Diaphragm for electrodynamic transducer

(42) Date of commencement of the patent: 15.11.1993 (45) Date of issue: 25. 7.1994

<td>(56) Documents:</td><td>(73) Patent owner:</td>

<td>US PS4122315</td><td>AKG AKUSTISCHE &amp; KINO-GERÄTE SOCIETY MBH A-1150 VIENNA (AT). (72) Inventor: PAVLOVIC DINO DIPL.ING. VIENNA (AT).</td>

(54) MEMBRANE FOR ELECTRODYNAMIC CONVERTERS (57) A membrane (1) with a voice coil (5) for electrodynamic transducers has in the center a dome (2), to the edge of the membrane towards a bead-shaped zone, which can also be provided with beads , connects. In this case, an outwardly opening, frustoconical collar (6) is mounted on the cap (2), which preferably consists of the same material as the membrane (1) whose circular edge (7) with the calotte (2) is mechanically firmly connected , The edge (7) of the collar (6) has a smaller diameter (D _k) as the voice coil (5; D).

<img file="AT397898B_D0001.tif" />

QQ

AT 397 898

Di® 0073318

AT 397 898 B

The invention relates to a diaphragm with voice coil for electrodynamic transducers, which in

Center has a dome, to the membrane edge towards a bead-shaped zone, which may also be provided with beads, connects. Such a membrane is used successfully in sounders and sound receivers.

Ideally, a membrane of the type mentioned should have the vibration behavior of a piston, which results in very similar vibration characteristics, such as those of the O-th order spherical radiator. It will therefore be particularly important in the manufacture of such a membrane, by particular choice of material and shape of the membrane to realize this ideal case as closely as possible.

Experience has shown that sees the vibration behavior of the afflicted with a voice coil assembly membrane at higher frequencies of up to 20 kHz and beyond range of transmission in that with increasing frequency, the sensitivity of the electrodynamic converter steadily decreases, which are observed in this frequency range periodic fluctuations in the frequency response. This gives the observer the impression that the acoustically effective membrane surface is steadily decreasing above about 5 to 8 kHz as the frequency increases. This phenomenon is already mentioned in AT-PS 382 281.

The worsening vibration behavior of the membrane at higher frequencies is known to be due to the increase of effects caused by bending waves in the membrane effects. How to counter such a kind of natural oscillations in conical membranes is treated in detail in DE-AS 10 92 061.

Also, it has hitherto helped in dynamic transducers with a membrane of the type mentioned to compensate for the sensitivity loss occurring at high frequencies as far as possible with a Helmholtz resonator. This self-resonance and quality of the resonator had to be chosen so that the desired frequency response of the transducer was actually achieved, which was not always associated with success, because bandwidth and quality of the resonator can not be determined in each case as this to an optimal Compensation would be required. Compromises had to be accepted or two-way systems were used.

Another proposal for improving the vibration behavior of membranes at higher and higher frequencies can be found in GB-PS 596 869, which refers either to the sandwich-like layering of the membrane with stiffening material or recommends the stiffening-acting embossing of the membrane with corresponding patterns. These enhancements are very much bound to the shape of the membrane and can not be arbitrarily transferred to any membrane.

Furthermore, a proposal for an improvement in the frequency response of membranes at high frequencies of the US-PS 4,122,315 can be seen, in which a system of three to four speakers is described in a space-saving arrangement, whereby the entire frequency range to be transmitted from 20 Hz to 20 kHz is divided into one woofer, one middle tone and one or two tweeters. The additional speakers are arranged in the free space before the cone of the woofer on a separate support frame. The use of multiple speakers leads to a balanced frequency response in the aforementioned transmission range, but above all to a significantly improved sound radiation at very high frequencies. However, such a system of speakers is very expensive and uneconomical for many applications. Also, such a speaker system does not solve the previously mentioned problem of improving the vibration behavior of a single membrane used for the entire transmission range.

The object of the present invention is to take such appropriate measures on a diaphragm for electrodynamic transducers with voice coil and arranged in the diaphragm center that their vibration behavior at high frequencies leads to a nearly constant sensitivity of the transducer and wavy fluctuations in the frequency response of the transducer be avoided.

According to the invention this object is achieved in that on the cap an outwardly opening, frusto-conical collar is attached, which preferably consists of the same material as the membrane whose circular edge is mechanically fixed to the calotte, and a smaller diameter than that Has voice coil.

The firm mechanical connection of the cone-shaped collar causes both the exposure of the bending waves on the Kalottenfläche within the collar border and by the collar surface itself, the increase of the surface acoustically effective on the vibration of the membrane. Experiments showed that a conical collar of the same diameter as the immersion coil in the frequency response of the transducer brought no change whatsoever. It is thus a very significant feature of the invention to make the diameter of the collar smaller than that of the voice coil, thus a

AT 397 898 Β effective effect occurs. The collar diameter determines very much the uppermost to be reached frequency limit of the transmission range, with a smaller diameter has a higher cutoff frequency result. In practical application, the optimum diameter will be determined from the condition imposed on the frequency response of the transducer. Although the height of the collar determines the size of the additional radiating surface, but you will keep it as low as possible, on the one hand to prevent possible bending waves on this cone, and on the other hand avoid too large a mass, so that the associated fundamental decrease in sensitivity remains within reasonable limits, and For example, the loss of 1 dB generally does not exceed.

