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Screen Wall Question

790 Views 5 Replies 3 Participants Last post by LarryChanin, May 9, 2006

Tom Harness

Discussion Starter · May 6, 2006

A common construction technique is to build a stage so it does not touch any walls and to fill it with sand. This helps to acoustically isolate the subwoofer and speakers from the rest of the structure.

However, when a screen wall is constructed, it seems to always be connected to the stage, walls and ceiling. This appears to me to short circuit the advantages of building an isolated stage. I realize it would be difficult to build a screen wall and not have it touch the stage, but can someone explain to me why it is important to take the trouble to isolate the stage and then couple the stage to the rest of the room via the screen wall?

Tom

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BroncoSport

· #2 · May 7, 2006

If I am not mistaken, the main reason to fill the stage with sand is to stop the resonating characteristics of a hollow box, under the speakers / sub. The proscenium walls are generally just framed "naked" and covered with GOM or other fabric, so they wouldnt resonate. But I do see where you are coming fromas far as touching the ceiling. I think the spacing of the stage away from the walls and filling the stage are meant to "decouple and en" the most you can. In my personal situation I will not have sand in my stage. I will not have any speakers sitting on the stage and the proscenium walls will not be on the stage itself, rather they will be on the floor.

Scott

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Tom Harness

Discussion Starter · #3 · May 7, 2006

Thanks for the reply Scott.

I'm sure your comments are right. Its a compromise to attach a screen wall to a de-coupled stage, but most screen walls I've seen aren't nearly as heavy as a typical wall and thus presumably are not as good at transmitting sound. There are some prosceniums made with MDF that do look pretty substantial though.

By the way, I'm enjoying your construction thread, Scott. Keep it up. We are at about the same point. My drywall is up and finished. I've completed a riser and will do the modest sized stage in a few days. That leaves me with soffits, furring, acoustic material and GOM. Then maybe I'll buy some equipment and watch a movie!

Tom

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LarryChanin

· #4 · May 8, 2006

Quote:

Originally Posted by Tom Harness
A common construction technique is to build a stage so it does not touch any walls and to fill it with sand. This helps to acoustically isolate the subwoofer and speakers from the rest of the structure.

However, when a screen wall is constructed, it seems to always be connected to the stage, walls and ceiling. This appears to me to short circuit the advantages of building an isolated stage. I realize it would be difficult to build a screen wall and not have it touch the stage, but can someone explain to me why it is important to take the trouble to isolate the stage and then couple the stage to the rest of the room via the screen wall?

Tom

Hi Tom,

To elaborate on the points that Scott made, the sand filled stage most importantly prevents the stage from resonating at its own natural frequency. However, it also absorbs the bass energy of the speakers sitting on it. Therefore, since stray bass energy has been significantly reduced by being absorbed by the sand, there is little residual energy to cause a serious problem by coupling the stage to the ceiling via the screenwall framing. In building my screenwall I found no reason to attach the screenwall to the side walls thereby avoiding at least one source of coupling.

One other mitigating factor is that the stages are usually covered with carpeting which can also provide additional damping between the framing connecting the stage to the ceiling. If you still have concerns you can insert a vibration isolator, like a sheet of neoprene, between the ceiling and framing. Since the carpet and the neoprene would have screws going through them into the stage and ceiling joists, the vibration isolation would be compromised somewhat. However, a much more objectionable issue than bass energy being transmitted into the structure is audible rattling of the screenwall framing against the stage and ceiling. This would be eliminated by the carpet and neoprene.

Larry

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Tom Harness

Discussion Starter · #5 · May 8, 2006

Thanks Larry.

Your explanation makes a lot of sense to me. I hadn't thought about the carpet and other factors you mentioned. You've been very helpful for me over the last few years I've generally been a lurker on the forum. Your theater looks great too! The glass art does add a nice touch of color to the room.

Tom

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LarryChanin

· #6 · May 9, 2006

Quote:

Originally Posted by Tom Harness
Thanks Larry.

Your explanation makes a lot of sense to me. I hadn't thought about the carpet and other factors you mentioned. You've been very helpful for me over the last few years I've generally been a lurker on the forum. Your theater looks great too! The glass art does add a nice touch of color to the room.

Tom

Hi Tom,

Glad I could be of assistance, and thanks for the kind words.

Good luck with your project.

Larry

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