JPH0129360B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a speaker diaphragm having a sandwich structure in which surface materials are bonded to both sides of a core material.

Conventional configurations and their problems In general, it is ideal for the diaphragm of a speaker to have the same phase on its entire surface over the frequency band used, that is, to vibrate as a piston, but the diaphragm deforms or causes split vibration during vibration. This deteriorates the sound pressure frequency characteristics, distortion rate, phase characteristics, etc., and impedes high-fidelity reproduction. In order to solve these problems, in recent years, planar diaphragms using a honeycomb sandwich structure or the like have been adopted. FIG. 1 shows an upper drawing showing the core shape by cutting out a part of the surface material of a diaphragm using a conventionally used aluminum honeycomb core. 1 is an axisymmetric core made of a radially expanded honeycomb made of aluminum with a thickness of 20 μm, and aluminum 2 with a thickness of 50 μm is bonded to both sides of 1.
The diameter of the diaphragm is 200 mm and the thickness is 6 mm. However, a planar diaphragm with a honeycomb sandwich structure has a complicated structure and requires dozens of manufacturing steps and many types of components, resulting in a considerable cost. It was difficult to make it cheaper. In addition, speakers using a planar diaphragm with a honeycomb sandwich structure use a so-called nodal drive method, in which a voice coil is glued to the nodal part of the diaphragm at the primary resonance frequency. However, there was a phenomenon in which the sound pressure peak at fh was considerably higher than that with cone paper. This high sound pressure peak at fh has the problem of making it difficult to design a speaker system. That is, even when a speaker has a high fh, when viewed as a system, it is necessary to flatten the frequency characteristics as a whole, and therefore, the level of high sound pressure peaks must be attenuated. This posed the problem of naturally limiting the usable frequency band because the level had to be lowered from fairly low frequencies.

OBJECT OF THE INVENTION The present invention overcomes the drawbacks of the prior art and
It is an object of the present invention to provide a diaphragm for a speaker that can significantly reduce the sound pressure peak without any decrease in the sound pressure and expand the usable band to near fh.

Structure of the Invention The planar diaphragm of the present invention is made by pasting surface materials on both sides of a core material in which at least three or more fan-shaped pieces having a plurality of ribs arranged at non-converging angles are assembled. The core material is a sheet made of high-density polyethylene as a base material mixed with high-elastic fibers as a reinforcing material.

With this configuration, the bending rigidity in the diametrical direction changes in the circumferential direction, so that the positions of the nodes of the entire diaphragm become wavy. When the center is driven by a circular voice coil, single resonance is less likely to occur, suppressing high-frequency sound pressure peaks and providing flatter high-frequency characteristics. In addition, since the core material is a sheet made of high-density polyethylene as a base material and high-elastic fibers are mixed in as a reinforcing material, the rigidity of the diaphragm is greatly increased.
It has the following.

DESCRIPTION OF EMBODIMENTS FIG. 2 shows a cross section of the diaphragm of the present invention assembled into a speaker. In this case, the open end of the coupling cone 4 is glued to the nodal circle a, and the other end is connected to the magnetic circuit via the voice coil. In FIG. 2, 5 is a yoke having a center pole 6, 7 is an annular magnet disposed on 5, and 8 is an upper plate disposed on 7, which allows the outer periphery of the center pole 6 to form an edge. It is supported by a frame 10 by a member 9.
The planar diaphragm 3 has an opening of a coupling cone 4 joined to its nodal circle a, and a voice coil 12 wound around a voice coil bobbin 11 provided at the other end.
is supported by a damper 13 within the gap of the magnetic circuit.

