WO2024095563A1

WO2024095563A1 - Bone conduction speaker

Info

Publication number: WO2024095563A1
Application number: PCT/JP2023/030020
Authority: WO
Inventors: 智也渥美; 幹夫福田
Original assignee: 株式会社テムコジャパン
Priority date: 2022-11-04
Filing date: 2023-08-21
Publication date: 2024-05-10

Abstract

[Problem] To address the problem of providing a dynamic-type bone conduction speaker suitable for outdoor use by a normal listener. [Solution] In the present invention, the following are incorporated into a unit case 1A: a yoke assembly 11 constituted of a yoke, a magnet, and a pole piece; and a voice coil 15. The voice coil 15 is fixed to a reverse surface of a first diaphragm 16 installed at a unit case 1 inner upper part. The yoke assembly 11 is fastened via a spacer 19 to a second diaphragm 18 installed on an elastic member 17 disposed on an inner bottom surface of the unit case 1. A space section 5 for generating air conduction sound is provided between the first diaphragm 16 and a top surface of the unit case 1. A sound-emitting opening 6 opening to the space section 5 is formed on the top surface. The sound-emitting opening 6 is covered with an acoustic braking member 7.

Description

Bone conduction speaker

The present invention relates to a bone conduction speaker, and more specifically to a dynamic type bone conduction speaker that has improved frequency characteristics, a wide frequency band when in use, and little sound leakage, making it suitable for use outdoors by people with normal hearing.

Bone conduction headphones are used as a device that allows listening without blocking the ear canal when using headphones outdoors to prevent danger, but the frequency characteristics transmitted by bone vibration have a large attenuation in the low and high ranges, and have been considered unsuitable for listening to music. Therefore, a method has been proposed in which air conduction sound generated from the speaker body is heard via the eardrum along with bone conduction sound (WO2008/029515, JP2007-103989, etc.). With this method, dynamic type bone conduction speakers can have a relatively wide frequency range due to their basic structure, so frequency bands that could not be reproduced using bone vibration characteristics can be added via the eardrum as air conduction sound, widening the reproduced frequency band.

In most typical dynamic bone conduction speakers, in order to ensure a larger vibration output, the voice coil is fixed to the housing and the yoke is held by a diaphragm, with the yoke vibrating in response to the input signal (see, for example, JP 2008-131470 A). With this configuration, it is possible to set the low-frequency resonance frequency, determined by the mass of the yoke and the diaphragm, to a sufficiently low value, making it possible to generate a large vibration output in the low-frequency range.

However, this configuration has the disadvantage that the entire case vibrates due to its structure, which can lead to a large amount of sound leakage to the surrounding area. In addition, the vibrating surface is part of the case (the surface to which the voice coil is fixed), and as there are restrictions on its shape, it is difficult to freely select the frequency characteristics. Furthermore, if the vibrating surface is designed to come into contact with the human body, there is the problem that the high-frequency characteristics will also change.

In view of these problems, the applicant of the present application has previously proposed a bone conduction speaker that solves the above problems by enabling air-conducted sound (air vibration) generated from the diaphragm of the unit to be heard more efficiently via the eardrum in the high frequencies that cannot be covered by bone vibration (WO2018/079340). The bone conduction speaker of this invention comprises a first diaphragm placed on the upper part of the container of the unit case and a second diaphragm placed below it, a yoke assembly is installed on the second diaphragm, a voice coil is installed on the back surface of the first diaphragm, the space above the first diaphragm is an air-conducted sound generating chamber, a sound outlet is formed on the side of the space, and the air-conducted sound generated by the vibration of the first diaphragm can be emitted via the sound outlet in a direction approximately perpendicular to the vibration direction of the bone conduction speaker.

Publication No. WO2008/029515 JP 2007-103989 A JP 2008-131470 A Publication No. WO2018/079340

In the case of the bone conduction speaker according to the above-mentioned conventional invention, the low-frequency resonance frequency of the speaker is determined by the compliance (following ability) of the second diaphragm and the mass of the yoke, but in that case, in order to change the low-frequency resonance frequency once it has been set, it is necessary to change the mass of the yoke, which in turn requires changing the dimensions of the yoke and also the dimensions of the entire speaker. In order to change the compliance of the second diaphragm, it is necessary to change its thickness and shape, but because the second diaphragm is created by etching, changing its thickness and shape takes time and effort, so there is a problem that it cannot be easily changed.

