JPS5828799B2 - electrostatic headphones - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electrostatic headphones, and particularly to electrostatic headphones that are effective when using an electret.

Conventionally, electrostatic headphones were manufactured by Japanese Patent Publication No. 48-158.
As an application example of 68, it had a structure as shown in Figure 1.

That is, it consists of a conductive vibrating membrane 2 stretched between insulators 1, back electrodes 31 and 41 installed to sandwich them from both sides, and electrets 32 and 42 attached to the back electrodes. Sound transmission holes 33 and 4 respectively
It consisted of two fixed electrodes 1 and 6 with 3.

On the other hand, the signal from the signal source 6 is boosted by the transformer 7, and the two commonly connected back electrodes 31 and 41 and the vibrating membrane 2
applied between.

Since the electrets 32 and 42 are charged with different signs and have positive and negative surface potentials, respectively, when a signal is applied as described above, the vibrating membrane 2 vibrates in accordance with the signal potential.

The acoustic force induced by the vibration of the vibrating membrane 2 passes through the sound transmission hole 33 and is radiated into a space surrounded by the earmuff 8 and the ear (not shown).

In electrostatic headphones with the above structure, the sound pressure is approximately equal to the force generated per unit area of the diaphragm 2, and this sound pressure is determined by the thickness dielectric constant of the electret 32, 42, and the charge accumulated per unit area. amount.

Although this is determined by the gap between the electret 32, 42 and the vibrating membrane 2, there are cases in which it is not always possible to obtain a sufficient sound pressure for practical purposes.

In view of the above points, an object of the present invention is to provide an electrostatic headphone having a relatively simple structure and excellent characteristics that can easily improve sound pressure.

The present invention provides a vibrating membrane having a plurality of vibrating sections on substantially the same plane, and a vibrating membrane in which the vibrating sections are alternately driven in geometrically opposite directions and are arranged opposite to the vibrating membrane. The electrostatic headphone is equipped with a fixed electrode and a lid that forms an acoustic path that acoustically couples the vibrating sections in series, and the fixed electrode includes regions having positive and negative surface potentials. These are electrostatic headphones that use fixed electrodes equipped with electrets.

Further, the vibrating membrane is divided into a first section vibrating section and a second section vibrating section by a dividing support frame, and the first section vibrating section and the second section vibrating section are arranged concentrically. , an even better electrostatic headphone can be obtained.

Next, the present invention will be explained in detail with reference to a schematic diagram and an equivalent circuit diagram of electrostatic headphones.

First, the electrostatic headphone according to the present invention is schematically shown as a vibration system as shown in FIG. 2a.

In other words, if the volume of the part formed by the first vibrating section 9a of the diaphragm and the anterior chamber A of the ear is Qo, and the effective area of the first vibrating section 9a is 81, then the compliance Co of the anterior chamber A is: becomes.

At this time, the vibration system as shown in FIG. 2a is represented by an equivalent circuit as shown in FIG. 2, that is, as shown in FIG.

S2: Effective area of the second section vibrating section F: Driving force of the first section vibrating section F2: Driving force of the second C Assuming a type of transducer, F and F2 are respectively expressed as: e: input voltage Eo: effective voltage of electret ε0: permittivity of vacuum, and sound pressure p becomes.

On the other hand, when a conventional electrostatic headphone as shown in FIG. 1 is schematically shown as a vibration system, it is shown as in FIG. a.

If the volume of the portion formed by the vibrating membrane 2 and the anterior chamber A of the ear is Qo, and the effective area of the vibrating membrane 2 is S, then the compliance C'o of the anterior chamber A is the vibration system as shown in Figure 3a. is expressed by an equivalent circuit as shown in Figure 3, ignoring the mass of the vibration system, and the driving force F'A becomes.

Therefore, the lowest resonant frequency f in the free space of the diaphragm.

If the patent is characterized by Co=4C'.

That is, the lowest resonant frequency fo is normally proportional to the reciprocal of the square root of the product of the mass of the vibration system and the compliance.

Also, the mass of the vibration system is considered to be proportional to the area of the vibration plate,
When 51=S2=S/2, the mass of each vibration system in the example according to the present invention becomes H of the conventional one, so the corresponding compliance becomes twice.

