Equipment for listening to music
It is unlikely that there will be many people on Habré who do not like music or cinema. But then you decided that you were tired of headphones, that you want to listen to how your favorite music really sounds, and, having accumulated a little money, you went to different shops from the heart and bought a good (to your taste) audio system.
More often than you want, such purchases do not deliver the expected satisfaction. When the speakers are placed where it is convenient and practical, the cables are connected and your favorite track is launched, it turns out that everything does not play 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 ignoring this fact that is the most common reason for meaningless additional costs for unnecessary components, convulsive throwing around the room in search of the correct speaker layout and other troubles. About what to do in order to return the charm to the sound, and to get the maximum sound out of the system, I ask for cat.
Below I will talk about music, but all that has been said applies to cinema and to any other kind of art with an audio component. Let's start with the typical enemies of good sound.
A room with approximately the same dimensions in any dimension.
Those who still remember physics will immediately guess what is the matter. But the matter, of course, is in spurious 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 dimensions in the room lead 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 highest volume will be at half the wavelength, then at a quarter, etc. The second problem is the attenuation of sound at these frequencies is much slower. The bass is already playing on a different string, and you still hear the echo of 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 2 meters in size, the frequency corresponding to the half-wavelength will be 82.75 Hz, and in a three-meter size we will get a buzz near your favorite 50 Hz.
In reality, there are a lot of standing waves in the room, since they go not only perpendicular to the walls and floor, but also from corner to corner, and to roughly calculate at what frequencies resonant modes will appear, 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 Hindicate 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, as a result of which the frequency response of the room is smoothed. If you are interested in the tangential mode for length, then put 1 over L , if the oblique horizontal mode (for example, from corner to corner), then put 1 over L and W , and if you need an oblique mode from the lower corner to the upper, then the formula contains all ones. Everything is simple. Kind people have long thought for us, and by googling you can find a ready-made Excel tablet with formulas (or a website with a script), where you insert the dimensions of your room and immediately see the whole picture.
Here one more simple truth must be taken into account: in music there are rarely frequencies below 30 Hz, and the sensitivity of our ear to these frequencies is much lower (we hardly hear them, but rather feel with the 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 worried about the quality of sound of a bomb explosion. In secret, I’ll say that the subjectively pleasant sensation of the whip of the “booms” sound, as well as the impact of the sticks on the drum, to a much greater extent 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 larger room with different linear dimensions. And the hell for bass happens in a 3 by 3 by 3 meter room, where listening to music will not work in any case,
And one more thing: the above formula works in the ideal case of absolutely reflecting 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 my own experience.
This material is attractive in that it allows you to quickly and cheaply build internal walls and bashfully cover up the failures of the domestic construction industry. But, unfortunately, a sheet of drywall (even double), attached to a metal frame with a standard pitch, is an excellent membrane. He will bury almost the entire bass alive, which your speakers will give out, tugging. And in the process of the funeral, he will also reflect this sound at his own resonant frequencies, sometimes very audibly tightening.
The question is what to do? If you got a finished room, a subwoofer can partially save the situation. If you read this article before the start of construction or repair, you can manage to take preventive measures. For example, you can make a more frequent step of the frame and add horizontal elements to the vertical posts. To some extent, this will improve the situation, but hoping for a miracle is not worth it: the tin frame itself is not rigid 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. And ideally, it is better to lay the wall with partition plates or (it will be a fairy tale in general) with a brick.
It’s easy to guess what bare walls threaten. Reflecting like a mirror, sound at any frequency will walk for a long time around the room, turning music into porridge.
Worst of all, bare concrete. Even the wallpaper is already a little save the situation. But if you take the sound seriously, then the use of various absorbent materials can not be avoided. It should be noted that it is not necessary to cover all the walls with an absorber. More often than not, this is not possible in a residential building. Therefore, you just need to drag into the room everything that absorbs sound: upholstered furniture, best of cloth, not leather, soft toys, a 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 slam sharply. If after a pop you hear an unpleasant metallic ringing, then something needs to be done.
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 to the wall, the higher the sound absorption begins at a higher frequency. We want to start at least with 300 Hz, this is the frequency at which the sound wave begins to become directed, the absorber actually begins to absorb, and you can purposefully place the absorber in the path of the reflected sound from the speaker to you. And we also remember that the rumble at these frequencies significantly affects the subjective perception of bass. The characteristic half-wave size for these frequencies is about half a meter, so it would be nice to place the absorber at about the same distance from the wall.
