JP2015170967A - Condenser headphone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an open type condenser headphone capable of suppressing irregularity of a frequency response by eliminating a reactance component in acoustic impedance on a rear acoustic terminal side.SOLUTION: An open type condenser headphone 1 includes a condenser headphone unit 5 in which a diaphragm 8 oppositely disposed at fixed electrode plates 9, 10. A rear part side of the condenser headphone unit is opened. At the rear part side of the condenser headphone unit, a rear end of the condenser headphone unit is provided so as to be annually opened. A rear acoustic terminal connection member 15 for connecting a rear acoustic terminal to the external air is provided. An inner peripheral surface of the rear acoustic terminal connection member is enlarged in diameter toward the rear end opening.

Description

  The present invention relates to a condenser headphone that emits a sound wave by utilizing a change in capacitance between a diaphragm and a fixed pole, and more particularly to a condenser headphone that suppresses a reactance component of acoustic impedance on a rear acoustic terminal side.

  Electroacoustic transducers (referred to as condenser headphone units) used for condenser headphones include a single type and a push-pull type. The single type has a fixed pole on one side of the diaphragm, and the push-pull type has a fixed pole on both sides of the diaphragm. Since the single type has a problem in lowering the low-band resonance frequency, it is difficult to realize the full band type. Therefore, as shown in Patent Documents 1 and 2, most of those currently in practical use are push-pull types.

As an example, FIG. 5 shows a configuration of a conventional push-pull capacitor headphone. FIG. 5 is a sectional view. The capacitor headphone includes a headphone housing 50 as its basic configuration. The headphone case 50 is supported by the headband 55 and is attached to the ear part of the listener.
The headphone case 50 is formed of a substantially cylindrical body. The opening side of the headphone housing 50 addressed to the listener's ear is covered with a perforated plate 51. An ear pad 52 is attached to the periphery of the perforated plate 51. The illustrated configuration shows an open type headphone. A large number of sound emission holes 56 are provided on the side surface of the housing on the support side by the headband 55.

Also, a push-pull capacitor headphone unit 60 as a speaker is housed in the headphone housing 50. The capacitor headphone unit 60 includes a diaphragm 61 and a pair of fixed poles 63 and 64 on both sides thereof. The diaphragm 61 is stretched in a state where a predetermined tension is applied to the diaphragm ring 62. The peripheral edges of the fixed poles 63 and 64 are supported by a ring-shaped insulating seat 66.
An extremely thin polymer film (about 1 to 3 μm) is used for the diaphragm 61. For example, polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyethylene naphthalate (PEN), or the like is used for the polymer film. Conductivity is imparted to both surfaces of the diaphragm 61 by metal vapor deposition or high resistance film treatment. The diaphragm ring 62 is made of a conductive material such as a brass alloy.

  The fixed poles 63 and 64 are made of a metal plate such as a brass alloy or aluminum. The fixed poles 63 and 64 have a large number of holes (diameter of about 0.1 to 1.0 mm) for emitting sound. In many cases, electret material is stuck to the fixed poles 63 and 64 on the surface facing the diaphragm 61. This electret material is a charged polymer film. In such a configuration, a polarization voltage is applied between the diaphragm 61 and the fixed poles 63 and 64, and an audio signal voltage is applied to the fixed poles 63 and 64. The diaphragm 61 is displaced by the electrostatic force generated between the diaphragm 61 and the fixed poles 63 and 64. As a result, sound waves are radiated from the diaphragm 61.

JP 58-27720 A JP 2008-42436 A

Incidentally, there is a front acoustic terminal 68 on the front side of the condenser headphone unit 60 (the side on which the listener touches the ear). The front acoustic terminal 68 is surrounded by an air chamber formed by the ear pad 52. Sound pressure is applied to the ear via the front acoustic terminal 68. As described above, the diaphragm 61 is as thin as 1 to 3 μm, and an equal driving force can be obtained between the fixed poles 63 and 64. Therefore, on the front acoustic terminal 68 side, a sound wave having no frequency dependency with respect to the applied audio signal voltage can be applied to the ear.
However, since the diaphragm 61 is actually thin, the mechanical impedance is low. For this reason, the influence of the acoustic impedance of the condenser headphone unit 60 on the side opposite to the ear side, that is, the acoustic impedance of the rear acoustic terminal 69, cannot be ignored. There is a problem that the acoustic impedance of the rear acoustic terminal 69 deteriorates the frequency response of the sound wave applied to the ear side (front acoustic terminal 68 side).

