I am building a closed box for the bass section of my otherwise open baffled speakers.
All walls, except front baffle, will be a sandwich of 18mm mdf, 15mm sand fill and 9mm mdf.
Has anyone built sand filled cabinet walls like this? Is a 15mm thick layer of sand good enough for dampening or should it be thicker? (one can assume thicker is better, but there is a trade of for volume) Any comments on the thickness of mdf layers? And would you put the thicker mdf layer as inner or outer layer?
Inner volume of the box is 3 1/3 cubic feet, and there will be two 10" woofers on each side.
All walls, except front baffle, will be a sandwich of 18mm mdf, 15mm sand fill and 9mm mdf.
Has anyone built sand filled cabinet walls like this? Is a 15mm thick layer of sand good enough for dampening or should it be thicker? (one can assume thicker is better, but there is a trade of for volume) Any comments on the thickness of mdf layers? And would you put the thicker mdf layer as inner or outer layer?
Inner volume of the box is 3 1/3 cubic feet, and there will be two 10" woofers on each side.
Been there. Done that. Did the sono-tube routine too. I learned to build better boxes instead. I build my sub boxes out of plywood. Midrange out of MDF. I am considering using foam for tweeters. An idea I have not tried.
Sand won't add any stiffness. Also, to stop deep bass frequencies, inches of mass won't do it, you need many feet to achieve isolation. You'll get some mass damping of the panels using sand, and the speakers will be well anchored to the ground.
With subs, it seems that stiffness is the key attribute, rather than minimising resonances, the cabinet shouldn't deform. Thick pine or spruce, birch plywood, could even laminate it with sheet steel or aluminium. MDF isn't very stiff, although weighing it down with sand might increase its inertia some.
With subs, it seems that stiffness is the key attribute, rather than minimising resonances, the cabinet shouldn't deform. Thick pine or spruce, birch plywood, could even laminate it with sheet steel or aluminium. MDF isn't very stiff, although weighing it down with sand might increase its inertia some.
I use ceramic floor tiles. 12 x 12 or 18 x 18 glued with PL to the plywood. Works very well for me.
I'll be the dissenting voice here. Sand filled walls are very, very dead. But you need to pack the sand. Properly done, you'll have no box sound. You won't be able to move it, either. 🙂
MDF isn't a good choice because the weight and pressure of the sand will bow it and maybe burst it - the walls need to be strong.
MDF isn't a good choice because the weight and pressure of the sand will bow it and maybe burst it - the walls need to be strong.
+1 I have also tried that to good effect. Just not on the rear panel! Plasterboard lath seems to work as a liner too.
I made me some big subwoofers 15 years ago using 12 mm MDF in three layers, where the middle layer had cut-outs that were sand-filled. It got heavy, but not at all any stiff. Very heavy bracing was necessary to avoid too much vibration.
As said before - stiffness is everything when it comes to woofer boxes. Plywood is good, bracing is good. Sand is a waste of effort in my opinion.
An other trick to reduce vibration is to isolate the boxes from the floor. This lowers the mechanical resonance between the box and the floor. Believe me, it works. The softer suspension you use, the better.
As said before - stiffness is everything when it comes to woofer boxes. Plywood is good, bracing is good. Sand is a waste of effort in my opinion.
An other trick to reduce vibration is to isolate the boxes from the floor. This lowers the mechanical resonance between the box and the floor. Believe me, it works. The softer suspension you use, the better.
Alternative
Sand filling works for high frequencies were panel resonances are within the frequency domain of driver output. Here increasing panel stiffness without introducing some form of internal damping will result in a "ringing" enclosure. A salami-slice enclosure design using plywood sheets will provide both the needed stiffness as well as the desired internal damping without the problems of sand filling or extensive bracing.
Regards,
WHG
Sand filling works for high frequencies were panel resonances are within the frequency domain of driver output. Here increasing panel stiffness without introducing some form of internal damping will result in a "ringing" enclosure. A salami-slice enclosure design using plywood sheets will provide both the needed stiffness as well as the desired internal damping without the problems of sand filling or extensive bracing.
Regards,
WHG
+1! 🙂
A post I did on this topic:
http://www.diyaudio.com/forums/multi-way/213765-concrete-cabinets-2.html#post3047190
Model is 3/4 inch ply exterior 1/2 inch interior with 1 inch spacing top and bottom and I believe 1 1/2 on the sides. Note however that the end result of "fill" space with the glued-on fabric is actually less than 1 inch (or 1 1/2 for the sides). You can of course use the ruler in Sketchup to get a better look at all the dimensions.
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Thanks for the link, Scott.
Of course a 3.3 cubic foot box isn't huge, so you may be able to do well with bracing and stiff panels.
Of course a 3.3 cubic foot box isn't huge, so you may be able to do well with bracing and stiff panels.
