Any thoughts on how well a 6 panel pine door would work in terms of a sound proofing application?

I've got 3 weatherstripped doors in my theater.

1 - 32" S&S door that leads to the rest of my unfinished basement
1 - 32" S&S door that leads to a small storage area (2nd fridge / sump pump)
1 - 31.25" S&S door that leads upstairs that opens inwards on a 12.5" wide jamb.

My preliminary testing says that the weak point of my setup is the door to the stairs. I am going to put up a 2nd communicating door in that jamb (being 12.5" wide, it will work fine with the hinges on the same side of the jamb). Preliminary testing was with a cheap portable CD player/radio tuned to a local FM station, and the volume was 'loud' in my yet to be carpetted room.

The problem is that the door frame in the loadbearing wall was framed wonky, and 31.25" was the largest I could safely fit in there. The custom Masonite S&S door was about $200cdn after taxes and about 2-3 weeks to arrive. I can't cut down a 32" wide door, because the 'splines' are too narrow.

Canadian HomeDepots have a 32" solid 6 panel pine door on sale this month for $60. They are an in-store item, and feel heavy. The only thing is that the door itself is the standard 1 3/8" thickness, but the panels themselves aren't full thickness. I didn't take a ruler to measure, but I would guestimate that the panels are milled from thinner stock. My guess is that the thickest part of the panel is only about 1" thick.

I could cut 3/8" of each side to bring it down to 31.25"'s and save a bundle of money, which is a concern to me, as I just ad libbed to the budget of the HT by looking for a used (consignment) Paradigm center, and coming home with a brand new (factory blem'd) CC-290v5, and a DSP 3100 :eek:.

I have a feeling adding a real sub will expedite the need to get a 2nd door on the main HT entrance leading upstairs.

If you're just looking to make that door "no longer the weak link", then any solid door that you put in there will make that better than the other 2 doors, assuming it fits right and has reasonable gap to the threshold. Even a hollow core door would probably improve it to be "no longer the weakest door system".

If you have decoupled walls, insulation, double drywall and green glue for walls, then heavy double doors will still be your weak link. The doors just aren't as massive as double drywall + studs, they are undamped, and no absorption in the air cavity. And this assumes you have 100% perfect seals.

The doors are always a compromize you have to deal with. The pine door isn't as heavy as others. Also panel door slabs lack the mass of a flat face (flush) slab. The indents of the panels are also weak points, whether Safe & Sound or not.

So a solid core smooth face (flush slab) door with seals is about your best alternative with off the shelf materials.

Definately communicating double doors. Actually a small "lobby" with a door on either side is better still. More air space = more absorption = lower resonance. But you'd have to double drywall the walls and ceiling of your little lobby also.

If you have decoupled walls, insulation, double drywall and green glue for walls, then heavy double doors will still be your weak link. The doors just aren't as massive as double drywall + studs, they are undamped, and no absorption in the air cavity. And this assumes you have 100% perfect seals......

Yeah all my non foundation walls are decoupled.

That wall that leads upstairs is:

1/2" drywall on one side on an original 2x6 loadbearing wall. I've added 3.5" of Roxul in that wall.

2" air space

then a 2x4" - 16"OC wall with 3.5" of Roxul in that. and DD (1/2" on walls) with 2 tubes green glue for each 4x8 sheet.

The seals aren't perfect on that door.

I'm hoping for $60, the pinedoor with weatherstripping will add noticeable improvements to the soundproofing.

If I'm still not happy enough with the results, I might screw some MDF to the inside of the pine door. MDF is pretty cheap, and I could add a 5/8" sheet to the door, leaving a 1/4" reveal around the doorjamb, chamfer the MDF with a 45 degree router bit. and paint it the same colour as my other doors/trim.

Last night I dug my 15-20yr old Paradigm speakers out of storage, and unboxed a new Paradigm cc-290 center channel and DSP-3100 sub. I was able to watch movies after the kids bedtime at 8pm at fairly decent levels without any complaints from my wife, or waking the kids (who sleep with their bedroom doors open :o ) The speakers were powered with a 4-5yr old entry level Sony 5.1 receiver, and I had the volume set on the digital dial between 35 and 45.

As you say, you can always augment doors later. And your initial sound test went well, so what the heck...

If I'm still not happy enough with the results, I might screw some MDF to the inside of the pine door. MDF is pretty cheap, and I could add a 5/8" sheet to the door, leaving a 1/4" reveal around the doorjamb, chamfer the MDF with a 45 degree router bit. and paint it the same colour as my other doors/trim.



I've been pondering that same scenario, buying a solid wood door, and then adhearing drywall to it with a green glue layer in between. But then I thought that might look, well, odd. :)

I originally planned on a Kintetics door, but their 35 STC model is $1300, and the 45 STC is $3000. :eek: I guess knowing the door will always be the weakest link helps keep me from going overboard on the walls. It's all well and good to make them 61 STC, but that door is still going to kill the average.

