John Sayers' Recording Studio Design Forum Archive

Ah I did dbc based on someone on here telling me to use ‘C’. Ok no probs, I’ll do another reading and report back.

Yeah my goal is so that if I’m working at about 85db then my neighbours pretty much can’t uear it if they were to stand the other side of the fence.

So I suppose my question is, how much isolation do I need for it to be barely audible at the fence (1m away the one side, 3m away the other end where the speakers will be)

Ah I did dbc based on someone on here telling me to use ‘C’. Ok no probs, I’ll do another reading and report back.

Right. That "someone" would be me!

This is often confusing, so let me explain:

"A" and "C" weighting are two different methods for adjusting the sensitivity of the meter to different frequencies. "C" is much more sensitive to low frequencies. There are other possible weightings too, but A and C are the most common. Here's a graph that shows the difference:
As you can see, in the low end of the spectrum, "A" (green curve) is much lower than "C" (black curve). At 40 Hz, for example, "A" is about 26 dB less sensitive than "C". On the other hand, in the high end "A" is a slightly MORE sensitive than C, between about 2 and 6 kHz.

The obvious question is: WHY?

Simple: That's the way our ears work! Our ears have different sensitivities for loud sounds and quiet sounds. The "C" weighting curve closely mimics how our ears respond to loud sounds, and the "A" weighting curve closely mimics the way our ears respond to quiet sounds: our ears are a lot less sensitive to quiet low frequencies, than they are to loud low frequencies.

So what does that mean for studios and isolation and legal regulations and sound level meters?

Also very simple: In your studio, you will be playing loud music, and you want to isolate that loud music: Therefore, to see how loud you are and how much isolation you need, you MUST measure using "C" weighting, because that's the way people perceive sound. So you turn on loud music in your studio, set your meter to "C", and measure the level inside the room, then again outside the room. The difference is how much isolation are getting. Even though it is quiet outside, you CANNOT use "A" here, because you need to know the DIFFERENCE in levels, so you have to use the same scale for both: you cannot compare "A" and "C" readings, because they are in different scales. That would be like saying that you drove your car at 60 miles per hour in the USA, then drove it at 100 kilometers per hour in the UK, and since the difference is 40, you must have been going 40 cubic feet per minute faster.... You cannot compare readings on different scales, so when you are testing for isolation, you MUST do both on "C", even though one is quiet and one is loud.

However, for measuring ambient sound (the low-level background noise around your building), you should measure using "A", since that's what is appropriate for quiet sounds. And also is the cops show up at your door with a noise complaint against you, you darn well better measure on "A", not on "C", because it gives you that 20 dB advantage in the low end, where drums and bass guitars live! So even if your music is loud outside, measuring on "A" will show it to be quieter than it really is... which probably helps you avoid a fine...

Regulations for noise levels are almost always written for "A" weighting, often expressed as "dBA", because they are measuring low levels usually. Unfortunately, workplace noise exposure levels are also measured in "A", which is kinda dumb when you think about it, because the sounds in a factory are LOUD, and often have low frequency content in them (big machines making big "thumps" and "rumbles"). Realistically, there should be two scales for workplace exposure: one for loud sounds on "C", and one for low level sounds on "A". But the powers that be have decided that "A" is the only wya to measure, even at 100 dB.... go figure!

So, getting back to your situation: if you want to check that you are legal, then measure using "A" weighting, and be thankful for the advantage it gives you. You must measure that way, because that's what the regulations use. But when measuring the isolation of your studio, and when calibrating your system, and when tuning your room, use only "C" weighting, because that's what your ears are really experiencing at typical studio levels.

Hopefully, that clears up the confusion...

If you want more details, then google "Fletcher-Munson curves", and also "equal loudness curves". Or ask, and I'll add some more info about that...


- Stuart -

Thanks for such a detailed reply Stuart, thats great and easy to understand, appreciate it

So, i work at about 90dbc in the current bedroom studio - Outside at home where my plot of land is, it reads 50dbc - So i require 40db isolation?

What i'm after basically is that when I'm working in my new studio at between 80-90db, it will be barely audible or not all audible at by my neighbours fence (1m away)

elastic wrote:Thanks for such a detailed reply Stuart, thats great and easy to understand, appreciate it

So, i work at about 90dbc in the current bedroom studio - Outside at home where my plot of land is, it reads 50dbc - So i require 40db isolation?

