JPS6247040B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of an electroacoustic transducer used in transmitting sound waves underwater or in the air. Simply put, an electroacoustic transducer is a transmitter for underwater use, and a speaker for use in air. Since the basic principle is the same for both types, we will mainly explain the electrodynamic type transmitter as an example.

Conventionally, electromagnetic type and electrodynamic type transmitters, as shown in Figure 1 or 2, attach a magnet 3 to a case 2 to create a DC magnetic field, and place a diaphragm 1 in this magnetic field. It had a structure in which a driving winding 4 was fixed to either the plate 1 or the magnet 3. When an alternating current from an oscillator 5 was passed through the driving winding 4, the transmitter generated vibrations approximately proportional to the magnitude of the current.

However, the one shown in FIG. 1 is suitable for small vibrations, and has the disadvantage that the diaphragm remains attracted to the magnet when vibrated at large amplitudes. Also the second
Although the type shown in the figure can vibrate with a large amplitude, it has the same drawbacks as the one shown in FIG. 1, such as complex vibrations parasitizing the diaphragm support 9 that provides restoring force.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electroacoustic transducer that overcomes these drawbacks, is capable of large-amplitude operation, and does not generate complex parasitic vibrations.

In order to achieve the above object, an electroacoustic transducer according to the present invention includes at least one diaphragm, at least one diaphragm, and two magnetic parts, at least one of which is interlocked with the diaphragm, and which are placed opposite each other. and,
A case that houses the two magnetic parts, an O-ring gasket that supports the magnetic part that works with the diaphragm in the case, and a case that generates magnetic fields such that the two magnetic parts generate opposite directions in the vibration direction of the diaphragm. and means for supplying a drive current to at least one of the two magnetic parts, and the pressure is reduced between the two magnetic parts surrounded by the case.

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 3a shows the first embodiment, in which the diaphragm 1
The drive winding 4 is fixed to the diaphragm support part 10 of the opening of the case 2, and the magnet 3' is further fixed to the bottom thereof (hereinafter, this assembly will be collectively referred to as the diaphragm assembly). It is fitted through a ring casket. Another magnet 3 is fixed inside the bottom of the case, and a pressure reducing valve 6 is provided near the bottom of the case. The above-mentioned magnets 3 and 3' are flat plate-shaped with smooth surfaces, magnetized in the thickness direction, and are opposed to each other in a direction in which they repel each other. Therefore, the magnet 3' balances the weight of the diaphragm assembly and remains stationary with a gap. However, the diaphragm 1 must be supported so as not to protrude outside the case, and must be supported as softly as possible to avoid causing complex vibrations. Therefore, a vacuum pump is connected to the pressure reducing valve 6 to reduce the air pressure inside the case 2. In the present invention, an O-ring gasket is adopted as the diaphragm support part 10, and since the O-ring gasket hardly impedes the piston movement of the diaphragm, the diaphragm assembly is attracted to the case side, and the spacing between the magnets becomes narrower. Balanced by interval D. D
is an effective means for increasing the electroacoustic conversion efficiency by narrowing the interval to a value close to the required amplitude of vibration.
Due to this pressure reduction, the air resistance (impedance) between the two magnetic parts inside the case 2 becomes smaller, thus making it possible to reduce the driving force of the vibrator. This greatly contributes to improving electroacoustic conversion efficiency. Next, the operation when the oscillator 5 is connected to the drive winding 4 and an alternating current is caused to flow will be described. When an alternating current is passed through the signal winding 4, an alternating current magnetic field is generated in the axial direction of the diaphragm in response to the alternating current, which is superimposed on the direct current magnetic field of the magnet 3' to increase or decrease the magnetic field. As a result, the diaphragm assembly is more repelled or attracted from its initial rest position, vibrates in response to the alternating current, and emits sound waves from the outer surface of the diaphragm. As for the magnet, a ferrite magnet is advantageous because of its low loss in the alternating magnetic field. According to this structure, since the driving force and the restoring force are applied to almost the entire surface of the diaphragm, the generation of parasitic vibrations is reduced and desired vibrations can be obtained. Another major feature is that the restoring force produced by this method is a simple elastic body when viewed from the diaphragm, and since the compliance is large, it is possible to easily manufacture a device with a low resonance frequency.

The above explanation is about a transmitter with a structure in which sound is radiated from one side of the case 2, but as shown in Fig. 3b, a structure in which the part of the case 2 facing the diaphragm 1 is replaced with a diaphragm 1' is also available. Then, it is possible to obtain a transmitter having a structure that emits compressional waves of the same phase from both sides of the case 2 using exactly the same principle. This double-sided radiation structure is advantageous when omnidirectionality is required, and since the radiation impedance can be high, the radiation efficiency is high and the utility value is high.

FIG. 4 shows a second embodiment of the invention. The principle is the same as that of the first embodiment, but both magnets are replaced with coils, and a DC power source 7 causes a DC current to flow so as to generate mutually repelling magnetic fields. Since coils can be made lighter in mass than magnets, they are advantageous when manufacturing transducers used up to high frequencies. This example shows a case where the DC magnetic field coil and the drive winding are shared. In this case, the driving force is the product of both magnetic fields, so the frequency of the driving force is twice the frequency of the current. Therefore, when used at a resonant frequency, the signal current must have a frequency that is 1/2 of the resonant frequency. It goes without saying that only one side in this example may be a magnet, and the current frequency in this case becomes the vibration frequency. In the figure, 5 indicates an oscillator, and 8 indicates a decoupling capacitor.

As explained above, the present invention creates a set of direct current magnetic fields that repel each other, and by making the diaphragm engage in space without using a mechanical elastic body, parasitic vibration is reduced and low frequency A transmitter that resonates at

Furthermore, this structure has the following advantages when used as a speaker. (1) As mentioned above, since the resonant frequency can be set high, a wide band frequency characteristic can be obtained. (2) Normally, a speaker has a case covering the back of the diaphragm, and a sound-absorbing material is placed inside to prevent the air inside the case from resonating or causing the box to vibrate through the air. In addition, the case is extremely large in size to avoid reactions of the air inside the case, but according to the structure of the present invention, the air pressure inside the case is low, so even though it is small, there is little reaction and there is no sound-absorbing material. It is also possible to suppress resonance to a low level.

[Brief explanation of the drawing]

1 and 2 are sectional views of conventional electromagnetic type and electric type wave transmitters, and FIGS. 3a and 3b and 4 are sectional views showing embodiments of the present invention. 1, 1'...Diaphragm, 2...Case, 3,3'...
... Magnet, 4 ... Electrodynamic winding, 5 ... Oscillator, 6 ... Pressure reduction valve, 7 ... DC power supply, 8 ...
...decoupling capacitor, 9,10...diaphragm support part.

Claims (1)

[Claims] 1. At least one diaphragm, two magnetic parts, at least one of which is interlocked with the diaphragm and are placed opposite each other, a case that accommodates these two magnetic parts, and a magnetic part that interlocks with the diaphragm. an O-ring gasket supported by the case; means for causing the two magnetic parts to generate magnetic fields reciprocally in the vibration direction of the diaphragm; and means for supplying a drive current to at least one of the two magnetic parts. An electroacoustic transducer, comprising: reducing the pressure between the two magnetic parts surrounded by the case.