Use of the subwoofer
As part of the home theater system, it is responsible for reproducing the low-frequency sound in the sound of the movie, which is used to make up for the low-frequency feeling of the main speaker, or the low-frequency and extremely low-frequency fields that cannot be achieved.
Subwoofer
If you distinguish between built-in amplifiers, you can divide two active subwoofers and passive subwoofers. If the box design is divided, the bass reflection design, the belt design, and the transmission line design can be roughly divided. If it is distinguished by the direction of sounding, it can be divided into sounding toward the front, making sounds toward the back, making sounds toward the ground, making sounds toward the top, and making sounds on the left and right sides. If it is distinguished by a single action mode, there is a push-pull type consisting of two speakers. In-phase sounding consisting of two or three, in-phase sounding consisting of a single passive radiator. Among them, the most ideal subwoofer is designed with a set of bass equalization lines in addition to the built-in amplifier. It can moderately attenuate the indoor low-frequency standing waves to a certain extent, so that the low frequency bands below 100HZ or 80HZ can be compared. Straight frequency response curve. Of course, the price of the gun in this design is also quite expensive.
Closed subwoofer
The box itself is sealed, and there is no hole or gap communicating with the outside world. The woofer unit can be placed facing the front, back, left, and right. This kind of box is the easiest to manufacture, and it is easy to meet the quality requirements. It has a quick response and can withstand large power. At the same time, the volume of the box can be made smaller.
Bass reflex subwoofer
The box itself has one or more bass reflex holes, so that the front wave of the woofer in the box can be transmitted out of the box through the bass reflex hole, and 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. The minimum intercept frequency of the bass reflex type can be lower than that of the closed case. However, the instantaneous reaction is not as good as the closed cabinet.
Belt type subwoofer
The belt-like housing design usually consists of two separate compartments, one hidden inside and one connected to the outside by a bass reflex hole. The box hidden inside is sealed. The woofer is mounted in this confined chamber with the diaphragm facing the other compartment outside. This woofer is not visible from the appearance of the cabinet. When the woofer starts to move, the air that drives the outer chamber passes through the bass reflex hole, forming an acoustic wave filter that produces four steps of filtering for a certain frequency band. Withstand power is the most different design of different cabinets. The transient response is only inferior to the closed design. This design cost is too low to be rare.
Transfer line subwoofer
There should be a closed pipe from the inside to the outside, the big one is connected to the back of the woofer, the back of the unit is back, and the small one is the exit. The length of the pipe must be at least one quarter of the wavelength of the lowest cutoff frequency, and the inner wall of the pipe needs to be placed with appropriate sound absorbing material. The function of the pipe is to extend the back wave of the woofer to extend the low frequency cutoff frequency to achieve a lower frequency response. The low frequency can be extended lower. The transmission cost of the transmission subwoofer is also the most expensive, so the gun of this design is even rarer. Welcome to China Home Theater Network
Passive subwoofer
In the early days, there was no special drive amplifier in the subwoofer. Only the passive crossover network responsible for frequency division was called a passive subwoofer. It was also called a passive subwoofer. There is no driving capability, it must be driven by an external power amplifier. The music signal is taken from the output of the power amplifier. It also has a set of signal output terminals to transmit the music signal that has been split to the main box. Since the main box and the gun are driven by the same power amplifier, the load of the power amplifier is increased and the driving force is dispersed. Now this kind of cannon is very rare, and it is not thankful.
Active subwoofer
With the development of a home theater surround multichannel system, the subwoofer must have a built-in amplifier. Therefore, a low level music signal can be obtained from the subwoofer output of the AV amplifier. In addition, the general active subwoofer will also have a high-level output terminal, which is to use the speaker cable to connect. In the home theater, it is impossible to connect the speaker cable, because the AV amplifier or the decoding pre-bass output is output via the low-level RCA terminal or CLR terminal, and is not output from the speaker cable terminal. In the case of a two-channel cannon, the music signal can be transmitted to the cannon through the second output of the previous stage or the subsequent stage.
[page]What is the magnification of the subwoofer built-in amplifier?
Most of the active subwoofer built-in amplifiers use Class D amplification. Because this method is very efficient, does not generate heat, the output power can easily reach hundreds of watts or even thousands of watts, and the cost is low. Moreover, the bandwidth of the woofer is about 20HZ-150Hz, and the distortion of the Class D amplifier is high, which is disadvantageous for the disadvantages of the medium frequency and the high frequency band in the use of the subwoofer. There are also a few high-end subwoofers that insist on using the AB type. The backside heat sink area of ​​such guns is bound to be quite large. The hundreds of watts of output power required for the heat sink is as large as a hundreds of watts of power amplifier heat sink.
