Abstract:
A horn or waveguide public address unit, enabling to adapt the dispersion characteristics of the horn or waveguide. The unit is provided with at least one profiling component ( 21   a   , 21   b ) constituting a removable dispersion shaper, capable of being mounted on the inner wall of the horn ( 13 ) or waveguide between the throat ( 17 ) and the mouth ( 19 ) thereof.

Description:
FIELD OF THE INVENTION 
   The invention relates to an electroacoustic sound reinforcement unit with a horn or an acoustic waveguide. It relates more particularly to an improvement for adapting the dispersion characteristic of said horn or waveguide as a function of the configuration of the site in which said sound reinforcement unit is installed. 
   BACKGROUND OF THE INVENTION 
   Electroacoustic sound reinforcement units with an acoustic horn or waveguide are often used in sound reinforcement systems for use out of doors or in large rooms. These sound reinforcement units are more particularly suitable for reproducing medium and high frequencies. A horn or acoustic waveguide is defined between a throat, to which an electroacoustic transducer (i.e. a loudspeaker or a compression chamber driver) is connected, and a mouth, from which the sound propagates into the exterior medium. The shape of the horn or waveguide can be characterized by a function defining the expansion of its cross section between the throat and the mouth, i.e. the variation of said cross section along a defined propagation axis between said throat and said mouth. The function can be linear, exponential or otherwise. It is generally an increasing function between the throat and the mouth. The three parameters previously cited, namely the area of the throat, that of the mouth, and the expansion function, determine the dispersion of the acoustic wave at the exit of the horn or waveguide. As a general rule, dispersion increases with expansion. At low frequencies, dispersion control improves as the area of the mouth increases and at high frequencies dispersion control improves as the area of the throat decreases. 
   The optimum dispersion characteristics vary with the configuration of the sound reinforcement site. An important part of the know-how of sound engineers therefore consists in choosing sound reinforcement units with the most suitable dispersion characteristics. They must therefore have available a large number of sound reinforcement units with entirely different characteristics, in particular different horn or acoustic waveguide shapes and dimensions. The invention overcomes this drawback. The basic idea of the invention is that the same sound reinforcement unit can have its dispersion characteristics adapted by modifying one or more of the parameters defined hereinabove and in particular the expansion function of the horn or waveguide. 
   SUMMARY OF THE INVENTION 
   To this end, the invention consists in an electroacoustic sound reinforcement unit having a horn or an acoustic waveguide defined between a throat to which an electroacoustic transducer is connected and a mouth from which sound propagates into the external medium, characterized in that it includes at least one profiling member that constitutes a removable dispersion shaping member and is shaped to be mounted on the inside wall of said horn or waveguide between said throat and said mouth to modify the interior shape of said horn or waveguide. 
   The profiling member can be a variable profile conduit defining the new expansion function. It is inserted into and fixed inside the horn or acoustic waveguide. In a preferred embodiment, there are two profiling members that can be fitted to two opposite interior walls of the horn or waveguide. 
   A profiling member of the above kind or a set of profiling members as defined above therefore changes the dispersion characteristic of the sound reinforcement unit, which may also be associated with a plurality of profiling members or sets of profiling members chosen by the technician to optimize the dispersion characteristic as a function of the configuration of the operating site. 
   For example, for a sound reinforcement unit of the type comprising a horn or waveguide having a plane of symmetry extending between the throat and the mouth, two of the profiling members previously cited could be fixed to the inside wall of the horn or waveguide, symmetrically to each other, and attached to said inside wall at locations such that said plane of symmetry is preserved. 
   Various shapes of the profiling members are described hereinafter. 
   A sound reinforcement unit of the invention, i.e. at least adapted to receive one or more profiling members as defined above, is therefore characterized in that said horn or waveguide includes means for fixing at least one profiling member constituting a dispersion adapter. For example, assembly means of the nut and bolt type or using adhesive or magnetic members may be used. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood and other advantages of the invention will become more clearly apparent in the light of the following description, which is given by way of example only and with reference to the appended drawings, in which: 
       FIG. 1  is a diagrammatic exploded perspective view of a horn sound reinforcement unit in the field of the invention equipped with two complementary profiling members for modifying its intrinsic acoustic dispersion characteristics; 
       FIG. 2  is a front view of one of the profiling members; 
       FIG. 3  is a profile view of the same member; 
       FIG. 4  is a perspective view of the same member; 
       FIG. 5  is a perspective view similar to  FIG. 1  showing the two profiling members in place inside the horn; and 
       FIGS. 6 and 7  are diagrams of variants. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 to 5  show an electroacoustic sound reinforcement unit  11  with a horn  13 , which here is relatively rigid, comprising an electroacoustic transducer  15 , or acoustic generator as it is otherwise known, connected to a small section opening  17  called the throat defined at the back of the horn. The horn  13  is fixed relative to the transducer  15 . The inside wall of the horn widens to a mouth  19 , which here is approximately rectangular, from which sound propagates into the exterior medium. A sound propagation axis can be defined passing through the center of the throat and through the center of the mouth. A propagation axis y′y of this kind is shown diagrammatically in  FIGS. 6 and 7 . The variation of the cross section of the horn along this axis represents the expansion function defined above. As such, the horn therefore has a given expansion function, depending only on the shape and the dimensions of its inside surface. This expansion function constitutes one of the parameters conditioning the dispersion characteristics of the horn (or the acoustic waveguide if the electroacoustic transducer is not connected to a horn as shown here). 
