[Home Theater Network HDAV.com.cn] originally wanted to write some more in-depth audio standards, but recently I have seen many friends in the forum about the concept of Subwoofer and LFE is rather vague, so I would like to write an article about Bass articles, after all, bass has a great impact on the effects of home theater.
An American home theater design guru once said that bass is like salt. The salt is less, the taste is tasteless; but it is more, and it masks the umami taste of the food. The bass is also the same. If there is a lack of low frequency, the appeal and impact of the audio and video programs will be greatly reduced; if the low frequency is too much, it will affect the clarity of the audio and video programs. Therefore, it is appropriate to be the right one.
The speaker configuration (Speaker Configuration) that everyone sees in the AV amplifier/decoder today, such as the channel Large, Small, etc., is the Bass Management system.
Bass management first originated in the 1980s, the combination of satellite speakers + subwoofer introduced by M&K and Triad. At the same time, Dolby Laboratories also introduced a low-frequency distribution system that allows the AV amplifier/decoder to distribute the low-frequency signals of the center channel to other channels for playback.
In 1990, Lucasfilm introduced the THX certification standard, which required a maximum sound pressure level (low frequency) of 105 dB per viewer position in a home theater to meet the standards of a movie studio. However, after the introduction of the standard, it was found that it was unrealistic to achieve a maximum sound pressure level of 105 dB in the low frequency band in the home. Unless the customer uses a very large speaker (double 12-inch or 15-inch woofer). As a result, THX developed a simple low-frequency management system that allows a single subwoofer to be responsible for the low-frequency restoration of all main channels (L/C/S). In this way, the size of the main box is greatly reduced while experiencing the bass in the home.
In 1995, Dolby Laboratories and DTS introduced separate 5.1-channel systems, adding a separate channel, LFE (Low Frequency Effects), which translates into low-frequency effects channels. When playing the signal of this channel, the highest sound pressure level at the viewer position can reach 115dB. If you don't experience the legendary "low-frequency heart-breaking" feeling, you can only show that your home system is not 115dB. The living room party is basically impossible. If it is true, it is estimated that it is not just the whole building. It is estimated that the neighbors of the whole community are coming to trouble you. 115dB is a feeling of sorrow, has the disco been visited? It is similar to that.
Let's talk about the difference between Subwoofer and LFE:
The LFE is a signal channel with a bandwidth of 20-120 Hz (DTS is 20-80 Hz), which is independent of the 5.1 sound track. It is also the least important channel in the 5.1 track. Its appearance is intermittent, not every moment. For an action movie, the total time of the LFE soundtrack may reach 20 minutes. And a literary film may be 5 minutes. LFE is missing, at most, the low frequency is not strong enough, but it does not affect the audience watching the movie. Can you imagine any of the L/C/R/Ls/Rs channels missing? So, back to the beginning of the article, LFE is like salt. Without salt, at least food can still be eaten.
The LFE channel is 10dB lower than other channels during recording, and the playback system automatically adds 10dB of gain during playback. Therefore, the signal-to-noise ratio of the LFE channel is 10 dB lower than that of the main channel, but the dynamic range is 10 dB larger. Since the frequency band of the LFE channel is narrow, it is more scientific to sacrifice the signal-to-noise ratio in exchange for the dynamic range. Please refer to the figure below.
Subwoofer is a sound channel. The low frequency signal played in Subwoofer includes the low frequency part of all channels (such as the part below 80Hz), and the LFE channel. So, in most cases, the subwoofer is responsible for the low frequency playback of the entire home theater system.
If my system uses a floor-standing speaker, do I still need to set the speaker to Small? Yes! If you must set the speaker to Large, then the speaker's woofer is at least 15 inches, or 12 inches, and withstand The power must be too large. However, even if you have such a large speaker, you should set it to small!!
Why? Because the low frequency standing wave in the small room seriously affects the sound quality of the low frequency. If you play the low frequency in the left and right main boxes, it is very likely that the position of the main box will stimulate a certain standing wave frequency in the room, thus degrading the low frequency. Sound quality. If you give all the low frequencies in the system to the subwoofer for unified management and restoration, then move the position of the subwoofer (the position of the left and right main boxes moves very small? Even if it can move, it may cause other problems. For example, room boundary reflection, etc., or using multiple subwoofers, it can suppress the low frequency standing wave.
So, starting today, your home theater system will no longer appear Large. Good low frequency sound quality, starting with Small!
Finally, let's explain some of the more practical problems.
1.LFE and LFE+Main
This is a very common setting in amplifiers. The author believes that such a logo is misleading, and the correct logo should be Sub Only and Sub+Main.
The LFE mode here is that in this mode, all channels set to small, their low frequencies are played in the subwoofer. If LR is Large and C/LS/Rs is Small, then LR speakers will only play their own low frequencies, while Sub will play the low frequency portion of C/LS/RS with LFE.
In LFE+Main mode (some amplifiers can only select one mode when LR is Large). If LR is Large and C/LS/Rs is Small, then LR speakers not only play their own low frequencies, but also play the low frequencies and LFE of C/LS/Rs; at the same time, C/LS/RS will also play in Sub. There are also low frequencies in the LFE. This mode, also known as Double Bass, means double bass. This mode is used when the LR is a large speaker and the Subwoofer's driving force is not enough. Increase the low frequency sound pressure level by playing twice the bass.
However, since the low frequency is played simultaneously in three different places, the degree of fusion of the low frequency at the viewer's position is very difficult to debug. To obtain a good low frequency effect, it requires some luck in addition to the later debugging. Therefore, this mode is not recommended for high-quality home theaters.
Therefore, the LFE mode is the mode that should be used by high-level home theaters. All you have to do is to use a small main box with good quality, excellent transients and sounds to suit your taste, and with a number of high-performance subwoofers to achieve good results.
Think about it, the home theater is to watch movies, not to watch the speakers, put such a large speaker on both sides of the screen, is it hindering the visual? Besides, with such a large main box, the amplifier is not Is the cost going up again? And the main box you bought can reach the 105dB limit low-frequency sound pressure level? In fact, the general retail type hifi floor box is basically impossible.
Large-volume speakers are generally used in large home theaters of 40 flat or more. But even in large home theaters, they are still set to small. Large home theaters generally have more than two subwoofers, so there is no need to increase the burden on the main speakers.
2. Corner frequency
The corner frequency setting inside the power amplifier can theoretically be seen when debugging. Generally, the spectrum analyzer is used to observe the low-frequency coincidence degree of the intersection. In the absence of professional equipment, generally choose 100Hz, because many speakers can not get 80Hz, especially surround speakers.
The frequency response range of the LFE channel is adjusted to 120 Hz. Dolby Digital's LFE can go to 120Hz and DTS is 80Hz.
Corner frequency on the subwoofer: set to maximum and at least 140Hz. Because the sub signal coming from the decoder contains LFE. If set here to 120Hz, the LFE low frequency will attenuate at least 3dB at 120Hz.
Low-frequency debugging is actually the most important part of the entire home theater. It is difficult to adjust to the optimal level without using professional instruments and test signals. The author is arguing today, and I hope that readers will not make some low-level mistakes at least in the setting of the amplifier.
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