Room equipment for listening to music
There are hardly many people in Habré who do not like music or movies. But you decided that you were bored with headphones, that you want to listen to how your favorite music actually sounds, and, having saved up some money, you heartily went to different shops and bought a good (to your taste) audio system.
More often than desired, such purchases do not deliver the expected satisfaction. When the speakers are placed where it is convenient and practical, the cables are connected and the favorite track is launched, it turns out that everything is not playing as expected. And the thing is that the room in which the music plays is an essential part of the audio system, and it is precisely this fact that ignoring this fact is the most frequent cause of the unnecessary additional costs for unnecessary components, jerky throwing around the room in search of the correct location of the speakers and other troubles. About what to undertake to return the charm to the sound, and pull out the maximum sound from the system, please under the cat.
Below I will talk about music, but all of the above applies to the movie and to any other art form with an audio component. Let's start with the typical enemies of good sound.
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A room with roughly the same size in any dimension.
Whoever still remembers physics, immediately guesses what's the matter. But the point, of course, in parasitic resonances. Sound energy from the speakers, being reflected from the walls, can accumulate at those frequencies at which a standing wave is observed. The same size in the room leads to two unpleasant effects at the same time. Firstly, at frequencies whose wavelength is a multiple of the size of the room, there will be a louder sound. The loudest volume will be at half the wavelength, then at a quarter, and so on. The second problem - the attenuation of sound at these frequencies is much slower. The bass guitar is already playing on another string, and you still hear an echo from the previous note. Since the typical sizes of rooms are from two to four to five meters, the main resonant frequencies are in the range from 30 to 50 Hz, in strict accordance with the formula:
where l is the wavelength in meters, and c is the speed of sound in air, equal to 331 m / s. In particular, for a room of 2 meters in size, the frequency corresponding to the half-wavelength will be equal to 82.75 Hz, and in the three-meter size we will get a buzz near our favorite 50 Hz.
In reality, there are many standing waves in the room, since they go not only perpendicular to the walls and the floor, but also from corner to corner, and in order to roughly calculate at what frequencies resonant modes will arise, it is useful to use this formula:
where the values of p , q and r are zero or one for different modes, and L , W and H denote the length, width and height of the room, respectively. We will not be particularly interested in mods above thirds, for the reason that the higher the frequency, the closer these modes are to each other, and the less their influence, with the result that the frequency response of the room is smoothed. If you are interested in a tangential mode for length, then put 1 over L , if an oblique horizontal mode (for example, from corner to corner), then we set 1 over L and W , and if you need an oblique mode from the lower corner to the upper one, then there are in the formula all ones. It's simple. Good people have long thought for us, and by Google you can find a ready-made Excel table with formulas (or a website with a script) where you insert the size of your room and immediately see the whole picture.
Here we have to take into account another simple truth: frequencies rarely below 30 Hz are rarely present in music, and the sensitivity of our ear to these frequencies is much lower (we hardly hear them, but rather feel them in our body). There are more of them in the cinema, where there are a lot of sound effects, but it is unlikely that you will be very concerned about the quality of the sound of a bomb explosion. In secret I will say that the subjectively pleasant sensation of the whipping sound of the “bubums” sound, as well as strikes of the drum sticks, to a much greater degree depends on higher harmonics, in the range of 150-400 Hz. From this simple theory, we make an even simpler conclusion: in order for the bass to sound even and without a hum, it would be nice to have a bigger room and with different linear dimensions. And the hell for bass happens in a room measuring 3 by 3 by 3 meters, where listening to music will not work in any way, unless you are a fan of baroque music.
And another thing: the above formula works in the ideal case of absolutely reflective walls. In a real room, the resonant frequencies will depend not only on this formula, but also on the material of the walls, neighboring rooms and the will of fate. I know from experience.
Drywall
This material is attractive because it allows you to quickly and cheaply build internal walls and shamefully cover up the failures of the domestic construction industry. But, unfortunately, a sheet of drywall (even double), attached to the metal frame with a standard pitch, is an excellent membrane. He will bury alive almost the entire bass, which, tsuzhas, will issue your speakers. And during the funeral, he will also re-echo this sound at his own resonant frequencies, sometimes very audibly podguzhivaya.
