There are some different approach to handle room acoustics. Here are the 2 that are quite well accepted.
Here is the information by Limage, a local Hong Kong well respected audiophile.
Few of us, except perhaps the rare species of odd fossils of the pre-historic era, would have questioned the paramount importance of speaker placement nowadays. What is more debatable is where and how the speaker positions are to be determined. I have been a faithful follower of the room-coupling school and I believe that should be the best way out.
Room coupling, I am quite positive by now, really goes beyond the deliberations over direct verses reflected sound sources, because the focal point remains relatively constant irrespective of what damping treatments we have on the wall surfaces in any given room. This focal point does not seem to move until the dimension of the room is drastically changed.
To achieve effective room coupling, one has to locate the focal spot of the room first. There is a simple yet effective method to find this spot but I shall come back to that a while later. Every room has its own peaks and valleys acoustically. The peaks are resonances and the valleys are just the opposite, the suck-outs as a result of phase cancellation. I used to believe the coupling point is the spot where multiple resonances gravitate since it clocks the highest sound level throughout the audio band. If we look at it the other way round, however, the focal point of the room should more correctly be taken as the spot where phase cancellation is the lowest.
When the speakers are placed along this focal spot, phase cancellation would be at its minimal obtainable within the room and the system will then be able to resolve, with the best of fidelity and the least of distortion, the myriads of spatial information contained in the recording. The width and depth, the ambience, the layering and instrument placements etc. will all spring to life. Proper sound staging, no doubt, has much to do with this phase coherency across the audible frequency range. We all know what would happen if one speaker is inverted in phase—there will be no imaging, no soundstage, and even no sense of direction. This is the result of serious phase cancellation. Even if the speakers are properly in phase, however, there would still be a fair amount of cancellation depending on where the speakers are placed.
Ideally speaking, the room should be symmetrical in overall shape and the speakers symmetrically placed along the lengths of the rectangle. If one speaker is close to the side wall while the other is in the middle of the room, a rather common sight given the popular L-shape layout of sitting rooms in HK, there exist more chances for cancellation taking place at various frequencies, rendering the imaging blurred, stage collapsed and ambience lost.
Once the speakers are coupled to the room, the two merge into one. The room becomes an effective extension of the speakers which in turn would cease to exist visually. Tuning for solid imaging then becomes much easier. Human ears locate the sound source by detecting the time difference of direct sound arriving at the ears. To achieve three dimensional imaging, all we have to do is to cut down secondary reflections from overwhelming the direct sound. While on this subject, I like to point out that I have tried the live-end-dead-end approach and it did not work to my satisfaction. I believe speakers are designed with the average western style living room in mind where upholstery, curtain, carpet and furniture all contribute to an acoustic environment which is neither too dead nor too live, but moderate throughout. This is something worth considering when we set about fabricating our listening area. It is not uncommon to find that the more elaborately contrived the HiFi room is, the less satisfactory it often turns out.
Some fellow audiophiles suspect that because of the rather up-front placement of my speakers and because they are dipoles which radiate both ways, the large volume of space behind the speakers is encouraging tremendous amount of diffused reflections to create an artificial depth of field. Not so. Multi-mike mixed down recordings are rendered as they are, with absolutely no depth and instruments do stick with the speakers whereas a good concert hall recording has the ability to project the soundstage well beyond the boundaries of my small room while the speakers, despite their imposing size, simply disappear without a trace. Artificial depth just cannot differentiate as such.
All in all, phase coherence does appear to be the key and with this key we stand every good chance to unleash a completely new dimension of audio realism.
Here comes the core—the action part of the whole thing, a method that has proven to work wonders for me over the last 30 odd years.
Have the speakers placed along the lengths of the room, about ¼ to 1/3 from the back wall, and ¼ the breadth roughly. Then play some vocal music, the hilarious type, the more instruments the better.
Now walk slowly to and fro along the mid-line between the speakers, from one end of the room to the other and then back, may be several times to get the mind set (if the speakers are standing low, you may well have to crawl). Somewhere along the aisle, you would hear the sound getting louder and at the same time it rises above your head, filling the ceiling as if you’ve entered a Gothic church. Bingo, that is it, the focal point.
Mark this focal point and drag your speakers over the lateral line crossing the spot. You’ve just coupled your speakers to your room. What is left, may be the crucial part yet, is to find the perfect stereo seat. As the name suggests, you’ll have to look for the widest stereo soundstage again along the aisle, between the speakers. If one side of the room does not give you the best definition and soundstage, try the other side. I was the one having my seat moved over to the wrong side of the room to get the best out of my system.
Final note, if you are unable to find the focal spot despite trekking up and down diligently the whole afternoon, your room dimension is probably too bad to be a listening room. Try another room if you have one. If not you’ll have to move house.
Here is the information by Barry Diament about setting up monitors for monitoring
Now that we’ve treated the listening space, it’s time to introduce the monitors.
In the old days, most folks thought they’d achieve stereo by placing their speakers on opposite sides of the room, often in the front corners. “Separation” was the goal and the reward was hearing those records that featured a marching band appearing to move from one speaker to the other. Or folks would marvel at recordings of small ensembles where the guitar was “on the left” and the piano was “on the right”. While this was entertaining, it wasn’t stereo.
