u boats on riser/floor?

You could consider the rubber isolators for the rim joists of your riser. No need in a basement, but I assume you're not in a basement since you mentioned "subfloor."

You could use 4x4s in the 4 corners and in the middle of the long runs. Lets say this raises the riser height by 10". Then build out the rest of the riser framing with 2x6 and joist hangers.

The result is a vey minimal contact riser.

Aha so you're really wanting the riser to act as a bass trap, then. Sorry I misunderstood.

I did it... Click here for a link in my build thread.

I also used U boats but did not do them on 16" centers went 24" or more in some places as I wanted my sub to get my riser moving

http://www.avsforum.com/avs-vb/showt...4#post11585004

Can anyone tell me why u-boats should be used in riser construction? I'm going to build my riser inthe back of my theater over a concrete slab. I don't plan to use it as a bass trap, so what are the benefits of using u-boats?

CJ

I'd like to know also. I'm gathering it provides a more tactile "ride" during heavy bass scenes?

Dennis wrote a pretty good article on buiding a bass trap into a riser. I don't recall that he recommended using u-boats, hocky pucks, or anything to keep it off the concrete.

CJ

I'm not thinking Dennis actually said that. I'm sure that's what the post you mentioned said, however.

Coupling the stage or riser to the walls is not great.

I can only chime in with why I did it. The pro's may not agree with my rational.

1. Poured concrete floors are not all that level. They are plagued with high spot (especially on seams). Using the u-boat on the outer edges allow you level and by selective placement of the u-boats with no "rocking" on high spots.
2. The u-boats get the riser off the floor thus eliminating the need for treated lumber.
3. The way I hung the center joists, it allowed me to cover the bottom thus not having insulation I filled it with in contact with the concrete.

I found a copy of Dennis's article from September 03. For using the riser as a bass trap, he did say to couple the riser to the walls. "First, install a 2x8 against the back wall, gluing and screwing the 2x8 through the sheetrock to the studs. ... Next, attach the two side 2x8s to each side wall, checking for level."

There was a sepatate sidebar for tactile response equipped platforms in which he advocated not coupling the riser to a wall, and only allowing the perimeter rim joists to touch the floor (floating the remaining joists 2" off of the floor using 2x6 joists with 2x8 rim joists).

A couple of notes ...

I would not suggest screwing the rim joists of the seating platform through to the studs. It would be to the HAT channel, or studs in a double wall or staggered wall construction. That would be required where the rim joists are not resting on the floor...something has to support the weight.

Typically, we damp the entire floor and therefore anything resting on the floor is damped from the rest of the structure. We do not place devices on the seating platform which create mechanical vibrations and hence don't see a performance decrease when the seating platform is in contact with a damped floor and damped walls.

OTOH, if you're all set to muck with the director's orginal intent and install butt kickers or other devices to the seating platform and convert the seating platform into a speaker, then you would need to keep the entire seating platform away from the walls and use something like rubber "U" sleeves to isolate the framing. (Is my bias against tactile transducers showing through?)

Not at all...