JPS5927159B2 - electrodynamic speaker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrodynamic speaker using a circular flat diaphragm, and by expanding the piston motion area,
The present invention provides an electrodynamic speaker with flat sound pressure frequency characteristics over a wide band and low distortion.

First, a conventional electrodynamic speaker of this type will be explained with reference to FIG.

In FIG. 1, 1 is a yoke with a center pole 2 integrally formed in the center of its upper surface, 3 is an annular magnet fixed on the yoke 1, and 4 is an annular plate fixed on the magnet 3. An annular magnetic gap is formed between the inner peripheral surface of the plate 4 and the outer peripheral surface of the center pole 2.

A frame 5 is supported by the plate 4, and a hole 6 is formed in the frame 5.

Reference numeral 7 denotes a circular plate-shaped vibrating plate, and this vibrating plate 7 is supported in a hole of the frame 5 via an annular edge member 8.

Reference numeral 9 denotes a reinforcing ring bonded to the lower surface of the vibrating plate γ, and a cylindrical coil bobbin 10 is fixed to this reinforcing ring 9.

Reference numeral 11 denotes a voice coil wound around the coil bobbin 10, and this voice coil 11 is arranged in the magnetic gap portion.

12 is a damper that supports the coil bobbin 10.

In an electrodynamic speaker using a circular flat diaphragm as shown in Fig. 1, ° is as shown in Fig. 2a at a given frequency.
As shown in FIG. 2, a nodal circle R is generated due to the first resonance, and a sound pressure peak of C occurs at the above-mentioned resonance frequency in the sound pressure frequency characteristic, making it impossible to expand the piston motion region.

On the other hand, as shown in FIG. 2, when the coil bobbin 10 having the same diameter as the nodal circle R is fixed to the nodal part of the diaphragm 7 and driven, the nodal circle is removed and the primary resonance occurs. The sound pressure peak caused by this is removed.

In order to eliminate the first-order resonance, one drive may be performed via a conical cone 13 having a large diameter portion having the same diameter as the nodal circle, as shown in FIG. 2C.

However, as shown in FIG. Sound pressure peaks occurred at certain frequencies.

In addition, when the mass of the coil bobbin, conical cone, etc. fixed inside the unit increases due to the nodal circle 1 drive, the secondary resonance frequency decreases and the reproduction band becomes narrower, as shown in Figure 3. there were.

In Fig. 3, the horizontal axis shows the ratio of MV (mass added to the nodal part in the first resonance) and MD (the mass of the diaphragm), and the vertical axis shows the ratio of f/20 (the mass added to the nodal part in the first resonance). (secondary resonance frequency when a mass is added inside the part) and f2o
(secondary resonance frequency of a single diaphragm).

To remove the second-order resonance, the second order resonance caused by the second-order resonance must be
This is possible by driving two nodal circles; however, in this case, although the second-order resonance can be removed, the first-order resonance cannot be removed.

The present invention provides an electrodynamic speaker capable of eliminating first-order resonance and second-order resonance, and the theory thereof will be described below.

The forced vibration solution ξ (displacement) of the peripheral free disk is expressed by the following equation.

Distributed driving force ′−″ Resonance mode reference function of m-th resonance that produces m nodal circles) Here, let us consider the case where the diaphragm is driven at a position with radius r1 + r2, where the radius of the diaphragm is a.

The bias is as shown in equation (2) below.

(F exists only in r1 to r1+dr7.r2 to r2+dl-2.

) where Fx = F2πr dr , Fx = F2π
r2dr21 1 1 2
Then, Ao is expressed by the following equation (3).

Substituting equations (2) and (3) into equation (1) yields /-, r2 In equation (4), Fx13 ()+FX25 ()
If is zero, the diaphragm always moves in a piston motion.

However, in reality, the mouth changes depending on the frequency and is not always zero.

The idea that the first-order resonance can be eliminated in the conventional example shown in FIG. 2 is similar to this idea.

However, driving the nodal circle of the first-order resonance does not eliminate the second-order resonance.

To remove both the first and second resonance, 2(r)
A driving part is provided at a radius r1゜r2 (this is called the nodal circle of the second resonance) that becomes It is necessary to set the driving force ratio.

In this case, it is necessary to drive the diaphragm perpendicularly to the rl r r2 position of the diaphragm, and a speaker constructed based on this concept has significant limitations on the voice coil and magnetic circuit.

The two drive cones of the present invention have the above-mentioned r1 + of the diaphragm.
Since it drives the position of r2, in the secondary resonance convex rl convex r2 (4), Fx10. T] (T) 10FX2. X, (=)
becomes zero and no secondary resonance occurs.

However, when a diaphragm is driven by a combination of two drive cones, the free vibration reference function 1 at the first resonance of the diaphragm changes significantly.

Therefore, simply driving the diaphragm with two drive cones does not eliminate the first-order resonance and the second-order resonance and ensure the band up to the third-order resonance.

The present invention uses two coupled drive cones to create a single diaphragm.
A speaker with a driving structure is analyzed using the finite element method, and if the joining position (radius r of the joining part) of the two drive cones to be joined satisfies at least the condition of the following formula, the first order of the diaphragm It is possible to remove resonance and second-order resonance and expand the piston motion vibration band to third-order resonance.

An embodiment of the present invention will be described below with reference to FIGS. 4a and 4b.

Note that in FIGS. 4a and 4b, the same parts as in FIG. 1 are given the same numbers.