This will be specifically described with reference to FIGS. The applicant of the present application changed the acoustic impedance of the rear acoustic terminal 69 in the configuration of FIG. 5 in stages, and measured and evaluated the change in frequency response in each case.
As shown in FIG. 6, in order to change the acoustic impedance of the rear acoustic terminal 69, a cylindrical member 70 having an inner diameter of 77 mm and a height h (mm) was provided on the rear side of the condenser headphone 50. The acoustic mass was changed by making the height h (mm) of the cylindrical member 70 variable.
The measurement result of the frequency response at this time is shown in the graph of FIG. In the graph of FIG. 7, the horizontal axis represents frequency (Hz) and the vertical axis represents relative amplitude level (dBr). Each line in the graph shows a frequency response in each of the following configurations. A solid line (curve A) indicates a frequency response in the case of the configuration of FIG. An alternate long and short dash line (curve B) indicates a frequency response when the height h of the cylindrical member 70 is 12 mm. A broken line (curve C) indicates a frequency response when the height h of the cylindrical member 70 is 24 mm.

  As shown in the graph of FIG. 7, the level of the resonance frequency near 1.5 kHz decreases as the acoustic mass increases (the height h of the cylindrical member 70 increases). From this result, if there is an acoustic reactance (an acoustic capacity formed by the inner volume of the headphone case and an acoustic mass of the sound emitting hole 56) on the rear acoustic terminal 69 side, resonance occurs. It can be considered that this resonance causes unevenness in the frequency response of the diaphragm 61.

FIG. 8 shows an equivalent circuit of a conventional capacitor headphone. As shown in FIG. 8, on the rear acoustic terminal 69 side, as the acoustic impedance, resistive air impedance R1, reactance X (acoustic capacity formed by the internal volume of the headphone case, and acoustics of the opening of the headphone case) Mass) is present.
As described above, the acoustic impedance on the rear acoustic terminal 69 side affects the frequency response of the sound wave applied to the ear side. Therefore, it is desirable that there is no acoustic reactance X on the rear acoustic terminal 69 side.

  The present invention has been made paying attention to the above points, and in an open-type condenser headphone, a condenser headphone that can eliminate the reactance component in the acoustic impedance on the rear acoustic terminal side and suppress the unevenness of the frequency response is provided. The purpose is to provide.

In order to solve the above-described problems, a capacitor headphone according to the present invention includes a capacitor headphone unit in which a diaphragm is opposed to a fixed electrode plate, and an open type capacitor headphone in which a rear side of the capacitor headphone unit is opened. The rear side of the condenser headphone unit is provided in an annular shape with an open rear end, and includes a rear acoustic terminal connecting member for connecting the rear acoustic terminal to external air, and an inner periphery of the rear acoustic terminal connecting member. The surface is characterized in that the diameter is expanded toward the rear end opening.
The rear acoustic terminal connecting member is preferably a horn-shaped member whose inner peripheral surface has a convex curve in a sectional view.
Alternatively, the rear acoustic terminal connecting member may be a cone-shaped member whose inner peripheral surface forms a straight line in a sectional view.

With this configuration, a horn type or cone type acoustic path is formed at the rear acoustic terminal. Therefore, the rear acoustic terminal of the condenser headphone unit and the external air can be acoustically connected without having a reactance component.
As a result, an acoustic matching is achieved at the rear of the condenser headphone unit. The acoustic impedance on the rear acoustic terminal side is only a resistance component, and it is possible to obtain a condenser headphone with no deterioration in frequency response.

  In an open type condenser headphone, it is possible to obtain a condenser headphone that eliminates the reactance component in the acoustic impedance on the rear acoustic terminal side and can suppress the unevenness of the frequency response.

FIG. 1 is a cross-sectional view of a condenser headphone according to the present invention. FIG. 2 is an equivalent circuit of the capacitor headphone of FIG. FIG. 3 is a cross-sectional view showing a modification of the capacitor headphone according to the present invention. FIG. 4 is a cross-sectional view showing a modified example of another condenser headphone according to the present invention. FIG. 5 is a cross-sectional view of a conventional open-type condenser headphone. FIG. 6 is a cross-sectional view showing a configuration in which an acoustic mass is added to the rear side of the condenser headphones of FIG. FIG. 7 is a graph showing frequency characteristics of the condenser headphones of FIGS. 5 and 6. FIG. 8 is an equivalent circuit of the capacitor headphones of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is applied to an open type condenser headphone whose rear side is open.
FIG. 1 is a cross-sectional view of a condenser headphone according to the present invention. The capacitor headphone 1 of FIG. 1 includes a capacitor headphone unit 5 as an electroacoustic transducer. The capacitor headphone unit 5 includes a pair of diaphragm rings 6 and 7 bonded to each other up and down in the drawing. A thin diaphragm 8 is stretched between the diaphragm rings 6 and 7.

The diaphragm rings 6 and 7 are each formed in a regular circular frame. The diaphragm rings 6 and 7 have a frame surface with a predetermined width in the vertical direction. The diaphragm rings 6 and 7 are made of metal, and may be made of, for example, an aluminum material or a brass alloy.
The diaphragm 8 is formed in a thin film shape having a thickness of 1.5 μm, for example. The diaphragm 8 is made of a polymer film such as PET, PPS, or PEN.

