Home theater decoration environment acoustic processing full analysis

[Home Theater Network HDAV.com.cn] First of all, to have a good voice, you must have a better environment. Sound absorption is one of the most important acoustic treatments in the listening room. It is directly related to whether the reverberation time of the room is appropriate. We must be soberly aware that proper reverberation not only beautifies the sound, but in essence it is the basis of Hi-Fi playback.

From the perspective of the acoustic processing of the listening room decoration, it is a big subject. After this content, the audio and video will be explained in detail. Today, I want to talk about the sound absorption treatment from the perspective of debugging. In the debugging stage, the decoration of the home is basically in place. It is impossible to decorate the building in the hard decoration. Therefore, it is necessary to move on the soft decoration. Brains.

The concept of reverberation time has a history of more than 100 years. The classic reverberation time (T60) is defined as the time required for the room sound pressure to decay by 60 dB after the sound source stops sounding. According to this definition, the numerical definition of the reverberation time can be theoretically derived:

T60=0.16V/A (seconds)

In the formula, V is the room volume (m3), and A is the total indoor sound absorption (m2).

The former definition is the physical basis for determining the reverberation time, and the latter definition provides the basis for controlling the indoor reverberation time. That is, for a room of a given size, as long as the total indoor suction is controlled, the reverberation time can be freely controlled. This important formula is called the “Sabin Formula”, which was originally established by Sabin through experiments.

Through a large number of investigations and analysis of the sound quality of the hall and its reverberation time, the acoustician proposed the concept of "best reverberation time". It tells us that to get good sound quality, the reverberation time of the room should not be too long, but it should not be as short as possible, but appropriate. This appropriate reverberation time range is called "best reverberation time".

The best reverberation time is the first objective parameter in the history of acoustics that reflects the sound quality of a room. We often say that "reverberation can beautify the sound quality", which is the effect of "reverberation appropriate". In fact, whether the room reverberation is appropriate is not only related to whether the sound is pleasant or not, but also directly related to whether the sound is true or natural. Many subjective listening evaluations, such as fullness, warmth, clarity, and sense of space, are closely related to whether reverberation is appropriate. Therefore, the importance of reverberation can be "in a word:"

Optimal reverberation time

To control the reverberation to an appropriate level, it is first necessary to know what the appropriate reverberation time is and what factors it is affected by. In this regard, many acousticians have provided us with recommended values. The picture above is a relationship between “best reverberation time” and room volume/music/language. In fact, this set of curves is not “absolutely accurate” and should be understood as the approximate value of the “best reverberation time” associated with room volume and sound category. There may be +10-20 for each actual situation. % range of changes. Still, it gives us two important pieces of information. One is to use our basic concept of quantity for "best reverberation time". The second is to provide some of the influencing factors of “best reverberation time” and its changing trend. To further understand the effects of reverberation on sound, here are some simple instructions.

First, if the room is large, the "best reverberation time" should be longer. This is because the room space is increased, it needs to be large, and a louder sound is required to make the sound sound more satisfying. Increasing the reverberation time can have a high loudness. The reverberation time of the concert hall (about 1.5 seconds) is much larger than the listening room, which is the reason.

Know the appropriate reverberation time

Secondly, the "best reverberation time" for the language is always shorter than the reverberation time required by the music. What is the reason? Both of these sounds can be regarded as a series of syllables or notes. Both of these sounds can be thought of as a series of syllables or notes. Each occurrence of a tone corresponds to a sound decay process measured by room reverberation time, as shown in Figure 2. If the room reverberation time is too long, the previous tone has not been fully attenuated, and the latter tone has arrived. The overlap between the two (shadow) will be too much. The two tones are easy to hear, and the sound appears to be a lake. Clear and turbid. And if the room reverberation time is too short, the two tones overlap very little or even apart from each other. At this time, each tone sounds clear, but it is often not loud enough and full, because the direct sound is not mixed. The powerful technique of sound, in terms of clarity, may not be able to reach the best level at this time. Obviously, only when the reverberation time is appropriate, it is possible to hear a loud and clear sound. Since people's satisfaction with the language mainly depends on the degree of listening to the content, it is more advantageous to have a shorter reverberation time. In contrast, people often don't want to hear every note on music, but often they want to "cover up" each other to avoid hearing some of the defects or deficiencies of the instrument, so the sound is more full and beautiful, so the reverberation time It is usually better than the length of the language. Welcome to China Home Theater Network

Finally, it should be noted that as a small-volume home listening room, most of them use music appreciation as the main purpose. When designing the listening room, the initial value of “best reverberation time” should be appropriately larger, at least should not be Less than 0.5 seconds. If necessary, on this basis, the reverberation time is gradually reduced, and it is easier to find the "best reverberation time" that matches the actual situation by audition.