In FIG. 4, reference numeral 14 and 15 are drive cones having a conical cylindrical shape, one drive cone 14 has its large diameter end fixed to the lower surface of the diaphragm 7, and the other drive cone 14
5 has its small diameter end fixed to the lower surface of the diaphragm 7.

Further, the lower end of each drive cone 14 , 15 is fixed to the upper end of the coil bobbin 10 .

The locations where the drive cones 14 and 15 are fixed to the diaphragm 7 are the nodal portions generated by the second resonance of the diaphragm 7.

The circular flat plate-shaped diaphragm 7 vibrates as shown by the broken line in FIG. 4a during the second resonance, but there are portions where it does not vibrate.

This non-vibrating portion is a nodal circle, and in the circular flat diaphragm 7, a nodal circle R1 with a radius r1 and a nodal circle R2 with a radius r2 are generated due to secondary resonance.

In the present invention, two drive cones 14 and 15 drive the inside of the two parts of the diaphragm 7.

In addition, in FIG. 4, 13 is a through hole formed in the center of the Senku pole 2.

Figure 5 a, b and c each show two drive cones 1
This figure shows the case where the lengths of the drive cones 14 and 15 are changed when the nodal portion is driven by secondary resonance using the drive cones 4 and 15.

In FIG. 5a, the length of the drive cone 14 is longer than the length of the drive cone 15, and the radius r of the lower end joint of the drive cones 14 and 15 is set to the radius r1+r2 of the nodal circle.
The case where r<(r, +r2)/2 is shown, and Fig. 5 shows the case where r 2 > r≧(r1+r2)/2.
Figure C shows the case of r-r2.

Figures 6a, b, and c are Figures 5a, b, respectively.

The first resonance mode in free vibration of C is shown.

As shown in FIG. 6a, in the case of r<(r1+r2)/2, and in the case of r-r2 as shown in FIG. 6C, the lower end of the drive cone 14°15 is coupled due to the first resonance. , that is, the point X is displaced in the vertical direction (direction perpendicular to the diaphragm).

On the other hand, as shown in Figure 6, r2〉r≧(r1
+r2)/2, the X point is displaced laterally but not vertically.

That is, as shown in Figure 6, r2>r≧(r, +r
2) In the case of /2, the X point is the point where the input mechanical impedance in the vertical direction in the first resonance becomes infinite, and if the coil pobbin 10 is attached to this X point and vibrates in the vertical direction, the mass of the vibration system will be reduced. Only the impedance proportional to is transmitted to the drive system, the driving force that induces the first resonance is not transmitted, and the piston vibrates due to the piston motion.

As described above, according to the present invention, since the nodal circle in the second resonance is driven, the second resonance does not occur, and the first
Since the driving force that induces the next resonance is not transmitted, the first resonance does not occur either.

Therefore, according to the electrodynamic speaker of the present invention, a flat sound pressure frequency characteristic can be obtained up to the frequency at which third-order resonance occurs.

FIG. 7 shows the sound pressure frequency characteristics of a conventional electrodynamic speaker and an electrodynamic speaker of the present invention.

In FIG. 7, A is the characteristic of the electrodynamic speaker of the present invention, and B is the characteristic of the electrodynamic speaker of the present invention.
C shows the characteristics of a conventional electrodynamic speaker that drives the center of a circular flat diaphragm, and C shows the characteristics of the electrodynamic speaker shown in FIG. 1. According to the present invention, third-order resonance is achieved. The characteristics are flat up to the generated frequency f30.

f in FIG. I f20 is the first and second resonance frequencies when the diaphragm is driven at the center, and f2o' is the first resonance frequency.
The second resonant frequency f30 of the electrodynamic speaker shown in the figure is the third resonant frequency.

The present invention has the above-described configuration, and has the advantage of being able to expand the reproduction band with a simple structure.

[Brief explanation of the drawing]

Figure 1 is a cutaway perspective view of a part of a conventional electrodynamic speaker, Figure 2a is a diagram showing the first resonance mode of a circular flat diaphragm, and Figure 2 is Figure 1. 2C is a sectional view of the vibrating part of an electrodynamic speaker shown in FIG. A diagram showing the change in mass and secondary resonance frequency,
Fig. 4a is a diagram showing the second resonance mode of a circular flat diaphragm, Fig. 4 is a half-sectional view of an electrodynamic speaker according to an embodiment of the present invention, and Fig. 5a''c is a diagram showing the second resonance mode of a circular flat diaphragm. Figures 6a to 6C show the relationship between the five drive cones and the diaphragm.
Figures a and 7 show the first-order resonance mode of the vibration system in Figures a and c, and Figure 7 is a sound pressure frequency characteristic diagram of the electrodynamic loudspeaker of the conventional example and the present invention. 1... Yoke, 2 ... Center pole, 3 ... Magnet, 4 ... Plate, 5 ... Frame, 7 ... Diaphragm, 8
...Edge member, 10...Coil bobbin, 11...Voice coil, 12...
Damper, 13... Through hole, 14.15...
...drive cone.

Claims (1)

[Claims] 1. An electrodynamic speaker that drives a circular flat diaphragm, having first and second conical cylindrical drive cones,
The large diameter end of the first drive cone and the small diameter end of the second drive cone are each radius r1 y r2 (r2> r
l), the other ends of the first and second drive cones were connected, and a coil bobbin with radius r was attached to this joint, so that r2>r≧(r1+2)/2. Electrodynamic speaker.