Furthermore, the compliance of the anterior chamber A of the ear as seen from the diaphragm is proportional to the reciprocal of the square of the area of the diaphragm, so it is four times as large.

becomes.

C’.

In other words, by making C10 as small as possible in the design, it is possible to easily improve the sound pressure of m C10.
．． If it is set to 1, the sound pressure will be improved by about 4 dB, if it is set to 0 or 05, the sound pressure will be improved by about 5 dB, and in an ideal state, an improvement of about 6 dB can be expected.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 4 is an exploded perspective view showing the structure of one embodiment of the present invention.

The conductive diaphragm 9 is held between both sides by a frame 10, and is further supported by a divided support frame 11 of the diaphragm.
It is divided into a section vibrating section 9a and a second section vibrating section 9b, each of which is configured to vibrate independently.

The frame body 10 and the divided support frame 11 of the vibrating membrane are held in contact with a fixed electrode L2 and a frame for driving the vibrating membrane.

The first fixed electrode 12 and the second fixed electrode 13 each have a conductive first back electrode 121 or a second back electrode 131.
The first electret 122 or the second electret 132 is attached to the electret.

Both the first electret 122 and the second electret 132 are charged with charges of different signs on the inside and outside of the portion of the vibrating membrane that contacts the divided support frame 11. The portions facing each other are also charged with charges of different signs.

That is, for example, the inner side of the vibrating membrane of the first electret 122 than the part that comes into contact with the divided support frame 11 is positive, the outside part is negative, and the part of the vibrating membrane of the second electret 132 that is inside of the part that comes into contact with the divided support frame 11 is positive. Negatively charged, outer side positively charged.

The first fixed electrode 12 is fixed to the frame 1.

The frame 1 has two acoustic paths formed in the frame 14 according to the division of the diaphragm described above, which is acoustically connected to the first vibrating section 9a of the divided diaphragm. The acoustic passage 141 opens to the external free space, and is acoustically connected to the second section vibrating portion 9b of the divided diaphragm.
42 opens into a space surrounded by the earmuff 15 and the ear (not shown).

The lid body 16 fixed to the second fixed electrode 13 has a recess on its inner surface, and has a first section vibrating portion 9 of the divided vibrating membrane.
It plays the role of acoustically coupling the first and second vibrating sections 92 together.

FIG. 5 is a schematic cross-sectional view taken along the line xx' in FIG. 4, and the operation will be explained according to this diagram.

The signal supplied from the signal source 17 to the primary side of the transformer 18 is boosted, and the conductive vibrating membrane 9 is connected to one end of the secondary side of the transformer 18, and the fixed electrode 12 is commonly connected to the other end. and 13 back electrodes 121 and 131.

At this time, since the electrets 122 and 132 are charged with opposite polarities on the inside and outside of the divided support frame 11 as shown, the corresponding divided parts of the vibrating membrane, that is, the first part inside the divided support frame, The section vibrating section 9a and the second outer section vibrating section 9b are driven in opposite directions with respect to the same signal voltage.

On the other hand, since the back surface of the fixed electrode 9 is sealed by the lid 16, the two divided first vibrating sections 91
The driving forces in the second section vibrating portion 92 are substantially in phase when viewed from the acoustic passage 142, and are biased against each other to increase the sound pressure in the acoustic passage 142.

That is, if an electret equivalent to that of the conventional example shown in FIG. The sound pressure in a nearly sealed space made up of ears (not shown) and the like can be made higher than in the past.

For example, using electrets with the same effective area,
When comparing the sound pressure of the structure shown in Fig. 1 and the structure shown in Fig. 4, the electrostatic headphone shown in Fig. 4 with the structure of the present invention had a sound pressure of 48 dB. An increase in pressure was confirmed.

Note that the effective areas of the first section vibrating section and the second section vibrating section were the same, and other conditions were kept as similar as possible.

As the fixed electrode, an electret (Teflon 75μ thick, 51φ2 surface potential +750V, -700V) provided on the surface of the aluminum substrate was used, and the static gap between the fixed electrode and the diaphragm was set to 0.35 degrees.

As explained above, according to the present invention, it is possible to obtain headphones with higher sound pressure sensitivity than the conventional headphones using the same electrets and the same components and structure as the conventional headphones.

