[Home Theater Network HDAV.com.cn] Many friends don't know how to set the crossover frequency of the AV amplifier and the cutoff frequency of the subwoofer when installing and debugging the home theater. First of all, before understanding the settings of these two aspects, you must understand AV. Why do amplifiers/subwoofers have such a design? Just understand their original design and all the problems are solved! So why is this design produced? This is also from the technology of Dolby (AC-3) and DTS. go with. 1) Dolby Digital surround sound The Dolby Digital Surround System (AC-3) is a fully digital audio pressure coding system newly developed by Dolby Laboratories. There are 6 (5.1) fully independent sound channels: 3 front left, center, right channels and rear left and right surround channels and subwoofer channels. The first five are full-range (20HZ~20KHZ), and the subwoofer channel has a frequency range of only 20HZ~120HZ, so it is called ".1" channel. The volume of the subwoofer is required to be 10 dB larger than the other channels, which has a more powerful low effect. Dolby Digital AC-3 is a coding system multi-channel surround sound developed based on the feeling. The frequency of each sound is divided into a number of narrow frequency bands according to the auditory characteristics of the human ear. In the encoding process, the sound psychology is analyzed according to the principle of sound psychology, the effective audio is retained, and the excess signal and various noise frequencies are deleted. The reproduced sound is purer, all the signals of the six channels are independently digitized, and the separation of each channel is as high as 90db, which is a prominent advantage of Dolby Digital. The Dolby Digital Surround System is also approved by Dolby Laboratories. 2) Digital Cinema System (DTS) DTS is the abbreviation of Digital Theater System, which is a digital cinema system. It is a digital surround sound system jointly launched by DTS and Universal Studios. The DTS system is similar to Dolby Digital. It is also a multi-channel compression coding technology that combines 6 or more digital soundtracks with the time specified by SMPTE (Film and Television Engineering Association). The code is synchronized and directly recorded in a movie copy or other software. The digital compression technology of the audio signal is actually a re-encoding process of the linear pulse code modulated digital signal. The DTS can perform 20-bit original sound quality on 6 channels. The audio signal is encoded and decoded. DTS uses CAC (Coherent Acoustic Coding) structure compression method different from Dolby Digital compression mode, the typical compression ratio is 3:1, only one quarter of Dolby Digital, the original signal loss is less, can be retained The original fine signal in the sound field, DTS 96KHZ sampling frequency is double that of Dolby Digital 48KHZ, and easily increase the data transmission rate to 1411Kbps, which is three times higher than Dolby Digital's 448 Kbps, so its reproduction The sound field is ideal in terms of continuity, breadth and hierarchy. Dolby AC-3 / DTS main performance characteristics table Category Dolby AC-3 DTS Number of channels on the software 5.1 5.1 Number of channels after decoding 5.1 5.1 Channel composition LCR SL SR SW LCR SL SR SW Round channel number two channel two channel Left middle right speaker frequency response 20Hz-20KHz 20Hz-20KHz Surround sound box frequency response 20Hz-20KHz 80Hz-20KHz Subwoofer speaker frequency response 20HZ-120HZ 20HZ-80HZ Dynamic range 105db 138db Inter-channel resolution 105db >105db Output signal to noise ratio 115db >115db Signal recording digital mode digital mode Everyone pays attention to the keywords: the frequency response range of each channel Dolby AC-3 LCR SL SR SW The five channels are all 20Hz-20KHz in full range! The frequency range of the subwoofer channel is 20HZ-120HZ! Stage summary: According to the technical specifications of Dolby AC-3, the most ideal configuration in extreme conditions is: 5 main/middle/loop speakers capable of restoring 20HZ-20KHZ. A subwoofer capable of restoring 20HZ-120HZ. The question arises: Is there such a main/medium/loop speaker in the world? Even if it is, its price + volume can be accepted by several people? Hahahahaha............. So, lj said: everything must be started from reality! Ok, now let's pair with the most common 5.1 AV system. Main box floor frequency response range: 40HZ-20KHZ Medium frequency response range: 80HZ-20KHZ Surround frequency response range: 80HZ-20KHZ Active ultra-low speaker frequency response range: 25HZ-200HZ Ordinary with decoding AV amplifier (without crossover adjustment function) According to the technical specifications of Dolby AC-3, what is the problem with this system? Answer-----The band is lost! The frequency band of LR main channel 20HZ-40HZ is lost! The frequency band of the center/surround 