With the old speaker arrangement, sound tended to localize at each speaker with the sound appearing to come “from the speakers”. Close proximity of the speakers to the front and side walls allowed early reflections to blend with the direct sound, smearing detail and altering harmonic balances. Further, the corner placement was very effective at stimulating every mode the room had, resulting in boomy bass and a loss of overall clarity.
As early as 1954, the English journal Wireless World published an article by Peter Walker that spoke about speaker placement for stereo reproduction but it took another three decades for the concept to really catch on. Walker found he could maximize the performance of his speakers by placing them 1/3 of the way along the room diagonals. And so was born what has come to be known as “The Rule of Thirds”.
Another strategy for speaker placement, from George Cardas, is based on the mathematical “golden ratio”, also called a “golden section” or “golden mean”, which Webster defines as “a proportion (as one involving a line divided into two segments or the length and width of a rectangle and their sum) in which the ratio of the whole to the larger part is the same as the ratio of the larger part to the smaller”. This can be expressed as a number equal to half the sum of 1 + the square root of 5, which would be 1.618.
Applied to speaker placement, the golden ratio dictates that the distance of a speaker from the nearer side wall would differ from its distance to the wall behind it by a ratio of 1.618. In other words, take the distance from the center of the speaker to the nearest side wall and multiply it by 1.618 to get the distance it should be placed from the wall behind it. Now take that number and multiply it by 1.618 and you should get the distance from the center of that speaker to the opposite side wall. That would give you one possible speaker arrangement. You could arrive at another possible placement by taking the distance from one speaker to the wall behind it and multiplying that by 1.618 to get the distance from the center of that speaker to the near side wall.
In my experience, a simplified placement approach that combines elements of both the Rule of Thirds and the golden ratio has worked successfully in every room in which I’ve heard it. Please keep in mind that your particular situation may well require some adjustments to what you’re about to read. What follows however, should provide you with a good starting point. First, decide which wall you want behind the speakers. Some prefer using the short wall, so the speakers fire down the length of the room. Others will use the long wall, which allows for more space between each speaker and the side wall it is closest to. Once you’ve decided which it will be, place the speakers so the space between them equals 1/3 of this wall’s length. Note we’re not using the center of the speaker as the reference here but its inside edge instead. Now measure the dimension of the room along which the speakers are firing (i.e. in the direction from the speakers to the listening position). Move the speakers forward (or backward) until the front of the speaker is 1/3 the length of this dimension from the wall behind it.
For example, let’s say you’ve decided to have your speakers fire down the long dimension of the room. This means the short wall will be behind the speakers. If your room measures 12′ by 19′, you’ll leave 4′ (i.e. 12′ divided by 3) between the inside edges of the speakers. If your speakers happen to be 1′ wide, this puts their centers 5′ apart, with 3′ from the outside edge of each speaker to the nearest side wall. The 19′ dimension divided by 3 will point to having the front edge of each speaker 6’4″ from the wall behind the speakers.
Let’s try another example, this time where the speakers are arranged against the long wall of the same room. In this case, we’d have 6’4″ (i.e. 19′ divided by 3) between the inside edges of the speakers. With our 1′ wide speakers, there would be 5’4″ from the outside edge of each speaker to the nearest side wall. Distance from the front edge of each speaker to the wall behind it would be 4′ (i.e. 12′ divided by 3).
Another approach uses the center of the driver element(s) in the speaker, the point(s) from which the speaker generates sound. Here, we’ll aim for the 29% points in the room, where excitation of room resonances will be minimized. The end result will not differ appreciably from the method outlined above.
However, there is a caveat. I personally prefer the method outlined above as it tends to place the listener a bit further from the wall behind them, particularly when using the long wall behind the speakers. In order to keep the listener well away from the nearest room boundary, I would always want to keep the listening position no closer than 24″ from the wall behind it. If necessary, I would move the speakers closer to each other in order to keep the listening position a minimum of 24″ from the wall behind the listener.
Going back to the first example above, using the short wall behind the speakers, we’ll measure 29% of 12′, which gives us 41.76″ (144″ * .29 = 41.76″). If desired, for convenience we can call this 41.75″ or 41 3/4″. Place the speakers so the centers of their drivers (or the center of the total driver area, if the drivers are offset from each other) are 41 3/4″ from each respective side wall. To find the distance from the wall behind the speakers, multiply 19′ by 29%, which gives us 66.12″ (228″ * .29 = 66.12″). Again, for convenience, we can call this 66″. Place the speakers so the center of each one’s drive area is 66″ from the wall behind it.
Applying this 29% approach to our second example, where the long wall is behind the speakers, we’d have the center of the drive area 66″ (29% of 19′) from each respective side wall and 41 3/4″ (29% of 12′) from the wall behind the speakers.
The final adjustment in either of these arrangements, will be to aim the speakers, sometimes called adjusting the “toe-in”. While making sure the front, inside edge of each speaker remains where we have place it (at the 1/3 points if using the first method or where it ended up in the above procedure if using the 29% method), rotate each speaker around this point until it aims at the center of the wall behind the listening position. In other words, you’ll be bringing the outside front edge of each speaker toward the listening position while leaving the inside front edge where we’ve already placed it. Note that the speakers will not be pointing directly at you but instead will converge at a point behind you.
