FR2532139A1 - Acoustic enclosure. - Google Patents

Abstract

The present invention relates to an acoustic enclosure 10 comprising a rigid box 11 on which are mounted an electrodynamic woofer 13, three elements constituting electrostatic loudspeakers 15 and two piezoelectric loudspeakers 14 and 17. The loudspeaker 13 is mounted on a second box 12 rigid with the box 11 and communicating with a labyrinth having a decreasing cross-section, arranged inside the box 11. The electrostatic loudspeakers are mounted on a support 16 fixed by way of electrical members. This enclosure brings together the specific advantages of the three types of loudspeakers used, and comprises a filtering circuit which eliminates the disadvantages thereof.

Description

Acoustic speaker
The present invention relates to an acoustic enclosure-comprising-a bowl-
rigid tier on which are mounted at least one speaker for repro
mute the bass tones, said bass speaker, at least one speaker to reproduce the mid tones said speaker
mids, and at least one speaker to reproduce the high tones
says treble speaker, as well as an electrical circuit to filter
signals transmitted to these speakers based on their frequencies.

We already know very many achievements relating to speakers
acoustic, based on a wide variety of principles. As early as 1927,
point of electro-static type single-acting loudspeakers
nant a thin insulated membrane on its outer face, conductive on its
inside face stretched on a grid or a perforated plate.

The same year the inventor Hans Vogt presented at the Berlin Radio Show a speaker of the electro-static type with double effect, ~ called "Push-pull" comprising an insulated membrane and two grilles arranged
on either side of this membrane.

Although they have had some commercial success, particularly in the United States
United, their lack of reliability and their insufficient performance made them
sink into oblivion.

However, the qualities of this transducer are remarkable in themselves, and it
was the first in the years 1955 to offer a bandwidth reproduc
health frequencies ranging from 40 to 14,000 Hz.

One of the most important improvements was to differentiate the cel
lules according to the register to be reproduced. So, for example,
cells 63 cm high, 10 cm wide and 3 mm apart
the perforated plates, arranged symmetrically, can reproduce
bass on a bandwidth of 40 to 500 Hz. Two other cells
63 cm high and 6 ~ cm wide arranged in the center reproduce
the mid band from 500 to 5000 Hz. The central tweeter takes the
laughed above 500 Hz. The distribution between the different frequencies
is assigned to an active filter.

 However the electro-static loudspeakers retain their faults, that is to say their capacitive load therefore their impedance is very low at high frequency, which poses problems of amplifier short-circuit, their directivity is important , their performance is poor, their response is poor for bass, and they require external power.

One of the aims of the present invention has been to conserve all the qualities of this type of loudspeaker while at the same time remedying its faults.

To increase the efficiency of an electro-static loudspeaker of the double grid type, one can act on various factors - decrease the distance between the fixed armatures, - increase the bias voltage and the voltage rise by the
coupling transformer, - lighten and increase the rigidity and surface area of the membrane.

By increasing the surface of the membrane and by decreasing the distance between the armatures, the capacitance of the capacitor is increased, hence an extreme drop in the impedance at high frequencies with of course the drawbacks mentioned above for the amplifiers.

The increase in the bias voltage and the transformer output increases the risk of ignition.

The increase in rigidity and the decrease in the distance between the reinforcements limit the bandwidth at the bottom of the sound spectrum.

The present invention proposes to overcome the drawbacks of existing systems by a new combination of means partially known per se leading to completely new results.

This object is achieved by the acoustic enclosure according to the invention characterized in that it comprises in combination at least one bass speaker of the electro-dynamic type, at least one midrange speaker of the electro-static type, and at least one tweeter of the piezoelectric type. The purpose of this combination is to use for each frequency domain the type of speaker having the best sound reproduction qualities. This combination is not obvious in itself and it was necessary to develop a filtering circuit which makes them compatible, and which moreover corrects certain defects of its components, in particular electro-static loudspeakers.

According to a particularly advantageous embodiment, the enclosure of the enclosure comprises a labyrinth of decreasing section with braked vent, this labyrinth being folded vertically, the two parts being separated by a panel disposed at an angle, and comprising at its upper end a exponential notch arranged to ensure communication between the two parts of the labyrinth. The choice of this solution avoids parallel walls and therefore makes it possible to strengthen the structure. Folding the labyrinth increases its length. The exponential notch avoids very pronounced resonances and therefore the accentuation effect of certain frequencies. The advantage of the braked vent is to limit stretching at very low frequencies.

The electro-dynamic bass speaker is preferably mounted on a second housing attached to the front face of the enclosure, at its lower part, and open at the rear to allow the rear wave to enter the labyrinth .

To reduce the directivity of the midrange speaker, the enclosure preferably comprises at least two midrange speakers each consisting of an elongated flat element, these elements being mounted uertically on a support integral with the front face of the enclosure, in such a way that their planes between them form an angle different from O or 1800.