20HZ-80HZ is lost! The frequency band of the subwoofer 20HZ-25HZ is lost! It can be seen that the subwoofer loses the least detail, and the main/medium/ring loses so much detail that you can bear it??? At this time, the little devil jumped out and said: "The world is the smartest of us, so we all call us a devil, let's solve it! Add a crossover management to the AV amplifier!" The AV function of the management function was born. It can assign the low frequency signal that can not be restored by the main/middle/ring to the subwoofer to handle it (who makes you have this ability and the most leisurely)! Hahahaha... Stage summary: Because most of the speakers can't restore all the low-tone signals of the channel, in order not to lose or minimize the loss, the AV power amplifier's crossover management function is also brought into play, and the human ear is also utilized. The low-frequency signal below 100HZ has no sense of direction. It is actually a compromise that is forced to helplessly. It is also a kind of deceptive deception........ Ok, see if everyone understands how to set the system's crossover point? Additional instructions: 1) The high-end AV amplifier (or the pre-decoding stage) has the independent crossover point setting function of each channel, so that different crossover points of each channel can be set according to different combinations, for example, the 5.1 system as exemplified above. You can set the crossover point of the main box to 40HZ, and the crossover point of the center/surrounding to 80HZ, which is closer to the requirements of Dolby AC-3. 2) Most AV amplifiers have only one uniform crossover point setting, so that in order not to lose the frequency band, only the center/around weakest point (the one with the highest frequency lower limit) is the best setting for the crossover point. 3) About the setting of the speaker size: If the crossover point has been set, if the main box is set to be large, then all the signals of the main channel are all given to the main box, and the subwoofer is not available at all! Unless you The main box can dive deeper than your subwoofer, otherwise the low frequency signal of the main channel will be lost more! If the main box is set to small, the signal of the main channel above the crossover point is still replayed by the main box, and the low frequency signals below the crossover point are all handed over to the subwoofer for processing. The size of other channels is set. And so on! 4) Most AV power amplifiers have a choice of “BOTH†in the subwoofer setting. In the case where the main box is set to a large size, the sound below the power amplifier crossover point can be simultaneously output from the subwoofer and the main box. Finally talk about the cutoff frequency setting of the subwoofer Most subwoofers have this setting knob on the rear panel. The general cut-off point is adjusted freely from 40HZ-120~200HZ. Which is the right button for this button?-------(Off-topic: Many people think this The cut-off point is set to be slightly higher than the crossover point of the power amplifier. In fact, it is wrong. Why do you say this? First of all, to figure out what the subwoofer under 5.1 is doing? Reviewing the above, according to the technical specifications of Dolby AC-3, this ".1" should be a completely independent channel! The theoretical frequency of this channel The range is 20HZ-120HZ. But the hateful devil in order to solve the problem of loss of the main/middle/ring band, through the frequency division management of the amplifier, added the low frequency signal of other channels (please note that it is added, not independent) The subwoofer channel is also brought in for mixing.) Therefore, the subwoofer is a heart-to-heart tube, doing both the work that you should do, and helping others to work! (Oh.. no way, the upper finger is sent) Then I will talk about what is called the "cutoff point"? Simply put, this "point" determines the working frequency range of the subwoofer. It doesn't matter if it is above the point. So how much is this "point" set up? A: 120HZ or a little higher!!! reason: 1) Technical specifications of Dolby AC-3/DTS, the frequency response range of the subwoofer channel is 20HZ-120HZ, and the production limit is 120HZ! 2) The lower limit of the low frequency of most speakers will be below 120HZ, which means that the crossover point of the power amplifier is rarely necessary to be set above 120HZ! Add a point: If you broadcast DTS, then the cutoff point can also be set at 80HZ (below the value of the power amplifier's crossover point), because the DTS ultra low channel frequency response range is 20HZ--80HZ, in short, it is not lost The principle is the principle! However, switching the track once it is necessary to adjust the cut-off point, it seems to be troublesome, so it is still set at 120HZ.
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November 15, 2024