JPS6219032Y2 - - Google Patents

Description

[Detailed explanation of the idea]

This invention relates to a diaphragm for an electroacoustic transducer that is made of a honeycomb structure including a honeycomb core and a skin material. Conventionally, a flat diaphragm using a honeycomb structure has been widely used as a diaphragm for electroacoustic transducers. This diaphragm is lightweight, has high bending rigidity, and can drive nodes in split vibration modes with a simple configuration, eliminating low-order split vibrations and expanding the frequency range of piston motion. As shown in Fig. 1, it usually consists of a honeycomb core 1 made of aluminum foil with honeycomb-shaped chambers, that is, many small hexagonal column-shaped chambers (cells) A, and a honeycomb core 1 made of aluminum foil. It is formed of skin materials 3 and 4 made of thin films having a high Young's modulus such as aluminum (Al) and fiber reinforced plastic (FRP), which are respectively adhered to both sides with an adhesive 2 interposed therebetween. By the way, when the entire diaphragm vibrates during driving,
A resonance phenomenon occurs for each cell A. This resonance phenomenon occurs because the honeycomb core 1 is not a continuous body (because it has cells A), and the skin materials 3 and 4 themselves vibrate as a membrane supported by each cell A of the honeycomb core 1. It happens. Therefore, if this resonant frequency exists within the used band of the speaker, it will have a negative effect on the frequency characteristics, so it is necessary to set the resonant frequency sufficiently high to bring it outside the used band, or to suppress the resonance. There is. Therefore, conventionally, as a means to suppress such resonance, a damping material made of a material such as a urethane sheet or a rubber sheet is interposed between the honeycomb core 1 and the skin materials 3 and 4 to suppress the resonance and, A diaphragm has been proposed in which the internal loss η of the entire diaphragm is increased to obtain good frequency characteristics. However, this conventional type had the disadvantage that it had a complicated structure and increased cost, and the weight inevitably increased due to the damping material, resulting in poor conversion efficiency. This idea was made in view of the above-mentioned points, and without increasing the weight of the diaphragm itself, the resonant frequency of each cell part of the honeycomb core is raised sufficiently high outside the frequency band in which the diaphragm is used. The present invention provides a diaphragm for an electroacoustic transducer that can be applied to a wide range of frequencies, and is characterized in that the skin material is formed into a three-dimensional surface shape instead of a conventional planar shape. This invention will be described in detail below based on embodiments shown in the drawings. FIG. 2 is a partially cutaway enlarged perspective view of a main part showing an embodiment of a diaphragm for an electroacoustic transducer according to this invention;
FIG. 3 is a sectional view taken along the line -- in FIG. 2. In these figures, the diaphragm 10 has a honeycomb core 1,
The honeycomb structure is formed by two skin materials 3 and 4 attached to both sides of the honeycomb core 1 via an adhesive 2, which is exactly the same as the conventional structure shown in FIG. However, the difference is that the surface portion of each skin material 3, 4 corresponding to each cell A is curved downward and upward, respectively, to approximately form a kind of shallow spherical cap 11. This spherical shell 11 is formed by pressing soft rubber or the like against a flat skin material to cause it to flex. _Here , if the plate thickness, radius, and deflection amount of the spherical shell 11 are respectively t, a, and h as shown in FIG. It will be given to you. however:

[Formula] E is Young's modulus, ρ is density, and σ is Poisson's ratio. Note that this Reisner approximation formula was originally based on the spherical shell 11
It is assumed that the periphery of the spherical shell 11 is circular, and a represents the radius of the circle, but in this example, the periphery of the spherical shell 11 is a regular hexagon defined by the cell A. Therefore, the average value of the radius of the inscribed circle and circumscribed circle of the regular hexagon is approximately substituted for a in the equation. _R of the spherical shell 11 can be obtained by the above Reisner approximation formula, and by this approximation formula,
than the lowest natural frequency (=2.98/2π・C・t/a ² ) of a planar disk with the same radius a

