i need help with doors

[genericperson]

hello everyone,

i'm building an iso booth right now. i'd like to build a double door entry to it, with a 24" wide door.

can anybody offer some suggestions?

i know they make Overly doors, but I'm looking to do-it-myself... I can't drop $3k on a door right now!

i'm sort of not having much luck at Lowes or Home Depot. it seems they are out of stock on metal doors. at minimum, i need a metal frame for the doors so they hang square and robustly.

my idea is to have a two doors in one big frame opening. then slap some drywall, limp-mass vinyl and sonex on the doors to improve the STC.

slapping the stuff up isn't the problem... the problem is finding the metal door frame to hang two doors!

(I'm in New Jersey and will drive two hours in any direction to get this stinkin' frame!).

I guess this isn't a gear question, but it's a "gear helper" question that is very important to me.

[tINY]

First, you don't need metal door frames if you build a solid wall (you know, with jack-studs and headers). You do need solid core doors and a good seal.

Second, don't use a single frame for the doors. Build a frame in each of the isolated walls (use offset studs if you must, but around the doors the plates need to be 2x8s). If you use the same studs to support both doors, the sound will couple from one door the other through the structure.

Rockwool and rigid fiberglass (Corning 702) are cheaper than sonex and probably work better on the doors. Also, adding some bracing to one of the doors can help by changing the resonance. That way the two doors don't pass the same frequencies by resonating alike.


-tINY

[jajjguy]

The weak link will be the seal around the doors. Until you add good gasketing on the top, sides, and bottom, it will be pointless to add mass to the door itself.

[AdAudioInc]

Agreed about not needing metal. I found heavey solid core wood doors at home cheapo. They are exterior doors almost 2" thick. Then build a frame with a door stop that goes all the way around including the bottom and use a good noeprene 3/8" seal. Also you can use the 3/8" seal between the 2 door frames. So you'll have a 2" solid door in it's own frame, a ~4" air space, then another 2" solid door - both sealed on all 4 sides.

Great idea about added mass to one door to change the resonant frequency - I'll have to try that for additional isolation - thanks.

Also a little absorbtion on the inside of the doors when closed is said to keep the air space from resonating - that might help as well.

[Riad]

Try Zero International for the seals around the doors. I bought the automatic door bottoms and jams. I avoided the $75 hinges (3 per door!! yikes) and bought 4" heavy duty hinges at home depot.

I also bought the solid core doors from home depot for $50 a door.

Rob-

[genericperson]

i actually saw something decent at home depot.

it was a metal door with a metal frame thick enough to accomodate a second interior door. and then in the speical order catalog they had these solid core doors called "safe and sound" that are meant for noise blocking.

so my idea right now is to get the metal door/frame and add this second door. then on the insides of the doors i would add a layer of 1/2 drywall to thicken each up and add mass. then in the remaining cavity area i would put a seal or a ring of sonex going around the trim. and then some people have talked about these spring-loaded plate things that you can rig up at the bottom of a door. i would put that on the inside of the metal door. that's my current idea-rendition on it.

the reason i want the metal door is that i really want the metal *frame*, and that's how to get the metal frame....less likely to warp or get torqued/skewed over time.

[juniorhifikit]

You've gotten good advice already:

First, you don't need metal door frames if you build a solid wall (you know, with jack-studs and headers). You do need solid core doors and a good seal.

Second, don't use a single frame for the doors. Build a frame in each of the isolated walls (use offset studs if you must, but around the doors the plates need to be 2x8s). If you use the same studs to support both doors, the sound will couple from one door the other through the structure.

Rockwool and rigid fiberglass (Corning 702) are cheaper than sonex and probably work better on the doors. Also, adding some bracing to one of the doors can help by changing the resonance. That way the two doors don't pass the same frequencies by resonating alike.


-tINY

Don't hang the doors on the same frame.
Rockwool and rigid fiberglass are great for absorbing high frequencies, but will do nothing for the STC.
Buy a book, maybe the Salter one, and check out all the Joiner-Rose data.

[tINY]

Putting rockwool in the cavity between the doors will damp out resonances in the cavity. Granted, between two isolated doors, it probably won't do much. But, for a few $$ of material, it might damp out a resonance that otherwise may pass energy through the seal.



-tINY

[genericperson]

why is it taboo to hang two doors on the same frame?

if the frame is metal and bolted into the joists, it should be plenty solid.

i know the idea of decoupling the walls. my walls are all going to be staggered-stud.

but for about 17 square feet of area, i dont' think it would be such a project-killer to have two doors in the same frame. especially since the frame is metal, and each door is going to be hopped-up with extra linings of drywall.

when it's all done, the metal door/frame will be about 100 pounds and the other one about 50 pounds. i can't see how the common metal frame would be a significant resonance factor under these circumstances.

but i could be wrong.

[juniorhifikit]

You gotta trust us on this one
You'll get the maximum sound transmission loss with two masses separated by an airspace. If the two doors are connected by the frame, they're CONNECTED. They act as one.

If you don't fully understand the physics of sound transmission (I don't) and aren't going to hire an acoustical engineer, at least buy a book and trust those who have done this before. You're getting free advice that an acoustical engineer would charge you hundreds of dollars an hour for.

Buy Charles Salter's book, and look up any of the studies the Joiner-Rose Group has done.

[tINY]

Having a single metal frame is fine as long as you aren't planning on attaching the doors to it solidly. The more solid it is, the worse it is.

If you want to prove it to yourself, take a hammer and press it against a running motor and then put your ear to it. The stiff handle transmits the the vibrations (noise) to your ear. If you have two doors solidly attached to the same frame, then one does a good job picking up the sound and then it is transmitted to the other door that radiates it on the other side.

You might get away with a single frame if it's attached to something really heavy like a reinforced concrete wall...



-tINY

[AdAudioInc]

The fact that the frame is metal makes this a very bad concept and effectivly ruins your time and effort put into a stager stud wall. Metal, because it is so dense will transmit more frequencies faster and easier than wood. Having a coupled metal frame between the 2 walls will be like having an open 1 1/2" PVC pipe between the 2 rooms.

Having to change it latter will suck. Check out "The Master Handbook of Acoustics" most of it is black magic and totally over my head, but there are diagrams and cut-aways of walls that will be very helpful. Also "How to Build a Small Budget Recording Studio"

Good luck.

[Riad]

For more detailed information please post this question on, John Sayers site and you will certainly get some very similar comments you are getting here. The people there are experts and I certainly trusted their suggestions when I was building my studio.

By connected two objects together with a solid mass you are in effect creating one object, and thus, negating what you are trying to do.

Sometimes with metal wall studs you can achieve better results because they flex slightly, it all depends on what you are trying to achieve.