Audio-visual room category The room used for viewing and listening is not the same. Different industries are called differently. Some are called listening rooms, audition room listening rooms, some are called tuning rooms, studios, control rooms, monitoring rooms, etc., and there are many names. In this article, they are grouped into three categories according to their main purpose:
1. The home listening room is mainly used by ordinary families to enjoy music.
2. The audition room is mainly used for the trial production and purchase of audio products for subjective sound quality evaluation. At present, we introduce the video in this piece, which can be said to be the audio-visual room.
3. The monitoring room is mainly used for monitoring and controlling the use of recording and processing programs (when there is no difference, this article refers to them collectively as the listening room).
From the point of view of the purpose of use and acoustic conditions, the audition room and the monitoring room are similar, focusing on requiring the room not to interfere with the listening to avoid affecting the judgment result. The home listening room focuses on asking for a better "live" atmosphere, preferably as if listening in a concert hall. In fact, many enthusiasts often use the home listening room to perform subjective sound quality evaluations of audio products, and thus often have something in common with the audition room. In addition, from the future research trends of the monitoring room and the audition room, they are also required to better reproduce the atmosphere of the recording scene. Therefore, there is no fundamental contradiction between appreciation and evaluation of sound quality. There is nothing wrong with being able to do both. Therefore, the basic requirements of the above three types of listening rooms are the same, and the theory and method of design are the same. Since the design criteria for the listening room are mainly for the audition room and the monitoring room, the experts also require them to approach the general level of the family living room when proposing these standards. Therefore, the requirements and design of the home listening room can be designed with reference to these standards. Under this general premise, some specific parameters are slightly modified to better adapt to their specific needs.
It should be pointed out here that people always hope that a listening room is perfect and can meet the needs of listening to all the tracks. However, it is recognized that the world is one of the best concert halls, and it is not the same perfect performance for all types of tracks. Therefore, we are not demanding on the listening room, we can only compromise.
basic requirements
In the 1960s, the importance of the listening room has drawn attention. Since the 1970s, acousticians have conducted extensive research on this and have achieved many results. On this basis, relevant international organizations and major countries have formed their own design standard documents to exchange and guide the acoustic design of the audition room and the monitoring room, and achieved good results.
Although the home listening room for listening to music is not exactly the same as the audition room and the listening room for sound quality evaluation, they are all the same in "listening in the room". Since the influence of the room on the sound quality has its advantages and disadvantages, no matter which kind of listening room, there must be something in common in the point of "growth and avoid weaknesses". This commonality forms some basic requirements for the listening room. The specific methods for meeting these requirements have been discussed in the previous section, and are only summarized here:
1. The buzz should be small and the sound insulation should be good. In order to avoid the masking of the minimum signal level, the sound of the indoor equipment and facilities itself should be small, and the sound insulation performance of the wall doors and windows in the room should be good. In general, the total beep level in the room is at least 10 dB below the minimum listening level. The extent to which it is as low depends on the lowest level of the program source and the highest level of playback. The relevant standard recommendation is lower than the NC-25 curve or 35dBA. Now there is a higher SACD and DVD-Audio than the letterhead, and the requirements for the noise floor of the listening room can only be higher and higher. Of course, as a general family listening room, it may not necessarily be so strict.
2. To control the standing wave As the monitoring room of the professional standard audition room, the recommended value of the maximum capacity is generally below 150 cubic meters (about 50 square meters). Home listening rooms tend to be smaller, generally around 20 square meters. But acoustically, they all belong to the "small room". One of the biggest problems with "small rooms" is that there is room resonance caused by standing waves below 300-500 Hz. If not properly controlled, it will produce significant sound. This is the main reason for the poor sound quality of the home listening room.
In order to reduce the standing wave sound, if possible, the room volume should be chosen to be larger. At the same time, the size ratio of the room should be appropriate. In addition, care should be taken to enhance the sound absorption or diffusion processing of these frequencies. This is beneficial to reduce the sound of the standing wave.
3, the reverberation should be appropriate Room reverberation, there are advantages and disadvantages to the sound quality, so the reverberation should be appropriate. This is the case for a "big room" like a concert hall, as well as a "small room" like a home listening room. The so-called "appropriate" means that the reverberation is too long and the "too short" is not good. This is easy to distinguish with the sense of hearing. Then there must be a compromise between "long" and "short", which is called "best reverberation time".