In addition, the low-frequency resonant frequency has a steep peak, but the above-mentioned conventional inventions do not consider how to suppress this peak and obtain good frequency characteristics. Furthermore, although the sound outlet is provided on the side facing the ear canal, no consideration is given to the possibility of improving the high-frequency characteristics by adjusting the air-conducted sound emitted from the sound outlet.

The present invention aims to provide a dynamic bone conduction speaker that overcomes the problems with the above-mentioned conventional inventions, improves on them, and further improves the frequency characteristics in both the high and low ranges, thereby expanding the frequency band during use, while minimizing sound leakage, making it suitable for use outdoors by people with normal hearing.

The invention according to claim 1 for solving the above problem is a dynamic type bone conduction speaker comprising a yoke assembly including a yoke, a magnet, and a pole piece, and a voice coil for driving the yoke assembly, the dynamic type bone conduction speaker being assembled in a unit case,
The voice coil is fixed to the back surface of a first diaphragm installed in the upper part of the unit case, and the yoke assembly is fixed via a spacer to a second diaphragm installed on an elastic material arranged on the inner bottom surface of the unit case,
This bone conduction speaker is characterized in that a space for generating air-conducted sound is provided between the first diaphragm and the top surface of the unit case, a sound outlet that opens into the space is formed on the top surface of the unit case, and the sound outlet is covered with an acoustic damping material.

In one embodiment, the acoustic damping material is made of nonwoven fabric, open-cell foam, or other breathable material, and has a density that provides the desired acoustic resistance. In another embodiment, the first diaphragm is made of ABS, polycarbonate, or other molding material, and the outer diameter and thickness are set to provide the desired high-frequency resonance frequency. The first diaphragm may be made of the same material as the unit case.

In one embodiment, the spacer has an outer diameter and mass that provide the desired low-frequency resonance frequency. In another embodiment, the elastic material is PORON (registered trademark), silicone sponge, or other damping material that can reduce the peak value of the low-frequency resonance frequency.

In one embodiment, the second diaphragm is made by etching a thin metal circular spring plate, with a central circular portion connected to the peripheral portion via an arc-shaped connecting band.

The bone conduction speaker of the present invention is as described above, and the yoke assembly is fixed via a spacer onto the second diaphragm placed on the elastic material, and the sound outlet is covered with an acoustic damping material, improving the low and high frequency characteristics and widening the frequency band during use. Furthermore, there is little sound leakage, which has the effect of providing a dynamic type bone conduction speaker that is suitable for outdoor use by people with normal hearing.

1 is a longitudinal sectional view of an embodiment of a bone conduction speaker according to the present invention. 4A to 4C are plan views showing examples of shapes of the second diaphragm of the bone conduction speaker according to the present invention. FIG. 1 is a diagram showing an example of a configuration in which a bone conduction speaker according to the present invention is incorporated into headphones. 1A to 1C are diagrams showing examples of the configuration of a support for supporting a bone conduction speaker according to the present invention. FIG. 2 is a frequency characteristic diagram of air-conducted sound generated in the ear canal of a wearer when the bone conduction speaker according to the present invention is placed near the wearer's tragus. FIG. 2 is a frequency characteristic diagram showing that the high-frequency characteristics of air-conducted sound frequencies are adjusted by an acoustic damping material in the bone conduction speaker according to the present invention. FIG. 1 is a diagram showing frequency characteristics of a bone conduction speaker according to the present invention when an elastic material is arranged and when it is not arranged. FIG. 1 is a diagram showing that when a person with normal hearing wears the bone conduction speaker according to the present invention near the tragus and listens to it, the frequency range is expanded by simultaneously listening to bone conduction characteristics and air conduction sound characteristics in the external auditory canal, making it possible to hear with good sound quality.

The embodiment of the present invention will be described with reference to the attached drawings. The bone conduction speaker according to the present invention is a dynamic type bone conduction speaker that is configured by incorporating a yoke assembly 11 and a voice coil 15 that drives the yoke assembly 11 in a unit case 1. Note that wiring is not shown in the illustration.

The unit case 1 consists of a bottom 2, a body 3, and a lid 4, which are joined together in the vertical direction. The voice coil 15 is fixed to the back surface of a first diaphragm 16, which is sandwiched between the body 3 and the lid 4. The first diaphragm 16 is installed with its peripheral portion sandwiched between a step 3a formed on the top of the body 3 and a ring frame 4a on the bottom surface of the lid 4.