Instead of drywall, I've heard of people using a layer of MDF with GG. I had planned on doing this myself. If you do that, make sure you beef up the hinges.

CJ

Drywall attached to a door or removable panel runs the risk of crumbling due to fatigue. Not too bad when sandwiched between plywood, though.

For doors and panels it would be easier and higher performance to go with the less destructible MDF as CJO says.

Drywall attached to a door or removable panel runs the risk of crumbling due to fatigue. Not too bad when sandwiched between plywood, though.

For doors and panels it would be easier and higher performance to go with the less destructible MDF as CJO says.

Is there a specific brand or type of solid wood door (preferably one available at lowes / home depot /menards) that is better than others? I was thinking of going with an exterior grade door for the seals vs. a solid wood door. Is solid wood superior to steel fire-grade doors with foam inside? Or is a choice in the door purely a question of mass?

i.e. it doesn't matter all that much what the door is made from, as long as it's really freaking heavy. :)

It's the mass. Better than a steel door. But then there's the seals...

Best to go to a door shop and have them custom hand a solid core interior door on an exterior jamb. Not for the folks at Lowes or Home Depot, but rather a professional door shop.

Thought I'd ask a related question here since this thread otherwise went quiet.

I am trying to address the door issue as well. My room has double stud walls on the door side. I plan to use a solid core heavy door on an exterior trim, weather-sealed, installed on the theater side stud wall. My contractor and I have been toying with also adding a pocket door into the outer stud wall, so when I want to get maximum containment, I close the pocket door, and then the heavy door.

That obviosly leaves an air gap area between the doors. Am I helping with this approach, or making the issue worse by creating a resonating space?

Hi Dixon,

Thanks for the resurrection. The double (communicating) door system that you're describing is advantagous in great part because of the air cavity. The incorporation of the cavity moves us from a simple Mass-based system (one door) to the classic Mass - Air- Mass system. A spring is created since the two doors are also decoupled from one another. Just like the double stud walls.

This works as long as they are well sealed. This is where the pocket door demonstrates its liability. No seals at all, really. They require hollow walls to store in, leaving a large section of wall acoustically compromised.

So they really should be engineered out of the design.

Can you add another solid door with hinges and seals?

Thanks Ted. I could probably add another hinged door, but the advantage to the pocket door on the outer wall (into a basement hallway) is that it easily passes the WAF. I think she is willing to let me play "soundproof guy" in the theater, but will rain on my parade when I start messing with the rest of the newly renovated place.;)

While I agree the air pocket for the pocket cavity isn't ideal, I could probably double sheetrock that outerwall, as it isn't a large sq ft area.

My hope is: the decoupled theater room with the weather-sealed solid door catches most sound, and the pocket door/double drywall on the outershell helps muffle some of the leakage through the theater door. In this particular case, I am less worried about preventing some minor sound leakage into that basement hall than I am making sure I knock it down to a level that is less likely to travel 15 ft around the corner and up a staircase to disturb the main level. So the pocket door just provides an extra buffer.

Glad to hear the air cavity is a plus, not a minus.

...The double (communicating) door system that you're describing is advantagous in great part because of the air cavity...

I have double walls with clips, double sheetrock/GG construction, which are giving excellent results, but the two solid-core particle-board communicating doors on separate, isolated jambs, are not as good as the walls.

I've added two layers of 1/2" cement board with GG to each slab and the insides of the jambs, and added extra seals to the existing Q-lon seals, which helped a fair amount, but not as much as I'd hoped. The doors still leak more than the walls. It seems that the sound is coming through the jambs, even though these are mechanically isolated from each other, and from the floor and walls.

My question is this: Since the air space between the doors is relatively small, would it be better to open the jambs into the wall cavity to share that air space for a lower resonance? Can you suggest any other treatment options to futher quiet these doors (short of replacing the slabs with MDF or $$$ accoustic doors)?

Thanks.

The doors can't be as effective as the walls. They have less mass, are not damped, less than 100% sealed and have an un-insulated air cavity. But we need 'em.

Adding mass and damping is a good thing. Your suggestion to increase the air volume makes excellent sense, but there is no data on this specifically. So you should be the test subject, I think. Like any other air cavity, bigger is better.

Before this however, try a small amount of insulation in the cavity. Perhaps a section of duct liner if you used that on your theater walls. Given that the doors are decoupled, the system should react well to the addition of absorption.

Let us know about that. Then try the open gap between the door jambs as you suggested. I have thought about this very thing for years but have never had the opportunity to even informally test this. This is a real opportunity if you can standardize the test sound source, the volume, and the measurement position outside.