Has anyone tried 1/2" concrete board (typ used under tile) as a liner? Seems like that would be the next best thing to sand walls - and a heck of lot easier.
A pretty small box for 8 10" woofers? My twin SDX10 box (the small one) is about 2 ft^3. The large one is twice that.
They are mounted push-push and i am going to see how the 15mm BB i built them out of fairs, before adding "cosmetic" layers (dissimilar cheap 18mm ply to create the rebate so that drivers are flush on the baffle, something solid for the fronts, and room to skin top, back & bottom if needed)
The boxes are quite managable without the woofers, with woofers installed they are heavy.
dave
Bob Brines did that with his MDF boxes. He has since switched to good ply and i don't know whether he still does.
dave
With two separated walls, you could get extra bracing effects by clamping them together, with something like a bolt through both of them and a spacer between them on the inside at that point. That should give you the small moment arm of the total thickness of the "sandwich" against the distance to the nearest box edge, for each point where you do it, especially if the spacers were large-enough, in the directions perpendicular to the bolt axis (or, place three or more bolts close together, each time). It would also help to keep the walls from bowing out from the weight of the sand. You could possibly also compress the sand, using them, if you left them a little loose until after the sand was added, assuming the spacers were like sleeves for the bolts rather than like wood blocks.
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I found it really handy for picking up the box to make the lip of the outer ("cosmetic" as you called it) layer of ply around the driver with enough clearance to get my finger tips under...
http://www.diyaudio.com/forums/subwoofers/140069-altair-sub-2x-trio8s.html#post1781007
my box had sand in it, but it was the Class D type 😀
Thanks to everyone for the replies.
Here are a few points:
I have two 10" woofers per side, not eight.
I am thinking 3.33 C^3 should be enough breathing space.
And these are not sub woofers.
They are vintage SEAS midwoofers with paper cones and smallish alnico magnets.
Mid Q, 90db, Fs=30 ish.
My plan is not a floating two box model.
I will sandwich and glue each wall with spacers and 2-3 vertical chambers of sand in the middle. And then I will build the boxes with one horizontal brace.
I already bought some castors thinking it is going to be heavy.
Here are a few points:
I have two 10" woofers per side, not eight.
I am thinking 3.33 C^3 should be enough breathing space.
And these are not sub woofers.
They are vintage SEAS midwoofers with paper cones and smallish alnico magnets.
Mid Q, 90db, Fs=30 ish.
My plan is not a floating two box model.
I will sandwich and glue each wall with spacers and 2-3 vertical chambers of sand in the middle. And then I will build the boxes with one horizontal brace.
I already bought some castors thinking it is going to be heavy.
hi
been there done that with the whole thicker must be better thing using mdf
imho it does not work as well (not even close) as a box built using marine ply with matrix style bracing
the best subs or bass cabs (any cabs for that matter) i have ever built were using 15mm (yes only 15mm) marine ply with interlocking matrix bracing and hardwood fillets in every 90 degree angle
bottom line is good quality ply 15 to 19mm thick and a smart bracing regime = excelent sound and no coloration
been there done that with the whole thicker must be better thing using mdf
imho it does not work as well (not even close) as a box built using marine ply with matrix style bracing
the best subs or bass cabs (any cabs for that matter) i have ever built were using 15mm (yes only 15mm) marine ply with interlocking matrix bracing and hardwood fillets in every 90 degree angle
bottom line is good quality ply 15 to 19mm thick and a smart bracing regime = excelent sound and no coloration
You mean 2 woofers per box? And 2 channels.with one box per channel?
My thinking was that a typical subwoof has 4 sides, so 2 drivers/side x 4 sides = 8 drivers.
I suggest mounting the drivers push-push -- this is the single largest technique you can use to reduce box vibration.
Personally i think your box plan is a solution looking for a non-existant problem (given the frequencies involved)
dave
E.G.
zmyrna,
Sounds like your mind is made up, however the folks on here have changed my way thinking. I was a huge fan of 1" mdf BR cabinets; never square/rectangle, always angle sides/walls.
About a year ago I was talked into 1/2" wood subwoofers (Pic).
The base pours out of these, and the vibration is almost non existent. I was more surprised than anyone!
I ended up making 5 of these in different configurations.
zmyrna,
Sounds like your mind is made up, however the folks on here have changed my way thinking. I was a huge fan of 1" mdf BR cabinets; never square/rectangle, always angle sides/walls.
About a year ago I was talked into 1/2" wood subwoofers (Pic).
The base pours out of these, and the vibration is almost non existent. I was more surprised than anyone!
I ended up making 5 of these in different configurations.
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Could you explain how push-pull is going to reduce cabinet vibration? This technique is occasionally used to reduce second harmonic distortion, but I have never heard of it having anything to do with cabinet resonances. I only tired it once and found I could not hear a difference and the aesthetics are hard to deal with. (ironic, it was in a twin wall , sand filled sono-tube 4 cu ft box)
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