I wanted to add a couple things for everyone to think about.
The first thing has to do with single-seat performance verses seat-to-seat consistency.
After re-reading some of the comments made here, I realize that some have started thinking the multisub approach can be used to smooth the response at a single listening spot
, which, of course, it can. But I do want all reading to remember that the whole purpose of the multisub configuration is to smooth the response over a large area, similar to the goal of uniform directivity from a waveguide.If you just want smooth subwoofer response at a single listening spot, sit on the sub.
Easy-peasy. The closer you are to the subwoofer, the more the direct sound will swamp the room modes.
There are also subwoofer positions further away that give reasonably smooth response at a single listening spot. If you just want to optimize single-seat response, you can do it with fewer subs than are required for seat-to-seat consistency, dialing them in with measurements. As I said above, you can even get one sub to provide good single-seat response if you put it in the right place.
Not to trivialize the matter, but it is, in fact, much less difficult to find subwoofer placements that satisfy the sole
condition required to achieve smooth response in one spot than it is to satisfy the simultaneous
conditions required to achieve smooth response in multiple spots, over a wider listening area. This is the goal of the multisub configuration.
I don't mean to diminish anyone's efforts that have used measurements to direct their placements to satisfy the single-spot requirement. That's always been the way to optimize single subs - Put the microphone in the listening spot and move the sub to find the place where response is smoothest. So adding a sub or two more can be used to make the single-seat response even better.
But again, this is not
the goal of the multisub configuration. It is suggested for satisfying the simultaneous goals of seat-to-seat consistency and
smoothness of response. Optimizing this requires multiple measurements taken from multiple positions. One can also use simulation software (like CARA
) to analyze the room and optimize the layout, taking measurements afterwards for verification.
The other thing I wanted to say was that whether of not you choose Welti or Geddes recommendations for distributed subs
, I suggest that you use flanking subs
to mitigate self-interference from nearest boundaries and higher-frequency modes. This is actually my biggest focus, not so much whether the distributed subs should be symmetrcially or asymmetrically placed, ordered or directed by measurements or whatever. My biggest focus is on bringing to attention the problems in the 100Hz to 200Hz region, because I think those are often as bad or even worse than the lower-frequency room modes.
It is extremely important to consider the problems of self-interference from nearest boundaries, and this is often overlooked in multisub discussions. People often talk about the response below 100Hz, but then overlook the response between 100Hz and 200Hz, which usually as bad or worse than the lower frequency modes. These are caused by the interaction between the direct sound and the reflection from the nearest boundaries, and they are not actually room modes at all. But they do cause severe response anomalies, and mitigation can be done in similar ways, using flanking subs.
Another way to deal with self-interference from nearest boundaries - the best way, actually - is to either mount the speakers in a soffit
or use constant directivity cornerhorns
. If the source lies right on the boundary, it will not create self-interference notches and there is nothing to mitigate. That's the best solution.
But for most people, these aren't options and more traditional loudspeaker installations are used, floor-standing or on risers of some sort, pulled a few feet from the wall. In that case, a helper woofer
or flanking sub
is very effective at smoothing the anomalies that are caused by nearest boundaries.