According to a preferred embodiment, the enclosure comprises three mid-range speakers mounted on a rigid support fixed to the front face of the housing by means of flexible damping members, and the loudspeakers are arranged in an arc forming a two by two an angle between 150 and 1700, and preferably 1610, such that their radiation lobe is regular over an angle at least approximately equal to 600.

The rigid support advantageously comprises an elongated rigid plate arranged to be mounted; on the front face of the shoemakers and provided at each end with an arm perpendicular to the plane of the plate, comprising means for fixing the plane elements constituting the loudspeakers electro-static, this plate being equipped with an elongated central element in the form of a dihedral, the surfaces of which constitute reflectors placed at the rear of said elements.

The treble speakers used in the c-adre of the present invention are piezoelectric speakers whose interest lies on the one hand in a higher impedance than that of the other treble speakers, and on the other hand in a bandwidth clearly exceeding 20 KHz.

These speakers combine the lightness of the mobile equipment, since no coil is necessary, with exceptional accelerations quite comparable to those obtained with electro-static speakers.

According to a preferred embodiment, the enclosure according to the invention comprises two piezoelectric speakers mounted in the axis of the other speakers, one in the vicinity of the top of the front face of the enclosure, the other between the midrange speakers and the bass speaker, in the lower area of said front panel.

The filtering circuit comprises a third-order Butterworth cell, which ensures an abrupt cut in the emission of the mid-range speakers at least approximately at the frequency of 12 KHz. Such a cell makes it possible, in known manner, to obtain a slope of the filter of 18 dB / octave.

A second order cell would allow a still acceptable slope of 12 dB / octave to be obtained.

The treble speaker circuit is mounted in parallel with the rest of the circuit and has an impedance of at least 50 ohms. In this way, the system impedance only drops below 5.5 ohms at 12 1z and has values in the range of 8.2 ohms at 24,000 liz, and 4.5 ohms at 6,000 Hz, i.e. acceptable ohmic values for almost any amplifier.

The midrange speaker circuit includes a step-up transformer, the secondary of which is connected to the armatures of the elements.

The present invention will be better understood with reference to the description of an embodiment and the appended drawing in which; Figure 1 is a perspective view of the acoustic enclosure according to the invention, Figure 2 shows a side view, partially cut from 112n- the enclosure of Figure 1, 'Figure 3 shows a partial view of the partition panel interior delimiting the two parts of the labyrinth of the enclosure according to the invention, FIG. 4 represents a partially cut perspective view of the support of the mid-range loudspeakers, and FIG. 5 schematically represents the filtering circuit of the loudspeakers of the enclosure according to the invention.

With reference to FIGS. 1 to 3, the acoustic enclosure shown 10 essentially comprises a first housing 11 and a second housing 12 attached to the lower part of the front face of the housing 11. The second housing which is open at the rear and communicates with the inside of the housing 11 serves as a support for a woofer 13 and a tweeter 14. The upper part of the front face of the first housing carries three elements 15 constituting the midrange speakers of the electro-static type mounted on a support 16, and a second treble speaker 17 disposed substantially in the axis of the other speakers. Inside the housing is provided a labyrinth comprising a first part 18 and a second part 19. These two parts are delimited by a panel 20 and possibly by a second optional panel 21, so that the section of the labyrinth is decreasing in the direction of the arrows A and B The upper opening 22, shown in more detail in FIG. 3, is exponential for the reasons mentioned above. Openings 23 formed in the rear wall of the housing 11 constitute the braked vent whose role is to limit the elongations at very low frequencies. The partitions that go into the composition of the two boxes are assembled very rigidly, preferably by screwing and gluing. The panel 20 is preferably at least partially coated with a material preventing reflections, such as for example glass wool. The support 16 is preferably mounted, by its rear plate, on the front face of the housing 11 by means of flexible shock absorbing pads made of rubber or any other equivalent material
FIG. 4 represents the three elements 15 constituting the loudspeakers of the electro-static type. Each of these elements is formed by a frame 3 (3 made of synthetic material, which holds together a front grille 31, a rear grille 32 and an insulating sheet of synthetic material such as, for example, nylon # or mylar #. three elements are screwed onto the support 16 or more precisely onto the arms 32 and 33 of this support by means of screws passing through the openings 34. The support 16 comprises a rear plate 35 perpendicular to the arms 32 and 33 and comprising in the center a
elongate element 36 in the form of a dihedral which constitutes a reflector for the rear waves of the elements 15. The angle which the planes of the elements 15 form between them two by two is substantially equal to 1610, and is preferably between 150 and 1700. The purpose of this arrangement is to obtain a regular emission lobe over an angle of approximately 600, and therefore to remedy the problem of the directivity of conventional electro-static loudspeakers.