In FIG. 1, fixed poles 9 and 10 are arranged above and below the diaphragm 4 with a predetermined interval (for example, about 0.3 to 1.0 mm), respectively. The fixed poles 9 and 10 are made of a metal plate (for example, brass alloy or aluminum) having a predetermined thickness (about 0.5 mm).
A number of holes (not shown) are formed in the fixed poles 9 and 10. The multiple holes are provided for emitting sound waves from the diaphragm. An electret material obtained by charging a polymer film is attached to the surface of the fixed poles 9 and 10 facing the diaphragm 8.
The insulating seats 11 and 12 are in contact with the peripheral edge of one surface of the pair of fixed poles 9 and 10. The insulating seats 11 and 12 are frame bodies made of an insulating material. The insulating seats 11 and 12 support the fixed poles 9 and 10 with an adhesive.

  The insulating seats 11 and 12 are fixed to one surface of a baffle plate 13 disposed on the peripheral edge of the capacitor headphone unit 5 with an adhesive. The baffle plate is annular and has a predetermined width. The ear pad 2 is provided on the other surface of the baffle plate 13, that is, on the ear part side (lower side in the drawing) of the listener. The ear pad 2 has an annular shape having a predetermined width and height. The ear pad 2 forms an air chamber. The front acoustic terminal 21 is covered with this air chamber.

On the other hand, an annular horn member 15 (rear acoustic terminal connecting member) is provided on the other surface of the baffle plate 13 so as to cover the insulating seats 11 and 12. In this embodiment, the condenser headphone 1 has an open type structure in which the rear side is opened. Therefore, the rear acoustic terminal 22 is surrounded by the horn member 15. The rear end of the horn member 15 has a large opening.
In addition, the horn member 15 has an inner diameter that is gradually increased in diameter toward the rear end opening as shown in the drawing. More specifically, in the cross section, the inner peripheral surface has a horn shape with a convex curve. The horn member 15 is made of, for example, an insulating material similar to the insulating seats 11 and 12.

  By configuring the rear side of the condenser headphone unit 5 in this way, the acoustic impedance of the rear acoustic terminal 22 is coupled to the acoustic impedance of air. FIG. 2 shows an acoustic mechanical equivalent circuit at that time. Here, the acoustic impedance R2 of air is a resistive impedance ρc (specific acoustic resistance of air) and does not have acoustic reactance. Therefore, the rear acoustic terminal 22 is terminated with a resistive impedance. Therefore, unevenness of the frequency response is prevented, and a flat frequency response can be obtained in a desired frequency band.

As described above, according to the embodiment of the present invention, the rear acoustic terminal 22 side of the condenser headphone unit 5 is formed into a horn shape, so that a horn-type acoustic path is formed. Therefore, the rear acoustic terminal 22 of the condenser headphone unit 5 can be connected to the external air without having an acoustic reactance component.
As a result, the rear part of the condenser headphone unit 5 is acoustically matched with the external air, and the acoustic impedance of the rear acoustic terminal 22 is only a resistance component. As a result, it is possible to obtain the capacitor headphone 1 that does not deteriorate the frequency response in the desired band.

In the above embodiment, the horn member 15 is provided as the rear acoustic terminal connecting member on the rear acoustic terminal 22 side. However, in the capacitor headphone according to the present invention, the horn member 15 is tapered toward the rear end opening. What is necessary is just to expand the diameter. Therefore, as shown in FIG. 3, instead of the horn member 15, a cone member 16 having a straight inner peripheral surface in a cross section may be provided.
Further, the opening angle and height dimension of the horn member 15 and the cone member 16 may be arbitrarily changed, for example, by forming the opening angle large as shown in FIG. By adjusting the opening angle and height dimension of the horn member 15 and the cone member 16, the capacitor headphones 1 having a desired frequency response can be obtained.

1 Capacitor Headphone 2 Ear Pad 5 Capacitor Headphone Unit 6 Diaphragm Ring 7 Diaphragm Ring 8 Diaphragm 9 Fixed Electrode (Fixed Electrode Plate)
10 Fixed pole (fixed pole plate)
11 Insulating seat 12 Insulating seat 13 Baffle plate 15 Horn member (rear acoustic terminal connecting member)
16 Cone member (rear acoustic terminal connecting member)
21 front acoustic terminal 22 rear acoustic terminal

Claims (3)

It has a condenser headphone unit in which a diaphragm is opposed to a fixed electrode plate, and is an open type condenser headphone in which a rear side of the capacitor headphone unit is opened,
On the rear side of the condenser headphone unit, the rear head is provided in an annular shape and includes a rear acoustic terminal connecting member that connects the rear acoustic terminal to external air,
A condenser headphone characterized in that an inner peripheral surface of the rear acoustic terminal connecting member is enlarged in diameter toward a rear end opening.   The condenser headphone according to claim 1, wherein the rear acoustic terminal connecting member is a horn-shaped member having an inner peripheral surface forming a convex curve in a sectional view.   The condenser headphone according to claim 1, wherein the rear acoustic terminal connecting member is a cone-shaped member whose inner peripheral surface forms a straight line in a sectional view.

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