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Old 24th August 2010, 02:28 PM   #51
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Sorry for barging in here, but has anyone posting on this thread actually looked at any of these glues and adhesives when dry and compared them to Green Glue?

I think you'll find that any competent (tested) damping compound does not resemble construction adhesives.
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Old 26th September 2010, 09:47 AM   #52
Studley is offline Studley  United Kingdom
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Default DCX question

I will be building my Abbeys soon and I'm thinking generally about the subs set up. The DCX manual seems to indicate that it can be set to sum the L and R stereo inputs you feed it so as to produce mono outputs. Is that correct?

(I want to feed each of my 3 subs with a mono signal for cable management reasons.)
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Old 26th September 2010, 12:53 PM   #53
tms0425 is offline tms0425  United States
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Quote:
Originally Posted by Studley View Post
I will be building my Abbeys soon and I'm thinking generally about the subs set up. The DCX manual seems to indicate that it can be set to sum the L and R stereo inputs you feed it so as to produce mono outputs. Is that correct?

(I want to feed each of my 3 subs with a mono signal for cable management reasons.)
Yes, that is correct, I use mine for 3 subs and apply crossover filters individually.
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Old 26th September 2010, 03:43 PM   #54
gedlee is offline gedlee  United States
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Correct - sum L & R and output the three individual channels modified appropriately.
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Old 28th September 2010, 01:31 PM   #55
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Default Sealed vs. ported vs. PR vs. bandpass

Hello. I am also interested in trying out a multisub approach. If I remember correctly, Dr. Geddes recommended using multiple subwoofers for 40-80Hz and one or two bigger subs for frequencies below 40Hz.

I wonder, what will I lose if I simply build three or four small subs and hope that they will cover the range from 20Hz to 80Hz? I think one reason to use separate subs for 20-40Hz is to ease the placement of the many subs that cover 40-80Hz, because that way they can be smaller. But if I build all my subs small, then this is not a problem.

I simply need to settle on a driver and a type of enclosure. There is a continuum from 1) dipole, 2) sealed, 3) ported, 4) passive radiator, 5) bandpass with one ported and one sealed chamber to 6) bandpass with both chambers ported. These are in the assumed order from "tight, clean and articulate" bass to less "clean and articulate" bass.

I need to know, if people rated these in a blind listening test, would dipole always come on top and would dual ported bandpass always end up last? Or are one or two of these always different from the rest? Do I gain or lose perceived quality if I go from ported to passive radiator or from ported to bandpass?

My second stated goal is to go as low as possible. Do any of these enclosure types allow that without eq? I know that the sealed box often matches the room gain. But I also know that many would rather tune a "house curve" than listen to a sealed box plus room gain resulting in a flat 20-80Hz response. Instead, a flat 20-80Hz anechoic response plus room gain often results in a kind of "house curve".

I also assume that driver harmonic distortion is not a problem per se, but power compression is. And to get less of that, I should rather use pro drivers than anything offered by Seas? To state my problem another way is, if it is possible to get good bass from multiple 1 cf cubes with any enclosure type at all? If my starting point is four Seas L26ROY with one passive radiator for each, where would you go and what would you do if you were me?
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Old 28th September 2010, 02:05 PM   #56
gedlee is offline gedlee  United States
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I would elliminate the dipole as its efficiency is not sufficient in the frequency range you are talking about. Then, as far as I am concerned, the rest are all about the same. I don't buy your "ranking" of subjective appeal. I use only bandpass subs and I find that they work just fine. Dual ported is a tough enclosure to get right. Easiest is closed box, but requires a big box to get down to 20-30 Hz. Passive radiators are great, if you can get a good radiator at a "reasonable" price (not what I have seen).

I would say that 1 cf cubes is not going to work very well as that is just too small. Bass takes power and size and nothing that I know of can get arround this simple fact.

My subs go much higher than 80 Hz. One goes all the way up to about 130 Hz. The big ULF only goes to about 80 Hz.
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Old 29th September 2010, 08:02 PM   #57
jzagaja is offline jzagaja  Poland
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100 liters seems enough for push-pull to get decent 30Hz at 91dB. 200-300 liters for higher sensitivity like ULF-18. There's another small solution - tapered transmission line - for example 1:10. Usually there's more subjective bass extension than simulated response suggest (room gain).
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File Type: gif Transmissionline and U-frame.gif (12.3 KB, 312 views)
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Old 13th October 2010, 06:25 PM   #58
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Quote:
Originally Posted by gedlee View Post
The Melamine glue just looks and acts like the Green glue, but I was not sure of what the ingredients were, just that Green Glue was far too expensive and Melamine glue was quite reasonable and works well. Thats what I would use if I do any wall structures again.

