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發表於 2011-12-21 11:19:36
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dt825 發表於 2011-12-21 10:59 
佢話先初步擺位待run-in一輪再請教你微調喎。
分享一下定位李師兄既經典文章比你朋友啦.
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Room Coupling
limage on SPEAKER PLACEMENT AND ROOM COUPLING (07-04-15).................
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.
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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.
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發表於 2011-12-20 23:04:11
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