4. Suppress harmful echoes From the concept of physics, all indoor reflections can be called echoes. Some echoes are combined with direct sounds, regardless of each other. Some echoes are not compatible with direct sound and can be heard separately. The latter are generally harmful echoes because they affect the clarity of the indoor sound, and it is also easy to distract the listener or to cause auditory fatigue.
The home listening room is small in size and is less prone to echo, and the room usually has sound absorbing materials or diffusion treatment, which are beneficial to suppress the generation of harmful echoes. In general, as long as you take a hand inside, it is easy to hear if there is an echo. If an echo occurs, it is usually caused by a large parallel and smooth wall. You can use heavy curtains to move on one wall to find out which part of the wall the echo is coming from. Then spread the appropriate size of sound absorbing material in the department.
The above four points are the common basic requirements for the listening room. Many of the past and present home listening rooms are also handled in accordance with the above principles. It should be said that the sound quality of the treated listening room is much better when compared to before the processing. But we must also see that even if the listening room meets the above requirements, they still have differences in sound quality. Moreover, this difference is often more common and more evident in the home listening room. This is what everyone does not want to see, because it is not convenient for everyone to exchange listening experience, and it is not convenient to make reliable sound quality evaluation of audio products. Of course, the actual effect of listening to music is not the same, some are better, some are worse, most are average.
The reason for the above phenomenon is not hard to imagine, that is, the size and shape of the home listening room are different, and the sound absorption diffusion process is different. That is to say, if the size and shape of the room are exactly the same as the sound absorption diffusion process, the sound quality of the two rooms will be the same. But the more practical question is how to make rooms of different sizes and shapes have similar (similar or substantially identical) sounds. A further question is how to make a room with the best (comprehensive) sound. To this end, we need to make a more subtle observation and research on the sound of the room and its impact on hearing, to guide its practice activities, in order to improve the design level of the current amateur listening room.
Echo map
We already know that the sound heard by the listener in the room, in addition to the direct sound, is the reflection of the direct sound. For just these two kinds of sounds, the impact on our hearing is often confusing. In order to understand this fan, the acousticians are also very busy.
In explaining the concept of reverberation time, we use a steady-state sound source to establish a stable sound field indoors, and then remove the sound source to observe the attenuation of sound energy at a certain point in the room. Instead, send a short pulse to the room and observe the attenuation of the sound energy at some point in the room.
Figure 1 is an experimental layout. When a short signal is input to a speaker, the listener first hears the direct sound from the speaker. Then you hear the sounds in the order of the length of the reflection path, once, twice, three times... or even multiple times. For the sake of simplicity, only six primary reflections are shown in the figure. If the indoor wall reflection is strong, then as time passes, the density of the reflected sound becomes denser and denser, and the intensity gradually weakens and eventually disappears.
The size of the room sound in Figure 1 is 4.9mX7.1mX3m. According to the method we have previously introduced, it can be roughly calculated that the intensity of its first primary reflected sound (1) is about 1 dB lower than the direct sound, and the time lag is about 1 ms. The intensity of the fifth primary reflected sound (5) is about 9 dB lower than the direct sound, and the time lag is about 12 ms.
The reflected sounds, including the reflected sounds that have not been reflected in Fig. 1, are arranged in chronological order, and the echo map (schematic diagram) shown in Fig. 2 is obtained. It reflects the time series of various intensity reflected sounds reaching the listening point. In order to understand the needs of the following, some important names are explained.
1. All reflected sounds are divided into early reflection sounds and late reflection sounds according to a certain time. The early reflection sound and the direct sound are combined, and the human ear can't distinguish it. It has the effect of enhancing the direct sound loudness and improving the straight sound clarity. The time of division is about 80ms for music, and about 50ms for language. China Home Theater Network
2. The late reflection sound is composed of reflected sound reflected by the wall surface multiple times, and is actually a fully diffused reverberation sound. The delay between adjacent post-reflected sounds is small. Although the intensity of the late sounds fluctuated slightly, the overall trend gradually declined. However, if there is an acoustic defect in the room, a particularly strong reflection sound (such as the vertical line in the shaded area in Fig. 2) may appear in the late reflection sound, which sounds like the second sound following the direct sound, that is, the echo is generated. . These strong late reflections are called tremor echoes if they appear consecutively in a series of identical or similar cycles. As mentioned earlier, both individual strong echoes and trembling echoes should be suppressed.
