Soundproof door idea..

This question is for Rod mainly, but I would like all opinions..

My idea is to use 2 sheets of 1/2 MDF, one on either side of a frame of 2"x2"s and then fill it with sand.. I estimate my door to be about 250lbs when built and filled. It would be actively closed by a pneumatic closer and the seals would be on the compression surface, closed celled silicone.

I've not seen a lot of information on the Sayers site nor anywhere else..

What you are doing sounds pretty good to me.

There is method in Everest's Master Handbook of Acoustics used to acoustically treat the periphery of the door further to the seal you are planning to use.

The frame is inset a few inches from the periphery of the door panels and mineral fiber fills in the gap, which is then capped off with perforated hardboard. To make the outer edge look nicer, you can sit the perforated cap into the door panels so it is flush.

Good luck!

I can't comment on it's acoustic effectiveness, but just a reminder to use very dry sand. MDF and moisture, a rotten combination. :green:

-Chris

I hate MDF personally. The dust from cutting it is terrible, and I like to avoid anything made with formaldehyde glue.

You can get formaldehyde-free plywood, its not weather-resistant though (not a problem here).

[quote author="Svart"]This question is for Rod mainly, but I would like all opinions..

My idea is to use 2 sheets of 1/2 MDF, one on either side of a frame of 2"x2"s and then fill it with sand.. I estimate my door to be about 250lbs when built and filled. It would be actively closed by a pneumatic closer and the seals would be on the compression surface, closed celled silicone.

I've not seen a lot of information on the Sayers site nor anywhere else..[/quote]

Svart,

you have your work cut out for you.

Any time you construct a door with a frame - the doors stability becomes an issue.

This is faced by even the best of door manufacturers.

Filling the door with a material that would love nothing more than to soak up some moisture makes it even more of a challenge.

I've seen people try this and have doors (some were actually quite good looking doors when finished) warp 2 or 3 inches and be completely useless.

So you take your chances with this.

On the other hand - constructing a solid door with no frame - and adding mass (such as lead) to it can produce some relatively stable doors.

And just adding mass to a real solid corre door is about the best way to go of all the options.

Sincerely,

Rod

the biggest problem with doors is not so much the mass of the door but the seal on the threshold.

I have had some good results in various home studio applications with a regular solid core door and a properly sealed threshold.

:thumb:

Cool guys.

I have the supplies to go either way so I might just try it and report back. If it fails then I'll just build the solid door instead.. Actually I need two doors so I will do one of each and report how each one works.

weld a sub structure out of steel channel or tube for stability and minimal affect from moisture; mind how heavy it will be--integrity of framing and hinges. wooden jamb may swell too. 2 heavy sealed doors may be better than 1 ultrasilly door. Ive seen 'fire rated' heavy doors used, filled with gypsum I believe. if seal and surrounding structure are not adequate/decoupled than an elaborate door may not be as effective as it should

> the biggest problem with doors is not so much the mass of the door but the seal...

Listen to Pucho.

A door has to be incredibly lame to leak as much as its cracks.

I think you need much more than a spring closer and sili-foam to justify any more than a standard solid-core door.

And I have real doubt about 250 pounds sand in a 2x2 and chitboard structure; as Rod says, stability is vital and sand is not stable. Aside from sagging structures more solid than your wood, it settles. Fill it, pack it, ram it, set the top-wood on... and next time you slam the door the top 2 inches is hollow-core again.

It is also folly to have a pretty decent solid door, as in the building where I work, and then have a contraction crack where the wall hits the roof. Don't haul door-sand until you cover *every* detail in the roo's many leakages. Weak link in chain, yada yada.

How much attenuation do you really need? A lot of good music has been done literally in a basement with the door open. (OTOH, there is a Belafonte track done in a "professional" studio, and you can hear the thunderstorm outside.) The door may make you happy. The music may make many people happy.

> Ive seen 'fire rated' heavy doors used, filled with gypsum I believe.

There are several grades of "fire rated door", used for different occupancies. My school has some just plain wood fire doors, but rated to be solid and not made with real flammable glues. They also have steel doors. The wood door will hold back office-type fire for many-many minutes; try it. Long enough to get everybody out. The steel door will continue to function longer, may assist (or impede) fire-fighters. Where you want a door (and walls) to resist a fully enflamed building and protect contents, gypsum-filled is an option because gypsum will absorb near as much heat as water. And if you've camped, you know how much wood it takes to hot-up a pot of water.

[quote author="PRR"]The door may make you happy. The music may make many people happy.[/quote]
"Now, 'happy' is something extremely subjective. One of our sillier Zemblan proverbs says: The lost glove is happy."

Vladimir Nabokov, from Pale Fire.

[quote author="PRR"]> the biggest problem with doors is not so much the mass of the door but the seal...

Listen to Pucho.

[/quote]

:shock: did hell freeze over?

Chris,

If you do go ahead with the sand idea, I just thought of a couple thoughts that might help with warping.

Metal studs instead of wood to avoid warping. Of course these are hollow, and can themselves be filled with sand, so you could run studs down the center of your door for added stiffness, and to prevent the MDF from bulging out under the sand's "hydrostatic" pressure.

Coat your MDF with Sanitred (www.sanitred.com). I used this product to waterproof my old basement. It gets as close to a "miracle product" as I have seen yet. It's a paint-on, 100% waterproof, elastomeric membrane. If you painted all your internal surfaces with Sanitred and sealed the joints with their liquid rubber base, you could literally fill your MDF door with water.

