Log Cabin into studio conversion

[KevinG]

Hi all,

I've been lurking here for a while, reading hundreds of posts (shed into studio, log cabin studio etc) as well as the stickies FAQs etc . So firstly, thank you for such an amazing resource and all the people that maintain it. I'm about to tackle the major one, converting my log cabin into something usable for music. I feel I have a basic idea of what to do, but I would really appreciate any feedback on my plans below. Various aspects I am not 100% sure on- please see my questions at the bottom for these. I've tried to address everything but I haven't gone into fine details, to reduce the size of this initial post.

BASICS
I'm in Manchester, UK. I've got a 3.5 x 3.5m log cabin (room space is 2.5 x 3.5m with a pent roof), built with 44mm T&G solid timber walls, 19mm roof and 19mm floor. Treated floor batons. The builder fitted some basic fluffy insulation under the floorboards. Unfortunately its not on a concrete slab. Instead, it is sat on EcoBase, a plastic grid (https://swiftfoundations.co.uk/ecobase-fastfit/. The gaps in it are filled with a ton of gravel (literally), so its rooted in place and a lot heavier than just plastic. I know its not ideal but I'm stuck with it.

Screen Shot 2017-04-19 at 15.06.52.png

It has double glazed glass in the windows and doors, with rubber gasket seals. I realise there are limitations to a log cabin like this, but please have a look at my plans below.

USAGE
I'm going to use the studio for electronic music, mixing mastering. No bands or 100db+ sound. Levels in my studio normally average 85-95db (I used to have a decent db monitor and kept track). Neighbours are approx 50ft away. I'm used to working in a semi, so I will tailor my volume to whatever is considerate. I'm just hoping I will be able to get away with a bit more loudness than in the untreated house (the inside studio is now a nursery). Generally I'd say my aim is to combat loudness, but with more attention on the low subs. I might not have the music loud, but from previous experience I know the bass can travel and annoy.

BUDGET
Approx 3-5k (GBP).

PLAN
So in rough terms a two leaf approach with plasterboard and insulation.
- first wrap the inside in Tyvek or similar.
- Second leaf. Build a frame for the internal walls and ceiling with 2x4 timber. I will follow the shape of the roof and have a sloped internal ceiling. Both for acoustics and to maximise space. Using a double top plate, staggered as advised on posts here.
- Rockwool RW5 100mm inside the frame for insulation throughout.
- Then 2 layers of high density acoustic plasterboard on top, sealing / caulking as I go (acoustic caulk). Using the 5/8" thicker board to target the low frequencies. I'll plaster / paint the walls and ceiling. If budget permits (!) I'll put a layer of green glue between the sheets.
- Floor. A 2 x 4 frame sat on small neoprene pucks (as suggested in 'shed into studio' in line with every other bearer underneath). Then this floor frame filled with more Rockwool RW5, a layer of OCB on top, followed by a wooden floor. Making sure it doesn't touch the walls
- Windows. A major weak point I guess. First a layer of thick perspex inside for security, screwed into place. Then I plan to have internal shutters to cover the windows and reduce sound escaping. See my question below about this.
- Existing door, more thick perspex for security. Then a solid heavy internal door fitted to my 2x4 internal frame, with an air tight seal. This door I'll make myself with timber frame, thick MDF and filled with RW5.
- Single hole for electric supply into studio, sealed with acoustic gel??? (I forgot the proper name!). All internal electrics surface mounted.
- Air con. This is definitely my weakest area of knowledge. I know I need a ducted system that minimises sound leakage. I've read this http://johnlsayers.com/Recmanual/Pages/ ... ioning.htm and the HVAC sticky, but any other links to info would be much appreciated. Once I understand 100% the other aspects above I intend to get to grips with aircon before I plan the final build. Obviously its an essential and expensive part of the plan!

