Home cinema: why not build a concert hall La Scala in a khrushcha??

At the moment when a musician decides to buy “serious” audio equipment, most often he does not even suspect that the acquisition of high-quality equipment is not enough. When he brings the equipment home, he is faced with the question of how best to arrange it? And, most importantly, where – in what room, with what walls?

A living room’s audio capabilities vary enormously, in size, configuration, and placement of furniture. Even if this condition is met, it is too early to say that all the problems are solved, since it is possible that the room itself will require some changes.

It should not be forgotten that loudspeakers and the room form together a single acoustic complex, which requires a coordinated solution, and changes in the location of speakers and measures to correct the acoustics of the room do not replace, but complement each other with mutual influence.

Let’s try to systematically understand the problems that may arise for those who want to achieve the maximum quality of listening with the existing equipment. First of all, let’s define the scope of the topic. We won’t speak about either palaces of oligarchs with huge halls or very small rooms, as in both cases using ordinary audio equipment makes no sense.

So let’s focus on a medium sized room in a standard city dwelling, from 15 to 30 sq.p.m.m. Most of the audio equipment is bought for such an area, by the way, not only in America, but all over the world.

Speaking also about the listening room arrangement, we will leave out of consideration the fans, capable to spend on arrangement of ideal listening environment means beyond the possibilities and needs of normal, – NORMAL music lovers. And one more limitation – preservation of comfortable interior and possibility of universal use of your room for listening.

But first let’s find out what’s going on at the other end of the food chain, i.e.e. how the phonograms are listened to where they are produced, in the recording studios. Recording studios, like any other production facility, come in small, medium and large.

Large ones are for recording orchestras, choirs, large ensembles, medium ones for rock and jazz bands, and small ones, also called project rooms, are used for recording singles with background music, vocalists or instrumentalists, announcers, etc.p.

The size of the room where a sound engineer sits is usually proportional to the size of the hall where the artists are located: in a small studio the sound engineer sits in a small room right in front of the mixing desk while in a big studio the sound edit room is big enough with chairs for the producer and the musicians so they can listen to the recording or mixing sessions. Accordingly, the acoustic systems, which are called in studios reference monitors, differ as well.

In a small studio you can place monitors only directly in front of the sound engineer, not more than a meter and a half away. Such monitors are called near field monitors. They are compact two-way systems, imitating hi-fi and multimedia speakers, with 6″ or less woofers and a low frequency range of about 70 Hz. The term “near field” here means not only the distance, but also the fact that the listener hears the predominant direct sound of loudspeakers with minimal ideally nonexistent influence of room acoustics.

Near-field first four , and mid-field fifth monitors

Bigger studios add two or three-way middle field monitors to the near field monitors, which are bigger in size the woofers are up to 8 inches , have the lower limit of the range at about 40 Hz and are set at a greater distance, up to two meters. They show the sound engineer roughly how a phonogram would sound on a Hi-Fi system.

Two on the left are midfield monitors, two on the right are nearfield

Finally, three- or four-way far-field monitors with a range up to 30-25 Hz at the bottom, available only for large studios, are designed to simulate powerful concert acoustics – of course, at a short distance of the studio room, at a distance of 3-5 meters.

Far-field monitor

Apart from the size and electroacoustic characteristics of speakers, the distance between them and the listener is also very important. This distance can greatly change the character of the sound, and not only in the sense of volume.

Small speakers have a fairly narrow pattern at high frequencies, and if the listener sits further away than recommended by the manufacturer, and the speaker axis is not aimed directly at him, the high frequency radiation will be significantly weakened, the sound will become more deaf, duller. By the way, the opposite is also true – listening in close proximity to the mid and far field monitors will disappoint the listener – you should work with them only at the recommended distance.

Apart from the distance from the listener to the monitors the acoustic environment of the studio is also important. It is clear that it should be as much as possible acoustically isolated from outside noise, and measures are taken for it during creation of studios by the way, very expensively , but the matter does not stop there. Adjustments are always made to the room’s own acoustics.

All of this is true for a room for domestic music listening.

