FR2582178A1 - Omnidirectional acoustic enclosure having, at constant output, a response over a wide band of audio frequencies - Google Patents

Abstract

Omnidirectional acoustic enclosure whose loudspeakers 3 and 4, outputting the middle and treble frequencies, whose known axes are placed vertically, are loaded by the axisymmetric horns 1 and 2 which, in a vertical diametral section, exhibit two mouthpieces which are symmetric with respect to the vertical axis, when drawn as a conic, and the throat 11 spreading over the whole of the periphery, its middle plane being horizontal. The device which is the subject of the invention can be used to obtain uniform stereophonic output reconstructing the spatial effect of the recorded orchestra, both in width and depth.

Description

PRESENT OMNIDIRECTIONAL ACOUSTIC SPEAKER,
AT CONSTANT YIELD, AN ANSWER ON A BROADBAND OF AUDIO-FREQUENCIES.

 A loudspeaker horn loaded in a known manner has a linear response in its axis. As soon as one deviates from it, the efficiency drops all the more the higher the frequency.

 It can therefore be seen that the energy field is restricted in an inverse proportion to the scattered frequency.

 This is how we find that as soon as we reach frequencies of 2,500 Hz, the response curve drops by around 6 Db per octave.

 Different means have therefore been used to restore the linearity of the response curve over the whole range of audio frequencies.

Thus it was put in series a filter composed of a condenser which reestablishes a certain constancy of the energy which makes it possible to reproduce the high frequencies.

 But even thus treated the known loudspeakers create a directive sound field, while the musical instruments emit in all directions. It is therefore difficult to restore the effect of sound volume, and in particular the simultaneous effect of depth and width which reproduces what may be called the spatial effect of the recorded sound source.

 To satisfy first the reproduction of the whole range of recorded audio-frequencies one commonly uses simultaneously speakers specially tuned on a zone of determined audio-frequencies: 50 to 500 Hz for the speakers of large diameter tuned on the bass, 500 to 3500 Hz for the midrange and 3500 to 20000 Hz obtained by tweeter type speakers thus specially tuned for the treble.

 However, the directivity of the sound sources thus tuned, which is all the more affirmed as the frequencies are higher, creates distortions which do not spatially restore the sterophonic effect of the musical source as well throughout the width of the field as depth. And the use which has been made of "lenses or acoustic prisms" intended to correct this directivity has not provided the hoped-for solution, independently of the considerable increase in cost of such installations.

 The object of the present invention device therefore aims to avoid these drawbacks and to ensure satisfactory omnidirectional spatial reproduction using high performance equipment but inexpensive because of its simplicity.

 For this, the midrange speaker as well as the tweeter of the treble are loaded by a pavilion of revolution with vertical axis developing in a conic shape and diffusing in the horizontal plane according to a perfect spatial distribution of the audio-frequencies, without interference distortion, the top -Loudspeaker whose directivity is low being treated in a known manner, associated with the previous ones, on the wall of! same speaker.

The accompanying drawings, given by way of example only, show an embodiment of the object of the present invention:
Figure 1 is a transparent schematic view of an acoustic enclosure equipped with the object of the present invention.

 Figure 2 is a schematic view in axial vertical section of the special pavilion object of the present invention.

 Figure 3 is a schematic view of said device.

 Figures 4,5 and 6 are diagrams according to polar coordinates of the spatial response curves of the bass, mid and treble speakers equipping a same enclosure provided with the device object of the invention, these tests having been carried out by the Acoustic Laboratory of the 'University of Toulouse (RANCE).

 As shown (fig. 1 and 2) on. device object of the invention consists of the pavilions of revolution 1 and 2 developing on 360, which are provided, independently of one another, the medium motor 3 and the treble motor 4 which can be superimposed on it the same vertical axis.

 Said pavilion of revolution (fig. 2) is constituted by the lower toroidal element 9 and the upper core 10 which form between them, in vertical diametral section a double horn symmetrical with respect to the vertical axis, of shape coming from a conical, hyperbolic or parabolic or exponential or other, according to the special curve known by the name of its creator, Iwata, for example, whose inlet hearing 12 is oriented along the vertical axis and whose mouth 11 develops peripherally , preferably without a radial intermediate partition, over all 360, in a horizontal plane.

 The development curve of each pavilion and its dimensions are tuned to the frequencies and the power of the acoustic motors 3 and 4 which is associated with each of them.

 An engine is also provided, which, suitably loaded, is capable of covering from the midrange to the treble. Only one suitably tuned revolution pavilion is necessary in this case.

 Likewise the dimensions of the pavilion of revolution as well as its coefficient of expansion are adapted to the range of frequencies which it is desired to reproduce and broadcast, a perfect adaptation to these desired frequencies being obtained by the choice of the particular shape of the pavilion of revolution which can thus have a parabolic, hyperbolic or other form depending on the acoustic results sought.

 The bass speaker 5, for its part, is normally placed on one of the vertical walls of the enclosure 6 which, moreover, can be provided at its base with vents 7 and 8. For even greater distribution of the bass , thin their almost total lack of directivity, its pavilion 9 is drawn according to the beginning of an exponential curve.

