JPS6161759B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electroacoustic transducer having a double sound emitting structure composed of a diaphragm and a sound emitting plate.

Conventionally, a double diaphragm structure in a speaker has been widely used in alarms such as watches as an effective structure for improving waterproofness, temperature dependence of sound pressure, tone color, etc. Its structure is shown in the simplified diagram of FIG. Here, 1 is a diaphragm directly driven by a converter 2 having an electrodynamic type, electromagnetic type, or other driving method, and 3 is a sound emitting plate (second diaphragm).
It is. 4 is a speaker frame forming a Helmholtz resonator, and 5 is a frame.

Furthermore, a speaker using a piezoelectric element, particularly a polymer piezoelectric element such as 8VDF, has a structure as shown in FIG. 2, where 6 is a polymer piezoelectric film, 7 is a foamed resin, and 8 is a It is a frame. However, this type of speaker has a low acoustic output, so it is mainly used as a headphone.

These electro-acoustic transducers are electrical → mechanical → acoustic,
In other words, it only has the function of a speaker,
Audio equipment that needs to input and output sound must be equipped with a microphone in addition to these speakers. However, as audio equipment becomes smaller and thinner, dividing the audio I/O section into two parts poses great design difficulties and is disadvantageous in terms of cost.

It is an object of the present invention to eliminate the above-mentioned drawbacks, to integrate a microphone and a speaker without degrading their performance, and to facilitate the design of small-sized audio equipment.

The present invention will be described in detail below with reference to the embodiments shown in the drawings, but first the difference in driving principle between the microphone and the speaker will be briefly described.

The acoustic output P of the speaker can be expressed as follows, assuming that the radiation area and driving force are constant.

P=C ₁ ω ² / | Zm | ² [W] (1) Here, C ₁ is a constant, ω [rad/s] is the angular frequency,
Zn is the mechanical impedance, and the angular resonance frequency is ω
If ω>ωo, then Zm≒jwm, where m
[Kg] is the total effective mass of the vibration system, and when ω<ωo, Zm=
1/jwCm, where Cm [m/N] is the vibration system support compliance. Therefore, from equation (1), in order for the acoustic output P to remain constant regardless of the frequency, it is necessary that Zm≈jwm. In other words, when ω>ωo, the acoustic output becomes P = C ₁ /m ² (2) and becomes constant. This means that the resonant frequency is the lower limit of the actual reproduction band, and this is called inertial control.

On the other hand, in the case of a pressure microphone, the diaphragm is
When receiving a driving force proportional to P [N/m ³ ] and assuming that the voltage sensitivity is E/P (where E is the electromotive force), when the driving force is constant, E/P must be constant regardless of the frequency. It won't happen. The way to express voltage sensitivity differs depending on whether the acoustic → mechanical → electrical converter is an electromagnetic type, an electrostatic type, or a resistance control type, but if we take the piezoelectric type (electrostatic type) here, E/〓=C ₂ /jωZm (3). Here, C ₂ is a constant, and Zm is a mechanical impedance like a speaker. Therefore, from the above formula,
In order for E/P to be constant regardless of frequency,
It is necessary that Zm≒1/jωCm, that is, ω<ωo, and then the voltage sensitivity is expressed as the following equation.

E/〓=C ₂ Cm (4) This means that the resonant frequency is the upper limit of the constant sensitivity band, and is called elastic control.

As mentioned above, the control methods for a speaker and an electrostatic microphone are different, and good characteristics cannot be obtained in principle if either one is used as both a microphone and a speaker.

The present invention solves this problem and provides a microphone/speaker having a structure in which elastic control is performed when used as a microphone, and inertial control is performed when used as a speaker.

In other words, the resonant frequency f ₀ of the speaker diaphragm is set to the lower limit of the reproduction band, and the resonant frequency f 0 of the microphone diaphragm (sound emitting plate when operating as a speaker) is set to the lower limit of the reproduction band.
By setting f ₀ ′ to the upper limit, each operation can be performed using the correct control method.

As shown in FIG. 3, 9 is a piezoelectric film having a resonance point in the high frequency range, and serves as a diaphragm when used as a microphone, and as a sound emitting plate when used as a speaker. Since the f ₀ ' of the piezoelectric film is too low if the film alone is used, it is also possible to attach a piezoelectric film 11 to a plastic or metal substrate 10 and set f ₀ ' to an appropriate value, as shown in Fig. 5. . 12 is a diaphragm to which a movable iron piece 13 is fixed by welding, gluing, etc.; 14 is a magnet;
15 is a coil, 16 is a magnetic core, 17 is a support frame, 18
is the speaker frame. The f ₀ of the diaphragm, the resonant frequency fa of the resonance chamber, and the f ₀ ′ of the sound emitting plate are respectively the buzzer sound,
It can be designed to an appropriate value depending on the type of input/output sound such as voice or music. For example, for audio, f ₀ =
You can choose 1KHz, fa = 4KHz, f ₀ ′ = 10KHz, etc.

FIG. 4 shows another embodiment of the present invention, in which the speaker is driven by an electrodynamic type. 19 is a diaphragm to which a voice coil 20 is fixed, and a magnet 21, a pole 22, and a yoke 23 constitute a magnetic circuit. Further, 24 is a piezoelectric film sound emitting plate,
25 is a speaker frame, and 26 is a frame. Since the electrodynamic speaker has a wider reproduction band than the electromagnetic speaker, the Helmholtz resonance chamber formed by the speaker frame 25 is not necessarily required. The same can be said for the electromagnetic type, but the shape of the diaphragm and sound emitting plate is not limited to a flat surface, but various shapes can be considered, such as those with edges, cones, and domes. In this case as well, f ₀ ' of the piezoelectric film (sound plate) is set to the high frequency limit of the microphone, and f ₀ and fa of the diaphragm and resonance chamber are selected depending on the type of sound to be reproduced.

As described above, according to the configuration of the present invention, it is possible to obtain an integrated microphone and speaker that satisfies the control method of the microphone and the speaker without any deterioration in the performance of each, which facilitates the design of compact audio equipment and reduces cost. It also has the effect of being advantageous.

[Brief explanation of the drawing]

Fig. 1 shows a conventional speaker with a double diaphragm structure, Fig. 2 shows a conventional speaker using a polymer piezoelectric element, Figs. 3 and 4 show a microphone/speaker according to the present invention, and Fig. 5 shows a radio speaker. This shows the structure of a tone plate. 1, 12, 19...Diaphragm, 3...Sound emitting plate, 2
... Electroacoustic transducer, 6, 9, 24, 11 ... Polymer piezoelectric film, 10 ... Plastic or metal plate.

Claims (1)

[Claims] 1. A microphone characterized in that, in an electromagnetic or electrodynamic electroacoustic transducer having a sound emitting structure using a double diaphragm, the sound emitting plate uses a polymer piezoelectric element to function as a diaphragm of the microphone. Cum speaker.