Sub on seating riser - good or bad? (1 Viewer)

Just getting ready for the construction of the seating riser - looks like it's going to be about 18" high in the back, over a concrete floor. The equipment as well as the sub is all located in the back of the room, right behind the last row of seating. It would be preferable to have the equipment at the same height as the last row of seating.
My question is - since the subwoofer needs to be up on the riser for space reasons, will that be good or bad for the bass response? And if I need to, what construction steps are necessary for the best sound?
This forum has been a wealth of knowledge, thanks to everyone that contributes!
Thanks,
Ben

Okay, no answer yet - so I'll tell you what I THINK I should do (please correct me if need be): I am planning on filling a 4-foot square area under the sub (it's in the corner) with sand, then tightly insulate the rest. I think this is consistent with what others have done under similar circumstances, however my riser is much higher (around 18") than any other example I've seen. Is this going to be a problem? Should I put more sand? Less? Will my bass dissappear?

So long as it doesn't rattle the frame of the riser it should be ok. The added sand would help stop some resonance that could add to a boomy sound but it might not be needed...in other words if possible I'd try it with out first and see if its needed as once you add the sand you aren't going to be able to move it very easily As for the over all sound its hard to say really if one corner would be better then another other then to say that since the sub isn't located near your mains I'd want to make sure its crossed over below 80 hz..likely a little below that if possible. I'd also want to have a processor that could set a delay for the sub based on its location since its going to be a long way from a typical placement assumed by the sound mix.

If you use sand, I would suggest you fill small individual bags full, and place them. That will help keep the sand contained, and allow you to adjust the amount of sand as needed.

Thanks for your replies! The receiver I'm using is a Denon 3805 which does have a delay setting, as well as the SVS PC+ 20-39 sub, so delay won't be a problem.
The bag idea for the sand sounds good, I might give that a shot.
I guess my biggest concern now is whether or not to do the sand. My common sense would tell me that it would be boomy if I didn't, but if I have the crossover set low, those frequencies wouldn't be coming from the sub anyway, right? The whole riser is about 10' X 15', most of it 18" high, a small section of it is about 6". I need to get this figured out because I'm starting it tomorrow.
Thanks guys!

My two cents? Sand won't hurt.

If you need to make a decision before you close up the riser I'd say go ahead as you planned and fill the section below where the sub will sit with sand. A couple of bags of clean, dry play sand will run you about $5.00. Personally I would line the cavity with 4-6 mil. plastic and then fill with sand. Leaving it in bags won't completely fill the space...you'll probably have some air pockets.

Filling it and finding out you didn't need the sand? $5.00. Not filling it and finding out later you should have? Well, not priceless but a big pain in the a$$.

A bigger factor to the overall bass in the room is going to be placement anyway. If you have limited options on where you can place the sub you may need to come up with additional means to tame it later anyway, sand or no sand. Hopefully you'll get lucky and your initial placement will be fine.

Another option over sand is to use kitty litter. Its cheap, heavy and absorbs moisture better then sand.

How about using a Gramma?

http://www.auralex.com/sound_isolati...ion_gramma.asp

I have six. Currently using four. Two under each sub. They do work.

but how much are they?

anyone know the price?
i couldnt find it on the site.