A space 5 is formed between the top surface of the first diaphragm 16 and the inner top surface of the lid 4. A sound outlet 6 that opens into the space 5 is formed in the lid 4, and the sound outlet 6 is covered with an acoustic damping material 7. The space 5 is provided to generate air-conducted sound (air vibration) by the vibration of the first diaphragm 16, and the air-conducted sound generated therein is emitted from the sound outlet 6. The acoustic damping material 7 serves to adjust the high-frequency characteristics of the frequency of the emitted air-conducted sound, and is basically made of breathable materials such as nonwoven fabric and open-cell foam material, and as described below, the acoustic resistance can be changed by changing the density (in other words, by selecting one with a suitable density), thereby suppressing resonance peaks and adjusting the volume level.

The high-frequency resonant frequency of the first diaphragm 16 is basically determined by its compliance (ability to follow) and the mass of the voice coil 15. In the present invention, the first diaphragm 16 is made of a thermoplastic resin material with excellent impact resistance, such as ABS resin or polycarbonate, and the high-frequency resonant frequency can be adjusted by changing the outer diameter and thickness. Furthermore, costs can be reduced by molding the first diaphragm 16 from the same material as the unit case 1.

The yoke assembly 11 is made up of a yoke 12, a magnet 13, and a pole piece 14, and is supported by a second diaphragm 18 arranged in the bottom 2 of the unit case 1, and is housed in the body 3. The second diaphragm 18 serves to improve the low-frequency characteristics, and is fixed onto an elastic material 17 arranged on the inner bottom surface of the bottom 2, with its peripheral portion 18c sandwiched and installed between a step portion 2a formed on the bottom 2 and a ring frame 3b on the bottom surface of the body 3. The bottom surface of the yoke 12 of the yoke assembly 11 is fixed and supported on the second diaphragm 18 via a spacer (also serving as a weight) 19, and the voice coil 15 is inserted between the inner peripheral surface of the yoke 12 and the outer peripheral surface of the pole piece 14.

The second diaphragm 18 is manufactured by etching a thin metallic circular spring plate, and for example has a central circular portion 18a connected to a peripheral portion 18c via four arc-shaped connecting bands 18b (see FIG. 2), with the peripheral portion 18c sandwiched between the bottom portion 2 and the body portion 3, and a spacer 19 fixed to the bottom surface of the yoke 12 is fixed to the central circular portion 18a. In this type of configuration, the central circular portion 18a is sensitive to vibrations because it is separated from the peripheral portion 18c and connected via thin arc-shaped connecting bands 18b.

As described above, the second diaphragm 18 is fixed to the bottom surface of the yoke 12 via the spacer 19, which also serves as a weight. In this case, by changing the outer diameter and mass of the spacer 19 (in other words, by selecting one with a suitable outer diameter and mass), it is possible to freely control the low-frequency resonance frequency without changing the shape of the second diaphragm 18.

The second diaphragm 18 is fixed onto an elastic material 17 arranged on the inner bottom surface of the bottom 2, and this elastic material 17 is provided to eliminate acoustic discomfort. That is, the low-frequency resonant frequency usually has a steep peak and produces large vibrations, which causes acoustic discomfort, so an elastic material 17 such as PORON (registered trademark) or silicone sponge is arranged as a damping material to lower the peak value. Figure 7 shows the frequency characteristics when the elastic material 17 is arranged and when it is not arranged. As is clear from the graph, when the elastic material 17 is arranged, the peak of the low-frequency resonant frequency is sufficiently suppressed compared to when it is not arranged, and it can be understood that this eliminates acoustic discomfort.

The bone conduction speaker according to the present invention is used by being incorporated into headphones or fixed to a support and positioned near the tragus. Figure 3 shows an example of a configuration when incorporated into headphones 21, where the bone conduction speaker S is installed inside the housing 22 of the headphones 21 with the acoustic damping material 7 blocking the sound outlet 6 facing the inner surface of the housing 22. The housing 22 is formed with a sound guide tube 23 that opens to the outside, and is configured to emit high-frequency air-conducted sound coming out of the sound outlet 6 in the direction of the ear canal via the acoustic damping material 7.

Figure 4 shows an example of a support, in which the support 25 is made up of an elastic adapter 26 with a protrusion 27 that fits inside the cavity of the concha 31, and a support post 28 that is raised on its upper surface and supports the bone conduction speaker S in a floating state. The elastic adapter 26 is circular and opens the ear canal 32. The bone conduction speaker S is supported by the support post 28 and positioned so that it is located near the tragus 33.

