Reall, really weird problem

[orbifold]

well, I have lurked for a couple months, and want to get started on a set of RS 3ways, L,R, & CC. I have an approx 11' x 21' x 7' space, but the space setup puts the goodies on one end, throwing sound and video across the 11' dimension. Instead of having a wall on both sides, I have only a wall on the left, and half height stair, open doorway at the top, and partial partition on the right. Existing system: very good computer speakers, Logitech Z680s, 500 watt 5.1 hooked up to an M-Audio Revolution 7.1 card on my Mac. So almost any good audio system will be great. Of course, I have to get the TV, and the amp/prepro (Ihope!) I'll have lots of ?? on those issues, But a weird thing has come to light.
Right now I'm tearing out and replacing ceramic tile, old built-ins and drywall. Turns out that the concrete slabe on the side on which the leftie will sit, has an air chamber under it!! While taking up the tile the hammer made a real echo all along this wall. Considering that this speaker will be sitting on ceramic tile, 1/8 inch of thinset mortar, and the crete, this is a disaster.
I wanted to get into things like. are the RS's mentioned too much for this little space? Etc, etc. And I'm going to consult with a city engineer on what I could do, but this scares me. My question here is, does it scare you, too? Really sorry for the crappy first post and more or less OT question, but since I don't really have much in the way of experience with good audio and what affects it, I just wanted to check with those who do to see if this is a killer. If someone just says, put a rug under it and everything will be fine, or this just won't work. Not expecting building expertise, that's my problem :cry:
I look forward to more prosaic posts. :B

[---k---]

I don't understand what you mean by an "air chamber". Do you mean that under the slab there is a void in the dirt below, causing echo? In which, I would be suprised if the slab wasn't cracked and you had setteling issue - if you don't it means that the void is small. You could core through the slab and pour concrete grout in there to fill the void.

Or is it just a delaminiation within the slab? A void or seperation of the concrete. To fix this, typically you chip out the loose concrete, clean it, get it wet and pour in new quick set concrete.

I don't think the floor will be a big issue, but it likely will be easy to fix if you're already doing a lot of work in the area. But, you need to describe the problem better.

[Dennis H]

Turns out that the concrete slabe on the side on which the leftie will sit, has an air chamber under it!! While taking up the tile the hammer made a real echo all along this wall. Considering that this speaker will be sitting on ceramic tile, 1/8 inch of thinset mortar, and the crete, this is a disaster.

I don't think it's a big deal. Consider that most wood floors make a lot of noise when you bang on them with a hammer but, in practice, they aren't a problem for speakers. You'll probably want to isolate the speaker from the slab rather than coupling tightly to it. You can do that with rubber feet, rugs, etc.

[orbifold]

Thanks, k, for the reply. I really think its some gopher of ground hog tunnel. Yes, a void with a discernible hollow sound when struck with the hammer. I may need to core a hole and fill as you said. No cracks are evident. Just wanted to get through getting the area prepped and get to cutting MDF, etc. maybe more time in constrution will allow more time to consider what wires go behind the drywall and so forth. I do want to connect the computer to this system, may want to leave wiring in the walls for 5.1 surrounds to come. Things like that. Will have the engineer take a look this week to see what to do.

[orbifold]

Thanks for the reassurance Dennis. I just went down and tried it again, and the effect doesn't seem so bad, but it is a temporary stoppage to correct the building aspect. I picked some MDF last trip to the HD, and I understand there is a sale in progress at PE, and my router and table saw are itching to go! You'll see a proper starter post soon to get some specifics before I really begin. Many thanks for all the expert info here.