DE8617965U1 - Part of a sound transducer - Google Patents

Description

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The innovation relates to a part of a sound transducer with | rotationally symmetrical, rigid membrane according to the preamble of claim 1.

German patent specification 863 084 describes a loudspeaker membrane with a high acoustic efficiency over the entire audio frequency range, whose stiffness decreases from the excitation point to the edge. This reduction is achieved by a thinning layer of lacquer. This is intended to lead to favorable acoustic properties because at low frequencies the entire membrane vibrates, whereas at high frequencies only the firmer, inner part vibrates.

Something similar is also described in the German patent specification 902 260, where, in order to reduce the distortion factor, it is stated that a lacquer coating should be applied in such a way that its thickness decreases from the drive system in the direction of sound propagation; the same purpose is pursued by the measure also specified therein of applying a layer of lacquer to the membrane from the drive side in the direction of radiation propagation.

to give a steadily decreasing cross-section. jj

A membrane with increasing thickness from the inside to the outside is described in DE-OS 26 51 026.

The aim of the innovation is to provide a part of a sound transducer with a membrane in which the distortions of the radiated sound vibrations are low compared to the vibrations of their drive.

04.01.1988 , , , ^ ^} I

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This object is achieved by the part having the features of claim 1*. Advantageous further developments are specified in the un*claims.

The innovation is based on calculations and tests which have shown that good mechanical properties of a membrane system can be achieved with the design specifications found, with the result that disturbing partial vibrations are largely avoided. In order to contain such partial vibrations, a certain progression of the bending stiffness and the area moment of inertia must be maintained on the membrane from the inside to the outside.

A preferred embodiment of the innovation is explained using the drawing.

Figure 1 shows one half of a radial section through a membrane M, which is provided at its inner edge with a radial guide Rf (not mandatory) and with an electromagnetic drive E, which acts in the direction of the membrane axis 1.

Figure 2 shows the enlarged section Ii.

The membrane M is rigid, ring-shaped, rotationally symmetrical and conical. Its wall thickness H, measured in the direction of the membrane axis 1, changes depending on a radial coordinate r, which begins at the inner edge of the membrane M with the value r=r= and reaches its maximum value r=R at the outer edge. There begins a fastening zonej in which there is a connecting ring V^ which is glued to the membrane M and is integrally connected to an edge ring Rr which is flexible and ring-shaped and has the shape of one or more beads. It has a wall thickness S, also measured in the direction of the membrane axis 1, which varies in the direction of a distance coordinate s of s=0

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* reduced starting at the outer edge at s-R~* The rim ring Rr has an annular extension F* on its outer ring which serves to clamp the edge ring S and thus indirectly also the membrane M and which is located within a fastening zone there (s^-R«)*

Within the inner attachment zone of the membrane at the

. inner edge (r=rj) of the membrane M is glued

a rotationally symmetric, rigid plate P, which serves as

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The wall thickness K of this plate P changes in

·· Dependence on the radial coordinate r, which is responsible for the

f ⁽ y plate P runs up to a maximum value r=R _Q , which is

&idigr; the fortification zone not shown in detail

(glue point) and for the sake of simplicity,

^! the radial coordinate r=r. of the membrane M is set. (The

The bonding point therefore has a fictitious extension of zero in the radial direction.

The wall thickness curves H, K* S depending on the respective coordinates r,s are given in the patent claims .,. When dimensioning the wall thickness S,

; that the maximum wall thickness S of the edge ring

Rr is specified at its inner edge, from which the wall thickness progression S results. At the outer edge at s='k ₂ ' the wall thickness S must not be zero in practice, but the edge ring Rf merges here with a finite wall thickness into the integrally formed extension F. The specified value depends on the material used, in particular on its strength and density.

In a membrane system with the features of the innovation, radial (nodular) partial vibrations occur only to a reduced extent. The membrane M and the plate P therefore vibrate to a good approximation like a rigid piston without free

04.01.1988

- 7 - BK86/12

Modes. Forced (circularly symmetric) modes through reversible shearing remain possible, however; these are desirable under strong damping for good radiation characteristics.

