The use of subwoofer
——As a part of the home theater system, it is responsible for regenerating the low-frequency sound effects in the sound effects of the movie, which is used to supplement the low-frequency volume experience of the main speakers or the low-frequency and extremely low-frequency areas that cannot be reached.
Classification of subwoofers:
It can be divided into active subwoofer and passive subwoofer according to whether it has built-in amplifier.
According to the cabinet design, it can be roughly divided into bass reflex design, belt type design, transmission line design, etc.
According to the direction of sound, it can be divided into front sound, rear sound, ground sound, top sound and left and right sound.
Differentiated by single action mode, there are push-pull type composed of two horns, in-phase sound type composed of two or three, and in-phase sound type composed of single passive radiator.
Among them, the most ideal subwoofer is a set of bass equalization lines in addition to the built-in amplifier, which can moderately attenuate the indoor low-frequency standing waves to a certain degree, so that the low frequency bands below 100HZ or 80HZ can be compared Straight frequency response curve. Of course, the gun of this design is also quite expensive.
Closed subwoofer
The cabinet itself is airtight, there are no holes or gaps to communicate with the outside world, and the bass unit can be placed facing the front, back, left, right, up and down. This kind of cabinet is the simplest in manufacturing, and it is easy to meet the quality requirements. It has a quick response and can withstand a large power. At the same time, the volume of the cabinet can also be made relatively small.
Bass reflex subwoofer
The cabinet itself has one or more bass reflex holes, so that the front wave of the woofer in the cabinet can pass out of the body through the bass reflex hole and be mixed with the positive wave of the woofer, thereby increasing the sense of low frequency. The distortion is relatively low, and the power amplifier is relatively large. Compared with the closed cabinet, the lowest cut-off frequency of the bass reflection type can be lower. But the instant response is not as good as the closed cabinet.
Band Subwoofer
The belt-type cabinet design usually includes two independent cabinets, one hidden inside and one communicated with the outside through a bass reflex hole. The box hidden inside is closed. The woofer is installed in this closed room, and the diaphragm faces the other box outside.
This woofer is not visible from the exterior of the cabinet. When the woofer starts to move, the air driving the outside chamber through the bass reflex hole forms an acoustic wave filter, which produces four order filtering effects on a certain frequency band. Withstand power is the most of the different cabinet designs. The instant response is only inferior to the closed design. This design cost is too high is relatively rare.
Transmission line type subwoofer
Inside, there must be a closed pipe from big to small. The big end is connected to the back of the woofer unit to receive the back wave of the unit. The small end is the exit. The length of the pipe must be at least a quarter of the wavelength of the lowest cut-off frequency, and the inner wall of the pipe needs to be equipped with appropriate sound absorbing material.
The function of the pipeline is to use the back wave of the bass unit to extend the low-frequency cut-off frequency downwards to achieve a lower frequency response. Low frequencies can extend lower. The manufacturing cost of the transmission subwoofer is also the most expensive, so this design of the gun is even rarer.
Passive subwoofer (that is, passive subwoofer)
In the early days, there was no dedicated driver amplifier in the subwoofer, only the passive crossover network responsible for crossover. This kind of gun was called a passive subwoofer (also called passive subwoofer).
It has no driving capability and must be driven by an external power amplifier. The music signal is obtained from the output of the power amplifier. It also has a set of signal output terminals to pass the demultiplexed music signal to the main box. Since the main tank and the gun are driven by the same power amplifier, the driving force of the power amplifier will be dispersed as the load increases. Now such guns are very rare.
Active subwoofer (i.e. active subwoofer)
With the development of a home theater surround multi-channel system, the subwoofer must have a built-in amplifier. Therefore, low-level music signals can be obtained from the subwoofer output of the AV amplifier.
In addition, general active subwoofers will also have high-level input and output terminals, that is, the use of speaker cables to connect. In home theaters, it is impossible to connect the speaker with a speaker cable, because either the AV amplifier or the decoded subwoofer signal output is output through the low-level RCA terminal or the CLR terminal, and is not output from the speaker cable terminal. If you add a cannon to the two channels, you can pass the music signal to the cannon through the second output of the previous stage or the second stage.
What amplification method does the built-in amplifier of the subwoofer use?
Most of the built-in amplifiers of active subwoofers use Class D amplification. In this way, the efficiency is very high, no heat, the output power can easily reach hundreds of watts or even kilowatts, and the cost is low.
The bandwidth of the woofer is about 20HZ ~ 150Hz, and the distortion of the D-type amplifier is relatively high, which is not conducive to the disadvantages of medium frequency and high frequency band. There are also a few high-end subwoofers that insist on using the AB type method. The area of ​​the heat sink on the back of this kind of gun is bound to be quite large. The heat sink required for the output power of hundreds of watts is as large as the heat sink of a power amplifier of hundreds of watts.
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