| Damping material placement [message #69265] |
Thu, 01 September 2011 09:25  |
doucanoe
Messages: 34
Registered: May 2009
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Baron |
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I was wondering what you recommendations are for fiberglass lining of the walls in the 4pi using the 2226. Which walls, thickness of batt material, etc.
If it matters, I constructed my pair using a 2.8-3 cu-ft LF sub enclosure tuned to 38 Hz for the 2226. Although I'm pretty darn pleased with the LF performance, I do believe I may have the enclosures a little over filled.
My original plan was to go a little heavy initially then reduce and note the changes. Then, settle on what I thought sounded best. Things sounded pretty good right from the get-go so I never made any changes. It's been a while so I would have to pull a driver to even tell you how I went about lining the cab.
I've tried to do some searching for the answer here (I'm sure you have addressed it a million times by now) but having a little difficulty finding anything that speaks to it directly.
Thanks,
RC
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| Re: Damping material placement [message #69273 is a reply to message #69269] |
Thu, 01 September 2011 13:19  |
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Wayne Parham
Messages: 18792
Registered: January 2001
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Illuminati (33rd Degree) |
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I hate to say it but with all those mods, all bets are off. However, insulation spanning the cross-section is a good idea in general for large cabinets used into the midrange. It helps damp standing waves at midrange frequencies where insulation lining the walls can't. But the best position to put the cross-section piece and the best positions of woofer and port are best found by extensive modeling and/or empirically by measurements.
The goal is to prevent standing waves from lining up in the box in the 100Hz to 400Hz range - above that and the insulation lining the walls will attenuate it. Below that, the Helmholtz resonance and woofer parameters are setting the curve.
The 100Hz to 400Hz range is tricky to deal with in larger cabinets the size of these, because it's right where the standing waves line up and yet the insulation lining the walls cannot do much. So you have to put the woofer and port in positions that prevent large peaks in that range, and use a section (or two) of insulation spanning the cross-section to damp what's left.
The position of the insulation is also important, because it needs to be where the standing waves are at energy maximums do do the most good. That's why the insulation lining the walls is almost useless at midrange frequencies, it's right at an zero-energy point. At higher frequencies, it's thick enough to span from the zero-energy out to a place where the wave has some energy but at lower frequencies, it's too small acoustically. So to help with that, we must space the damping material out away from the walls.
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