What i'm after basically is that when I'm working in my new studio at between 80-90db, it will be barely audible or not all audible at by my neighbours fence (1m away)

So filtering on from what Stuart says, measure again in the evening/night at on A weighting. This will give you a lower ambient level than 50dBC. Add 10dB to this for the legal limit.

With regards to your question about being barely audible at the boundary, if you're producing 90dBC and outdoors is 50dBC then attaining 50dB of isolation will put you below the ambient levels and it should just blend into the background.

I would just aim for 50dB isolation in your situation, which coincidentally is exactly the amount I'm aiming for myself.

Dan

You were right - just measured at 11pm -

Ambient noise in garden - 37dba / 45dbc

I’m thinking a 2 leaf system will be the way to go.

So going from out to in — 2 layers or gypsum, wood stud wall filled with a insulation like rock wool - air gap - studwall filled with rock wool, then 2 layers of gypsum again.

Don’t know what density rock wool yet
Don’t know what air gap size to leave yet
I saw you mention a breathable membrane or something? Not sure where that slots in yet. Will re read your post tomorrow and try and work it out.

I will make the 2 leaves a slightly different construction, I heard that helps. So the inner leaf could have different density rock wool or different thickness gypsum. Sound ok?

Looking at using green glue to bond the 2 layers of gypsum together, again heard it was good stuff to dissipate sound waves.

Feel free to add or hammer my thoughts! All help is welcome and appreciated.
Willing to learn

Thanks guys

So I’m thinking I need about 50db isolation.

Now, my question is, do I actually need to do a room within a room system?
Would I be better off using resilient channels or genie clips/RISC-1 clips, just like you said Dan before?

What about doing 2 layers of acoustic plasterboard, stud wall with insulation, resilient bars with 2 more layers of acoustic plasterboard on the inside?

Struggling to find out how much isolation that would give me. Some websites for acoustic plasterboard don’t tell you how much isolation they give you.

Now, my question is, do I actually need to do a room within a room system?
Would I be better off using resilient channels or genie clips/RISC-1 clips,

I doubt you'd get 50 dB isolation like that. 40-something, probably, but getting over 50 with resilient connections is going to be problematic.

Some websites for acoustic plasterboard don’t tell you how much isolation they give you.

That's because plasterboard by itself is only part of the solution! It's how you use it, in combination with the rest of the building materials that you need, that defines what your isolation will be. One piece of plasterboard by itself can be tested to see how much isolation it will give, yes, but that won't tell you how much isolation the completed wall will give.

Do yourself a favor: Forget "acoustic plasterboard", and just go with ordinary, common, fire-rated plasterboard. Sound waves cannot read the price tags on the materials you use, so they won't be impressed if you paid double the price for a certain amount of mass. Sound waves are stopped by mass, not by price tags. Don't be fooled by the fancy marketing hype put out by manufacturers who are only interested in selling really expensive products for questionable benefit.

- Stuart -

Ah ok. Appreciate that advice. Back to the 2 wall method. And thanks for the heads up on the plasterboard!

So, I’m thinking

Wood cladding on the outside of the building -
2 layers of plasterboard held together with green glue
2x4” staggered stud with insulation
Air gap - what size?
2x4” staggered stud with insulation
2 layers of plasterboard held together with green glue

How does that sound? I still don't know the isolation values for each part of the wall, so i don't know if im overdoing it or undergoing it? E.g how much db reduction will standard fireproof plasterboard give me as part of this setup? Same with the air gap, the insulation, the wood cladding...

As I understand it, it’s better to construct one of the walls a different density to the other?

I have attached a pic of how i will build my walls.
Thanks

elastic wrote:Ah ok. Appreciate that advice. Back to the 2 wall method. And thanks for the heads up on the plasterboard!

So, I’m thinking

Wood cladding on the outside of the building -
2 layers of plasterboard held together with green glue
2x4” staggered stud with insulation
Air gap - what size?
2x4” staggered stud with insulation
2 layers of plasterboard held together with green glue

How does that sound? I still don't know the isolation values for each part of the wall, so i don't know if im overdoing it or undergoing it? E.g how much db reduction will standard fireproof plasterboard give me as part of this setup? Same with the air gap, the insulation, the wood cladding...

As I understand it, it’s better to construct one of the walls a different density to the other?

I have attached a pic of how i will build my walls.

IMG_2802.JPG

Thanks

You can use the MSM calculator http://www.johnlsayers.com/phpBB2/viewt ... =1&t=21770 to work out your estimated isolation with a fully decoupled wall.

