Abstract: In view of the shortcomings of traditional speakers, a design of a flat panel speaker is proposed. The speaker is composed of a soft magnetic material, a voice coil, a flat sounding disk, a circular conductive coil, and a bias magnetic coil, and the voice coil is fixed on a semi-closed magnetic circuit formed of a soft magnetic material, and a current formed by the sound image generates mutual magnetic resonance through the conductive ring. In turn, the sounding disk is forced to vibrate, thereby causing the diaphragm of the speaker to vibrate and sound. Practice shows that the speaker has the characteristics of wide frequency response, high power, small distortion and simple structure. It can meet the requirements of high-fidelity audio and home theater systems, and can be applied to the miniaturization requirements of multimedia audio systems. It has a good application prospect. .
Keywords: flat panel speaker; soft magnetic material; voice coil; bias coil
0 Introduction Traditional loudspeakers use a voice coil to propel a fixed-sized cone of paper. The structure and characteristics of the loudspeakers determine that the loudspeakers cannot be flattened and miniaturized. Secondly, the fixed diameter of the vibrating basin makes the speaker passband narrow and the amplitude-frequency characteristic is very poor. The whole frequency response characteristic has a single-peak characteristic at its mechanical resonance frequency point, so that the high-fidelity speaker has to be high, medium and low. The speaker is implemented by a frequency division combination. The voice coil is a pusher and part of the sounding body. Its own mechanical structure and performance conflict with each other. Especially in high-fidelity systems, to achieve a large dynamic range, the power is required to be large, so that the voice coil is The mechanical strength requirements are high, the coil has to be made stronger, but the mechanical inertia of the voice coil is increased, and the high-frequency characteristics are greatly reduced. In order to meet the requirements of both mechanical strength and high-frequency characteristics, the voice coil usually works at the limit. In the environment, it is extremely easy to burn. Therefore, high-fidelity speakers designed and manufactured with conventional speakers are bulky, costly, and have poor reliability.
In order to meet the requirements of modern audio for the wide frequency response, wide directivity and miniaturization of the speaker, the flat panel speaker began to “surface†and showed its attractive application prospects with its outstanding advantages. More typical are NXT flat panel speakers and equal magnetic field belt speakers, but they all have shortcomings such as insufficient low frequency response and poor sound quality. This paper presents a flat panel speaker system. By analyzing its structure, it can be used as a sounding body for high-fidelity speakers, which can significantly improve the low-frequency response of the flat-panel speakers, making the frequency response characteristics of the flat-panel speakers flatter.
1 Flat speaker structure and principle
1.1 Structure of the flat panel speaker The structure of the flat panel speaker is shown in Figure 1. It is mainly composed of soft magnetic material, voice coil, flat sounding disc, circular conductive coil and bias magnetic coil. The structure requires that the voice coil be fixed on a semi-closed magnetic circuit with a soft magnetic material as a support. The vibration sounding disk is a four-side fixed tension flexible conductive disk or a flexible circle with a plurality of (three or more) concentric conductive rings embedded therein. The disc is constructed and the magnetic circuit is completely passed through the vibrating plate. The function of the biasing coil is to add a suitable DC or super-audio AC bias current when the loudspeaker is working, so that the audio magnetic field in the magnetic circuit avoids the nonlinear region of the magnetization curve.
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The structure of the flat speaker sounding disk is shown in Fig. 2. Fig. 2(a) shows the sounding disk of the annular conductive ring. The inner conductive coil is embedded in the inner part of the ring. The distribution of the sound is required to be as dense as possible. Preferably, the inner aperture determines its high frequency characteristics. The larger the ratio of the inner and outer annular conductive coil diameters of the sound disk, the wider the amplitude frequency characteristic, the more the number of conductive rings, the more uniform the distribution, and the flatter the amplitude-frequency characteristics of the speaker. Fig. 2(b) is a flexible conductive disk composed of a flexible conductive film or a flexible metal mesh film, which requires good flexibility. The outer diameter of the vocal disc mainly determines the low frequency characteristics of the speaker, and the larger the lower the frequency characteristics, the wider the amplitude frequency characteristic.