I use polyurethane foam to seal cracks and holes, but not as the CLD layer.
This CLD detour in the thread has caught my interest, so I'm making some simple tests and observations to compare Melamine Glue to Green Glue. I hope to compare some other adhesives/sealants later as well.

Green Glue indeed has done a great job of documenting its performance. I've no doubt that melamine glue will also "work well". What I want to figure out is 1) is GG essentially the same stuff as melamine glue?--does melamine glue damp as well as GG? And 2) if not, I'd like to determine some point of diminishing returns. I'm pretty sure that point is well below the present cost for GG, and somewhere above the cost for cheap latex caulk.

Context: I'm simply observing the glues - No formula discovery or CLD performance conclusions at this stage. I'm no chemist. I do have some experience in room acoustics. In the end, I'm shooting for best bang for the buck backed by at least a little bit of science. 'Just a guy documenting practical differences or similarities between these glues.

So far I've simply laid down similar "lines" of each glue, and also adhered some materials together with the two glue types.
The "lines" I've laid were to obseve such things as viscosity, skin time, cure time, etc. I put the lines on a piece of flexible vinyl, so I can observe flexibility & elasticity after cure, etc. Each line was about 1/4" wide/round, and 4 inches long.

Observations over a 28 hour period: The glues are not the same. They smell somewhat similar, but are distinguishable from one another. 'Hard to put useful layman's words on this aspect.
Viscosity: The GG is more viscous than the Melamine. The MM glue consistency is similar to white/yellow wood glue, while GG has the "gooeyness" of a runny sillicone adhesive. Within the first few hours, the MM line spread and flattened to about 150% width. The GG didn't change much, maybe 110%.

Skin: The melamine glue skinned nicely in a couple hours, and was smooth & dry to the touch after about 4 hours; The GG is still tacky after 28 hours as I type this.

I've also adhered some pieces of vinyl together with the glues to observe shear behavior (difficult to observe using small pieces of drywall-- too thick relative to the sample size; can't proportionately flex like a full sheet of drywall will).

I'll have to wait until the GG is cured before offering any more observations on cure time, shear, bond etc.

-- Mark
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Old 16th October 2010, 05:43 PM   #59
pjpoes is offline pjpoes  United States
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I'm not sure Dr. Geddes was saying they were the same thing. I had thought that too at first, but I think he was just suggesting it to be as effective as GG. I think to really prove or disprove that would require tests of STC and damping properties. Damping could arguably be tested with an accelerometer I would think. STC would not be feasible on a small scale to the same level that a lab would test it. However I wouldn't be surprised if you could approximate the results on a small scale. Make a sound proof box, that is as sealed and "soundproof" as possible on 5 of it's 6 sides. Leave it open on the 6th side. I would want the box to be in the range of 4'x4'x4' or so. suspend the test microphone inside the box, a good 2' from the front of the chamber. Test the box open, with a sound source, and see what the response is. This is the baseline, you will zero out to this. Then connect a single 1/2" piece of drywall, with screws to the front, and test again. This is your "business as usual" type test, the baseline that any old home would have. Then test each of your test solutions, and compare the sound transmission loss seen with each.

It's not a perfect test, it won't equal what Green Glue, for instance has done, but it would at least give you something to consider. I think doing it right, like that, would cost you more than just buying some Green Glue, so if you are testing to see if Melamine Glue is cheaper, it would be a pretty silly thing to do. On the other hand, if you want to try a product that is cheaper, that a PhD Acoustical Physicist feels confident would work well enough, then use the Melamine glue.
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Old 16th October 2010, 08:04 PM   #60
gedlee is offline gedlee  United States
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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.

It's like the screen in my HT. It's a bed sheet. Is it "identical" to "micro-perf" (or whatever the new buzz word in screens is?) No, of course not, its a cotton fabric not a vinyle screen material! Does it work the same? No, not actually, it works better. Getting the best function at the lowest cost is what its about.

Last edited by gedlee; 16th October 2010 at 08:34 PM.
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