If the hawkers deign to the topic, in the next article I will gladly share the ideas of home-made designs for absorbers.
A couple more practical tips for placing sinks. The space between the columns on the wall behind them, as well as the wall opposite the columns, is very suitable for them. Side absorbers, 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 on the wall so that you see the speakers. But with such an absorption can not be overdone. If you drown too much the sound reflected from the side walls, then you will hear the stereo effect only in a narrowly defined place. A little to the right and left - the sound picture 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 decisiveness, you can drown the ceiling. It can be jammed everywhere: according to experience, an overcrowded room is better than an undercooked one. Unless you should think about the power of the amplifier and speakers: muffle - it will be quiet, and add volume - distortion will go. Therefore, it is necessary to add absorbent material gradually, checking at each step the result. It can be checked 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 of calculating the required amount of absorbing material.
Well, the carpet on the floor between you and the speakers never hurts. Best of natural material: such a carpet will have a more even absorption.
Mysticism with “bass absorbers”
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 subject. Various assumptions are made, however, with the term “bus trap” (bass absorber), I do not really agree. In my experience, from such designs the bass does not get smaller, but even quite the opposite. Another thing happens: room resonances are significantly weakened. My unconfirmed theory is as follows (criticism is accepted in the comments). The largest 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 sound is a transverse wave, and near the wall the amplitude of this wave, naturally, is zero. A standing wave needs to be pumped to continue its existence, and it is pumped by frequencies close to the resonant one. This pumping does not occur through amplitude, but through sound pressure, that is, it occurs at the nodes of the wave, where the gas density is higher. By analogy: it is easier to swing a stretched rope at the point where it moves least. If we place an absorber at these points, then the quality factor of the resonance decreases, and the pumping of the resonant waves weakens. As a result, subjectively, the bass becomes more, not less, because it does not go into the hum of a standing wave. Not to mention the quality of this bass. I don’t know how my theory suits you, but in practice I did the measurements and the result is unequivocal: when adding the absorber at the corners, the resonance peaks dropped significantly and the frequency response dips in the low frequency region rose
More practical tips
In the end, I’ll 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 ideal frequency response. This is not entirely true and difficult to achieve. The fact is that our rumor is quite adaptive: fans of the “Time Machine” equally like the concert of this group in completely different rooms and even in the open air. In a room familiar to hearing, we easily mentally compensate for the influence of the room, quickly forget about it and enjoy it, whether it be a movie or music, unless, of course, the acoustic effect of the room does not go beyond certain comfortable limits. In particular, the reverberation range that is comfortable for us for music is quite wide, and reaches about 0.8 seconds. At 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 the acoustics of the room do not have any oddities, such as large peaks or dips or tricks with reverb, as well as various secondary overtones. Everything else is a matter of taste.
Regarding the placement of the speakers: the sound you hear very much depends on how far the speakers are from the wall and from each other. The distance from the wall can be adjusted the amount of bass. The closer the speakers are to the wall, the more they basy. But you should not overdo it: the closer they are to the wall, with the greater zeal they excite room resonances. By changing the distance between the speakers, you control the distribution of the bass: the closer they are, the more the upper bass sticks out, the further - the more low frequencies stand out. Well, one should not forget that our task is to ensure the sound symmetry of the speakers, so they should be placed more or less symmetrically in the room if possible. And one more thing: you need to minimize any equal or multiple distances. For instance,
The subwoofer needs to be placed at the point where it excites resonances less, but you can hear it well. Put it in the center of the room; it will most likely not be heard at all. Put it right against the wall - resonances will stick out. The correct way to find a starting point for experiments is this: turn on the music with an abundance of drummer and bass (a modern blues recording is good) 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 first selecting the place, and then the parameters of the subwoofer, either by ear or by measurement. 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 there will most likely be no bass. 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 more bass, but the more booming it is. Here it is also necessary to experiment.
The design of most speakers suggests that they are aimed at the listener, although there are instances with a wide beam pattern of midrange and tweeter speakers. In any case, do not put them parallel to each other. You must also respect the height of the speaker: it affects the sound, even if you raise the column a couple of centimeters.
Well, and the last: 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 the formulas become very approximate. Therefore, rely more on turn-based experiments and simple and logical arguments. This, by the way, is very exciting.
If you have reached this point, the topic interests you, you want to know more, and English is no stranger to you, I highly recommend the fundamental work of F. Alton Everest, Ken C. Pohlmann, Master Handbook of Acoustics.
I will be glad to read about your own research in the field of home acoustics in the comments.