ELECTRO-ACOUSTIC TRANSDUCER

Abstract: By means of an elongated, electrically conductive diaphgram (1, 1A, 1B) in a strongly magnetic field, a linear and an elongated sound source giving a high sound energy is obtained. At least two elongated diaphragms (1, 1A, 1B) are in accordance with the invention positioned between intermediate and enclosing protracting magnet elements (2, 2A, 2B, 4), whereby the transverse length (A) of the diaphragms (1, 1A, 1B) are at least of the same size as that (B) of the intermediate protracting magnet elements (2, 2A, 2B, 4). In this way, a sound without considerable interference merges at a short distance from the sources of the sound. By placing additional such sources of sound alongside each other, a broad sound source with a surface producing an essentially homogeneous sound field is achieved.

Description: Electro-acoustic transducer. This invention involves electro-acoustic transducers. The specific electro-acoustic transducers referred to produce a homogeneous high-power acoustic field from at least two linear sound sources or from a widespread area. Electrostatic speakers are known for producing a homogeneous sound field from an area. However, these have only been used to a limited extent. One reason for this is their restricted acoustic power per unit area. By means of an elongated, electrically conductive diaphragm within a highly magnetic field, a linear source of sound, giving a high sound energy, is obtained. At least two elongated diaphragms with intermediate and enclosing elongated magnets are in accordance with the invention arranged in such a way that the transverse length of the diaphragms becomes at least the same as the transverse length of the intermediate elongated magnets. The sound from the two diaphragms will in this way merge without considerable interference at a short distance from the sound sources. By positioning several such sound sources side by side, a broad sound source with an area producing an esentially homogeneous acoustic field is acquired. Such a broad sound source may be adjusted for the entire or part of the audio band of 0-50 kHz, without the requirement of a matching transformer or a crossover filter. This is possible through the diaphragms of conductive materials being electrically connected in series and/or in parallel, making the driving amplifier detect a primarily perfect resistance which may be varied optionally within the range of 2-90 Ohm, for example. The area of the widespread sound source may be varied within a wide range to obtain the desired directional effect and characteristic. The sound source can accordingly be curved to partly or wholly form, for instance, a cylindric area, with the sound transmitter in the latter case acting as a radia pulsating cylinder for all the frequences of the audio ba or optional parts thereof. Further advantageous characteristics are evident from patent claims and the detailed description of embodiments the invention. Figure 1 shows schematically a cross-section of part of a device according to the invention. Figure 2 shows an alternative arrangement. Figure 3 shows schematically, seen from the front and from one end, a module of a plain unit according to invention, containing six elongated diaphragms. Figure 4 shows a cylindric sound transmitter according to invention. Figure 5 shows schematically an enlarged part of the cylindric area as shown in Figure 4. Figure 6 shows a cross-section of the sound transmitter as shown in Figure 4. One of the designs according to the invention is essentia made up of fundamentally linear and elongated sound sour as shown in cross-section in Figure 1. A protract electrically conductive diaphragm 1 is arranged in the between two elongated magnet elements 2A and 2B. In additi similar diaphragms, 1A and IB, may be arranged in gaps opposite sides of the magnet elements. The protracted mag elements both have an elongated magnetic pole along one the long sides of diaphragm 1 and an opposite magnetic p along the other long side of diaphragm 1. In case electric flows along the length of the diaphragm (into or out of horisontal paper) the diaphragm will be influenced by a po across the diaphragm (upwards or downwards) depending on direction of the current. When running a current of so frequency, the entire length of the diaphragm functions a loudspeaker diaphragm. The magnetic elements 2A and 2B are positioned in protracted bodies 3, giving mechanical support to the magnets which are effected by the same cross-power as diaphragm 1 when electricity flows in the diaphragm. The dimensioning of the diaphragms and the magnetic elements are of imperative significance in order to obtain a high sound effect and a homogeneous sound field. The magnets 2A and 2B ought to be permanent magnets, producing a powerful magnetic field. The relation between the width A of the diaphragm and the width B of the magnet and its supporting body 3 should be such that any significant interference between the sound waves from adjacent diaphragms is non- occurent. This condition is fulfilled if A is at least of the same size as B and preferably double the size. The distance C between the diaphragm and the magnet should be marginal, but large enough to give the diaphragm sufficient range when vibrating. To prevent the diaphragm from partly slipping outside the direct influence of the magnet elements during transport or otherwise, the bodies 3 may be fitted with guides, normally not touched by the diaphragms. At the embodiment as shown in Figure 2 the bodies 3 are eliminated through the magnets 4 being made of ceramic material, providing both sufficient magnetic field and an adequate mechanical durability and rigidity. The cross- section of the magnets 4 is designed so as not to have a negative affect on the sound field of the diaphragms. Diaphragm 1 does preferably consist of a thin strip of aluminium, although it would be possible to use other suitable materials such as other types of metal or alloy, conductive plastics or combined materials. The plain sound module as shown in Figure 3 has six diaphragms 1 positioned side by side, each enclosed by a magnet element 2. To keep the diaphragms in position, holders 5 in the form of nylon clips or similar are evenly arranged. Only four of these holders are shown in the drawing. Other devices may alternatively be used for this purpose, fo example some type of elastic suspension devices. Each of t diaphragms ends are fixed to the end pieces of the module a have electrical attachments for optional connections i series or in parallel. A preferred embodiment of the invention is a cylinder as i shown in Figure 4, constructed from end pieces 11 and envelope surface 12 with a large number of sound producers the type described above. The cylindric area may constructed from modules 9 consisting of for example a hal or a quarter of a circular arc as shown in Figure 5, whic otherwise is built as the plane module in Figure 3. T diaphragms 1 are for example made up of approximately 10 wide strips of aluminium, which with air gaps 10 o approximately 0.15 mm between the adjacent magnetic bars and the diaphragms are held in place by nylon clips 5. T aluminium strips can have a thickness of between 7-14 μm a are preferably wholly or partially folded to attain th appropriate elasticity lengthwise. As shown in Figure 6, the enclosed cylindric sound produc 13 is fitted with a noise-supressing material 14, whi preferably has a star shaped cross-section and which clos to the centre of the cylinder consists of a higher densi material to achieve an efficient suppressing of sound towar the centre of the cylinder, at the same time as a homogeneo sound field is extended radially outside the cylinder. It is also possible to accomplish a widespread sound sour according to the invention in the form of a truncated cone part thereof, which would produce a suitable sou distribution when for example positioned in the centre of t ceiling in for instance a large arrival hall. In order accomplish this shape, the diaphragms and the gaps betwe the elongated magnet elements are made narrowing. It is al possible to construct the truncated cone from narrow a plane sound transmitters, each having a few diaphragms a elongated magnet elements. To achieve a powerful directional effect, a special design can be made by using an omnidirectional cylinder mounted inside a cone shaped horn. The sound transmitting qualities thereby become analogous to those of a spotlight, i.e. a strong concentration of the transmitted sound energy may be achieved. The sound transmitter may in this way be regarded as a separate broad-band element in a horn-shaped casing. For lower energy levels, the omnidirectional cylinder may be replaced by a small number of line sources, whereby the horn is designed to obtain the desirable directional effect. The above description of the invention has been made with reference to some preferable embodiments. Other designs are also possible and the patent is only to be limited by the wording of the patent claims.