The effect achieved by the inventive measure is solely due to the design of the cone-shaped collar and its fixed mechanical connection with the membrane salmon. The assumption that the cone-shaped collar can make a better acoustic adaptation of the membrane to the surrounding medium, is not true, because for the frequency range to be considered already existing adaptation to the air wave resistance at the existing dome diameter. The opening angle of the collar is of less influence on the highest frequency to be transmitted, decisive only the surface enlargement of the membrane achieved with it. The decisive advantage of the inventive measure lies in dispensing with the previously essential Helmholtz resonator and the associated greater independence in the structural design of the converter protective housing.

An expedient embodiment of the invention consists in the fact that the frustoconical collar consists of a material other than the membrane material, for example of a metal foil, of paper or the like.

In order to achieve an improved effect according to the invention, as well as to favorably influence the bending waves and the mass of the collar in addition to the membrane mass, the use of a metal foil or also of paper is advantageous for the configuration of the frustum-shaped collar.

A further advantageous embodiment is that the frustoconical collar or the like at its circular edge by gluing, ultrasonic welding. is mechanically firmly connected to the calotte. A firm connection of the collar placed on the calotte is indispensable, if only to avoid being excited to vibrate at higher-frequency vibrations, but to conform to the movements of the calotte in conformity. In addition, the circular attachment zone on the dome to form a forced discontinuity line for bending waves, which also keeps the area within the circular connection of collar with dome free of bending waves. For this purpose, a solid mechanical connection of both parts is required, which is to be realized especially by appropriate bonding or ultrasonic welding. But there are also other types of connection, such as thermoplastic fusing or heat sealing conceivable.

The invention will now be illustrated in more detail in the following description with reference to drawings. 1 shows the membrane according to the invention with the frustoconical collar attached to the cap, FIG. 2 shows the frequency curve for an electrodynamic transducer with a conventional membrane, FIG. 3 shows a membrane with a collar of the same diameter as the plunger coil, and FIG electrodynamic transducer with membrane according to the invention.

In Fig. 1, the known in conventional construction membrane 1 for an electrodynamic transducer with preferably cylindrical voice coil 5 is shown, which has a dome 2 in the center, to the membrane edge 4 toward a bead-shaped, preferably annular zone 3 is connected. According to the invention, an outwardly opening, frusto-conical collar 6 is attached to the calotte 2 by fixed mechanical connection along the circular edge 7, wherein the diameter D_k of the collar 6 is smaller than the diameter D._s the voice coil 5.

The inventive design of the membrane 1 with the collar 6 leads to a significant improvement in the frequency response for the electrodynamic converter at high frequencies. A frequency course known in the conventional sense is shown in FIG. 2 shown, which is characterized in the range of high frequencies by a steady drop in the sensitivity, wherein the periodic ripple can clearly see the influence of forming on the diaphragm bending wave. The inventive measure occurs in the frequency response of the transducer, a noticeable improvement at high frequencies, which is not only in the same sensitivity, but also in the decrease of the effect caused by bending waves effect.

This visible improvement is shown in Fig. 4, in which the curve a again shows the frequency response of a transducer with a conventional membrane, the curves b and c with the membrane according to the invention. Since the diameter D_k, with which the collar 6 rests on the calotte 2, is of importance for the uppermost to be reached frequency limit of the transmission range, this circumstance was

AT 397 898 Β

Curves b and c clearly highlighted. As already mentioned, a smaller diameter leads to a higher frequency in the range extension, which can be seen from the curve c. In addition, the curves b and c show that an increase in the curve by means of a Helmholtz resonator is no longer required in the region of high frequencies.

Finally, in FIG. 3 illustrated embodiment in which the voice coil radius and collar radius are equal. As already mentioned, no detectable effect can be achieved because, despite enlargement of the radiation surface of the membrane, the extinction effect caused by bending waves predominates. It is this area of ​​the membrane, in which the voice coil is glued to the membrane firmly, as an excitation center for bending sometimes to consider. Such an arrangement with collar on the membrane leads to a Frequenzveriauf for the converter according to FIG. Second According to the invention, other forms of the membrane than circular are conceivable, such as those with an oval or rectangular edge. Likewise, the voice coil must not necessarily be a cylinder with circular cross-section, but it is also a coil oval or rectangular cross-section conceivable. On the particular presentation as a drawing was omitted for the aforementioned embodiments, because they concern only by their shape an extension in the measure taken in accordance with the invention, but not in the principal solution of the invention.