3. Initial time delay (ITD). This is the time gap between the direct sound and the first reflected sound. This is an important parameter that has an impact on the sense of space. Please note that the ITD of the small room as shown in Figure 1 is only about 1ms. The ITD in the concert hall often reaches about 20ms.
In addition, for a small room with strong sound absorption, the post-reflection sound in Figure 2, that is, the reverberant sound field is often not established, which is another difference between the home listening room and the concert hall. Let me first mention these basic concepts, and we will use this concept in the future.
"Hedgehog map"
The echo map is a time series of reflected sounds, and the reflected sound arriving at the listener at different times has a different influence on the subjective sense of hearing. In addition, the reflected sound has a directional characteristic, and the reflected sound from different directions also has a great influence on the subjective sense of hearing. The intensity of the reflected sound and its direction received indoors can be visually represented by the "Hedgehog". Figure 3 is the "Hedgehog" of the direct and reflected sounds in Figures 1 and 2. For the convenience of the general reader, the two parts are divided into vertical and horizontal parts, and in each part, the direct sound is separated from the early reflected sound and the late reflected sound. The direction of the sound reaching a point in the room is indicated by an arrow, and the intensity is indicated by the length of the handle. The direct sound on the vertical plane in the figure is indicated by the dashed line because it is the direct projection of the direct sound on the horizontal plane. Early reflections only draw 1-6 one-time reflections. The late reflection sound is fully diffused, and the late reflection sound of a certain point comes from all directions and has the same intensity. If we compare Figure 3 with Figure 1, it is not difficult to understand. In fact, the sound lines in the figures in Figure 3 are concentrated at one point. There are many different "stabs" of different lengths and different lengths, which are named after a "hedgehog". Obviously, the echo maps at different points in the room are different, and the "hedge map" is different. The combination of the two fully demonstrates the intensity, direction and timing of the various sounds received at a certain point in the room. It is just that the spectral structure of the reflected sound is not the same, so it is almost impossible to hear the exact same sound in a room of different size and shape. Strictly speaking, the sounds are not the same in different places in the same room. In this case, it is very frustrating. However, fortunately, there is a limit to the auditory power of the human ear. Acoustics have seen hope and prospects. It is not entirely impossible to hear similar or similar sounds in different rooms as long as proper control of the reflected sound in the room is made, and it is not entirely impossible to hear certain sound effects similar to a large room in a small room. Everyone must remember that Yamaha, Japan, said when introducing their digital home theater that they surveyed the sound field characteristics of the world's famous concert halls and other performances, and then used DSP (digital sound field processing) technology in the ordinary listening room. The original scene effect is reproduced in the middle. Among the measured sound field characteristics of the scene, the most important one is the echo map. The difference is that Yamaha uses multi-channel electroacoustic technology to imitate the field effect, while the acoustician uses purely acoustic means to implement it. The difficulty can be imagined.
Sense of space
When you enjoy a large symphony with a two-channel stereo device in your home, there will be a “sound stage†between the two speakers. It usually appears on the line between the two speakers. It has a certain width and sometimes feels There is a little depth (Figure 4). In general, people can correctly distinguish the left and right positions of the voices on the "sound stage", and sometimes they can feel the difference between the instruments. This "sound stage" is impressive, which is the charm of two-channel superior to mono.
When enjoying a large symphony in a concert hall, it is generally only the audience in the front middle seat that can clearly hear the left and right and front and rear positions of the instrument on the stage. When the band symphonic performances, the various parts are coming and going, making each other a great artistic enjoyment.
However, a listener who sits farther or deviates from the middle area usually feels that the band on the stage has a certain width and cannot make a clear distinction between the position of the instrument. But they all feel that the sound in the concert hall has a "space sense" - the feeling that the listener is surrounded by sound. In recent years, the sense of space has become an important sound quality feature of the concert hall, and it has received more and more attention from acousticians, architects and listeners. However, the sense of space is a subjective feeling that is currently lacking in the family listening room. It can't be said that there is no sense of space in the home listening room. The "sound stage" between the two speakers can also be said to be a sense of space (really a part of the sense of space), and then feel the space in the concert hall. Compared, it seems that there is still a world of difference. When talking about this matter, the senior enthusiasts will inevitably be "heroic short-lived". They always think that their "dwelling house" is difficult to look forward to the concert hall, and they sigh. As a matter of fact, Big difficulties, small and small benefits", no matter from the sound quality or convenience, you can find out that there are many places in the concert hall that are not as good as the family listening room. It should be said that the sound quality of a well-designed listening room is quite good, and there should be such a basic estimate. The main problem at the moment is that most home listening rooms are not subject to good acoustic design and processing. Not to mention how to apply new concepts and new theories to improve the sound quality of the home listening room. As for improving the sense of space, it is a topic that is not marginal.