The circuit shown diagrammatically in FIG. 5 comprises a filtering circuit composed of the induction coils L1, L2 and the capacitor C1 connected to the bass speaker W, and of a third degree Butterworth cell connected in parallel.

The armatures of the midrange loudspeaker D are attacked by a transformer TR boosting alternating multilayer voltages for the pri-.

mayor and secondary. The TWB tweeter constitutes a filling cell, that is to say that it constitutes a complementary loudspeaker restoring the part of the signals not reproduced by the first TWA tweeter. These two loudspeakers are piezoelectric loudspeakers whose impedance is relatively high, which has the advantage of not notoriously reducing the impedance of the system during a coupling in parallel.

This circuit is designed so that the bandwidth of the electrostatic loudspeakers is limited to 12 KHz. The impedance of the system is linearized by a parallel RLC circuit up to 6000 Hz. Limiting the bandwidth of the electro-static mid-range speakers makes it possible to avoid a drop in impedance for high frequencies. A cutoff is made abruptly by the third-order Butterworth cell, which allows an impedance of the order of 6 ohms at 12 KHz, 9.9 ohms at 24 KHz, and 4.9 ohms. at 6 KHz.

For example, the electro-dynamic bass speaker used has a diameter of 30 cm, a very low natural resonant frequency of around 17 Hz and a 50 mm coil on an aluminum core. The cutoff frequency is 250 Hz. The cutoff slope is 19 db / octave.

All the induction coils are air and the capacitors are paper capacitors.

The midrange loudspeakers consist of three electrostatic elements of the so-called "Push-Pull" type, 60 mm wide and 570 mm long.

The distance between the reinforcements is 4 mm. The membrane is made of Nylon (R), t the steel frames are perforated by square holes 5 mm wide.

The tweeters are piezoelectric and have a compression chamber and a horn intended to remedy their low efficiency. They are surmounted by a flexible, almost exponential synthetic membrane.

Of course the present invention is not limited to the device described and illustrated by the figures, but can undergo various modifications obvious to those skilled in the art.

Claims (10)

Claims 1. Acoustic enclosure comprising a rigid housing on which are mounted at least one speaker for reproducing bass tones, said bass speaker, at least one speaker for reproducing medium tees said medium speaker, and at at least one loudspeaker for reproducing high tones, as well as an electrical circuit for filtering the signals transmitted to these loudspeakers according to their frequencies, characterized in that it comprises in combination at least one bass loudspeaker of the electro-dynamic type, at least one speaker of the electro-static type means and at least one treble speaker of the piezoelectric type. 2. Enclosure according to claim 1, characterized in that the housing comprises a decreasing section labyrinth with braked vent, this labyrinth being folded vertically, the two parts being separated by a panel disposed at an angle and comprising at its upper end an exponential notch arranged to ensure communication between the two parts of the labyrinth.  3. Enclosure according to claim 2, characterized in that it comprises a second housing attached to the front face of the enclosure and open at the rear to communicate with the entrance to the labyrinth, this second housing serving as support for a built-in speaker. bass speaker. 4. Enclosure according to claim 1, characterized in that it comprises at least two mid-range loudspeakers each consisting of an elongated flat element, these elements being mounted vertically on a support integral with the front face of the enclosure, in such a way their planes form an angle different from 0 or 180 o 5. Enclosure according to claim 4, carac'6risde in that it comprises three mid-range speakers mounted on a rigid support fixS on the front face of the housing by means of flexible damping members, and in that the speakers are arranged in an arc of a circle, forming two by two an angle between 150 and 170, and preferably equal to 161, so that their radiation lobe is regular over an angle at least approximately equal to 60 o 6. Enclosure according to claim 5, characterized in that 1 rigid support eonorte an elongated plate arranged to be mounted on the front race of the housing, and provided at each longitudinal end with an arm perpendicular to the plane of the plate and comprising means for fix the planar elements constituting the electro-static loudspeakers, this plate being equipped with an elongated central element in the form of a dihedron whose surfaces constitute reflectors placed at the rear of said elements. 7. Enclosure according to claim 1, characterized in that it comprises two piezoelectric speakers mounted in the axis of the other speakers, liun in the vicinity of the top of the front face of the enclosure, the other between the midrange speakers and the ~ bass speaker, in the interior area of said front panel. 8. Enclosure according to claim 1, characterized in that the filtering circuit comprises a third-order Butterworth cell to ensure an abrupt cut-off of the emission of the mid-range speakers, at least approximately at the frequency of 12 KHz. 9. Enclosure according to claim 8, characterized in that the treble speaker circuit is mounted in parallel with the rest of the filter circuit, and has an impedance at least equal to 50 ohms. 10. Enclosure according to claim 1, characterized in that the filtering circuit comprises a step-up transformer whose secondary is connected to the armatures of the elements constituting the loudspeakers of mediums.