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It turns out that Toole and Harman are about to set the industry on its, er, ear. Before we spoke, however, Toole suggested I read a white paper published by his colleague Todd Welti, "Subwoofers: Optimum Number and Locations," an extremely detailed analysis of Weltis search for some answers to the hit-or-miss nature of subwoofer placement.
Its worth reading, if only for fun: Welti has considered the placement of 5000 subwoofers in a room. He asked, "Can a sufficiently large number of subwoofers cancel out all room modes?" His conclusion: "Theoretically, yes. Practically, NO!"
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However, if there is only one listener -- or only one listener who matters -- you can provide good results with a single subwoofer, as long as you realize that, in the end, youre going to have to equalize everything. And were not talking about the one-third-octave graphic-equalizer BS that the industry has purveyed for decades.
That said, no matter how many subwoofers and how many listeners were talking about, equalization should be the final step to make it sound right. A single subwoofer can entertain a single listener with equalization -- good sound is possible. But once you have more than one listener, then you need multiple subwoofers.
At that point, the problem can be divided into two separable categories: one where the room is a regular rectangular shape, and the other where the room is not perfectly rectangular or symmetrical, which is the sort of room most of us live in.
The problem Todd solved in the white paper we published concerned perfectly rectangular rooms with fairly "normal" middle-of-the-room seating. For that, there are some fairly standardized arrangements of subwoofers that work -- or at least reduce the variations from seat-to-seat performance. Of course, once you reduce the seat-to-seat variations, any equalization you apply will apply, more or less, to all of the seats.
WP: Todd, is it possible to synopsize the conclusions of your white paper?
Todd Welti: It was surprising to me that I was able to come to as distinct a conclusion as I did. When I first started working on it, I assumed that I would come up with a solution for a theoretical room but it wouldnt work for real rooms. But I was pleasantly surprised to find that it worked in real rooms as well. From reports Ive been getting from the field, it not only works in our room, but most other rooms as well.
The conclusion I came to was that two subwoofers give you about 90% of the performance that is possible, and that four take you about as far as you can reasonably expect to go. Anything more than four is not going to get you much in the general sense -- and these are general conclusions.
WP: So the 5000-subwoofer solution just didnt work out.
FT: Acoustic wallpaper, as I call it.
TW: In terms of recognition, it sure got a lot of peoples attention, but no, four subwoofers seems to do the trick -- and we came up with three configurations out of about 100 that we looked at that are the cream of the crop. Actually, theres a fourth solution -- one that Floyd came up with -- that worked even better than the others, but it involves bringing the subwoofers out from the walls, which I generally didnt consider.
FT: Its not very practical, unless you could put them in the ceiling. It uses four subwoofers located at the 25% points from all four walls.
TW: In other words, you shrink the whole room by 25% and put the subwoofers at the corners of that virtual room. You get incredible performance, but thats just not practical in most rooms. But if you use two or four subwoofers in the corners or the wall midpoints, you can get pretty good performance -- and thats about as succinct as I can get.
WP: Thats pretty succinct. But youve continued to do research, and now youre trying to crack the conundrum
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