 The tests carried out by the laboratory of the University of Toulouse by means of an enclosure fitted with the device which is the subject of the present invention have demonstrated the regularity of the spatial response obtained at the level of each of the three loudspeakers which cover practically all the range of audio frequencies, as well as practically the linearity of the output at all frequencies in all azimuths.

 Figures 4,5 and 6 give the diagrams according to polar coordinates at the output of the three loudspeakers at a distance of one meter from the axis of the mid and treble motors, the enclosure having been rotated around their axis.

 Curve 4 gives the responses for 250 Hz, 500 Hz and 1000 Hz.

 Curve 5 for 2 KHz, 4 KHz and 8 KHz.

 And the curve 6 for 12, 5 KHz, 16 KHz and 20 KHz.

 On each of these diagrams one notes a very great homogeneity of the responses in all the azimuths and the linearity of their output all the more even as one increases in frequency.

 We then understand that the recorded sounds are thus reproduced with the fidelity that the motors of the loudspeakers used allow, but also that the spatial image of the recorded sound source is reproduced in a homogeneous manner both in depth and in width, restoring perfectly the original instrumental omnidirectional notion.

 The invention is not limited to the example or to the examples which have been described therein, any variant, considered as an equivalence, which cannot modify its scope.

 Thus the pavilions of revolution 1 and 2 could be constituted by acoustic horns having the same radial development curve, organized contiguously or not around the axis of the corresponding acoustic motor.

 The device which is the subject of the present invention is therefore particularly well suited for the reproduction of sound volume effects both in large places of public hearing and in more restricted private atmospheres, the homogeneity of the reproduction allowing a sound yield of 91 dB / W / m, which ensures excellent hearing over the entire range of audio frequencies emitted, without the need to increase the volume of the sound emission.

 Thanks to the absence of directivity thus obtained, the musical atmosphere is freed from the notion of point source. The scattered energy is also constant over the entire frequency range, unlike known speakers whose energy decreases with frequency. The dynamics of the transient frequencies is therefore respected in its recording values.

 The spatial effect thus obtained frees from the need for a privileged listening position for stereophonic hearing. And the signal / noise ratio is also improved by the omnidirectional diffusion of the breath which is less oriented towards the listener.

Claims (9)

Characterized by the fact that the motor (3) of the loudspeaker whose axis is vertical is loaded by a flag of revolution (1) having the same axis, developing over 360 and being in vertical diametral section forming a double symmetrical horn with respect to the vertical axis of the device, and the inlet of which (12) is located vertically in the axis of the loudspeaker, the mouth (11) of said horn developing on! has all of its periphery, its axis forming a horizontal median plane, said horn conforming to the shape of a conic.  1) -Acoustic enclosure,  Characterized by the fact that the pavilion (I) of revolution which develops over 360 and which presents in vertical diametral section the shape of a double horn symmetrical with respect to the vertical axis, which itself develops according to a hyperbolic curve , whose mouth (11) thus formed develops over the entire periphery of said pavilion.  2) -Acoustic enclosure according to claim 1,  Characterized by the fact that the pavilion of revolution which develops on 360 and which presents in vertical diametral section the shape of a double horn symmetrical with respect to the vertical axis, which itself develops according to a parabolic curve, the mouth (11) thus formed develops over the entire periphery of said pavilion.  3) -Acoustic enclosure according to claim 1,  Characterized by the fact that the pavilion (1) of revolution which develops over 360 and which presents in vertical diametral section the shape of a double horn symmetrical with respect to the vertical axis, which itself develops according to an exponential curve , whose mouth (11) thus formed develops over the entire periphery of said pavilion.  4) -Acoustic enclosure according to claim 1,  Characterized by the fact that each of the mid-range (3) and treble (4) loudspeakers superimposed along a vertical axis is individually equipped with a pavilion of revolution, the mouth (11) of which extends over the entire periphery of said pavilion.  5) -Acoustic enclosure according to any one of claims 2 to 4,  Characterized by the fact that it is equipped with a single covering motor! he midrange and treble loaded with a single pavilion of revolution whose mouth III develops over the entire periphery of said pavilion.  6) -Acoustic enclosure according to any one of claims 2 to 4,  Characterized by the fact that the enclosure (6), which carries at its upper part the motor (s) (2) and (3) oriented along a known vertical axis and loaded by the pavilion (s) (1) and (2), comprises on one of its vertical walls the loudspeaker (5) intended for bass, and itself equipped with a flag primer itself drawn according to a conic of the same family as that adopted for the flag (s) superiors.  7) -Acoustic enclosure according to any one of claims 5 or 6,  Characterized by the fact that the pavilion (s) of revolution (1) and (2) are constituted by acoustic horns having the same radial development curve, organized contiguously around the axis of the corresponding acoustic motor (3) and ( 4).  8) -Acoustic enclosure according to any one of claims 2 to 4,  Characterized by the fact that the pavilion (s) of revolution (1) and (2) are constituted by acoustic horns having the same radial development curve, organized in a non-contiguous fashion around the axis of the corresponding acoustic motor (3) or (4).  9) -Acoustic enclosure according to any one of claims 2 to 4,