The optimal listening position will be just outside of an equilateral triangle, meaning there will be slightly more distance from either speaker to the listening position than the speakers’ centers are from each other.
The arrangement described here will put both you and the speakers at a good distance from the room’s walls, ensuring you’ll hear the direct sound from the speakers before any possible influence from the room will make its contribution. Although similar benefits are derived from what has come to be known as “near field” listening (i.e. sitting very close to the speakers), there are significant differences, the primary ones being this arrangement allows full bass response and stereo imaging to develop.
A few final points regarding speaker placement. Aim for symmetry between the left and right sides, particularly in the part of the room where the speakers are. A large object near one speaker will skew the soundstage. Try to keep the area between and near the speakers as open as possible. This means staying away from alcoves too. The same goes for the space between you and the speakers. Having a table (or mixing desk or video monitor) in front of you will provide an early reflection surface that will confuse the stereo imaging and alter the frequency balance from the speakers. (Recording or mixing set ups with a desk in front of the listener cause midrange or presence dips that engineers will tend to “compensate” for with unnecessary midrange boosts. Better to drop the height of the desk by at least a foot or move the controls off to the side so they don’t interfere with what the speakers are trying to tell you.)
The importance of proper speaker placement can’t be overemphasized. While treating the room’s acoustics is also of highest importance (the room is after all, part of the system), I am tempted to say I’d rather hear well placed speakers in an untreated room than poorly placed ones in a room full of traps. Of course, both are required for the best monitoring environments.
It was quite a magical experience when I first encountered this kind of speaker placement. The sound was no longer confined to the speakers, which in fact, now seemed harder to identify as the sources of what I heard. Instead, the whole front part of the room came to life, containing the sonic equivalent of a hologram. It was as though that part of the room now opened out into another space, the one occupied by the musicians. Instruments that were in the background actually seemed to originate from a point far behind the speakers. I’d been a hi-fi hobbyist as well as an audio pro for years but now I finally understood what the term “stereo” means.
How does digital room correction come into this?
Well, I recently had the honor to visit Limage’s place. His system is simple but truly impressive. I now understand what is soundstage, in no where else have I heard such a good sound stage, including all home visits and dealer setup. Using his technique will bring music to life without the need of absorber and diffuser. On top of this, I think digital room correction can find tune it to make things even better.
Just an example of how such a room can be built!
Winston Ma was my colleague as well as my mentor who first brought me into the doorsteps of audio lunacy many years ago. He is now in Seattle, still actively engaged in recording and probably anything relating to audio gadgets. The following is an extract I read from www.stereopal.com :-
Winston’s listening room is, by far, the most dedicated audio room there is, a combination of the most thoughtful design, careful acoustically measured, and most advanced technology; it was designed and constructed by Winston over the course of 18 months with the help of many elite industry designers and professional engineers.
First of all, the foundation of the room was designed to be built on an absolute solid ground. It was constructed in the follow ways:
1. 4’ concrete wall to form the basin of the foundation. Inner sides of the wall are covered with a special wood-based soft board forming an effective isolation from outside vibration and resonance.
2. The ground of the foundation was machine compressed, then filled with 1st layer of rough gravels, 2nd layer of fine gravel, third layer of rough sand, and fourth layer of fine sand, all machine-compressed.
3. Then cover with special 2” foam which can stand tones of weight and can last for 25 years.
4. Finally, on top of the foam is 6” of reinforced concrete block to achieve solid, no ringing but live floor for clean and solid bass performance.
The studs used were 8”x4” reinforced high density wood-chip frame with special insulation within, instead of the standard 4”x4”. The room was built on a concept of “room-within-a-room” with 3 layers of wall; the exterior wall was built affixed to the solid concrete wall of the foundation, where the inner wall of the listening room was built on the floating slab, so that the vibration from outside room does not transmitted to the inner room. The easiest way to imagine, it is a room on a vibration isolation platform.
The room is measured approximately 17’ (W) x 27.506’ (L). The ceiling is on an ascending angle at 10 degree from 10.51’ (front H) to 16.51’ (rear H); what you get is a perfect size room with a golden ratio (1 : 1.6 : 2.5). On the power side, there are 4 units of isolation transformers of 30KW @ 117V for front end equipment, two of which are for digital gear. Two separate isolation transformers of 45KW @ 117V isolation transformers for sub-woofer amplifiers and two 45KW @ 240V isolation transformer for four high/mid mono amplifiers.
The room environment is computer controlled at 22 ~ 24 Celsius temperature and at 39 degree humidity without any noise of the fan nor the air flow. When the door is sealed, the room is drawn into its pitch black quietness. The interior wall colors differ by just a nick of degrees to give you a good sense of 3-D space, yet its soft color tone allows you to forget about its boundary quickly. Winston refers this as the wonderful design of psycho-acoustic engineering. There are a number of acoustic treatments all around the room, positioned by specified calculation then fine tuned by ear.