What type of door for a single wall system

[Oyvine]

Hey.

I'm planning to build an iso booth for vocal practice using a single wall system of the following format:

The inner leaf will consist of a 5/8" plasterboard, this will hang on a 2x4 frame which will be filled with rockwool insulation, then the outer leaf will consist of a 5/8" plasterboard which will be mounted on a flexible channel which again is mounted on the outer side of the frame. According to John Sayers STC chart this will result in a STC rating of around 47.

What type of door would be the best fit to be used on such a wall, when my goal is to get a STC rating as close to 47 as possible for the door?

I've been thinking of building a single door using 2x4's (lying the thin way) as the perimeter with 2" of rockwool inside with at least one layer of 5/8" MDF on each side. As far as I know this will yield around 44-48 STC if I am careful with the sealing. Or am I wrong about this?
Another problem I guess this solution will lead to is coupling, because the single door frame will couple the inner and outer wall. How much will this reduce the STC rating?

I have also been thinking of using two solid core doors with an airgap in between to create an MSM effect, but I wonder if this effect will be negated by coupling problems due to their shared frame?

Anyways. What would be the best door solution with this walll system to achieve a goal of around 47 STC?

[Soundman2020]

Hi there "Oyvine", and Welcome!

The inner leaf will consist of a 5/8" plasterboard, this will hang on a 2x4 frame which will be filled with rockwool insulation, then the outer leaf will consist of a 5/8" plasterboard which will be mounted on a flexible channel which again is mounted on the outer side of the frame.

It would be better to invert that: Have the outer-leaf drywall attached to the framing directly, and hang the inner-leaf drywall on the resilient channel (RC).

According to John Sayers STC chart this will result in a STC rating of around 47.

Theoretically, yes, assuming that your ventilation system and door also are built to the same level, and assuming perfect materials and perfect construction technique. In reality, it will be more like 40 to 45. Also, using STC is fine if this is ONLY a vocal booth, but if you wanted to also record instruments in there, or if there are noises outside that you want to block and those noises are not in the vocal range, then STC is not the correct system to use for evaluating isolation: STC does not take into account the bottom two and a half octaves of the musical scale, nor does it take into account the top two and a half octaves: It only considers the middle of the scale, which is voice frequencies and typical office and home sounds. But not music.

What type of door would be the best fit to be used on such a wall, when my goal is to get a STC rating as close to 47 as possible for the door?

A single door rated at STC-47 would be hard to find, and hard to build. If you wanted to buy one, this is what it would look like:

http://alkuhaimi.com/acoustical.html

http://isostore.com/shop/product/isodoo ... tion-door/

And it would cost probably US several thousand dollars. The first one above includes "special construction with gypsum board, lead and fiberglass insulation and seals".

Making a door rated at STC-47 is a big deal. Not easy at all.

I've been thinking of building a single door using 2x4's (lying the thin way) as the perimeter with 2" of rockwool inside with at least one layer of 5/8" MDF on each side. As far as I know this will yield around 44-48 STC if I am careful with the sealing. Or am I wrong about this?

That would probably get you about STC-25 to STC-30. It would a be an unsealed fully coupled light-weight single-leaf hollow door, which is not going to isolate.

Another problem I guess this solution will lead to is coupling, because the single door frame will couple the inner and outer wall.

Correct.

I have also been thinking of using two solid core doors with an airgap in between to create an MSM effect, but I wonder if this effect will be negated by coupling problems due to their shared frame?

that would be a much better plan, for overall isolation, but as you point out there is still the limiting factor of the frame. However, the flanking limit of the frame is likely still higher than what you can get with typical doors, so I doubt it would be an issue.

What would be the best door solution with this walll system to achieve a goal of around 47 STC?

I'm not sure for STC-47, as I vary rarely use STC when designing studios, but to get 47 dB of transmission loss (isolation) in a single-leaf door, Mass Law says that the surface density of the door would have to be around 250 kg/m2. It would have to made using some very high density materials, which is why those commercially made doors (links above) use lead and thick drywall, and have very heavy duty hinges and latches, plus automatic door closers: they are way too heavy to be able to close safely by hand.

The equation for calculating the empirical isolation of any single-leaf barrier is:

TL = 14.5 log (Ms * 0.205) + 23 dB (where: Ms = Surface Mass in kg/m2 ).

With a pair of back-to-back doors, it's a lot easier to get high isolation. Here are the doors in a studio that I designed for one of my customers in Australia:

door-threshold-Photo 00-00-0000 00 00 00 pm_ENH-SML.jpg

That's a view of just the inner-door in place, showing the seals around the edges, and the threshold. The outer door is not yet installed in this photo above, but it is in this one below:

door-seals-in-Photo 28-02-2016 3 51 31 pm-SML.jpg

Note the heavy duty hinges on both doors: Important. They are heavy


Here's a view of the outer door from outside, showing the automatic door closer at the top:

Entry-door-from-outside-20160417 164004-SML-ENH.jpg

In this case, both doors together provide a bit more than 50 dB of isolation. Each door measured by itself provides a bit less than 40 dB. That's roughly what you can expect from well-designed doors.

They key to getting good isolation from doors, either single leaf or double leaf, is mass and seals. You need high surface density, and you need at least two full-perimeter seals on each door.


- Stuart -

[Oyvine]

Thanks a lot. Will a 2x4 frame be able to support the two doors though?

[Soundman2020]

Will a 2x4 frame be able to support the two doors though?

A single 2x4 frame: No. I always go triple framing for this type of door. One cripple stud on each side for creating the actual rough opening, then another two king studs on each side of that, and triple cross-bracing over to the next stud. Like this:

Door-Framing-IMG_5203-SML.JPG

That's the same door system as above, from the inside of the room. You can see the triple studs on each side, and also the triple horizontal cross braces. There is also a very solid, large lintel above the doorway, not visible in this photo as it is hidden behind the HVAC duct that runs across the top of the door, which provide extra rigidity to the overall frame.

Done like that, it can handle the weight of the door.

Each of those doors is made up from three layers of solid wood, plus Green Glue, plus the glass which is 16mm laminated glass with acoustic PVB inter-layer. Each door weighs about 90 kg, fully assembled. That's why the door closer is needed: you can't control that amount of mass safely by hand: You don't want it slamming into the jambs and seals. The door closer makes sure that it closes smoothly and softly, then provides pressure to keep it closed.


- Stuart -

[Oyvine]

Ok thanks a bunch for detailed answers.