   According to an important feature of the invention, the sound reinforcement unit is completed by at least one profiling member  21  constituting a dispersion adapter and shaped to be mounted on the inside wall of the horn or waveguide, between the throat  17  and the mouth  19 . By inserting and fixing one or more profiling members of this type into the horn, the interior shape of the horn or waveguide, and consequently its dispersion characteristics, can be adapted as a function of the configuration of the operating site. In the present example, two profiling members  21   a ,  21   b  are used, and are adapted to be fitted to respective similar opposite faces  25   a ,  25   b  of said inside wall of said horn. In the example shown, said horn has a plane of symmetry P extending between the throat and the mouth. The two profiling members  21   a ,  21   b  are symmetrical and can be fitted to the two faces  25   a ,  25   b , respectively, at locations such that said plane of symmetry P is preserved. In other words, the plane of symmetry P of the inside wall of the horn, as seen in  FIG. 1 , remains the plane of symmetry of the inside wall of the modified horn, i.e. when the latter incorporates the two profiling members  21   a ,  21   b , as shown in  FIG. 5 . 
   In the present example, each profiling member has a first guide surface  27  substantially parallel to the plane of symmetry P when the profiling member is fitted and a second guide surface  29  extending said first drive surface and defining therewith an approximately obtuse dihedron. Said second guide surface is nevertheless very slightly curved. 
   In the example shown diagrammatically in  FIG. 6 , each profiling member  121   a ,  121   b  has a guide plane  30  inclined to a plane surface of the inside wall  13  of the horn. The guide plane and the plane surface join in the vicinity of the throat  17 . On the other hand, in the  FIG. 7  variant, each profiling member  221   a ,  221   b  has a curved profile guide surface  32  with a throat portion  34  substantially parallel to said plane of symmetry, in the immediate vicinity of the throat  17  of the horn, and a mouth portion  36  diverging from the plane of symmetry, starting from the throat portion. The two portions  34 ,  36  join together with no discontinuity. 
   Different solutions can be envisaged for fixing the profiling members to the wall of the horn. In the example of  FIGS. 1 to 5 , the horn  13  (or waveguide), on the one hand, and the or each profiling member  21   a ,  21   b , on the other hand, includes nut and bolt type assembly means. Consequently, holes formed in the wall of the horn or in each profiling member can have threaded portions or portions equipped with captive nuts. The holes in the profiling members are here formed in columns  40  that engage in holes  42  of the wall of the horn. If the nuts are attached to the horn, the heads of the bolts bear on shoulders formed inside holes formed in the profiling members. 
   Alternatively, the horn (or waveguide), on the one hand, and/or the or each profiling member, on the other hand, can include adhesive assembly means, for example double-sided adhesive tapes. 
   Another alternative is for said horn (or waveguide), on the one hand, and/or the or each profiling member, on the other hand, to include assembly means employing magnetic members. For example, if the horn is made from a metal with magnetic properties (iron, steel), the profiling members can be fitted with magnetized pads. The converse arrangement is possible. The horn and the profiling members could also be fitted with magnetized pads cooperating in pairs. 
   As can be seen in  FIGS. 5 to 7 , placing the profiling members inside the horn modifies its expansion function by defining a new inside surface of the horn that is substituted for the original surface. This modification of the expansion function adapts the dispersion characteristic of the sound reinforcement unit. Of course, any sound reinforcement unit with a horn or waveguide defined between a throat to which an electroacoustic transducer is connected and a mouth from which sound propagates into the external medium lies within the field of the invention provided that said horn or waveguide connected to said transducer is provided with means for fixing at least one profiling member constituting a dispersion adapter.