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Has anyone tried filling the voids behind the basshorn sidewalls, to damp cabinet resonances? If so what did you use? And was was the outcome? It seems to me that substances such as sand or leadshot would add a tremendous amount of weight and present possible structural issues.
Input, anyone?
Dave
Greets!
This is one of those subjects that's been repeatedly 'beat to death' on various forums, but surprisingly I didn't have much luck Googling http://www.hostboard.com/forums/ , so FYI, I prefer Kitty Litter as a good trade-off between weight/damping, though some folks are pleased with just filling them with Great Stuff expanding foam. You must be careful with it though as it can bow out or blow loose the flares.
To maximize the benefits, you must also do the sloped flare and add another 3/4" layer of plywood or MDF to the top of the cab. The rest of the cab needs similar attention.
GM
I have the sealed 828 cabinets. I sand filled the cavities by cutting a 2" hole in the top over the cavity and putting in heavy duty trash bags (3 mil) before putting in the sand. No leaks or distress in the cabinets yet. They get a workout since I have also installed JBL 2245's in the bottoms as sub woofers.
Jim N
Thanks! I had considered the Great Stuff idea, but was concerned about the foam generating pressure as it expanded. Hadn't considered kitty litter though-------good idea. Any problems with leakage?
Again, thanks!
Dave
So, how much sand did it take to do the job?
Dave
I used expanding foam to fill in behind the curved walls. With the cabinets face down, the openings at the back became the top of the containers to be filled. It took several applications, because if filled all at once, there's a tendency for the top to dry solid, but the middle will remain liquid, lacking the exposure to air needed for full reaction. Expansion of the foam began within the confines of the cacity and proceded upwards. The open 'top' provided less physical resistance than the wooden walls, so once filled up, it simply overflowed the top, (no sideways deformation the walls). When dried, I trimmed the top to the height of the baffle board to which the woofer is mounted. Simple, light weight, and fairly easy. Sand may be more effective, but the foam seemed to make sense at the time, so I went with it. Plywood reinforcement of the flat planes of the bass horn is a good idea, and I did that too. Good luck with your A7s! Robert
I'm sorry, and I apologize but foam does nothing...absolutely nothing to diminish resonance. Weight deters resonance and sand is the most effective way to do this. Resonance is distortion, plain and simple. I've built 6 or 8 huge sub woofers and used concrete, sand, double skinning, 2x4 braces internally and the only way to stop resonance is with weight.
Now if you listen to your music not too loud and never crank the SPLs then you can live within a design or compromise.
Sometimes just a well placed brace can make a big difference in distributing mass. In other words a speaker wall where the resonance is peak can braced to another wall to prevent the wall from moving and if there is enough mass in the overall speaker cabinet, you may effectively dampen the "distortion".
If I remember right, it was on the order of 40 to 50 pounds per side. They definitly pass the knuckle test. Absoultly dead. I put the bags in through the hole and then "inflated" them with the blow end of a vaccum cleaner. A cut off milk jug makes a great funnel.I have been intending to go back and check for sand settlement but with 1005's and 811's stacked on top, it is a pain to move.
Jim
Allright, thanks guys! Looks like I'll be going with the sand. I'll be ungodly heavy, but I think it will have the greatest result, sonically. I'll also be getting some baltic birch ply to reinforce the cabinet as a whole.
May end up with casters on the bottom, 'cuz these guys will endup over 300lbs. a piece, to be sure.
Dave
Ooops! I meant to say THEY will be ungodly heavy.
I'm already ungodly heavy-----without the sand.
Dave