Ideal door STC rating for garage studio conversion

[DanGo]

Hi All,

I'm in the process of converting my garage into a high-quality control-room/mix/project studio and have a question about doors. My contractor and I will be putting in ZeroInternational seals with a raised threshold, but we're uncertain about the STC rating of the solid core door that will lead to the outside.

Because of various space considerations, a traditional double door won't work.

Will an STC rating of 41 be sufficient? Or should I aim for a higher rating?

The walls and floor and ceiling will be isolated from the studs with special clips and I'll have heavy insulation plus 2 layers of drywall and will caulk up all air holes, gaps...

Thanks!

Dan

[DSD_Mastering]

Guess it depends on the ambient noise outside. If it only reaches 60-70dB, then no problem! Now if you want to keep the drum noise down and not disturbing your neighbors.... good luck! I used a double door design going to my outside... but then again I have neighbors that use lawnmowers and leaf blowers!

Regards,
Bruce

[DanGo]

That's a fair response. I don't tend to monitor too loudly, but occasionally I like to mike up my Vox AC 15...again, not too loudly. Hard to say what the ambient noise will be coming from my studio as I have never set up in that space before... I will not be recording drums.

Honestly, I think my bigger concern is keeping things quiet inside the studio!

So, if that's the case, would an STC of 41 be adequate?

[numrologst]

What is your wall construction?

If you want to max STC, the STC of your door needs to be equal to or greater than the STC of your walls.

Then remember STC does not take into account frequencies below 125hz... So you should only put a bit of stock in STC numbers. Don't ignore them because they are helpful... But realize you aren't getting the full picture

[DanGo]

That makes sense. I don't know offhand what the STC of the walls will be, but the construction will be (from outside to inside) 1/2 plywood outside (stucco'ed ultimately), then 2 x 4 studs, then RSIC-1 sound dampening clips attaching to SoundBreak gyp board and then another layer of standard gyp board. We're going to try to stuff r16 insulation in between the studs (even though r13 might be a more traditional choice...

I hadn't realized that frequencies below 125Hz weren't accounted for in the STC rating... That said, I will be treating the inside of the room with some bass control traps, etc., later on, so maybe that will help, too?

[paul101]

A single solid core door with added mass should work. (Plywood etc. stuck to the one side to beef it up)
Just make sure your door frame is up to the extra weight.

I've opted for two doors which certainly works, but I know from reading Rod Gervais's book that he prefers your method and goes into great detail on how to achieve the most from it.

[DanGo]

Thanks for that input. I will look into adding mass to the door and I'll see if I can locate Rod Gervais' book.

The door frame is being built now with the idea that it will need to be a monster...

My contractor already beefed up my roof beams for the same reason: tons of gypsum board hanging over my head...in earthquake territory!! Who says making music ain't dangerous anymore?

[numrologst]

I'm not a big fan of SoundBreak... but using it is your decision... I've seen better results with green glue than soundbreak, and it is a little cheaper.

Your inner wall is fine... Like I said, SoundBreak is your choice. The RC is nice too. I'd add another layer of gyp before the plywood.

R13 should be fine for you.

The way you are talking about the build, a 41 STC door will be a weak link. Likely, I would do a double door... Then you will be in the neighborhood of what your walls are doing.

Bass traps aren't gonna do anything for low frequency TL. That's interior acoustics, not soundproofing. The only thing that you can do at this point for low freq TL is to add more mass... That will have diminishing returns though. The next step is more air between.

I have triple gypsum with green glue, rc, staggered stud, plus 12" air gap... There ain't shit that transmits through the wall...We have to use double acoustic doors with an even bigger airlock to make up for it.

I hope I helped you find your solution... I would go with a double door for sure.

[Clueless]

Here's the product sheet that describes the doors we plan to use. We're going for 3.5" thick doors with an STC of 51-54.

You can see how dramatically the soundproofing drops at 125Hz and below...

[philosi]

If you are going to add mass to the door, sandwich in a layer of vinyl sound barrier. They sell it at Canal Rubber in Manhattan, incredible stuff, but pricey... Two layers of drywall is great but add a layer of homosote in between and its many times better. I assume your drywall is 5/8"? Homosote is 1/2" and they say it's good to vary the thickness of layers. BTW, Homosote is not "soundboard" Homosote is 10 times better and probably twice the price, but worth it.