When a person with normal hearing places the bone conduction speaker S of the above configuration, incorporated in the headphones 21 or supported by the support 25, near the tragus and listens to it, the person can simultaneously hear sounds with bone conduction characteristics and air conduction sound characteristics in the ear canal, making it possible to hear sounds with a wide frequency range and good sound quality (Figure 8). At this time, the bone conduction speaker S is located very close to the ear canal 32, so in the ear canal, not only is there a sufficient level of air conduction sound generated by the vibration output of the bone conduction speaker S in the ear canal, but also the high-frequency air conduction sound generated by the vibration of the bone conduction speaker S (see Figure 5) reaches the eardrum, providing sufficient volume and good frequency characteristics.

The air-conducted sound generated by the bone conduction speaker S can leak to the outside if its level is high, so sound leakage to the outside can be suppressed by adjusting the high-frequency level with the acoustic damping material 7 that blocks the sound outlet 6 at the top of the first diaphragm. Figure 6 shows the air-conducted sound characteristics of the air-conducted sound generated in the wearer's ear canal when the bone conduction speaker S is placed near the wearer's tragus 33 and used with and without the acoustic damping material 7 covering it.

As described above, in the case of the bone conduction speaker according to the conventional invention, in order to change the low-frequency resonance frequency once it has been set, it is necessary to change the dimensions of the yoke part in order to change the mass of the yoke part, and also to change the dimensions of the entire speaker. Furthermore, in order to change the compliance of the second diaphragm, it is necessary to change its thickness and shape. In contrast, in the case of the bone conduction speaker according to the present invention, the low-frequency resonance frequency once it has been set can be changed and adjusted without incurring any cost by simply changing the outer diameter and mass of the spacer 19, without changing the shape of the second diaphragm 18, and without changing the dimensions of the yoke part and the entire speaker. In addition, the problem of acoustic discomfort caused by the peak of the low-frequency resonance frequency not being suppressed can be solved by arranging an elastic material 17 (see Figure 7).

Furthermore, in the case of bone conduction speakers according to the conventional invention, no consideration was given to improving the high-frequency characteristics of the air-conducted sound emitted from the sound outlet. However, in the bone conduction speaker according to the present invention, by covering the sound outlet 6 with an acoustic damping material 7, it is possible to adjust the high-frequency level, thereby suppressing sound leakage to the outside (see Figure 6).

The bone conduction speaker of the present invention has the above-mentioned configuration, and the yoke assembly is fixed via a spacer onto the second diaphragm placed on the elastic material, and the sound outlet is covered with an acoustic damping material, improving the low and high frequency characteristics and widening the frequency band during use. In addition, there is little sound leakage, which results in a dynamic type bone conduction speaker that is suitable for outdoor use by people with normal hearing, and has great industrial applicability.

Claims

A dynamic type bone conduction speaker comprising a yoke assembly including a yoke, a magnet, and a pole piece, and a voice coil for driving the yoke assembly, the dynamic type bone conduction speaker being assembled in a unit case,
The voice coil is fixed to the back surface of a first diaphragm installed in the upper part of the unit case, and the yoke assembly is fixed via a spacer to a second diaphragm installed on an elastic material arranged on the inner bottom surface of the unit case,
A bone conduction speaker characterized in that a space for generating air-conducted sound is provided between the first diaphragm and a top surface of the unit case, a sound outlet that opens into the space is formed on the top surface of the unit case, and the sound outlet is covered with an acoustic damping material.
The bone conduction speaker according to claim 1, wherein the acoustic damping material is made of nonwoven fabric, open-cell foam, or other breathable material, and has a density that provides the desired acoustic resistance.
The bone conduction speaker of claim 1, wherein the first diaphragm is made of ABS, polycarbonate or other molding material, and has an outer diameter and thickness set to obtain a desired high-frequency resonance frequency.
The bone conduction speaker of claim 3, wherein the first diaphragm is made of the same material as the unit case.
The bone conduction speaker according to claim 1, wherein the spacer has an outer diameter and mass that provide a desired low-frequency resonance frequency.
The bone conduction speaker according to claim 1, wherein the elastic material is a damping material such as PORON (registered trademark), silicone sponge, or the like, capable of lowering the peak value of the low-frequency resonance frequency.
The bone conduction speaker according to claim 1, wherein the second diaphragm is made by etching a thin metal circular spring plate, with the central circular part connected to the peripheral part via an arc-shaped connecting band.