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In Reply to: RE: "extending the lower bass of the panels" ... posted by Roger Gustavsson on March 19, 2017 at 04:38:08
The room reinforcement from early front wall reflections would reinforce the bass by 3 dB at half a wavelength path length difference, so if the speakers are 5' from the front wall you'd get cancellation at 100 Hz (10' wavelength and path length) and reinforcement at about 50 Hz (20' wavelength and 10' path length) rather than the bottom octave. At 20 Hz you're talking a 50' wavelength so you'll get a fair degree of cancellation from a 108 degree net phase shift. So it seems to me that a very effective bass trap could potentially increase bottom octave response, though of course it will ultimately be limited by the woofer's resonance.
I didn't see much bottom octave bass when I measured my IVA's but there are two important caveats -- I've moved them and there's delam on the lowest frequency resonant sections. So the measurements probably aren't meaningful and since I'm in the middle of some long-overdue Ebay selling it's going to be a few days before I have a chance to take some new measurements (as a matter of curiosity, I want to compare the response before and after the delamination is repaired).
Follow Ups:
I think it is a complex mix of reinforcement and cancellation from reflections. Not only from the wall behind and beside the speakers but also from the area around the listening posistion.
Definitely. A room mode calculator will predict what happens pretty well for a rectangular room if you remember that with dipoles, a node is an antinode and vice-versa, and that dipoles excite fewer modes than omnis because of the dipole null, which I think is one of the main pluses for planar bass.
Josh, I'll gladly display my ignorance in exchange for you explaining your statement "with dipoles, a node is an antinode
and visa versa". If you share your knowledge with me (and others), assume I know nothing, which ain't far from the truth! I understand that bass frequencies collect in a room at locations (nodes/modes. Are they one and the same? Also called standing waves, right? More things I don't know!) and frequencies determined by the rooms dimensions. What is an antimode, and why the reversal with dipoles? Thanks---Eric.
Edits: 03/20/17
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