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Geddes Bandpass Subs and the Multi-sub approach

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I never said that they were the same thing. It doesn't really matter does it? It's function that matters and I suspect that they do work the same or similar . . .

I try to take everything online with a grain of salt, but the word "identical" was used . . . See post 41-
http://www.diyaudio.com/forums/gedl...ss-subs-multi-sub-approach-5.html#post2280509

No big deal.
I completely agree--if it wasn't clear in my post--that I don't need identical inputs, just comparable results/function. My '99 Civic gets me to work in the same amount of time, at a much lower cost, than a Lexus does. Good enough for the daily grind.

Nearly any non-hardening CLD goo, when used in conjunction with decoupling from the stucture (resilient channel, hanger springs, isolation clips, whatever) should be at least as effective as Green Glue sandwich screwed directly to studs as prescribed on the GG site. Tests over the years show that of all possible interventions for non-transmission of sound by absorption (as opposed to non-transmission by brute reflection -poured concrete, etc), decoupling is hands-down the first step to take.

pjpoes- I "get" your testing - I often do similar 'unofficial', but insightful tests at work. Here it's not necessary, unless one is trying to "prove" or create a competing product. I'm just taking a practical approach to comparing alternatives before slapping walls up, and joining the leagues of folks posting anecdotes on the forums.

FWIW, a follow-up to my previous look at GG: The stuff never fully "cures" - seems to remain gooey and tacky indefinately -- it hasn't changed a bit in several days now. It definately would dampen very well, and is very elastic when subjected to shear forces. The cured melamine glue is quite flexible, and does not break when subjected to reasonable shear, but it does not allow the constrained layer sandwich to flex as easily as the GG does.

The melamine glue (as well as underlayment glue, etc) are real glues - wallboard screws can (& should) be removed after curing. The GG is so elastic that it would surely result in wallboard resting on the floor within a day or two.

Given the resources, I would love to test how GG (which requires screws) would fare against a lesser CLD assembly that allows removal of screws. Any peformance gap might narrow considerably.

While this comparison may be impractical from a commercial standpoint (typical contractor just isn't going to wait for no glue to cure & then remove screws before patching, and you are a meddling idiot cuz he's been doing this forever and ain't no homeowner gonna tell him how to put up a wall), it does makes complete sense to a DIY'er or acoustic specialist.

I suppose all of this should have been started as a new thread . . .

-- Mark
 
I try to take everything online with a grain of salt, but the word "identical" was used . . .
-- Mark

Hi Mark

Yes, thats true. I think that I cleared that up in my next post - that I meant "performance" and not "composition". At any rate, we are all on the same page. For what its worth, I don;t use any of that stuf anymore, because I found a two part polyurethane that cures very fast and is reasonably compliant and well damped, so I use this for all my CLD work now. The air-dry glues all seem to take too long to cure and most tend to harden completely as they age. I've also had Liquid Nails explode on me due to the solvents used.
 
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I am designing a system of subs, and I'm trying to make use of the space below my mains directly beneath my woofer. It's a little over a couple of feet from the wall.

I want two subs that reach up above 100Hz, and one that reaches down to 20Hz.

My problem is that the main woofers go down to 70Hz. I would therefore like to put a 20Hz-70Hz woofer in the cavity beneath the mains but, it isn't large enough for that (1.5'^2).

So, do I choose to run over 100Hz and overlap the mains even though it will be so physically close to the mains that it risks causing a needless peak? or do I leave that space alone?
 
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Thank you. I'd have been well tempted to use that space ;)

If I may ask another question, if I want to put a sub in a corner, is it reasonable to run its output behind a corner bass trap or does the front of the bass trap become the 'new' corner?
 
No you cannot average impulse responses. The averaging must be done in the frequency domain. The issue of weather to average dB or linear is interesting, but the correct way is to average the dB, because that what the statistics are in. But it makesa very little difference either way - linear or dB - except at very low nulls there is no difference at all.
 
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