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In Reply to: REVIEW: Audiokinesis The Swarm Speakers posted by Mickey Bob on April 2, 2007 at 19:21:33:
The Swarm subs are based on work by Earl Geddes. If I recall correctly, however, at least one should be installed off the floor in order to address the floor-ceiling modes.Also, don't four 5" drivers add up to the area of a single 10" driver? Pi-r-squared and all.
Looking at your room dimensions, no wonder you have trouble with resonances!
Follow Ups:
You are absolutely correct, the scattered multiple subwoofer configuration is based pretty much entirely on conversations with Earl Geddes. In fact, Earl has applied for a patent on a subwoofer system whose principles I'm using - and just for the record I built the Swarm with Earl's knowledge and with permission to incorporate his concepts. Several other researchers have recommended multiple subwoofers, though usually with more symmetrical placement (Welti, Griesinger).The woofers are nominally "6 inch" units. The frame diameter is nearly 7 inches, and the cone area is 140 square centimeters. Four of them would be 560 square centimeters, which is about right for a single 12" woofer.
The woofers I use have a theoretical maximum linear excursion of 13 millimeters. With the vented alignments I use, they don't reach 13 millimeters excursion anywhere within their passbands, and the plate amp has a high pass filter that should protect against over-excursion below the tuning frequency.
A 5" driver is really has 4" cone, a 10" driver has an 8" cone, a 12" driver is really a 10" cone.2 squared x 4 = 16, 4 squared = 16, so 4x5" = 1x10".
It's got to be bigger drivers than that. Who sells a 5" subwoofer? You'd need at least 4 8" drivers to be worth much, but 10" or 12" makes more sense because you're going to get a lot of cancellation from the "swarm" approach. You could do a "swarm" with NHT's modular U2 setup with 4x 12" for $2500.
The ideal setup would be 8 woofers, each in a corner, floor *and* ceiling. That would be cool.
I'd have preferred to use larger drivers, all else being equal - but all else was not equal. One of my concerns was price point, and another was enclosure size. The 4 X 12" NHT system would probably kick my system's little butts (all four of them) in many areas, but mine has sufficient extension for most music and sufficient headroom for use with most planar systems (Maggies and Quads).Of course I have a "SuperSwarm" on the drawing bored, but want to see how this one does in the marketplace first.
Just for the record I cannot agree with your suggestion to place subwoofers in corners if the goal is smooth bass. Corner placement will give you loudest-deepest-possible bass, but also maximize excitation of room standing wave modes so you'd have relatively pronounced (and therefore audible) peaks and dips. The more randomized location approach I advocate results in smoother bass because each sub will generate a unique peak-and-dip pattern at any given listening position.
Below is a link to a simulation run by Earl Geddes comparing corner placement of four subwoofers with randomized placement of four subwoofers. Each of the different-colored curves is the summed bass response for a different listening position.
Duke
Well, you can't really translate 4 subs in corners to subs in all 8 corners. In theory, that would largely cancel all three major modes. In theory, I've never tried it, it would be a hassle hanging 4 of the subs. Besides, I've never been a fan of subs in the corners anyway and prefer the more "random" method in practice. I just haven't tried my 8 corner theory yet.
Intersting that you have gravitated towards a more random configuration. I didn't exactly gravitate; more like someone hit me upside the head with ye olde two-by-four and then it made sense to me.How would having subs in all 8 corners cancel all three major modes? I don't see how it would.
Thanks,
Okay, let's say you have a 20' room that has a 28Hz (40') standing wave. The bass is coming from the front, it bounces off the back wall. As it bounces, it's at the rarefaction stage. At the same time, the subwoofers are all beginning to reproduce the compression state of the 28Hz wave. So, the sub in the back is putting out a 28Hz compression that is lining up with a smaller 28Hz rarefaction and it cancels it, leaving only a little 28Hz energy. This works for lateral and vertical waves because there is a "cancellation" device at every room boundary. Of course, there are other ways to do it and this may not be the best since I haven't tried it, but just a theory I have. Not quite the "active cancellation" I have, but I'd be curious if someone has ever tried this.
I don't think that would work.I think you would get some smoothing, but I think the two bass pressure waves will largely pass through one another rather than the one neatly cancelling out the other throughout the room. The simulations and measurements I have seen for subwoofers in corners doesn't show evidence of global cancellation of the primary room modes. Recall the link above showing subs in four corners - it looks to me like more than one room mode is still significantly excited, and if having subs in opposite corners suppressed room modes we'd expect that four subs in floor corners would only leave the floor-to-ceiling 71 Hz mode unsuppressed.
Asymmetrical placement of multiple subwoofers doesn't rely on cancellation - it relies on summation smoothing due to each subwoofer generating a unique peak-and-dip pattern at any given listening position.
You need 9.
Don't forget to hang one from the ceiling fan so as it spins,it can take care of "random" room nodes caused by rarefied, gaseous air caused by farting guests ??
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> Looking at your room dimensions, no wonder you have trouble with resonances! <
Amen to that, brother!
I'm not sure how it adds up - I may have the driver diameter wrong. FOr specifics on the dimensions and any technial matters, give a holler out to Duke, a frequent participant in this forum.For most of my evaluation I had two of the speakers off the floor - about two feet off.
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