The basic properties of room acoustics

Before we speak about the room acoustics, let’s consider the patterns of sound wave distribution.

As you know, sound waves travel in all directions, so at a certain distance from the source to the listener there comes not only a direct signal, but also reflections from the walls. The bigger is this distance the more reflections in sound which are heard by the listener.

Sound reflections

This phenomenon is called “reverberation. You get more reverberation in a large room and less in a small one. Everybody knows how loud an empty room with no furniture sounds and how it gradually becomes more and more deafening as the room fills up. But an empty ringing room is good for singing, and listening to music is best in a room devoid of its own sound. Sometimes it is claimed in articles on this subject that there are “good sounding” rooms, which supposedly give the sound fullness, etc.p. But do not forget that

everything that should be present in the sound is already done by a sound engineer in a recording studio, and our task is to make sure that the original, that is direct signal reaches the listener’s ears with minimal changes, and ideally without any.

The room must not add anything to the sound of the finished phonogram!

So it is necessary to neutralize the sounds in the room as much as possible.

Standing waves.

Apart from reverberating reflections, rooms – especially small ones – can have “standing waves”, which are places in a room where low frequencies are either amplified or attenuated. Standing waves can also form in large rooms, but at such low frequencies that they are negligible, but for small rooms they can be a real problem.

A related problem to standing waves is the room’s own resonance.

In a large room the resonance frequency is very low, units of hertz, and cannot be heard, but in a small room the resonance frequency of the room gets into the audible range, and in a very small volume, like a toilet or a closet “mother-in-law’s room”, even the low notes of the male voice can resonate. Therefore, listening to music in very small rooms is undesirable even in the direct radiation of near-field loudspeakers.

Wall vibration.

If you are doing it in a “khrushchevka”, do not overdo with the force of the impact, in order to avoid the appearance of “additional windows”. It may sound funny, but one of my classmates told me that a neighbor across the wall was inserting lines into her conversation with her parents..

Brick walls practically have no such properties, as they are made up of many separate elements, but a solid panel can be vibrating.

To check it out – just hit the wall with your fist, preferably in an empty room: if you hear a soft thud very shortly – the wall does not resonate, and if the sound is slightly humming for a long time – the wall vibrates and can accumulate and recoil low frequency vibrations. To an even greater extent this applies to wooden houses of timber or cladding.

The harm of reflections

As it was said before, reflections add missing components to the original recorded signal, i.e. e. additional sounds. So you don’t hear exactly what the engineer in the studio recorded. Reflections blur fine details in the sound called transients , change the tonal balance of the recording, and can therefore add unwanted coloring to the overall sound.

Sound reflection and absorption

Anyway, even in a room with no audible resonance or standing waves, you need to take steps to absorb reflections. It’s not hard to attenuate high frequencies – you just need lots of soft objects in your room: armchairs, sofas, and fabric products like carpets, thick window blinds and so on.p., But it is much harder to fight low frequency reflections because the low frequencies have a long wavelength, up to several meters, and carry more energy which takes longer to decay.

An inexpensive way to reduce the bass in a room is to install wall mounted panels with lots of small diameter holes.

Large quantities of these panels were produced in the USSR, where they were used to decorate the walls of offices and public places with high noise level, such as post offices, post offices, bank offices, hotel lobbies, etc.p. They looked good at the time, but now it is better to look for their more aesthetic analogues, which will fit into the interior of the modern house.

For example, very popular are flexible sound-absorbing boards of domestic production “Shumanet”, which are available in different types, sizes, colors, etc.p.

Another problem is reflection from the back wall, especially noticeable if the listener sits in an armchair or on a sofa close to the wall. If you can’t move your chair a meter away from the back wall, you can hang a soft, thick rug or tapestry on the wall. You can even put there an open bookcase or shelves on which to arrange books of different sizes and, importantly, putting them at different distances. Analogous to an acoustic diffuser. The same way with open bookshelves can be applied to the side walls.

