There are permanent magnets and voice coils in the speaker unit: the permanent magnets generate a magnetic field in the annular air gap of the magnetic circuit through the yoke, and the voice coil connected to the speaker diaphragm is inserted into the annular air gap. The voice coil is a cylindrical object wound by an elongated metal wire. The current signal output from the amplifier passes through the voice coil to form an electromagnetic field according to the principle of electromagnetic induction.
When the sound passes through the voice coil in the form of current, a correspondingly varying electromagnetic field is generated according to the strength and frequency of the current, and the direction of the magnetic field is determined according to Faraday's right-hand law. The magnetic properties of the electric coil change continuously with the intensity of the current, and interact with the permanent magnet to generate vibration, which drives the diaphragm to move the piston, and then emits sounds of different frequencies and strengths.
Phase plug
In fact, the ultimate goal for all sound systems is to faithfully restore the original appearance of the sound source. So any form of tone is actually a distortion. Therefore, various methods should be taken to avoid such distortion.
The phase plug can avoid the problem of splitting the common dust cover and can help the heat dissipation of the magnet system to withstand higher power, and also short-circuit the eddy current in the voice coil to reduce distortion. Therefore, in addition to consolidating the diaphragm, the phase plug can also improve the high-end off-axis frequency response diffusion characteristics of the unit and improve the audiovisual performance, while balancing the air pressure in front of the diaphragm to significantly reduce distortion; another advantage is to prevent the direction near the point of separation. A sudden change in characteristics to avoid midrange rendering.
The working principle of the phase plug first look at the structure of the speaker unit 
In the above picture, you can see the structure of the various parts of the speaker unit (compensation magnet and magnetic shield ensure that the speaker can be placed next to the display without magnetization effect) 
The figure below shows the unit structure of the Z-680. You can see a phase plug instead of the traditional dust cover.
While the speaker unit is operating, the diaphragm is moving and the phase plug remains constant. It is this movement that lays the working principle of the phase plug.
When the diaphragm is moved in front and rear of the piston, the resulting sound waves radiate outward to form a sound. However, not all sound waves diffuse directly outward, and some of the sound waves will be cross-reflected on the diaphragm before being sent to the listener's ear. The acoustic wave reflection path generated on the left diaphragm can be seen in the following illustration. In a traditional unit, the sound waves will be reflected to the other side and then reflected to the listener. Since these sound waves are actually generated at the same time but are heard at different times, this forms a standing wave distortion. The phase plug can quickly emit the second reflected wave, reducing the hysteresis time. Therefore, the phase plug can effectively improve the frequency response characteristics, prevent standing wave and crossover distortion, and make the off-axis frequency response diffusion characteristics and the axial frequency response diffusion characteristics smoother, avoiding the off-axis frequency response often occurring in multimedia speakers. Peak and valley phenomenon. 
In addition, the dust cover on the conventional unit increases the quality of the diaphragm. We know that the diaphragm must have the characteristics of light weight, high rigidity and high internal damping to get close to perfect piston motion. Therefore, this will reduce the sensitivity of the unit, and the unit with the phase plug is more sensitive than the unit. 
At the same time, an air cavity is formed behind the dust cover. When the diaphragm moves as a piston, the cavity will be compressed or stretched in the opposite direction, causing a decrease in efficiency. In addition, when the current passes through the voice coil, a large amount of Heat, and an increase in temperature will increase the impedance of the speaker unit, requiring more current to drive, causing a decrease in efficiency. However, the voice coil and the drive magnet are sealed inside the unit and cannot be in direct contact with the outside air, so the heat dissipation is very slow. The phase plug has two features that help to dissipate heat:
1. Because the characteristics of aluminum metal itself will be used as a huge heat capacity;
2. The phase plug is directly exposed to the air and can dissipate heat quickly.
36 Inch Ceiling Fan,36 Inch Outdoor Ceiling Fan,36 Inch Indoor Ceiling Fan,Ceiling Fans 36 Inch With Light
Jiangmen MagicPower Electrical Appliances Co.,Ltd. , https://www.magicpowerfan.com