Film-Tech Forum ARCHIVE: Acustical Problems

This is topic Acustical Problems in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=000742

Posted by Ian Price (Member # 14) on 03-13-2000, 01:43 PM:

We have a funky 5-plex with a few acustical problems. Our #4 screen's theatre has the booth floor over the auditorium. You can hear the Speco platters rumbling in the auditorium. There is also a bit of hallway in the room. About 10 feet of parallel walls that are un-treated.

What can I do to quiet the rumble?

What can I do to quiet the hallway?

Posted by Gordon McLeod (Member # 33) on 03-13-2000, 05:34 PM:

We often put hockey puck under the platter and rectifier s to stopp vibration transmition into the floor
AirConditioner contractors also carry issolators

Posted by Ian Price (Member # 14) on 03-13-2000, 06:03 PM:

Guys, to clarify some.

We have two problems in the same room.

Problem one is transmission of unwanted sound from the booth above the auditorium.

Problem two is the echo in the hallway of the unwanted sound from above.

Solutions for the first problem, I have been told, are to add more mass and stiffness to the floor under the platter. Could a layer of 1.5 inch plywood help? Or could the plywood be laid over a layer of acoustical material that would help isolate the rumble?

Solutions for the second problem have been suggested as to carpet the walls with acustical carpet? One person said that that wouldn't cut down the noise much. Or to use acousitcal panels covered with cloth, held off the wall a couple of inches to create a sound trap?

I appriciate your input.

Posted by Lance C. McFetridge (Member # 95) on 03-13-2000, 06:12 PM:

Ian,
There is a product on the market that is called Silent Step. It can be found at a floor covering store and is used under Pergo flooring as well as hard wood floors to reduce sound transmission. Another thought is if your booth is a framed floor rather than a concrete floor, blown in insulation between the floor joists would certainly help stop unwanted vibration transmission.

Posted by Ian Price (Member # 14) on 03-13-2000, 06:15 PM:

Yes, It's a framed in floor. Long live concrete and all of its uses.

Posted by William Hooper (Member # 71) on 03-14-2000, 01:56 AM:

If it's mechanical rumble, thump, & clatter transmitted directly to the floor, check out Unisorb's stuff
http://www.unisorb.com

I had VERY good results with a few of their Red Line pads used to isolate a monstrous Spencer Turnbine blower (not in a booth, isolated from transmitting to the slab).

--------
Carpet on the walls gets nasty. Acoustical tile gets chewed up fast in mechanical rooms. Standing acoustical tile off 1" or more basically only adds bass traps, so you'll need to decide if that's what you need. Sonex will gobble up room noise (except lowest freq's, you'll need to create bass traps for that), but it's expensive. There's some Sonex-knockoff sheets in the Holy Grainger Catalog under Acoustical Foam, but it's still not cheap.

Wall treatments (like Sonex) do almost nothing to reduce noise transmitted directly to the ceiling, wall, or floor.

If the problem is really horrible transmission through the floor, lay a new isolated floor on top of the old one. It may wind up being cheaper than Sonex & isolation pads.

Posted by Mark Gulbrandsen (Member # 72) on 03-14-2000, 06:31 AM:

The rubber squares that are used under the corners of speakers in THX systems work very well for platter noise. I will post a place you can get them later today. They also work well under rectifiers.
Mark

Posted by John Walsh (Member # 168) on 03-14-2000, 09:32 AM:

Yeah, I ws going to suggest those THX/speaker rubber squares also. Fairly cheap and easy.

I'm not sure what you mean about sound in a hallway. Do you mean a hallway leading to the booth, or a hallway (down below) leading to the auditourium?

If the hallway is in or leading to the booth, and you want to kill some of the (higher freq) noise from the booth, maybe you could make some free-standing panels. Get or make some of those panels like they use to make office cubicules and just "wall-off" the area on each side of the projector and/or platter. Maybe a panel about 4ft x 8ft. Buy some 2x2's to make a frame and glue or nail some acoustic ceiling tiles to it. Either free-standing, or bolt it to the front wall so it could be removed to get more room when servicing. Recording studios use something like that to localize each instrument or singer, while allowing all the artists to see and hear each other.

I realize it seems sort of a cheap thing, but since your place just opened, you might be a little cash-short. It would be cheap to make one and try it. 2x2's are $2-3 each (5 of them or so) and a box of 10 (2x4) tiles are about $20. If it works, it might be cheaper than doing an entire wall(s).

Posted by Mark Gulbrandsen (Member # 72) on 03-14-2000, 04:19 PM:

Those THX rubber squares are available from Imbert Corp in Chicago. The number is 773-777-4020. Ask for Mason Super W durometer 40. As I remember they come in 3 foot square sheets. Imbert will cut them for you into the 2 inch squares if you ask them.
Brad, You may want to list this on the link page even if there is no link to them. These can be hard to find and Imbert always has them in stock.
Mark

Posted by Dave Williams (Member # 299) on 03-15-2000, 02:37 PM:

Ian, coming from a purely mechanical engineering aspect, the rubber pads should do the trick. If you look at how freeway overpasses are layed on dozens of rubbler layers, ok thats rubber layers, it becomes a little clearer. The reason for the freeway rubber is to absorb all of the rumble and vibration from the vehicles going over the overpass, if it didnt, then the overpass would simply absorb it itself and crumble.

So with the specos rumbling, which i have the same problem, the platter itself is absorbing the rumble, and with nowhere to spit it out, it sends the noisy vibrations into the floor (we have the same setup I believe).

The rubber pads should do the trick and absorb a good portion of the vibrations. You should still look into filling the void in your floors with insulation to remove the rest of the noise.

Then again, If i had taken a career in mechanical engineering, you know, like desiging platters and projectors, well digital cinema would probably look pretty good. Damn good thing I am nothing more than a movie jockey.

Than again I could be wrong.

------------------
"If it's not worth doing, I have allready been there and done it"

Posted by Dave Williams (Member # 299) on 03-15-2000, 02:42 PM:

Ian, in follow up, on the specos, they sit on three metal screw posts, that adjust for hieght. You will need to put a block of 1" thick wood about 6" by 6" under each post, with a rubber pad between the post and the block, then the rubber pads, about three of them, the same size as the block, under each of the wood blocks.

This should eat up most of the vibrations.

Then again, I am just a film junkie, what the hell do I know?

------------------
"If it's not worth doing, I have allready been there and done it"