Don't include the cladding as part of your isolation calculation as it won't be sealed, as it requires a ventilation gap behind it. It may add a tiny bit of additional isolation but can't easily be calculated.

Just find out the densities of the sheeting materials you will be using and drop them into the calculator.

You don't need to have different densities really, you can add extra to one leaf if you want, but definitely don't reduce it on either.

By the way you would usually replace the first layer of plasterboard with OSB3 or plywood, to provide structural support. If you don't you will need to provide many noggins and bracing. Also you can't have plasterboard on the outside of your outer leaf, it's not weather resistant.

I've attached an image I found on the Internet of a standard cladded wall design. You'll see a breather membrane on the exterior sheathing, then battens screwed vertically to the face of it and cladding attached to the batten.

In your case though you'll need to add a second timer frame wall on the inside to hold the inner sheathing (with its own structural sheathing or noggins / bracing), under the inner sheathing you put a vapour barrier in the UK, with this design.

Dan

Great info. Thanks

Re reading it many times to try and understand it.

May I ask, what’s a ‘timer frame wall’? - edit - just re reading and guess you meant timber. Sorry haha

That OSB you mention, should that just be on the outer leaf or both?

In my head now, I’m going -

Cladding / membrane / OSB / plasterboard / stud wall / air gap / stud wall / 2 layers of plasterboard

My head is fried

Haha!

EDIT - oh so no plasterboard AT ALL on that outer leaf? Just sheathing and OSB then the stud wall?

Yep you're right, should be timber not timer

You still need to beef up the outer leaf, but you have to use options that don't expose unsuitable materials to the elements. For example you could use a layer of cement board (cement board) on top of the OSB3 before the membrane.

Or, a second layer of OSB3.

Or as I chose to do, install plasterboard, but cut it to fit in between the studs of the timber framing, up tight against the back of the OSB3.
This is cheapest in materials but takes an absolute ton of time. And boxes of caulk. I kind of regret doing it.

I would go with cement board if I did the studio again.

That would be:
Cladding (on 50mm stand-off battens) / breather membrane / cement board / OSB3 / timber frame / cavity / timber frame / vapour barrier / OSB3 / plasterboard.

Dan

Got you. I read somewhere that square edge board is better than tapered as tapered you need to fill them gaps where they join at corners?

I will investigate Osb board and cement board.

How come in Rod Gervais book he says it’s best practice to put 2 layers of plasterboard on the outside of each leaf? Can’t work that one out. Not doubting you at all, just interested. See pic[attachment=0]

I need to learn how to use that MSM calculator. Will do that later and see how I get on

One important clarification...

2 layers of plasterboard held together with green glue

Despite the name, Green Glue is not actually glue, and cannot be used to "hold things together". I really wish they would have chosen a better name for their product! It's confusing...

This is NOT an adhesive, and is not meant to stick things together. It has one very specific use, which is as a constrained layer damping compound. It damps certain types of resonance in the wall structure itself, and it does it very well when used correctly.

So, you will still need to use nails or screws in the normal manner for your plasterboard, and following the approved fastening schedule provided in your local building code.

- Stuart -

elastic wrote:Got you. I read somewhere that square edge board is better than tapered as tapered you need to fill them gaps where they join at corners?

I will investigate Osb board and cement board.

How come in Rod Gervais book he says it’s best practice to put 2 layers of plasterboard on the outside of each leaf? Can’t work that one out. Not doubting you at all, just interested. See pic

3948F9A2-7D7D-485E-9846-232A0654A051.png

[attachment=0]

I need to learn how to use that MSM calculator. Will do that later and see how I get on

Square edge is better, tapered is used to allow to you to dry line the boards instead of skimming them. If you used tapered you would have to dry line (plaster over the joints) even if there was another layer being installed on top.

With regards to Rod's book, that refers to internal walls. You can do two layers of plasterboard for the inner leaf, but you will have to put noggins and bracing in to prevent racking and twisting. It would be cheaper than an OSB3 layer, but takes more time cutting and installing the additional timber. A structural sheeting at least 9mm thick will provide all the support required without any noggins.
The equivalent density of OSB3 to a plasterboard layer is the 18mm thickness.

Dan

Duly noted sir Thanks!

Maybe a silly question, but can I use regular screws, nails for construction? Just like on a normal building job.
I realise the screws or nails can’t go through and make contact with the other leaf, just curious and want to do it right.

Thanks