Furthermore, by changing the material and shape of the lid 16, it is possible to create headphones with various tones, which has the advantage of being easy to design to meet the diversified demands of users.

In addition, headphones that use electret are usually sealed with an acoustically transparent moisture-proof membrane to protect the electret from moisture, but in the conventional case, two fixed electrodes were each required on the outside. However, in this embodiment, only one moisture-proof film is required on the outside of the fixed electrode 12 on the front side, and the number of parts in the vibration system can be reduced. Therefore, quality control can be facilitated, and product variations can be reduced. As a result, the yield is expected to improve.

Another embodiment of the present invention is shown in FIG.

This embodiment differs from the previously described embodiment shown in FIG. 5 in the way the electret is charged, the structure of the vibrating membrane, and the way signals are applied.

In this embodiment, the vibrating membrane 19 consists of an insulating base 191 and conductive layers 192 and 193 formed on each surface of the base 191.

The conductive layers 192 and 193 are formed only on the outside or inside of the vibrating membrane division support frame 20, respectively.

As shown in the figure, the electrets 21 and 22 are negatively or positively charged on one side.

The signal source 23 is connected to the primary side of the transformer 24, and the intermediate tap on the secondary side of the transformer 24 is connected to the back electrodes 25 and 2 of the fixed electrodes.
6 in common.

One of the other terminals on the secondary side of the transformer 24 is connected to the conductive layer 193 (
The remaining end of the transformer 24 is connected to the conductive layer 192 (first vibrating section) of the divided vibrating membrane outside the divided support frame.

With this configuration, the inside and outside of the vibrating membrane divided by the divided support frame (the first section vibrating section and the second section vibrating section) are driven in opposite directions, and the fifth section is driven in opposite directions.
The same effect as the previous embodiment shown in the figure can be obtained.

Another embodiment based on the present invention is shown in FIG.

In this embodiment, in addition to the embodiment shown in FIG.
This is an example in which the vibrating membrane is divided into three vibrating sections by adding a dividing support frame 26 for the vibrating membrane, and is an example of an application that can be more effective than the embodiment shown in FIG.

In the above embodiments, the diaphragm and the divided diaphragm parts were described as concentric circles for convenience of explanation, but it goes without saying that the shape of the diaphragm does not matter as long as each of the diaphragms is on substantially the same plane. That's a good thing.

For example, an exploded perspective view shown in FIG. 8 is also equivalent to the present invention.

Further, in the above description, an example of back electret type complementary push-pull drive is shown, but it goes without saying that other drive methods such as single drive or membrane electret can be similarly implemented.

Furthermore, it goes without saying that the present invention can also be applied to electrostatic headphones that do not use electrets by providing an appropriate electrode structure and DC bias.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a structural example of a conventional electrostatic headphone, FIG. 2a is a schematic diagram for explaining an electrostatic headphone according to the present invention, and FIGS. Figure 3a is a schematic diagram for explaining conventional electrostatic headphones; Figure 3 is an equivalent circuit diagram of the schematic diagram shown in Figure 3a; Figure 4 is an equivalent circuit diagram of the schematic diagram shown in Figure 3a; An exploded perspective view of an electrostatic headphone according to the present invention, FIG. 5 is a cross-sectional view of FIG. 4, and FIGS. 6 and 7 are cross-sectional views showing other embodiments of the electrostatic headphone according to the present invention. FIG. 8 is an exploded perspective view showing another embodiment of the electrostatic headphone according to the present invention.

Claims (1)

[Scope of Claims] 1. A vibrating membrane having a plurality of vibrating sections on substantially the same plane, and a vibrating membrane facing the vibrating membrane so as to drive the vibrating sections alternately in geometrically opposite directions. An electrostatic headphone comprising: a fixed electrode disposed to face the vibrating membrane; and a lid body forming an acoustic path for acoustically coupling the vibrating sections in tandem. . 2. An electrostatic headphone according to claim 1, characterized in that the fixed electrode is equipped with an electret having a region with a positive surface potential and a region with a negative surface potential. 3. In claim 1, the diaphragm is divided into a first section vibrating section and a second section vibrating section by a dividing support frame, and the first section vibrating section and the second section vibrating section Electrostatic headphones are characterized by the fact that they are arranged in concentric circles.