[Formula] Increase by double It is understood that here,

If [Formula] is K, then the condition that satisfies K>1 is 2σ ² −5σ−7<0 (where h>0) (2σ−7)(σ+1)<0 However, since σ>0, 0<σ<3.5 Furthermore, since Poisson's ratio σ usually takes a value of 0.2 to 0.4, K>1. Now, as the skin materials 3 and 4, aluminum foil (σ = 0.35) with a thickness t = 36 μm is used, and h = 0.1
Considering the case where it is bent by mm (however, cell A = 1/4 inch), becomes. In other words, when the skin materials 3 and 4 are bent by h=0.1 mm, the lowest natural frequency _R of the spherical shell 11 increases by 2.75 times compared to that of a flat disc. By the way, the resonant wave number of cell A (1/4 inch)
For example, when skin materials 3 and 4 made of duralumin with t = 36 μm are used, the resonant frequency of the inscribed circle is _1N if the adhesive 2 is not considered _.
At 6.8KHz, the resonant frequency _OUT of the circumscribed circle is 9KHz, and ₀ can be considered to be the same as the resonant frequency of a fixed peripheral disk whose radius is approximately halfway between the inscribed circle and the circumscribed circle, so it is about 8KHz, Also, t=72μm
FRP film (Young's modulus E=0.65×10 ¹¹ dyne/
cm ² , density ρ = 1.49) as adhesive 2, ₁ = 15KHz, ₂ = 11.3KHz, and ₀ is 13.3K
Hz. As is clear from the above, when the diaphragm 10 is formed using the three-dimensional surface-shaped skin materials 3 and 4 having the spherical shell 11, the weight of the diaphragm 10 itself is not increased at all. The resonance frequency ₀ of each cell A can be eliminated to a sufficiently high band outside the band used by the speaker. Therefore, not only can good frequency characteristics with little distortion be obtained, but unlike conventional damping layers, the structure is simple and can be manufactured at low cost. FIG. 5 is a longitudinal cross-sectional view of a main part showing another embodiment of this invention. In this embodiment, the portions of the skin materials 3 and 4 corresponding to each cell A are recessed into a hexagonal pyramid shape, and the adhesive is omitted in the figure. Even in such a configuration, since the skin materials 3 and 4 have a three-dimensional surface shape, it is obvious that the resonance frequency ₀ of the cell A inevitably increases as in the above embodiment. In addition, in each of the above embodiments, skin materials 3 and 4 are used.
Although a case has been described where each of the holes is recessed to form a three-dimensional surface shape, the invention is not limited to this in any way; for example, it may be made to bulge as shown by the chain line in FIG. As explained above, in the electroacoustic transducer diaphragm according to this invention, the skin material adhered to at least one surface of the honeycomb core is formed into a three-dimensional surface shape, so that the resonant frequency of each cell can be adjusted to the frequency band used by the speaker. It can also reach sufficiently high external bands. Therefore, since it does not have any adverse effect on the frequency characteristics of the speaker and does not add weight, it is highly efficient and suitable for large-output, large-amplitude speakers, and has very great practical effects.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a main part showing an example of a conventional diaphragm for an electroacoustic transducer, FIG. 2 is a partially cutaway enlarged perspective view showing an embodiment of this invention, and FIG.
A line sectional view, FIG. 4 is a diagram for explaining the lowest natural frequency of the spherical shell, and FIG. 5 is a sectional view of a main part showing another embodiment of this invention. 1... Honeycomb core, 2... Adhesive, 3, 4...
...Skin agent, 10...Vibration plate, 11...Spherical shell, A
……cell.

Claims (1)

[Claims for Utility Model Registration] (1) In a diaphragm for an electroacoustic transducer that constitutes a honeycomb structure by coating at least one surface of a honeycomb core with a skin material, the skin material is formed into a three-dimensional surface shape, A diaphragm for an electroacoustic transducer, characterized in that the resonant frequency of each cell of the core is higher than the frequency band used. (2) The diaphragm for an electroacoustic transducer according to claim 1, wherein the surface of the skin material forms a part of a spherical shell for each cell of the honeycomb core.