The question is what to do? If you got the finished room, the subwoofer can partly save the situation. If you read this article before construction or repair, you can have time to take preventive measures. For example, you can make a more frequent frame step and add horizontal elements to the vertical uprights. To some extent, this will improve the situation, but hope for a miracle is not worth it: the tin frame itself is not hard enough, and the drywall will still resonate and absorb, but the effect will be weaker and you may be able to get rid of the buzz. But ideally, it is better to lay out the wall with partition walls or (it will be a fairy tale in general) with bricks.
Bare walls
It is easy to guess what threatens the bare walls. Reflecting as if from a mirror, the sound at any frequency will walk around the room for a long time, turning the music into a mess.
Worst of all is bare concrete. Even the wallpaper is a little save the situation. But if you take sound seriously, then the use of various absorbing materials can not be avoided. It should be noted that it is not necessary to cover all walls with an absorber. Most often in a residential area it can not be done. Therefore, you just need to drag everything into the room that absorbs the sound: upholstered furniture, best of all made of cloth, and not leather, soft toys, carpet on the floor (or on the wall, if
A good test for the result: sit where you are going to listen to music and clap hard. If after the clap you hear an unpleasant metallic chime, then you need to do something.
If you want to go further and equip the room with special sound-absorbing structures, it is important to try to place them a little further from the wall, and not directly on the wall. The thing is that the closer the absorber is to the wall, the absorption of sound starts from a higher frequency. We want to start at least 300 Hz, this is the frequency at which the sound wave starts to become directional, the absorber really begins to absorb, and you can purposefully place the absorber in the path of the reflected sound from the speaker to you. We also remember that the hum at these frequencies significantly affects the subjective perception of the bass. The characteristic half-wave size for these frequencies is about half a meter, so it would be good to place the absorber approximately at the same distance from the wall.
If habrazhiteli deign to the affected topic, in the next article I will gladly share ideas for homemade designs for absorbers.
A couple of practical tips on placing sinks. For them, the space between the columns on the wall behind them and the wall opposite to the columns are very well suited. Side sinks, it is better to put in two (or rather, four, taking into account symmetry) places. First place: this is the path of the reflected sound from the speaker to the point where you will sit. To find this place, you need to put a mirror against the wall so that you can see the speakers. But with such absorption it is impossible to overdo it. If you too much muffle the sound reflected from the side walls, you will hear the stereo effect only in a narrowly defined place. Just to the left and right - the sound image will be lost. The second convenient place is on the perpendicular line from your ears to the side walls, if they are not very far from you.
If you are ready to show even greater determination, you can drown out the ceiling. It can be jammed everywhere: by experience, the over-muffled room is better than the un-muffled one. Is it worth to think about the power of the amplifier and speakers: turn off - it will be quiet, and add volume - distortion will go. Therefore, it is necessary to add absorbing material gradually, checking the result at each step. You can check it with your ears, but you can measure it. Again, if there is interest, in the next article you can delve into the available measurement methods and methods for calculating the right amount of absorbing material.
Well, the carpet on the floor between you and the columns never hurts. Best of all from natural material: this carpet will have a more even absorption.
Mystic with “bass sinks”
In practice, it has been verified that placing sound-absorbing material in the corners of a room is useful for bass (and not only). I could not find a reliable theory on this topic. There are various assumptions, but I do not really agree with the term “bus trap” (bass absorber). In my experience, from such structures the bass does not become smaller, but even quite the opposite. There is another: room resonances are significantly weakened. My unconfirmed theory is as follows (criticism is accepted in the comments). The greatest sound pressure is concentrated in the corners of the room, since there is the smallest amplitude of the sound wave (the amplitude and pressure in the sound wave are inversely proportional). This is due to the fact that the sound is a transverse wave, and near the wall the amplitude of this wave is naturally zero. A standing wave needs to be pumped to continue its existence, and it is pumped with frequencies close to the resonant one. This pumping does not occur through the amplitude, but through sound pressure, that is, it occurs in the nodes of the wave, where the density of the gas is greater. By analogy: to swing the strained rope is easier at the point where it moves least. If at these points we place an absorber, the Q-factor of the resonance decreases, and the pumping of the resonant waves weakens. As a result, subjectively bass becomes more, not less, because it does not go into the rumble of a standing wave. Not to mention the quality of this bass. I don’t know how you like my theory, but in practice I did measurements and the result is unambiguous: when adding an absorber in the corners, resonance peaks significantly decreased and frequency response dips in the low-frequency range were raised, and the reverberation at resonant frequencies was also significantly reduced without any general fall in the average level on the low bands.
