that the first two members (1, 2) are symmetrical about a vertical plane and constitute the outer half-shells between which the said inner body (3) is fixed, each shell having a rear flange (4 or 4') and a front flange (6 or 6') connected by a bracing plate (5 or 5') which is partially deformed in order to determine the housing of the inner member (3).
6. Waveguide according to Claim 5, characterized by the fact that the rear flanges (4 and 4') are positioned in line with each other, that they each have circular cutouts (10, 10') facing each other after assembly in order to determine the inlet orifice (11).
7. Waveguide according to Claim 6, characterized by the fact that the front flanges (6 and 6') each have rectangular cutouts (8, 8'), facing each other after assembly, in order to determine the said outlet orifice (9).
8. Waveguide according to any one of Claims 4 to 7, characterized in that the inner body has, in horizontal axial section, the shape of a quadrilateral which is symmetrical with respect to an axis lying between a point on the body, flush with the surface of the circular inlet orifice, at the centre of the circle, and a ridge oriented parallel to the outlet orifice and flush with the area of the latter, and has, in vertical axial section, a triangular shape.
9. Waveguide according to any one of Claims 4 to 7, characterized by the fact that the inner body has, in horizontal axial section, a geometrical shape with five straight sides, this shape being symmetrical with respect to an axis lying between the centre of the circles forming the annular inlet orifice and a ridge on the said body extending vertically and flush with the area of the outlet orifice, and has, in vertical axial section, a trapezoidal shape, the large base of which is formed by the said ridge and the small base of which corresponds to the diameter of the annular inlet orifice.
10. Waveguide according to one of Claims 8 and 9, characterized by the fact that the inner body (3) is fixed inside the outer shell by means of tongues (22) parallel to its axis and enabling it to be held evenly spaced from the internal walls of the outer shell in order to form the said continuous passage.
11. Diffuser including several waveguides according to any one of the preceding claims, characterized by the fact that the waveguides are mounted in line (each at the output of an electroacoustic transducer) so that the rectangular areas of the outlet orifices (9) are all in one and the same plane and in line with each other.

Images