Thank you very much. Please feel free to email me with any thoughts etc. I would love to help.

Do you have pics of the seals?

I've been a few basement theaters now with that double door and a few feet in between. Very inpressive isolation performance not to mention ,for us baby boomers , it gives that retro fallout shelter/bunker feel.:D

Art

Hey Art! This is what excites me about this potential test. The air volume would potentially change things enormously

Hey Art! This is what excites me about this potential test. The air volume would potentially change things enormously
Yes. And you know the fact that you can't simply add transmission loss numbers for multiple layers? I.e., a layer with a transmission loss of 30 plus another layer with transmission loss of 30 will not give you a transmission loss of 60?

Well, the presence of a very deep air space changes this. If the air space depth is large enough compared to a wavelength of the sound you want to block, then the transmission losses will approach being additive! Of course, the air space depth won't be at all large for low frequencies, but it can be for mid to high frequencies.

Regards,
Terry

Yes. And you know the fact that you can't simply add transmission loss numbers for multiple layers? I.e., a layer with a transmission loss of 30 plus another layer with transmission loss of 30 will not give you a transmission loss of 60?

Right. The figures are logarithmic

Well, the presence of a very deep air space changes this. If the air space depth is large enough compared to a wavelength of the sound you want to block, then the transmission losses will approach being additive! Of course, the air space depth won't be at all large for low frequencies, but it can be for mid to high frequencies.

Regards,
Terry

What's your feeling on the size of the opening between the jambs, Terry? The size of the gap, that is. My previous ponderings have been left with the thought that the narrow gap required for aesthetics might very well limit the benefit

What's your feeling on the size of the opening between the jambs, Terry? The size of the gap, that is. My previous ponderings have been left with the thought that the narrow gap required for aesthetics might very well limit the benefit
Honestly, the best thing is to make a (sound-isolated) vestibule. Feet rather than inches! :D Then you can make a very serious impact on the lowest frequencies.

No question, but given the circumstance presented I'm wondering about the potential for improvement with a slot between the jamb sections.

As I said, I have always been concerned about the limited slot size

No question, but given the circumstance presented I'm wondering about the potential for improvement with a slot between the jamb sections.

As I said, I have always been concerned about the limited slot size
Not exactly sure what you mean by a slot, Ted. But if you could, say, open the upper gap between the two door frames so that it communicates with a very large (otherwise well-isolated) volume above the ceiling, a high-pass acoustic filter would be created. This is similar to the use of a plenum expansion chamber in commercial HVAC duct construction. The side branch "T" expansion chamber, if it is large enough, will reduce the low frequencies that get transmitted.

Regards,
Terry

Hi Terry. That's what I'm talking about. If a gap existed between the door jambs, maybe 3/4", you would be uniting the "between door" air cavity with the large airspace within the walls / ceiling.

That's been the obvious plus. The negatives are the look / practicality of this big gap as well as the usefullness, given the narrow width of this gap.

The only oppotunity I have for opening the jambs into the wall cavity is to cut a slot in the sides of the jambs. I share Ted's question about what size of slot to cut into the jambs.

Since the wall cavity energy is not necessarily in-phase with the room energy, and the door slab will have a different phase response than the walls, how does the slot modify things? Could a mismatched phase response potentially increase transmission at higher frequencies as slot and slab energies add instead of cancelling?

Terry, do you have any simulations you could apply to this to see what slot size would be most effective, and whether any damping material should be added to the slot before I start cutting?

The door cavity is approx 31"x79"x9", and the door slabs are 1-3/4 SC particleboard with 2 layers of 1/2" HardieBacker 500 (2.6lbs/sq') separated by two layers of GG (adds ~85lbs to each slab). I assume the wall cavity resonance is sufficiently lower (<10x) than the door cavity resonance. The walls are 2 layers of 5/8 type-x sheetrock separated by GG, mounted on hat channel attached to wood framing with WhisperClips. The wall cavity is filled with fiberglass insulation.

Thanks.

Terry, do you have any simulations you could apply to this to see what slot size would be most effective, and whether any damping material should be added to the slot before I start cutting?

Unfortunately, not :(. This is the very first time I have thought about this particular problem. I don't even know how much study and simulation would be involved.

Of course, if someone wanted to hire me to find out [attention, all former presidents of the Green Glue Company :D], I could.

Regards,
Terry

... if that was for me, I wasn't the president back then. Am now (different company), wasn't then...

As far as the gap, I'd start with 1/2" or so if you can. I wouldn't concern yourself with phase

So did we decide my pocket door idea was a waste of $$, or would likely provide a reasonable (albeit not perfect) solution/improvement? ;)

I would not do it at all.

Interesting. Thanks as always for the replies.