Homasote Company - 440 SoundBarrier®

Canal Rubber Supply Company

[avare]

What you want to is mass, mass, and mass. Rubber,vinyl, homasote are NOT what you want. If have the money include a layer of lead. The best source for details is Rod Gervais' book.

Good luck!

Quietly:
Andre

[DanGo]

Thanks, gang, for all the varied opinions... I'm a little uncertain now of what direction to take.

To be honest, the wall composition is just what George Augspurger suggested to me after seeing the space, so I figure that while you all probably are right, I'd be just plain silly to pay George only to ignore his advice. There must have been a reason why he suggested the arrangement he did. I'm wary of using lead because I've got a toddler and another kid on the way... and this will be a studio in my backyard: no way am I gonna be able to keep them out...

Sounds to me like I should definitely go higher than 41 STC. The double door would be cool, but the space is only 10 feet wide (before drywall!!) as it is, and I can't afford to sacrifice that much space. I'd move the walls out and give myself more space, but getting permits for this stuff in LA is a nightmare, so I think I'll end up going with at least a 55 STC solid core and possibly augmenting with vinyl or something...

Again, thanks for all the advice.

[avare]

Originally Posted by DanGo

Thanks, gang, for all the varied opinions... I'm a little uncertain now of what direction to take.

I'm wary of using lead because I've got a toddler and another kid on the way... and this will be a studio in my backyard: no way am I gonna be able to keep them out...

Get Rod's book.

The lead is sandwiched between other materials. completely enclosed. Lead is used because it dense. If you are still wary of lead, you can usesteel, iron, or some other heavy metal.

If to see some additional tests on door blanks BBC RD1994-14 has several tested. (Added later) Looking at the report, the best bang for your buck, if that is a priority, is to use roofing felt in the sandwich. See fig 6 on pdf page 9.

Let us know how things turn out.

Fenestrationingly:
Andre

[Anderson]

I'd say 41 dB R(w) won't be enough....

~53 dB R(w) doors are usually enough and offer the best soundproofing/€/$. IAC-Boët was mentionned, they're good doors indeed, there is also Merford in The Netherlands whom I work with and they do a very good job as well.

Careful with the weight of those babies and have them placed by pros...

I'd say 41 dB R(w) won't be enough....

[avare]

Originally Posted by DanGo

That makes sense. I don't know offhand what the STC of the walls will be, but the construction will be (from outside to inside) 1/2 plywood outside (stucco'ed ultimately), then 2 x 4 studs, then RSIC-1 sound dampening clips attaching to SoundBreak gyp board and then another layer of standard gyp board. We're going to try to stuff r16 insulation in between the studs (even though r13 might be a more traditional choice...

I had a look at PAC Int'l's website and this looks close to your wall. The STC is 59 with around 56 dB of TL around 2.5k.

Andre

[bob katz]

Originally Posted by DanGo

Hi All,

I'm in the process of converting my garage into a high-quality control-room/mix/project studio and have a question about doors. My contractor and I will be putting in ZeroInternational seals with a raised threshold, but we're uncertain about the STC rating of the solid core door that will lead to the outside.

Because of various space considerations, a traditional double door won't work.

Will an STC rating of 41 be sufficient? Or should I aim for a higher rating?

Probably not. You have to have a survey of the outside noise. If you are on a cul de sac and very few cars pass by during the day you might get away with that, but it is unlikely if you are doing recording in that garage. You probably need double walls, a double door, and an isolation corridor with the door on the outside wall. At that point, an outside door with 41 STC in a wall with much higher isolation, followed by an air gap and another isolating wall with another 41 STC door and now you're talking!

In addition, STC rating is highly deceptive, significant low frequency noise gets through. It's impossible to make satisfactory isolation for a recording studio with a single door to the outside.

If you are NOT doing recording in there, and if the street is not noisy, then you may tolerate the occasional truck going by outside, which you will clearly here through that single door you are proposing.

[numrologst]

If you have the cash and resources to make your room bigger, don't worry about the permit process. We've all gone through the BS of the permit process, and it's just a rule of the game... You need to have permits for what you are doing too.

As far as your question goes:

1) Double solid core door
2) Add another layer of gyp to the outer wall
3) Add some more air gap

[chrisgraff]

In the process of building my guitar overdub room, I learned my AC15 outputs about 105db. Not much below 125hz.

An STC rating of 41 wouldn't be adequate for drums or monitoring loudly. It will be just fine for keeping an AC15 in check, however. Don't let the acoustics forums scare you.

