http://www.audiocircle.com/index.php?topic=71030.0ฝรั่งคุยกันพอดีได้ความรู้ดีครับ...และก็ จัดวางลำบาก....ต้อง
ฮาร์ดคอร์ กันทีเดียว.....
Remember that once the sub is in a room, you cannot separate its response from what the room does to it. And the room's effect is dominant. We do not even hear "direct" and "reverberant" bass energy in our home listening rooms; it takes the ear more than one cycle at low frequencies to even hear bass, and by that time the room's effect is in full swing.
For a single subwoofer, there is no possible placement that will result in smooth in-room bass. Let's say we have in-room response that is plus or minus 6 dB, with those peaks and valleys caused by the way the reflected low-frequency energy re-combines in-room - sometimes adding in-phase, and sometimes adding out-of-phase and thus cancelling. Now suppose we have two subs placed asymmetrically. Each by itself will produce a plus or minus 6 dB response, but they will be dissimilar. Combined, they will be audibly smoother than either one alone would have been because they will not both be zigging and zagging at the same frequency. They will smoothe one another out precisely because their room-modified outputs will not be adding in-phase. And because it takes the ear a long time (relatively speaking) to hear low frequencies, these multiple sources don't actually sound
multiple sources (though you need a steep enough low-pass filter to prevent audible lower midrange energy from leaking through).
By the way, Earl Geddes and yours truly are two sub manufacturers who recommend asymmetrical placement of multisubs. Earl recommends three subs with one in a corner, one along an opposite wall, and one near the ceiling. My system uses four subs with slightly looser placement requirements (in-room smoothness goes up as the number of distributed bass sources goes up, so if you can't place one near the ceiling then you can make up for that to a certain extent by adding another sub).
