Originally Posted by Martycool007
I just don't like the idea of using a transducer. In my opinion bass sounds & feels best when your room is on a crawl space foundation, and being that my room is concrete on all 4 walls and the floor, I would really like to recreate the same visceral sensation that I got in my old home. I wish that someone knew more about the floating floor with springs idea that I am considering, although, building a conventional riser that has slots cut at the rear, corners on the rear wall and sides in order to function as a bass trap, sounds pretty awesome as well!
I guess I disagree. Every experience I ever had with an unsolid foundation with regard to bass performance was highly undesirable for me. It's very hard (almost impossible) to get a room or riser to move with the bass perfectly but not resonate, add unwanted noises, or pollute your sound quality. As soon as you design a riser to do such a thing it's likely to resonate like a drum. I hate that. I have a guitar amp stack and drum kit at my house and when I would play the guitar through the cab the bass freqencies would vibrate the drum kit and the drums and they would resonate and make a very annoying noise- different freqencies specific to each drum and size of it. The snare drum was the most annoying because the snare band of springs would make terrible noise from it, I would have to go and take off the tension anytime I wanted to play guitar alone without that annoying sound. This is what happens when you get loud sound waves in a tight space - they interact with different things. Personally I hate it.
My fear is that any riser that is not properly damped will resonate like a drum head at whatever frequency excites it and totally ruin your sound quality, noise floor and otherwise smooth response. A proper riser should be IMO stuffed with pink fluffy insulation or sand to prevent resonating - and it should be built solid. There is a reason why professional theater builders and experienced builders (think amateurs on their second or third build revision) use 3 layers of plywood on the riser, with green glue and 30lb roofing felt. Roofing felt under the boards and joists and in between layers of wood. It's because they do not want the undesirables associated with otherwise (or what you are thinking of doing).
I too love the tactile feel. I want the bass to hit me in the face and chest, make it hard to breath at times and shake the sh!t out my chair, myself and my room for that ultra impressive experience. But my opinion on getting that isn't from building a resonating riser. Transducers are way cheaper and easier and can be mounted on your chair - they can provide even more "tactile feel" directly to where you want it and most importantly they can also be turned off if you don't want it or don't like it. It's cheaper and easier and can easily be undone. Very hard to undo a bad riser design and result. I'm not saying you can't do it or should not do it- I am just cautioning you that if you do decide to do it- you should take great care to make sure you do it right.
I've been researching theaters, and build process for a while now. I don't think many more have done as much as I am in this regard that are not professionals or have not already build a theater and completed the process by living through it.
It seems like most of the people that are trying to do what you want to do, or desire it - they tend to be uninformed and beginners. <-I hate to say that and I say it with as much respect as I can, I am not calling you or anyone else a beginner and I am a beginner as well. I just want to highlight that it seems like it's a beginner thing and more often than not it's not executed very well. My hope in saying this all is not to persuade you from your dreams, but help you realize them but making sure you don't fall into the same trap. If you do it, then execute it well.
My dream bass response is the same as your's I think. I just have a different approach. I want to build the room solid as can be (double walls, double sheet rock with GG, putty on box outlets, double doors for entrance with weatherstrip seal, no windows, and everything bolted down and nailed down tight including riser with 2 or three layers of plywood to make it very solid and stuffed with pink insulation to make it quiet) - but I still want to shake the sh!t out of myself and guests when the content is there. So focus on low response, and high SPL in the 5hz to 35hz region. This means a bass system with overhead and headroom and enough power and driver surface area to make enough output to rattle my tight room. It's going to feel way better if your riser is still moving because you have enough bass to move that solid three layer riser stuffed with insulation- or you have enough power to move the entire floor (which can be double floored with the upper level "floating") or best yet shake the entire room.
If you want direct tactile feel use a transducer system (even directly on your chair if you wanted) or just employ a bass solution that will shake the entire room including a solid and otherwise quiet riser.
I have a suggestion: Could you build an 18" ported sub that has a tune like 10hz and place it near field to your seat ? It should work well with your other ported subs but get you that response you are missing with the higher tune on the others. You really should not mix ported and sealed, and ported has a steep roll off lower than port tune so you lose a lot of output at 5-15hz with typical ported enclosures. You could add a near field sub ported even lower than your other subs for that extra brutality you seem to want. It might be easier to do that than risk messing up a riser.