Originally Posted by bob katz

Probably not. You have to have a survey of the outside noise. If you are on a cul de sac and very few cars pass by during the day you might get away with that, but it is unlikely if you are doing recording in that garage. You probably need double walls, a double door, and an isolation corridor with the door on the outside wall. At that point, an outside door with 41 STC in a wall with much higher isolation, followed by an air gap and another isolating wall with another 41 STC door and now you're talking!

In addition, STC rating is highly deceptive, significant low frequency noise gets through. It's impossible to make satisfactory isolation for a recording studio with a single door to the outside.

If you are NOT doing recording in there, and if the street is not noisy, then you may tolerate the occasional truck going by outside, which you will clearly here through that single door you are proposing.

Good point from Bob : standard STC wall or door rating is just not enough for studio acoustics -- you need to look at transmission loss (TL) in 31 to 8000Hz octave bands.

You also need to look at the entire door and not just one piece of it. If your walls are single layer on wooden stud and expensive garage door with STC >50dB will be agreat expense to have low transmission loss walls. Very marginal improvements.

If you really consider a studio room in your garage : look at the entire place ceiling walls, windows and doors and consider TL ~60dB for decent playback conditions in order to get yourself a certain quality of silence.

Already reaching NC=25-30dBA in those conditions with revised HVAC (for low noise) will be challenging and expense higher than a single garage door.

Both level (and spectrum) of background noise and interior room acoustics is a considerable investment to consider -- if you want to achieve a certain level of result.

Originally Posted by bob katz

Probably not. You have to have a survey of the outside noise. If you are on a cul de sac and very few cars pass by during the day you might get away with that, but it is unlikely if you are doing recording in that garage. You probably need double walls, a double door, and an isolation corridor with the door on the outside wall. At that point, an outside door with 41 STC in a wall with much higher isolation, followed by an air gap and another isolating wall with another 41 STC door and now you're talking!

In addition, STC rating is highly deceptive, significant low frequency noise gets through. It's impossible to make satisfactory isolation for a recording studio with a single door to the outside.

If you are NOT doing recording in there, and if the street is not noisy, then you may tolerate the occasional truck going by outside, which you will clearly here through that single door you are proposing.

Good point from Bob : standard STC wall or door rating is just not enough for studio acoustics -- you need to look at transmission loss (TL) in 31 to 8000Hz octave bands.

You also need to look at the entire room as a whole and not just one piece of it. If your walls are single layer on wooden stud and expensive garage door with STC >50dB will be agreat expense to have low transmission loss walls. Very marginal improvements.

If you really consider a studio room in your garage : look at the entire place ceiling walls, windows and doors and consider TL ~60dB for decent playback conditions in order to get yourself a certain quality of silence.

Already reaching NC=25-30dBA in those conditions with revised HVAC (for low noise) will be challenging and expense higher than a single garage door.

Both level of background noise and interior room acoustics is a considerable investment to consider -- if you want to achieve a certain level of result.

Knowing your end target would make it easier to answer your true questions.

[chrisgraff]

Originally Posted by High Fidelity

You also need to look at the entire room as a whole and not just one piece of it.

That reminds me...

Beware that many "Solid Core Doors" are actually hollow at the top & bottom (maybe an inch). I'd recommend looking at a salvage yard for a true solid door.

[DanGo]

Thank you all of you...

Chris, ironically, my main guitar amp is also a Vox AC 15, so it's good to know how much a door with an STC-rating of 41 cuts down the amp's volume.

After talking some more with George Augspurger, I'm going to go with a solid-core metal/wood door with an STC of 53. It comes with its own sealing door frame and is designed for studio use, so I think I'll be cool there.

I realize that floating a room and having corridors and double doors would be ideal, but compared to what I've been dealing with for the last 1 1/2 years, this is gonna be heaven! And as I said, my garage just isn't big enough to do the full on floating room. If I did that, I'd have such a small space, I'd have monster bass issues. As it is, it's a little small, but I think I read somewhere about the ideal acoustic dimensions working out to a ratio that would dictate a space that's 10' x 16'. I'll be just under 10 feet wide, so I'm hoping this does the trick.

Again, thanks to all of you. When I'm farther along, maybe I'll post some progress pictures. Could be interesting as what I'm doing is aiming really high acoustically, but keeping it oriented towards project/guerilla recording budget-wise.