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In Reply to: RE: Rock and Roll! posted by josh358 on November 05, 2015 at 19:01:38
When you have the woofers more than 2' closer than the MT then you should swap polarity on the woofers.. You won't be in time but you would be in phase.
And back again if they are more than 5' out.
Have you tried the woofers with the deep bass at a right angle to the sidewall and adjusting the midbass angle by ear?
The deep bass panel was roughly 3' in front of the mid panel's plane and phase on the bass was reversed. I don't remember the exact figure but I did it by placing the bass panels in front of the mid tweets where the XO suckout was worst and then reversed polarity on the bass panels. Then I started playing with their particular arrangement.
Follow Ups:
Well I know they were a bit out of phase because I could hear a bit of a suckout and just guesstimating the distance to the acoustic centers told me they were off -- we're talking what, a 4 foot wavelength at the XO point. I probably could have improved things some just by flipping tweeter phase but my objective was to see what it did to the imaging when I got the woofers out of the way. But I remembered your post about the woofers in front arrangement and had it in mind, just didn't have time to experiment with woofer position -- actually first I had them parallel to the side walls which actually worked and then tried folding the panel closer to me so it touched the wall, but that was it.
Once I have a feel for what works both by way of imaging and sight lines I can fine tune the woofers but my feeling was that it isn't going to be right until I get the DSP/biamping up and can keep things in time. Even then, it's going to be tweaky around the 250 Hz XO point if I have that much axial separation. A more modern crossover would likely improve that some, e.g., L-R, since the lobing will be symmetrical and won't have the rise. (I still haven't had time to run the numbers so I'm not sure if I can do FIR at 250 Hz. without too much latency to use my keyboard.)
All of this reminds me that I want is my M-T panels to go down to 80 Hz!
Well, you will have some flexibility with the Neo8 line - Below 200hz is dfinitely possible, but I don't see below 100 hz as realistic without baffle reinforcement for the mids a la IRS mid tweet section. I would guestimate a 1' baffle on both sides (with tweeter and mid array) might get you close to 100 hz..
I did do the woofers in parallel to the sidewalls on the long wall but got a discontinuity in the bass with a huge lump centered on 33 hz - that was when we were discussing the 1/4 wave room mode cancellation - which did not occur when you are sitting well away from the plane of the bass panel output.I EQ'ed it out but still lacked energy in the octave centered around 80-100 and it didn't change much with any reasonable degree of EQ.
I did not try it on the short wall arrangement since that would lose me the deep bass modes I like so much. That would obviously not be an issue with your squarish geometry. So that is probably something worth optimizing.
I don't think I'd want to cause diffraction and resonances by adding a baffle. Or lose too much max SPL. Even the Neo 10 would be a stretch. I think it would be more realistic to use the mid woofer panel. I'll have to experiment but that's more work because I'll have to disconnect the panels and kludge some extra feet.
When I had them parallel to the wall they were actually in front of me. So I must have been getting some dipole attenuation but in my brief listen it sounded surprisingly good. If I have some time I'll experiment with the RTA but chances are I won't be able to get to it for at least three weeks since I'll be out of town.
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