With the popularization of home theater AV systems, subwoofer speakers have also received more and more attention and a large number of applications. In fact, not only the use of subwoofer speakers in AV systems, but also in the ranks of popularizing high-fidelity two-channel, has also begun to receive the attention and application of audiophiles. For example, the famous LS3 / 5A has a subwoofer specially designed and manufactured for it abroad. Used well, it can indeed increase the overall atmosphere of the Hi-Fi system and play the "final finishing touch" effect. The subwoofer can be made into a closed type, can also be made into an inverted type or other types. Most of the products that are currently on the market are these types of products. The ASW speakers used for subwoofers abroad, because of the special cabinet design, even if no crossover circuit is used, it can easily filter out components above 200Hz (see figure). The subwoofer unit of this speaker is installed in a closed In the box, the sound from the front of the speaker is released in a form similar to an inverted speaker. Because the box contains a lot of materials that absorb mid- and high-frequency components, and the relationship between the length of the sound path in the box and the wavelength, so Only low-frequency components are released from the sound hole. In fact, the speakers of ASW speakers are not radiated directly to the surroundings like ordinary speakers. They are only used to excite the inverter speakers at the resonance frequency. The volume of air, because of the characteristics of the inverted speaker itself, makes it radiated through the inverted hole, and the distortion of low-frequency components is minimum. The "Cannon Cannon" subwoofer launched by the American BOSE company is another high-efficiency design. It also has the function of filtering out high-frequency components. Its principle is based on the theory of acoustic tube resonance. The front and back of the horn are composed of acoustic wave pipes of different lengths. And each section of sound pipe before and after can be regarded as a pipe with one end blocked. When n = 1 / 4λO is odd, resonance occurs, that is, when n = 1, 3, 5 ..., the acoustic wave tube plays a role of suppression, that is, the opening of the acoustic tube is in antiphase relationship with the acoustic wave behind the horn unit At this time, for the resonant frequency fo of the speaker unit, the radiated sound has the lowest efficiency, and for the low frequency that we need to increase, such as 1 / 2λO integer multiple frequency resonance, the playback channel plays a role in low frequency For the lifting effect, the opening of the pipe is in phase relationship with the back of the horn unit, so the low-frequency energy radiated is also the highest. The working feature of this acoustic tube is that it suppresses the resonance frequency fo of the horn itself, which can effectively reduce distortion and enhance the dive ability of low frequencies. It improves the required low-frequency range. It has the advantages of flat characteristic curve and high efficiency. As long as the speaker unit in the sound tube does a small amount of vibration, it can obtain a large energy sound wave output. Although the effect of this "Cannon gun" subwoofer is very good, if you want to emit a frequency of 20Hz, the length of the playback pipe is very long. Therefore, the volume is very large, which is more suitable for large-scale applications such as theaters. For home use, in order to reduce the volume, the sound tube can be folded like a labyrinth speaker. Unlike the labyrinth box, the sound of the subwoofer unit is released through two folding pipes of different lengths. The amateur production of the Cannon gun design and manufacture this subwoofer system. The length of the front and rear sound wave pipes can be calculated as follows: the length of the front sound tube L1 = c / 4f0, the length of the rear sound tube L2 = L1 / 3 Sound velocity 3.44 × 10ªCM / S fo = resonance frequency of the speaker unit. Take the BOSE "Cannon gun" as an example to illustrate the calculation method. The resonance frequency of the woofer used by the BOSE "Cannon gun" is f0 = 30Hz. Therefore, L1 = 344/4 × 30 = 2.86m, L2 = L1 / 3 = 2.86 / 3 = 0.95m, L2 = 0.95m, L1 = 2.86m. Through the above simple calculation, the use of the labyrinth structure with the front and rear sound tubes folded can easily design home subwoofer speakers and Hi-Fi speakers, and the volume can also be controlled to a certain extent, not too large. In designing and manufacturing this kind of speaker, there are several points to be noted: First, the cross-sectional area in the sound tube must not be less than the effective area of ​​the cone unit of the applied speaker unit, and secondly, the sound absorption material must be attached to the inner wall of the completed sound tube to Absorb unnecessary high-frequency frequencies. In the working frequency range of the subwoofer, the amplitude in the pipeline is extremely large. If the rigidity of the speaker is not good, it is easy to produce clutter output, make the low frequency turbid, and also cause loss of power. In view of this, it is proposed When making, we must choose materials with high density, heavy weight, not easy to vibrate, with a certain thickness and strength, and pay attention to the use of strengthening measures. Many previous articles have pointed out that frequencies below 300 Hz have no directionality, so they can be placed with one (3D) at will. And think: the human ear can not feel the positioning of the low frequency below 300Hz, can only experience the weight of the low frequency, and cannot judge its direction. Practice has proved that the subwoofer also has the problem of positioning. To achieve a perfect restoration, positioning is also very important. Genesis has proposed placing the subwoofer behind the right side of the left and right channels. It is true that this kind of pendulum is conducive to the positioning of the cello and other instruments when listening to the performance of the orchestra, so that the overall effect is better. The placement of the subwoofer in the middle of the main channel back a little bit can significantly improve the positioning of the bass drum and pop music. Therefore, the positioning of the subwoofer still exists. It is recommended that the best way to play is to use two subwoofers to place them on the rear outer side of the left and right main channels. You will definitely further appreciate the subwoofer's positioning and wonderful effect, and it can also effectively prevent the positioning of the low frequency parts from being confused.
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At present, there are two types of common subwoofers: one is an active subwoofer with amplifier phase adjustment. In addition to accepting low-frequency signals from the previous stage, it can also be directly input from the amplifier stage, and It is convenient to adjust the crossover point, so it is the mainstream in the market. The other is a subwoofer that requires a separate amplifier to drive, also known as a passive subwoofer. It can be equipped with different amplification systems according to the taste of enthusiasts.