So I went back and talked about the sense of space in the concert hall. When it comes to the concert hall, people always think of its unique and extraordinary acoustic space, and the resulting sense of space that the family listening room can't match. However, it has been found that the sense of space in the concert hall does not uniquely determine the size of the space. In the same size concert hall, the sense of space is not always the same, and there is a lack of space for a smaller concert hall than for the larger concert hall (a similar situation in terms of sound quality). Therefore, improving the sense of space in the home listening room is not completely impossible. Some practices have shown that there is a sense of space in a small room. Of course, the sense of space in the small room can not be compared with the concert hall, but with the deepening of the theory of spatial sense, the well-designed home listening room is likely to get a better and better sense of space. China Home Theater Network
In the study of the sound quality of the concert hall, the acoustician divided the sense of space into two parts. One is the apparent sound source width ASW, and the other is the listener surround feeling LEV, as shown in Figure 4. It is not difficult to understand that they are equivalent to the "width sense" and "enveloping sense" that enthusiasts often say (this article uses these two common names to denote ASW and LEV). Since the sense of width and the sense of envelop indicate that the space occupied by the sound image can be perceived in the concert hall, it is collectively referred to as a sense of space. At the same time, because they are relatively independent of the two subjective feelings, the acoustic conditions for forming these two sensations are also different. The sense of width is mainly related to the early reflection sound, and the sense of envelop is related to the late reflection sound (reverberation sound), so The spatial sense is decomposed into two name representations, which are easier to describe and deal with separately.
In the two-channel stereo home playback system, the sense of width is definitely present, and it is also obvious. As for the sense of envelop, it should be possible, because the reflection of the wall surrounds the listener, but why is the sense of space in the home listening room not as obvious as the concert hall?
To do this, let's take a look at Figure 4. Although it is only a schematic diagram of the concept of space, it seems to give us the suggestion that the influence of envelopment on subjective sense of hearing (space sense) is greater than that of sense of width. Because whether it is a concert hall or a home listening room, the space occupied by the sense of width is always smaller than the space occupied by the sense of envelopment. If this kind of guessing is not too biased, then the sense of encirclement is related to the fullness of the indoor reflection (reverberation). It was also mentioned in detail that the small sound-absorbing room often cannot establish a fully diffused reverberation sound field, so it is not surprising that the surround sound of the home listening room is far less than the concert hall.
If the above explanation is true, then the main reason for the poor sense of space in the home listening room is the sense of envelopment. As long as we can improve the sense of envelopment in the home listening room, and at the same time try to improve the sense of width, both of them can improve the sense of space in the small room. Of course, this requires constant practice and exploration, but only by practicing the existing acoustic theory, can we achieve the desired effect and do more with less.
summary
A lot of space has been said about the situation in the concert hall. The purpose is to tell the enthusiasts that for the home listening room, the acoustic theory that has been established can be used for design and processing. The problem is not that there is no theory at first, but that we have not mastered too little, and have not absorbed new concepts and new theories in time, so that we have long stayed in the traditional theory of reverberation and sound absorption (which is of course important).
We should clearly understand that the sound quality design of the concert hall that acousticians are trying to explore is not fundamentally different from the sound quality design requirements of the home listening room. The research results of the sound quality of the concert hall are not related to the family listening room, but it is too close and too important. It can be said that only the sound quality design of the concert hall can be satisfactorily solved, and the acoustic design of the home listening room is likely to be finally solved. Therefore, before this time comes, we should pay more attention to the progress of the sound quality design theory of the concert hall on the basis of trying to master the existing acoustic theory and technology, and be brave in practice and innovation. Only in this way can we improve the level of amateur design. To make a breakthrough in the sound quality of the private home audio-visual room.
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