This results in good mechanical strength, a flat frequency response and low distortion. (This also applies if the membrane is designed as a less steep cone or as a flat membrane and the plate P is flat rather than a dome). The best properties of the edge ring are achieved if the wall thickness profile corresponds as closely as possible to the formula given in claim 5, preferably if the tolerance range is reduced to 10 % .

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Claims (7)

04.01.1988 AfST Nachrichtentechnik GmbH L32/Wn/fa Gerberstrasse 33 BK 86/12 ( ) D-7150 Backnang Protection claims Part of a sound transducer with a rotationally symmetrical, rigid membrane (M), on the inner edge or in the center of which there is a drive (E) acting in the direction of the membrane axis (1) and whose wall thickness changes depending on a radial coordinate (r) emanating from the center and running perpendicular to the membrane axis, characterized in that the wall thickness (H), measured in the direction of the membrane axis (1), in the area between fastening zones for the drive (E), dome (P) and/or edge ring (Rr) from the inner edge (r=r^) or center (r=0) to the outer edge (r=R) has a course which gradually approximates a continuous course, preferably a continuous course, and initially increases up to a maximum (H at rr _m ) and then decreases again, the maximum (H ) being closer to the inner edge (r=r _i ) or center (r=0) than to the outer edge (x±R). &bull; « ·· «14« I * * * # · * I 1*1« II ■ II III - 2 - BK86/12 2. Part according to claim 1, characterized in that a flexible, annular, clampable edge ring (Rr), preferably with a circumferential bead, is coaxially fastened to the outer edge (r=R) of the membrane (M), the wall thickness (S) of which, measured in the direction of the membrane axis (1), decreases continuously, preferably continuously, between fastening zones at the edges (s=0, S=R ₂ ) in pieces as a function of a radial distance coordinate (s) which runs perpendicular to the membrane axis (1) and counts from the fastening zone on the inner edge (s=0) of the edge ring (Rr), the inner edge (s=0) of the edge ring (Rr) being connected to the outer edge (r=R) of the membrane (M) by a connecting ring (V) which lies within the inner fastening zone. 3. Part according to claim 2, characterized in that the membrane has a rotationally symmetrical, rigid plate (P) coaxially within its circular inner edge (r=r.) and within the fastening zone there, the wall thickness (K) of which, measured in the direction of the membrane axis (1), runs continuously, preferably continuously, in parts and from the membrane axis (1) in the direction of the radial coordinate (r) starting from the center to the outer plate edge (r=R ) initially increases up to over half (Rg/2) of the plate radius hindus and then decreases again. 4. Part according to claim 3, characterized in that the wall thickness (K) of the plate (P) decreases again before reaching 90 % of the maximum (r=R _Q ) radial coordinate. 5. Part according to claim 2, 3 or 4, characterized in that the wall thickness (S) of the edge ring (Rr) in dependence on its distance coordinate (s) with a 04.01.1988 O Λ �I Deviation of maximum £ 20 % based on the maximum
Wall thickness (S _1n ) equal is with s = distance coordinate, S _ffl = maximum wall thickness at the fastening zone | at the inner edge (s=0) of the edge ring (Rr), | R ₉ = fflax-iffiais distance coordinate s at dsr ■ Fastening zone on the outer edge of the \ edge ring (Rr). ! 6. Part according to one of the preceding claims, characterized in that the membrane (M) consists of homogeneous material and the material density is independent of the radial coordinate (r) or of the Distance coordinate (s) is constant as far as it is
usual production methods. 7. Part according to one of claims 1 to 5, characterized
characterized in that the material density of the membrane (K)
from a core area into both
axial directions (A,B). 8i Part according to one of claims 1 to 5, characterized characterized in that the membrane (M) consists of a
foamed or as a framework or honeycomb
formed core between two cover layers.