Sand sandwich

[Vikash]

I've decided on sandwich walls for my new sub enclosure (~32 litres with one Peerless 10" XLS and one 10" passive): thick MDF / sand / thin MDF

I undersand that sand is useful in this scenario as it will convert motion energy to heat, but would concrete be better with the increased rigidity it provides?

Also, how thick should the panel layers be? I was thinking 18mm MDF / 18mm sand / ~6mm MDF, but I don't know if the end panel should be a different material or whether the different thickness will be enough to ensure different resonance properties?

[454Casull]

Something infinitely rigid will have no internal damping.

[Timn8ter]

How do you ensure there will be no air gaps as the sand settles?

[Ron E]

I think sand is overkill.

With a subwoofer, it is a trivial matter to brace the cabinet enough to get the first resonance above the operating range, assuming you won't cross higher than 100-125Hz. Sand will mass-load the panels and could actually bring the first resonance down into the operating range.

With all those layers, you have many times the chance for a cabinet buzz or a loose joint.

Keep it simple, simon....

Cheers

[Guss]

Originally posted by Timn8ter
How do you ensure there will be no air gaps as the sand settles?

If the sand settles, it mean that it has not been compacted enough.... Must we compact the sand properly or just fill the gap?

[MITMechE]

I'm not an expert on sand for power dissipating purposes, however my general understanding is that the coulombic friction between adjoining sand particles dissipates power and acts as a damper for the enclosure. So, with that understanding, I think it'd be best if the sand had some freedom of movement, i.e. I would just pour the dry sand in and pack it a little to make sure there's no large air pockets.

[FlaCharlie]

For what it's worth . . . I've heard some vintage Wharfedale speakers used sand as dampening. Heavy suckers I imagine . . . Charlie

[sreten]

Originally posted by Ron E
I think sand is overkill.

With a subwoofer, it is a trivial matter to brace the cabinet enough to get the first resonance above the operating range, assuming you won't cross higher than 100-125Hz. Sand will mass-load the panels and could actually bring the first resonance down into the operating range.

With all those layers, you have many times the chance for a cabinet buzz or a loose joint.

Keep it simple, simon....

Cheers

I'm completely with Ron E on this one.

The sand will be ineffective in a subwoofer application.

Decent bracing and descent eventual sub c/o slope is the way to go.

Your sub will also be smaller in every dimension by 2" which is a lot.

sreten.

[Rudolf]

Also, how thick should the panel layers be? I was thinking 18mm MDF / 18mm sand / ~6mm MDF, but I don't know if the end panel should be a different material or whether the different thickness will be enough to ensure different resonance properties?

If you are going with the sandwich 18/18/6 should be more than sufficient AFAIK. Outer and inner walls will be decoupled by the sand, so you need not worry about resonance. I would look at the inner panel purely as a means to keep the sand together, so it could be even less than 6 mm thick.

Rudolf

[markp]

I've built several sand filled enclosures with great results. Just leave a hole in the top of the box play the speaker for a while and the sand will fill the voids then top-off the sand. The box is very inert and does not resonate on the outer shell as the sand dampens it well. It takes a whole lot of energy to get something that heavy to vibrate. Also, use sterile play sand from the local home center, the grains are smaller and more uniform.