Claims: What is claimed is: 1. An electro-acoustic transducer, characterized by a least three elongated magnet elements (2,2A,2B,4) positione in parallel with at least two intermediate extended gaps an diaphragms (1,1A,1B) of electrically conductive material, movably placed in the gaps and connected to conduct drivin currents in the lengthwise direction of the diaphragms, whereby the transverse extension (A) of the diaphragms is a least of the same size as that (B) of one of the elongate magnet elements. 2. The electro-acoustic transducer according to claim 1, characterized by the transverse extension (A) of th diaphragms (1,1A,1B) being at least of double the size a that (B) of one of the elongated magnet elements. 3. The electro-acoustic transducer according to claim 1 or 2, characterized by the transverse extension (A) of th diaphragms (1,1A,1B) being 5-15 mm, preferably approx. 10 mm. 4. The electro-acoustic transducer according to any of th previous claims, characterized by the diaphragm (1,1A,1B) being composed of strips of aluminium, preferabl folded. 5. An electro-acoustic transducer, characterized by it being made up of several elongated diaphragms (1,1A,1B), each enclosed by protracted magnet elements (2,2A,2B,4) according to any of the preceding claims, whereby th diaphragms and the intermediate magnet elements form at leas a part of a cylinder area (9,12). 6. The electro-acoustic transducer according to claim 5, characterized by the cylinder area (9,12) being a least half made up of the elongated diaphragms (1,1A,1B). 7. The electro-acoustic transducer according to claim 5 o 6, characterized by a noise-suppressing material (14) being positioned inside the cylinder area (9,12) and the cross-section of the noise-suppressing material (14) being wholly or partially star-shaped. 8. The electro-acoustic transducer according to any of the preceding claims, characterized by the ends of the elongated diaphragms (1,1A,1B) and the magnet elements (2,2A,2B,4) being fixed to end pieces (11), primarily consisting of circular surfaces or parts thereof. 9. The electro-acoustic transducer according to any of the preceding claims, characterized by the elongated magnet elements (2,2A,2B,4) constituting or being placed in holders which primarily connect the end pieces (11) of the transducer, said end pieces (11) also carrying the ends of the diaphragms (1,1A,1B). 10. The electro-acoustic transducer according to any of the preceding claims, characterized by the elongated magnet elements (2,2A,2B,4) being made up of permanent magnets with the poles oriented across the length of the magnets.

Inventors: BENGTSSON BO, BENGTSSON, BO
Applicants: BENGTSSON BO, CENTARA PATENT AB, BENGTSSON, BO, CENTARA PATENT AKTIEBOLAG
Application year: 1995
Main classification: H04R9
IPC codes: H04R7, H04R9