1.2 Working principle of flat panel speaker When the audio current amplified by the power amplifier passes through the voice coil, the audio magnetic flux generated by the audio current in the soft magnetic material passes through the sounding disc, and the conductive loops in the flat sounding disc generate mutual magnetic flux. The mutual magnetic field interacts with the audio magnetic field to force the sounding disk to produce mechanical vibration of the sound and sound. Since the magnetization curve of the soft magnetic material is non-linear, the zero-crossing point of the audio current causes a large distortion. Therefore, a biasing coil is added to the magnetic circuit, and a constant DC or super-audio AC bias current is applied to accurately adjust the magnitude of the bias current and the amplitude of the audio signal, so that the audio flux avoids the nonlinear region of the magnetization curve.
2 Tablet speaker application and feature analysis
2.1 Flat panel application The application of the flat panel speaker is shown in Figure 3. The super audio AC oscillator circuit or DC regulated power supply provides the bias current for the bias coil, and R is the current limiting resistor. Short-circuit audio flux, R is required to be as large as possible. RW is the best bias regulator. Adjusting its size ensures that the DC (or AC) bias applied to the speaker just makes the magnetic field of the audio signal linear in the magnetization curve of the soft magnet. Middle of the paragraph. The audio signal outputted by the power amplifier is added to the voice coil, and the audio current is converted into a magnetic field of the audio change. The magnetic field passes through the conductive rings of the sounding disk, and the mutual magnetic field of each conductive ring interacts with the audio magnetic field to promote the high fidelity of the sound disk. Sound field.
2.2 Analysis of the characteristics of the flat panel speaker The flat panel speaker has the characteristics of wide frequency response, high power, small distortion, thin body shape, random shape, simple structure, convenient processing, not easy to break and no magnetic interference.
(1) The frequency response is wide. Since the speaker vibration sounding disk is embedded with a plurality of radially arranged concentric conductive rings, the radius of each ring is different, and each ring has a different mechanical resonance frequency when acting alone, and the more the number of conductive rings, the more uniform the distribution. The flatter the amplitude-frequency characteristic of the speaker, the smaller the amplitude-frequency characteristic of the single-peak peak is not fixed in the conventional speaker. The larger the outer-outer ratio of the sounding disk, the wider the amplitude-frequency characteristic; it is easy to implement on one speaker. Flat amplitude-frequency characteristics from 20 Hz to 20 kHz.
(2) The output power is large. Since the voice coil is fixed on the magnetic circuit, it can be made thicker and stronger. There is no traditional speaker voice coil which is easy to burn, easy to vibrate and loose, and the circular conductive coil in the sound plate further strengthens the sound film. It has stronger mechanical properties than traditional speaker sounding membranes, resulting in greater output power.
(3) The distortion is small. The flat panel speaker adds a biasing magnetic coil to the magnetic circuit, and the appropriate DC or super audio AC bias current is added to the bias coil when the speaker is working, so that the audio magnetic field in the magnetic circuit avoids the nonlinear region of the magnetization curve, and the audio signal The magnetic field is applied to the sound disk with almost no distortion, so that the distortion of the speaker is very small.
(4) The body is thin. The speaker uses a flat sound plate, so the speaker can be made thin, and its thickness is mainly determined by the space required for the magnetic circuit structure and the vibration of the sound disk.
(5) The shape design is arbitrary. In the speaker, as long as the magnetic flux passes through the center hole of the sound plate, there is no requirement for the shape of the magnetic circuit, and the sound plates do not have to be circular, and they can be designed into any shape according to aesthetic and mechanical requirements. The surface is the best place to live in a variety of art paintings.
(6) The structure is simple, the processing is convenient, and it is not easy to be damaged. The magnetic circuit of the speaker has a simple structure, and the matching precision of each part is not high. The voice coil, the magnetic circuit and the sound disk can be installed by the ordinary user after being manufactured by the manufacturer. Since the sound plate uses a plurality of conductive ring driving methods, even if a certain portion of the conductive ring is damaged, the other rings can still work normally without causing a fatal effect on the speaker. The traditional voice coil drive method, once the voice coil is burned out, can no longer be used.
3 Conclusion The biggest advantage of flat panel speaker technology is the small size, which is very consistent with the trend of miniaturization of modern hardware devices. The designed flat panel speaker can meet the wide frequency response and wide directivity required by high-fidelity audio and home theater systems, and can also be applied to the miniaturization requirements of multimedia audio systems, and has a good application prospect.
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