I spoke with my builder today about sand filling the riser for the second row of seating and he wasn't comfortable with this idea. The room is in the basement and he is concerned that there would be some moisture in the sand and then we're piling it on top of a concrete floor and sealing it all up creating a potential mold issue down the road. He said that in the past he has filled home theater risers with icynene and had good luck. I can't find any examples of anyone else doing this so I was just wondering if anybody had any comments on this...

Thanks,
Jeff

How can sand go moldy? Sounds like a weird concern. I haven't heard of icynene so can't help you there. I had a sand filled riser in my basement in GA. Never any problems and that has been installed for 7 years now. My buddy bought the house and a little bit of mold is enough to give him a massive asthma attack. He hasn't had any issues with mold there.

I'm not sure he was thinking the sand itself would get moldy, but rather that if the sand was trapping moisture in the area that the concrete floor, wood, etc. could grow mold.

The icynene stuff is an expanding foam insulation product. I've seen it mentioned on here before for walls, but I don't recall it being discussed in a riser.

http://www.icynene.com/

The more I think about this... why don't I just fill the thing with concrete? Any downside to that other than the "permanent" factor?

I don't see any compelling reason to fill a seating platform with sand. Filling with an expanding foam product ... you're better off spending that money on room finishes, treatments, or upgrading your equipment...what's wrong with fiberglass batts? The use of fiberglass will then allow you to use the seating platform as a broadband or tuned absorber.

Don't you just love it when the cheap and easy solution IS the best solution.

My understanding was, if it's a riser for seating only the pink insulation is sufficient, however, if it may have a subwoofer on it - and it may - then I need something to greatly increase the mass. Sand is commonly recommended, but in this case if the builder is pushing back on me concrete seems to be a logical alternative.

Is anyone claiming that even if there is a sub on the platform I would still only need the pink insulation?

Thanks everyone.

When I said sand filled riser, I meant sand filled proscenium. The riser was just filled with insulation batts.

Concrete has moisture in it too. I just don't see how sand is going to cause you problems.

Don't use concrete unless you want to hear your sub throughout the house.

Thanks everybody for the replies, I definitely appreciate it.

My second sub will be on the concrete floor so am I really buying myself anything by avoiding concrete in this location?

My understanding was, if it's a riser for seating only the pink insulation is sufficient, however, if it may have a subwoofer on it - and it may - then I need something to greatly increase the mass. Sand is commonly recommended, but in this case if the builder is pushing back on me concrete seems to be a logical alternative.

Is anyone claiming that even if there is a sub on the platform I would still only need the pink insulation?

Thanks everyone.

In my case I have one of my subs on the riser because I wanted to increase the tactile response produced by my Bass shakers. My riser is filled with Pink insulation and open at the back. Now if I had filled it with sand, Hm 15" of sand UGH! but anyway if I had it would have defeated the purpose of placing the sub there in the first place.
Tactile response asside I think you would be fine with the Pink stuff and no worry about sand getting damp or leaking out the bottom or anything else.
you are decoupling your riser are you not?

If your sub is moving your seating platform, your sub is producing energy to move the platform, not produce sound. If you want tactile response, use a tactile device. You are not well advised to use a Volkswagen Bug to transport ore in an open pit mine, nor well advised to haul your kids to school in a 100 ton mover. Both will work...just not well advised. :)

But, Dennis, wouldn't you agree that the sub is going to produce mechanical energy regardless of the substrate it sits on? It seems a question is whether you want to harness the energy for a secondary, symbiotic purpose (shaking a ridgid platform) or dump it as waste energy (damping it with sand or insulation). I didn't read McCall's comment to mean she put the sub on the riser primarily for tactile response - only that the sub had to go somewhere, and she chose to harness the otherwise wasted mechanical energy to augment the tactile response of her bass shakers.

That's why mounting speakers to something of far more mass than the speaker becomes important. I cannot move it, so that energy is applied to it's primary purpose. Yes, there will always be come kinetic transfer...you minimize it and damp what's left over.

So again, if the rest of my room is a concrete floor anyway, it still seems that filling the riser with concrete is a suitable approach, is it not? If nothing else it would seem that you'd want the whole surface to be homogenous. At least one sub will be sitting on the concrete, so why not both?

I put the Sub on the riser, it is my second sub to improve the overall sound and it does, however the fact it is on the riser does "assist" the Bass shakers mounted in my riser. The idea to try that was one I first found on here, I ran the idea past some people who would know if it was an okay idea and they said try it. I did and it works very well.
If I were transporting ore it would have to be behind my electric scooter, you use what you have, but then I often find that ingenuity aids invention.
I have never claimed to be any kind of expert, but I try things, some work some don't, some work that the experts say shouldn't or are a bad idea. Personally I think sometimes experts can be too set in their ways to try things just to see what the results are.
Anyway it works extremely well for me and that in the end is all that matters, and if someone else wants to try it and see what happens and if it works for them, more power to em.

If you know where the sub is going to go, could you build an isolated section of riser and fill it with sand instead of the entire thing?

My understanding from reading other posts was that partially filling the riser in just the speaker location didn't add enough mass to really achieve the intended purpose. As I understand it, you aren't filling the whole thing with sand to allow for the speaker to be placed in any spot on the riser, you are simply trying to add the maximum amount of mass that you can.