Reverberation uniformity requirement

The "best reverberation time" discussed above is the value at an intermediate frequency of 500 Hz. At present, the frequency range involved in indoor acoustics is mostly limited to 125 Hz to 4000 Hz. Therefore, the control of the reverberation time also includes the frequency response problem of controlling the "optimal reverberation time". Regarding the frequency response of the reverberation time, it is generally desirable to be substantially flat and uniform from low frequency to high frequency. However, the flat high-frequency response is good for some instruments, and may be too harsh for other instruments with rich overtones. Taken together, the high frequency allows for appropriate reductions to be more appropriate. As for the low-frequency sound, it can be improved a little, which is beneficial to improve the low-frequency playback effect of the small room, because the reverberation frequency characteristics of Figure 3b are also good. However, when the low-frequency standing wave in the small room is relatively serious, the low-frequency sound absorption is enhanced, and the low-frequency reverberation time is smoothly and slowly decreased from the intermediate frequency. It is also a commonly used reverberation characteristic, especially in the case of a small room using a large speaker. More suitable. Welcome to China Home Theater Decoration Network

What is to be avoided is the undulating reverberation characteristic as shown in Fig. 3d. The reverberation time of the frequency f1 corresponding to the peak is long, and the reverberation time of the frequency f2 corresponding to the valley value is short, and f1 will have a "masking" effect on the signal of f2, especially when the amplitude of the f2 signal is small, a few complete It is "submerged" by f1, which loses a lot of subtle music that can be heard, which is naturally unfavorable for hi-Fi playback. When the resonance caused by the standing wave in the room is not well suppressed, the above situation often occurs in the low frequency band, thereby causing distortion or staining of the sound. Therefore, when designing the listening room, it is particularly important to prevent the "degenerate" of the low-frequency resonance frequency and enhance the sound absorption processing thereof.

In short, for the reverberation characteristics of 3a~3c, it is not good to say which is better or not, because it is related to the room standing wave and the type of music. However, roughly speaking, compared with the intermediate frequency, the high frequency reverberation time is expected to be controlled within the range of 0~-10%, and the low frequency reverberation time is controlled within the range of +50~-20%, which is generally acceptable. .

After initially selecting the "best reverberation time" and its frequency response requirements, the next step is to make a rough arrangement for the sound absorption of the room.

We can calculate the specific surface area of ​​the home according to the sound absorption coefficient table, calculate the total sound absorption according to the Sabin formula and different materials, compare it with the required “best reverberation time”, and then according to the actual situation, Some of the materials that increase or decrease absorption or diffusion are difficult to increase or decrease after renovation, and some are easier to add, such as the third type of material.

The third type of material is made up of porous cotton wool fabrics. Carpets and curtains (ie curtains) are representative varieties and the earliest sound absorbing materials used in history. The characteristics of this type of material are high middle and high frequency sound absorption coefficient, and low frequency sound absorption coefficient is low, so it is generally used as a medium and high frequency sound absorbing material. Because carpets and curtains are originally household sound absorbing materials, but because it mainly only absorbs sound from the middle and high frequency, it often leads to confusion between sounds and poor definition. Perhaps for this reason, plus the materials and structures that can now be used for sound absorption, (or even homemade), it is very convenient to use household sound absorbing materials, especially it has adjustable sound absorption within a certain range. The characteristics of the coefficient are more suitable for amateur use of sound absorbing materials. The folding area (%) refers to the ratio of the area of ​​the unfolded portion of the curtain hanging suspension to the area when the hanging portion is fully suspended. The sound absorption coefficient during folding suspension is greatly improved, mainly after folding, which increases the thickness of the curtain itself, and thus the sound absorption coefficient increases. In addition, when the folding (%) is increased to a certain extent, the sound absorption coefficient exhibits a distinct peak shape characteristic. This is because when the folding (%) is large, the thickness of the air layer after the curtain is also increased to form a sound absorbing characteristic similar to that of the resonance sound absorbing knot. The velvet curtains in the table also have similar characteristics. As long as we fully understand the above characteristics of the curtain, and then use it with the low frequency sound absorbing material, it can fully achieve the desired sound absorption characteristics in the whole frequency band.

How much material needs to be arranged depends on the specific situation and the reverberation of different rooms. In the amateur condition without a reverberation measuring instrument, the calculation of the reverberation time of the room seems to be of no practical significance. In fact, the opposite is very necessary. Therefore, it is convenient for us to roughly set up a variety of different room reverberation characteristics, so that it is possible to find the most satisfactory reverberation characteristics from various room reverberation characteristics through audition and comparison. This to some extent compensates for the lack of reverberation measuring instruments.

For enthusiasts who have been involved in "room fever" for the first time and who have time, energy and interest, it is recommended to start from a simpler and more flexible, more convenient and less costly listening room treatment program, which will help to gradually accumulate experience and finally reach More ideal results.
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