Sound dispersion

Another way to dampen side reflections is the use of special textile materials. This material resembles dense felt or thick felt, and is about a centimeter thick. It’s glued to the wall like wallpaper, which reduces reflections and improves soundproofing at the same time.e. Keeps sound out of the room. But these materials are expensive, so it is worth to think what is more important to you – better acoustics or a good interior and a good relationship with your spouse.

Once upon a time, amateur school, etc. recording studios were finished with a commonly available diffuser made from cardboard egg crates. This product does not give any soundproofing, but with the task of scattering, i.e.e. absorbing frequencies over a wide range, including low frequencies, the material does an excellent job. Filled with porous foam construction and glued over an insulating material, it’s as quiet as a professional studio.

But, – alas, the view of the room, pasted over with egg-cells, even painted, suitable for home interiors, only if you are engaged in contemporary art, or convinced bachelor. There are modern analogues of cellular absorbers, such as the Italian Akustik STOP, which are plates with convex pyramids of polyurethane foam. They don’t really fit in all living areas, but they work fine, so you decide if you want to sacrifice the decor for the sound.

Akustik STOP diffusion material

Why do you think there are so many “Napoleons of sound” among the exhibitors and visitors at any Hi-Fi exhibition?? People studied wave jamming in rooms with soft walls and didn’t have time to adapt..

Professional studios use so-called “bass traps”. Put simply, these are vertical cylinders made of soft materials like the rollers of antique sofas placed in the corners of the room at a short distance from the walls. They prevent resonance at low frequencies in the corners, which are, in fact, analogous to horn sockets.

You can look at home or in a furniture store something similar to the above-described soft rollers, if you have corners of your rooms are not filled with anything.

One more point – even in a quiet muffled room there may be resonances of certain interior items at certain frequencies. On a low-frequency sliding tone the glass of windows and cases, doors, picture frames on the walls, ashtrays or dishes on the coffee table, etc. may rattle. p. If this rattling or audible vibration is detected, find and fix the “guilty” items with pads made of soft fabric, rubber, etc. p.

Let’s assume that we have rid the room of resonances and reflections. Now let’s turn to speaker placement. I’d like to point out at once that

In articles on setting up a home audio system it is often advised to experiment with the speaker setup first, before moving on to the next room. This is never done in professional studios,

– There designing the room and its finish with specific models of speakers and their placement in mind beforehand. In our case we can guarantee that in a properly prepared room different acoustics will sound good – in different ways, but good.

If you have a large room, you can place both small “near-field” speakers but you will have to sit in close proximity to them and medium sized “mid-field” speakers. This is true, IMHO, for cases where small and medium-sized speakers are installed in the apartment.

Location for small speakers

The placement for mid-range speakers

Large acoustic cabinets of far-field, although regularly exhibited at Hi-Fi exhibitions as “the highlight of the program” are purchased very rarely for a typical home, because they sound good at a distance of more than 5 meters in a heavily drowned room. That’s for owners of mansions we’ve put out of the scope of our topic!

As already said, small speakers normally work at a distance of no more than one and a half meters better not more than a meter , with a greater distance greatly weakened the already poor bass component of the signal.

“Shelf acoustics” is a purely domestic concept, it includes both near-field speakers and the middle field, whoever wants to. We use the term “Listening Distance”, but generally speaking, for home environments the term “Middle Field” applies.

In recent years, there has been a compromise between the two, the so-called “2-Way Configuration.1”, when small speakers are “backed up” by a bass speaker – a subwoofer.

The only good thing in it is that low bass really appears in the sound, but there are enough disadvantages: distortion of tonal balance because the sound of the bass and treble/midrange speakers is unbalanced if the phase does not match , blurred sound clarity in the whole range, the bass may be detached from the overall sound picture, the sound of the middle frequencies and the bass may be distorted in timbre, etc.d. etc.p.

In any case, System 2.1 is a commercial compromise to get the bass up to “kick in”. If you have 6-7 inch LF speakers working at 40-45 Hz, you do not need a sub at home you need it at the discotheque , but if you have “kids” with 4-5 inch woofers, you need a sub, but the sound will not be great, though the bass will appear.

