Purpose of subwoofer
As a part of home theater system, it is responsible for reproducing low-frequency sound effects in movie sound effects, and is used to make up for the insufficient low-frequency volume of the main speakers, or the low-frequency and ultra-low-frequency areas that cannot be reached.
Differentiation of subwoofers
If it is differentiated by whether it has a built-in amplifier, it can be divided into two types: active subwoofers and passive subwoofers. If it is differentiated by the box design, it can be roughly divided into bass reflex design, bandpass design, transmission line design, etc. If it is differentiated by the sound direction, it can be divided into sound emitting to the front, sound emitting to the back, sound emitting to the ground, sound emitting to the top, and sound emitting to the left and right sides, etc. If it is differentiated by the single-unit action mode, there is a push-pull type composed of two speakers. The same-phase sound type composed of two or three, and the same-phase sound type composed of a single passive radiator. Among them, the most ideal subwoofer is designed with a set of bass equalization circuits in addition to the built-in amplifier, which can moderately attenuate the indoor low-frequency standing waves to a certain extent, so that the low-frequency band below 100HZ or 80HZ can achieve a relatively flat frequency response curve. Of course, the price of this design is also quite expensive.
Sealed subwoofer
The box itself is sealed, with no holes or gaps connecting to the outside world. The bass unit can be placed facing the front, back, left, right, up, or down. This type of box is the simplest to manufacture and is easy to meet quality requirements. It has a fast instantaneous response and can withstand a large power. At the same time, the box size can also be made relatively small.
Bass reflex subwoofer
The cabinet itself has one or more bass reflex holes, which allow the front wave of the woofer unit in the cabinet to pass out of the cabinet through the bass reflex holes and mix with the positive wave of the bass unit to increase the volume of the low frequency. The distortion is relatively low and can withstand a relatively large power amplifier. Compared with closed cabinets, the lowest cut-off frequency of bass reflex cabinets can be lower. However, the instantaneous response is not as good as that of a closed box.
Bandpass subwoofer
Bandpass cabinet design usually includes two independent chambers, one hidden inside and one connected to the outside by a bass reflex hole. The hidden chamber is sealed. The bass unit is installed in this sealed chamber, with the diaphragm facing the other chamber outside. The bass unit cannot be seen from the outside of the cabinet. When the bass unit starts to move, it drives the air in the outer chamber through the bass reflex hole to form a sound wave filter, which produces a four-order filtering effect on a certain frequency band. The power handling is the highest among all different cabinet designs. The instantaneous response is only inferior to the sealed design. This design is too expensive and is relatively rare.
Transmission line subwoofer
There should be a sealed pipe that gradually decreases from large to small inside. The large end is connected to the back of the bass unit to receive the unit back wave, and the small end is the outlet. The length of the pipe should be at least one-fourth of the wavelength of the lowest cutoff frequency, and the inner wall of the pipe needs to be placed with appropriate sound-absorbing materials. The function of the pipe is to use the back wave of the bass unit to extend the low-frequency cutoff frequency downward to achieve a lower frequency response. The low frequency can extend lower. The cabinet manufacturing cost of the transmission-type subwoofer is also the most expensive, so this design of subwoofer is even rarer.
Passive subwoofer
In the early days, there was no dedicated driver amplifier in the subwoofer, only a passive crossover network responsible for frequency division. This type of cannon is called a passive subwoofer or a passive subwoofer. It has no driving ability and must be driven by an external power amplifier. The music signal is obtained from the output end of the power amplifier, and it also has a set of signal output terminals to transmit the music signal after the crossover to the main box. Since the main box and the cannon are driven by the same power amplifier, the load of the power amplifier will increase and the driving force will be dispersed. This type of cannon is now very rare and thankless.
Active subwoofer
With the development of home theater surround multi-channel system, subwoofer must have built-in amplifier. Therefore, low-level music signal can be obtained from the subwoofer output terminal of AV amplifier. In addition, active subwoofer will also have high-level input and output terminals, that is, it is connected by speaker cable. In home theater, it is impossible to connect the cannon with speaker cable, because the subwoofer signal output of AV amplifier or decoder pre-stage is output through low-level RCA terminal or CLR terminal, not output from speaker cable terminal. If there is a cannon in two channels, the music signal can be transmitted to the cannon through the second set of output of the pre-stage or the post-stage.