More practical tips
At the end I will add a few more practical tips, tested on my own experience.
Understanding the purpose of your actions is very important. I often hear the statement that the task of acoustic design of a room for listening to music is to achieve close to perfect frequency response. This is not quite true and difficult to achieve. The fact is that our hearing is quite adaptive: the fans of Time Machine equally enjoy the concert of this group in completely different rooms and even in the open air. In our usual room for hearing, we can easily mentally compensate for the influence of the room, quickly forget about it and enjoy, be it cinema or music, unless, of course, the acoustic effect of the room goes beyond certain comfortable limits. In particular, the reverb range for music that is comfortable for us is quite wide, and reaches about 0.8 sec. With a not very significant distance from the speakers, the main volume of sound comes to us directly from the speakers without any distortion. The main thing is that there are no oddities in the acoustics of the room, such as large peaks or dips or tricks with reverberation, as well as various secondary overtones. Everything else is a matter of taste.
Regarding the placement of the speakers: the sound that you hear is very dependent on how far the speakers are from the wall and from each other. The distance from the wall you can adjust the amount of bass. The closer the speakers are to the wall, the more they bass. But you should not overdo it: the closer they are to the wall, the more eagerly they excite room resonances. Changing the distance between the speakers, you adjust the distribution of bass: the closer they are, the more the upper bass sticks out, the farther away - the more low frequencies stand out. Well, we still have to remember that our task is to ensure the symmetry of the speakers, so they should, if possible, be placed more or less symmetrically in the room. And more: it is necessary to minimize any identical or multiple distances. For example, the distance from the two adjacent walls to the column should be significantly different and not multiple.
The subwoofer should be placed at the point where it excites less resonance, but you hear it well. Put it in the center of the room, it probably will not be heard at all. Put right on the wall - will resonate resonance. The correct way to find the starting point for experiments is this: turn on the music with an abundance of drummer and bass guitar (modern blues recording goes well) without a subwoofer, find the point where, from your point of view, the bass sounds most seamlessly and try to put a subwoofer there. And then you have to experiment with the selection of the first place, and then the parameters of the subwoofer, either by ear, or by using measurements. However, if you have the ability to measure, then the starting point is better to find the most even frequency response at low frequencies, and not by ear.
If you sit in the middle of the room, then the bass, most likely, will not. Therefore, from the very beginning it is better to plan a place near the wall opposite the columns. Again, the closer to the wall, the bigger the bass, but the more it is booming. Here we must also experiment.
The design of most speakers assumes that they are aimed at the listener, although there are instances with a wide MF and tweeter pattern. In any case, do not put them in parallel to each other. It is also necessary to respect the height of the column: it affects the sound, even if you raise the column a couple of centimeters.
And finally: be careful with any theoretical calculations regarding the acoustic design of small rooms. All canonical theories are much better suited for large halls. In a small room there is such a thickening of many factors that formulas become very approximate. Therefore, rely more on step-by-step experiments and simple and logical arguments. This, by the way, is very exciting.
If you have reached this line, you are interested in the topic, you want to know more, and English is not alien to you, I strongly advise the fundamental work of F. Alton Everest, Ken C. Pohlmann, Master Handbook of Acoustics.
I would be glad to read about your own research in the field of home acoustics in the comments.
Source: https://habr.com/ru/post/250247/
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