Subwoofer is appropriate for a disco, where the main thing is to make the bass “kick” and “pump”, and no one is going to listen to the fine details of the sound. That’s why the discotheque acoustics is usually much cheaper than the concert acoustics, not to mention the studio one .

If you, using small speakers, feel evident lack of bass, turn on the subwoofer at a low volume, so it only “thickens” the bass line a little. Or better yet, get a larger midrange speaker.

The general rule for placing a stereo system is to create an equilateral triangle formed by the lines between the two speakers and the listener. The triangle may be pulled slightly toward the listener. In practice this means that if you increase the distance to the listener and the speakers should be spaced accordingly wider. The question is often asked whether it is better to direct the speakers’ emission axes towards the listener or to leave the cabinets standing straight up – perpendicular to the back wall?

The answer is that for some models of speakers it is not necessary to turn them toward the listener, for others it is necessary, so, – in general, it is better to turn, but if it looks unaesthetic, you should try whether such a turn gives a sonic effect. If not, it means you’re lucky, you got a speaker with a wide angle of sound dispersion in professional slang it is called “angle of opening” . This means that high frequencies are emitted in the direction of your head, not past.

Radiation at low, mid, and high frequencies

It is usually indicated in the speaker’s documentation and can be referred to as such. For example, the angle of dispersion is specified as 40 degrees in the horizontal plane. Go up to your speaker and place a ruler perpendicular to it and another ruler at a 20 degree angle to it and see where the end of the ruler points, then do the same in the other direction. If it points to a place outside your listening area armchair, sofa, etc , it’s OK – you are in the right place.p.If it points outside your listening area armchair, sofa, etc , everything is OK – you are in the uniform axial radiation area.

Correct placement vertically

As a matter of fact, studio monitors and consumer speakers have a much narrower angle of opening in the vertical area than in the horizontal, and if the speakers are set too high or too low, or tilted vertically, the listener is off the axis of radiation, so the best height for the speakers is when the tweeters are flush with the listener’s ears. For a seated person the height is one to one and a half meters, depending on the height of the seat.

The placement of the speakers in depth – how close they are to the back wall – is very important. If the speaker is installed at some distance from the wall – but not more than a meter, it sounds linear, without resonances. Placing it against the wall will amplify the low frequencies, even if there is no reflex port on the back of the cabinet.

How corner placement affects the bass level

By placing the speaker system in the corner, you will amplify the bass signal even more, and placing the speaker system on the floor in the corner will be the equivalent of increasing the bass amplification power of 12(! times! It is clear that you can’t put speakers like that to listen to music, unless it’s for dancing.

It is interesting that if you immure the speakers into the wall flush with its surface forming a so called sound screen the increase of recoil at the bottom though will be but less than if they are placed next to the wall. That’s why in recording studios placing monitors, especially the far ones, into the wall is a common practice, they often do it in cinemas, too. Of course, for the home such a solution is almost unrealistic, but if you place the speaker between two large mirrored cabinets on the same plane, you get a similar effect.

But even a speaker placed away from the wall is a counterphase phenomenon, which should not be confused with a standing wave. Counter-phase occurs when the radiator is a quarter of a wavelength away from the back wall. At 80 Hz a quarter of the wavelength is about 1 m, at 60 Hz about 1.5 m and at 40 Hz about 2.2 m. So, a distance of one to two meters is the most dangerous in the sense of counterphase and to put the speakers in such a way that the cone is at a specified distance from the wall, is impossible.

Not only the lowest frequencies can fall into antiphase, but also higher ones, and the combination of these antiphases gives a lot of peaks and dips, called comb filtering AFC graph becomes like a comb . Thus, a small distance of less than a meter remains for an acceptable placement of the speakers, because, as mentioned above, to put the speakers up against the wall is also not possible. There is only one way out – the maximum damping muting of the wall behind the speakers to reduce reflections from it.

True, there is one more way to improve the acoustics of a room – the use of special devices and computer programs that make frequency corrections in the amplified channel when you play records, but that’s another topic altogether…

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