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[Helge A Bentsen]

Depending of the amount of reduction needed, I've had pretty good results using MDF/drywall in a sandwich construction.
A inner shell of MDF with enough space for the sub(s), two layers of drywall and one outer layer of MDF with as little as possible physical connection to the rest of the stage. Easy to build and easy(ish) to modify later down the road. Also made the stage floor of the same sandwich type, put a pair of SB1000z under there and it worked well.

[Tim Weaver]

If sand worked before, what about using a CMU block wall that is internally filled with sand. Cap this with the drywall, or drywall-mdf sandwich.

CMU blocks are pretty easy to knock out with a sledge if you later need to reconfigure. I know years ago we would use similar construction in dance clubs to make mounting platforms for the turntables. This would decouple the TT's from all the vibrating wood that made up the DJ booth.

[dave briar]

Depending of the amount of reduction needed, I've had pretty good results using MDF/drywall in a sandwich construction.
A inner shell of MDF with enough space for the sub(s), two layers of drywall and one outer layer of MDF with as little as possible physical connection to the rest of the stage. Easy to build and easy(ish) to modify later down the road. Also made the stage floor of the same sandwich type, put a pair of SB1000z under there and it worked well.

I like the sandwich idea. No 2x4’s needed.  Bunker thickness is somewhat limited by the need to keep the stage as low as possible to maintain view lines from under the mezzanine.
Curious how the two layers of drywall in the stage deck are holding up?  I’ve been looking at using two layers of 3/4” HDF glued and screwed to the joists. Drywall would certainly add mass but drywall underfoot is not a “normal” application I’ve ever heard of. Just curious.

[dave briar]

If sand worked before, what about using a CMU block wall that is internally filled with sand. Cap this with the drywall, or drywall-mdf sandwich.

CMU blocks are pretty easy to knock out with a sledge if you later need to reconfigure. I know years ago we would use similar construction in dance clubs to make mounting platforms for the turntables. This would decouple the TT's from all the vibrating wood that made up the DJ booth.

That’s a pretty practical solution. There is sufficient room to the back and sides of the sub-cluster so CMU block could fit. Sand is cheap.  Building it during stage construction would be easy. Knocking it out and replacing it with the stage deck on would be more difficult.  Great idea though.

[Helge A Bentsen]

I like the sandwich idea. No 2x4’s needed.  Bunker thickness is somewhat limited by the need to keep the stage as low as possible to maintain view lines from under the mezzanine.
Curious how the two layers of drywall in the stage deck are holding up?  I’ve been looking at using two layers of 3/4” HDF glued and screwed to the joists. Drywall would certainly add mass but drywall underfoot is not a “normal” application I’ve ever heard of. Just curious.

MDF forms the outer layers of the sandwich, so people are  performing on top of a solid surface. It's 1" MDF top/bottom with two layers of 3/4" drywall in-between, feels very solid to walk and perform on. Certainly  more  solid than most regular stage decks.  The sandwich floor is on top of 2x4" beams/legs not  connected to the sub bunkers. We used industrial carpet on top for less HF reflections from the floor and vacuum the  stage regularly.
I have no data on how effective this solution is, it was conceived as a cost effective solution using available materials and for ease of installation.
I've had several performers comment on how little sub there is up on stage after we did this compared to past experiences in the same room.

[Ivan Beaver]

Google says the density of drywall is 724kg/m³ whereas concrete is 2,400kg/m³ but no question Sheetrock would be easier to build and modify.  If it were me the Sheetrock option seems much more workable (I’ve never been enthralled with working concrete) but if the owner wants to indulge in some creative bunker construction that will work too.

If you use sheetrock, it is advisable to use them double thick with alternating seams, glued and screwed.

That gets a lot closer to concrete density.

But hey, if he wants concrete, then just do that, but he must understand that he is pretty much stuck with the size for future sub choices.

[Dave Garoutte]

You could do the MDF/sheetrock with a gap filled with sand.  The sand should be very absorbative due to the fact that it can move.

[dave briar]

MDF forms the outer layers of the sandwich, so people are  performing on top of a solid surface. It's 1" MDF top/bottom with two layers of 3/4" drywall in-between, feels very solid to walk and perform on. Certainly  more  solid than most regular stage decks.  The sandwich floor is on top of 2x4" beams/legs not  connected to the sub bunkers. We used industrial carpet on top for less HF reflections from the floor and vacuum the  stage regularly.
I have no data on how effective this solution is, it was conceived as a cost effective solution using available materials and for ease of installation.
I've had several performers comment on how little sub there is up on stage after we did this compared to past experiences in the same room.

Very interesting.  An alternative I have considered is adding a layer or two of 1/2” “cement-backer-board” (normally used behind ceramic tile in showers) between the two layers of HDF.  The cement board pencils out at ~1,200kg/m³ but drywall would no doubt be less expensive. Also planning on framing the stage on 12” centers — but that’s likely a discussion for a different thread.   Thanks for the details.

[dave briar]

…
But hey, if he wants concrete, then just do that, but he must understand that he is pretty much stuck with the size for future sub choices.

True that for sure but worse case would be bringing the fork lift, lifting the bunker out (it will not be attached to the floor — except by gravity), carrying it to the dump trailer, and building new ones. Modifying a sandwich construction bunker would certainly be more feasible if we need it smaller but making it larger would likely be easier to just build over as well.  But wise council nonetheless. Thanks.

[Ivan Beaver]

True that for sure but worse case would be bringing the fork lift, lifting the bunker out (it will not be attached to the floor — except by gravity), carrying it to the dump trailer, and building new ones. Modifying a sandwich construction bunker would certainly be more feasible if we need it smaller but making it larger would likely be easier to just build over as well.  But wise council nonetheless. Thanks.

Most people don't have the luxury of being able to bring a fork lift into the venue.

How would you get it out from under the stage?  Remember that the bunker needs to be airtight (or pretty close) in order to prevent leakage from getting under the stage.  That usually means attached to the stage itself, with a good seal against the floor, and the front of the stage. 

Were you also planning on removing the stage and front in order to get the bunker out?

[ProSoundWeb Community]