FIG. 3 shows an embodiment of the above-mentioned plane diaphragm 3. In Figure 3, 21 is heartwood;
A surface material (not shown) is attached to the front and back surfaces using an adhesive. The core material 21 is composed of an aggregate of six fan-shaped pieces 22, each of which has a corrugated cross section as shown in FIG. 3b, and has a plurality of parallel ribs 2.
It has 3. The extension lines of the ribs 23 of the six fan-shaped small pieces 22 are the core material 2.
They are gathered to intersect with the center line of 1. The nodal circular shape of the first resonance of the planar diaphragm constructed in this manner is formed in a wavy shape centered on a circle that is approximately 68% of the outer diameter of the diaphragm, as indicated by the broken line 24 in FIG. This is because the bending rigidity of the diaphragm differs in the diametrical direction, and the portion where the core is bonded to the surface material from the center to the outer periphery has the highest rigidity, and the position of the nodal circle is closer to the outer periphery. In the opposite position, the nodal circle moves closer to the center. Therefore, the positions of the nodes of the entire diaphragm can be made into a waveform. The circle indicated by the solid line 25 in FIG. 3 is a nodal circle of a conventional diaphragm using a centrosymmetric aluminum honeycomb core, and is approximately a perfect circle. The above-mentioned speaker diaphragm has a voice coil bobbin glued onto its nodal circle to perform nodal driving, but in this case, a circular voice coil bobbin is used as in the past. At this time, since the nodal circles are wavy, it is possible to achieve the same effect as driving a diaphragm with a perfectly circular nodal circle with a wavy voice coil bobbin. This means that since the nodes are dispersed, the sound pressure peak at the high frequency limit frequency fh of the speaker using the node drive method can be made gentler.

Specifically, we created a diaphragm with a diameter of 200 mm and a height of 6 mm, and measured its frequency characteristics when used as a bass speaker. First, as the core material, 70 parts of high-density polyethylene fiber and carbon fiber (fiber length 6mm, fiber diameter 10μ
30 parts of m) were added to form a sheet of 200 g/m ² and this was thermoformed into the shape shown in FIG. 3 to form a core material.
A diaphragm was created by pasting aluminum foil with a thickness of 50 μm on both sides of this core material using an EVA-based hot melt adhesive. When the obtained diaphragm was assembled into a speaker in the same manner as in the conventional example, the sound pressure frequency characteristics were measured and are shown in FIG. 4a. For comparison, the characteristics of a conventional example are shown in FIG. The frequency characteristics were measured using a JIS standard box at 1 m/1 W.

As can be seen from this result, in this example, the peak level at the upper limit frequency fh was reduced by about 8 dB. Although carbon fiber was used here as the reinforcing material for the core material, other high modulus fibers (Aramid fiber, glass fiber, etc. with Young's modulus of 1×10 ¹² dyn/cm ² or higher) may also be used.
Similar effects can be obtained by using . These composite materials have a relatively large internal loss compared to aluminum, and contribute to a considerable reduction in sound pressure peaks.

In addition, the biggest advantage of using a plastic composite material for the core material is that it can be molded in one piece in a short time, so it can be produced in about 1/20 of the man-hours compared to conventional aluminum, making it cheaper and significantly improving quality stability. be.

Effects of the Invention As detailed above, according to the present invention, a composite sheet of carbon fiber and high-density polyethylene is used as the core material of the planar diaphragm, and at least three fan-shaped pieces having parallel ribs are assembled. Since the planar diaphragm is constructed by configuring a circular core material and adhering surface materials to both sides of the core material, the nodal circular shape of the first resonance mode can be made into a waveform.

Therefore, by driving the nodes of the waveform with the circular voice coil bobbin, there is an advantage that the level of the sound pressure peak at the high limit frequency can be reduced and the frequency characteristics can be flattened. In addition, since the sound pressure peak level is small, it is easy to take measures to attenuate the sound pressure peak level when designing a speaker system, and this has the advantage of making system design easier.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway top view showing a conventional flat diaphragm, Fig. 2 is a sectional view showing the structure of a speaker unit using the diaphragm of the present invention, and Fig. 3a shows an embodiment of the present invention. FIG. 3B is a sectional view taken along line A--A, and FIG. 4 is a comparative characteristic diagram of sound pressure frequency characteristics according to an embodiment of the present invention and a conventional example. 3... Vibration plate, 21... Heartwood, 22... Small piece,
23...Rib.

Claims (1)

[Claims] 1. A diaphragm in which at least three fan-shaped small pieces having a plurality of ribs arranged at angles that do not converge are assembled to constitute a circular core material, and a surface material is attached to both sides of the core material, and the core material is 5-40% carbon fiber, aramid fiber, or glass fiber as reinforcement material on base material made of high-density polyethylene
(weight ratio) A speaker diaphragm characterized by being thermoformed by mixing.