Subwoofer must have input and output terminals
In the case of an active subwoofer, it must have a low-level output and an input. Some also have a Link Out to connect the second gun. High-level speaker line input and output. There must be crossover adjustment, volume adjustment, phase adjustment or phase switching. A few guns do not yet have a high-pass output. The so-called high-pass output is to filter out the frequency band below the crossover point, so that the frequency band above the crossover point passes. The low-pass output is inverted, allowing the band below the crossover point to pass.
Phase adjustment and phase switching
Phase adjustment is continuous or segmental adjustment from 0-270 degrees, while phase switching is only two phase shifts of 0 degrees or 180 degrees. Why do you need phase adjustment? Simply put, when the low frequency emitted by the subwoofer is mixed with the low frequency emitted by other speakers, if the phases of the two are the same or close, the total low frequency sense is the sum of the two. Welcome to China Home Theater Network
Conversely, if the phases of the two are opposite or close to each other, the total low frequency sense will be subtracted. Theoretically, when the gun is placed on the same horizontal line as the main box and the center, its low frequency phase should be the same as or close to the main box and the center. In fact, many factors can't place the gun on the same horizontal line as the main box and the center, but in the corner or side. At this point, the sound phase of the gun may be different from the other channels. It can be adjusted with phase adjustment.
The guns that switch between 0 and 180 degrees are best placed between the corners or the main speakers, as close as possible to the main or center channel. The 0-270 degree segmentless or segmented phase adjustment gun is more flexible. The selectivity is high. How to determine the phase of the adjustment is correct? You only need to use your ear to choose the frequency band that has the most abundant low-frequency sense. A pink noise test disc is a very good test software. Test the frequency of each segment from 20Hz to 150Hz, or select a single frequency to listen. A careful comparison will reveal the most abundant frequency bands.
Super subwoofer placement
The gun should also pay attention to the position as the main speaker, because the subwoofer will also be affected by the reflection of the adjacent wall or the ground, and the enhanced (positive phase) effect at certain frequencies will also produce offset at certain frequencies ( Reverse phase) effect. In addition, the low-frequency or low-frequency standing waves that are inevitable in the listening space also affect the performance of the subwoofer.
So, when you choose the position of the gun, the first thing to consider is: Do I need to increase the volume of the subwoofer by the low frequency enhancement of the wall solution. The second thing to consider is whether the standing wave (caused by the left and right channel elements) that originally existed in the listening space will enhance (positive phase) or cancel (invert) the sound waves of the subwoofer. That is, when we are placing the guns, we must not only consider the opposite phase of the sound waves between the gun and the left and right channels, but also consider the opposite phase between the gun itself and the adjacent ground and wall. problem.
The positive phase and inversion problems caused between the gun and the left and right channels can be solved by the phase adjustment of the gun. As for the positive phase and reverse phase problems caused by the gun itself and the wall surface, it can only be handled by the position of the gun, except for changes to the environment. Simple placement involves many complex considerations. The best way to solve this problem is to keep the sound waves reflected by the adjacent walls and the sound waves regenerated by the subwoofers in the same phase, that is, they are in phase with each other.
To maintain the four sound waves of the subwoofer, the ground, the side wall, and the rear wall, the safest method is to keep the reflected sound waves and the subwoofer sound waves within 90 degrees. If the 90 degree phase is converted to a wavelength, it is within a quarter wavelength.
However, since the sound wave will reach the wall and then be reflected back from the unit, the travel route is already twice, so we divide the quarter wavelength by two, which is the eighth calculation of the actual wavelength. can. For example: the choice of the gun's crossover point is 100Hz, then we take the highest 100Hz wavelength to calculate (other lower frequencies are covered).
The wavelength of 100 Hz is 340 meters (the approximate value of the sound wave per second speed) divided by 100 Hz, which is equal to 3.4M. The one-eighth wavelength of 3.4M is 42.5CM. Therefore, we should place the guns at a distance of no more than 42.5CM from the side wall, the back wall, and the ground. As a result, the sound waves reflected from the back wall, side wall and ground can be combined with the subwoofer unit. The main sound wave emitted maintains a positive relationship.
When all the reflected waves are in positive phase relationship with the main wave, it is the time when the low frequency is the most abundant. This is why the gun can be placed in the corner to get the most abundant low-frequency feeling. There is also the advantage of placing the gun in the corner, that is, because the low frequency is very good, you can turn down the volume, which means that the amplifier does not have to output so much power, and the unit does not have to move so fiercely. Helps reduce distortion.
If you think that the above method is too complicated, you can use a simple method to play your familiar clips or music, and try to change the position of the gun. This method is the most direct, but you must have confidence in the content played, and determine the effect of the low frequency. How to behave correctly, and you must also have a correct understanding of the low frequency performance of the instrument.
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