-Chris

I'm not sure what the concern for warping is coming from.. If the door is squared(the edges, not actually a square door..), the perimeter frame is solid, and door frame is level and true, then why would the door spontaneously warp? The plan is to have two heavy hinges on top and two heavy hinges on bottom. The door closer is not simply a spring but a commercial pneumatic door closer for heavy industrial doors. This is the only problem I see, the door twisting slightly from the uneven pressure from the closer, but any door could do that.

Now I do understand the bulging door issue. perhaps a stud up the center of the door to tie the MDF together and keep it from bulging?

Lumber, even kiln dried, is not always done warping and twisting when you get it from the home store. I have a kitchen cabinet door that sat flush against the frame when it was first installed last year. 1 year later, the top of the door closes flush, the bottom has a 1/4" gap. Moisture will accelerate/aggravate any potential to warp.

Sand inside a door can pick up moisture in 2 ways: 1) chemisorption. This is how desiccants work. We don't care about this type of "moisture" because it won't be "wet", and most likely, any sand you buy will be fully hydrated already. 2) Condensation. A door filled with sand has a HUGE heat capacity and a HUGE amount of surface area. When the door get cool over night and it gets humid in the morning, the temperature of the door/sand is below the dew point of the humid air. There are millions of nucleation sites on the sand for the water to condense onto. This means that humidity will preferentially condense on the sand than on the smooth painted outside of the door. Sand deep within the door will get wet by drawing water from the outside through capillary action. Sealing the door will help (although without a moisture barrier like sanitred, it will be tough to make it impervious to moisture). Air conditioning will help too. However, when your AC cuts out on a humid day, the newly humidified air contacting the cold door won't be good.

Regards,
Chris

[quote author="Svart"]I'm not sure what the concern for warping is coming from.. If the door is squared(the edges, not actually a square door..), the perimeter frame is solid, and door frame is level and true, then why would the door spontaneously warp? The plan is to have two heavy hinges on top and two heavy hinges on bottom. The door closer is not simply a spring but a commercial pneumatic door closer for heavy industrial doors. This is the only problem I see, the door twisting slightly from the uneven pressure from the closer, but any door could do that.

Now I do understand the bulging door issue. perhaps a stud up the center of the door to tie the MDF together and keep it from bulging?[/quote]

Gravity. How wide is the door in question? You've got a couple hundred pounds (100 kilos, 14 stone) of door hanging from one edge. The outer frame of the door is under a lot of stress and MDF isn't helping much. If you used 1/2" 5-ply plywood for the skins then you'd have something approximating a box beam which would be quite rigid.

To prevent your rectangle becoming a parallelogram it might be wise to add a diagonal member from the upper hinge side corner to the lower swinging side corner (look at any wooden frame gate and you'll see this same thing). Triangles are structurally superior to rectangles. A "stud up the center" of the door won't do crap by comparison.

And of course the "moisture + wood = bad" thing just adds to the problem as others have noted.

I've built several doors pretty much as analogpackrat described. The largest studio door being about 46" wide, filled with sand too.
What I remember of the details:
It was made up of a simple frame ripped from old and dry relcaimed 2X4's for stability, 1/2" (?) plywood skins, and 1/16" ply veneer.

The frame rabbeted around the edges for double seals (the black 3/4" closed-cell neoprene from the hardware store). It was divided into three vertical "cells" to prevent "ballooning" when the sand was added later. No cross-bracing was needed because the plywood skins on both sides act as a box-beam.
It was hinged using five heavy duty ball-bearing hinge sets. The closer was a heavy duty commercial unit as well. I remember a dado'ed in drop seal in the bottom.

The trick in building your own door is getting it flat when you assemble it, and that's hard to do in even the best workshop. Just the least bit of unflatness on the work surface will show as warpage on the finished door.
What I used to do was to pre-hang the raw frame into the jamb. I would install temporary stops where the finished edge of the seal would end up (not where the finished stop would go). Then true up and screw the frame into the temp jambs from the backside so it's locked into what will be it's final placement. Then I would glue and stitch the outer skin onto the frame. Once done, you can release it from the temp stops and it will stay perfectly square. I would then swing it open and stitch the remaining skin.

As far as the sand, I used kiln-dried (playground sand) and filled it through holes bored through the top edge of the frame, and capped them. I let it settle for a few days and topped it off.

Man, that b*stard was heavy! The door functioned smoothly, but it took some pull to get it moving! People had a real hard time getting it off the stops and swinging. So it tended to get propped open all the time. LOL I eventually drained the sand and lightened it up. Still had good isolation...
Hope that helps!

awesome! that's pretty much what I planned on doing.

As for the door, it's going to be 76"x32". It's a small access door for loading and unloading gear into the workshop area. It shouldn't be used very much at all.

ok so I got the chance to come home early from work..

I cut the door out and built it. It's about half filled with sand and rock solid. i don't see any bulging, twisting or warping so far.

The bolt at the bottom is for two things.. First it has a ramp on the bottom so that when pushed down, it squeezes the door into seals making them as tight as possible. The top will have one too but I haven't done it yet. Secondly, it locks the door in case anybody were to break into the outer areas.

The hinges are super heavy duty ones. I took this picture before I installed the last one on the bottom.

What is covering the framing behind the hinges?

Rod

So far, nothing but drywall. This was a test fit. The drywall buts directly against the door frame with no gaps. This portion will be cut back about 1/4" and sealed with silicone. The hinges will be covered from the front to hide them