QUESTIONS
- 2 x 4 framing / base plates- One point I really need clarifying here is do I attach (screw) this to the original floor of the log cabin? Also I see a few mentions of beads of caulk under/ around the base plate, is this correct?
- I'm planning NOT to use resilient bars as I understand that it is not as effective for low frequencies? Also it adds another level of complexity and cost to the build. Any thoughts on this?
- Internal window shutters. Has anyone done this or can advise on materials? I know blocking them permanently is best, but I want the option of daylight
- Separating floor from the wall? Is a strip of neoprene around the side of the floor enough for this?
- I am unclear on the roof space, do I need to vent this area somehow? I remember seeing one post somewhere about it becoming a haven for wildlife if I'm not careful.

Thats it for now, thanks for taking time out to read the above. Please let me know if I've omitted any essential info.
Kevin

[Soundman2020]

Hi Kevin, and Welcome!

my aim is to combat loudness, but with more attention on the low subs.

... which is the hardest part of the spectrum to isolate! In fact, of you have good isolation in the low end, you are guaranteed to have great isolation in the high end! But the inverse is not true...

I might not have the music loud, but from previous experience I know the bass can travel and annoy.

Yep. Very true.

- first wrap the inside in Tyvek or similar

Nope. The outside should have been wrapped with Tyvek before the siding went on. What you need on the inside is vapor barrier, not a breathable water barrier. And you need it on the inside of your inner leaf, not the inside of the outer leaf. It must go up against the warmest surface in winter, to prevent condensation from forming and thus creating problems with mold and rot inside your walls.

- Second leaf. Build a frame for the internal walls and ceiling with 2x4 timber. I will follow the shape of the roof and have a sloped internal ceiling. Both for acoustics and to maximise space.

Right!

Using a double top plate, staggered as advised on posts here.

What do you mean by "staggered"? What is it that you want to stagger?

- Then 2 layers of high density acoustic plasterboard on top, sealing / caulking as I go (acoustic caulk). Using the 5/8" thicker board to target the low frequencies. I'll plaster / paint the walls and ceiling. If budget permits (!) I'll put a layer of green glue between the sheets.

Right!

- Floor. A 2 x 4 frame sat on small neoprene pucks

No. You cannot float a floor like that. Here's why not: http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

- Windows. A major weak point I guess. First a layer of thick perspex inside for security, screwed into place.

Perspex is not much use, acoustically. Very low mass, as compared to glass.

- Single hole for electric supply into studio, sealed with acoustic gel??? (I forgot the proper name!). All internal electrics surface mounted.

Right! You seal the conduit with caulk.

- 2 x 4 framing / base plates- One point I really need clarifying here is do I attach (screw) this to the original floor of the log cabin?

First you'll need to hire a structural engineer to tell you how much extra weight you can put on that floor.

Also I see a few mentions of beads of caulk under/ around the base plate, is this correct?

Correct.

- I'm planning NOT to use resilient bars as I understand that it is not as effective for low frequencies?

RC is effective, but you don't need it. You will already have a decoupled inner-leaf frame, so there's no point trying to decouple again.

- Internal window shutters. Has anyone done this or can advise on materials? I know blocking them permanently is best, but I want the option of daylight

Then use glass! Forget the shutters, and just put glass in your inner-leaf. Done!

- Separating floor from the wall? Is a strip of neoprene around the side of the floor enough for this?

No. For the same reasons given in the floating floor thread I mentioned above. Floating a wall is basically the same as floating a floor.

- I am unclear on the roof space, do I need to vent this area somehow?

Probably. Check your local building code to find out for sure.

- Stuart -

[KevinG]

- first wrap the inside in Tyvek or similar

Nope. The outside should have been wrapped with Tyvek before the siding went on. What you need on the inside is vapor barrier, not a breathable water barrier. And you need it on the inside of your inner leaf, not the inside of the outer leaf. It must go up against the warmest surface in winter, to prevent condensation from forming and thus creating problems with mold and rot inside your walls.

OK got you. Although I do not have siding. Its a log cabin, as in just stacked logs to make the wall. Same process re inside?

Using a double top plate, staggered as advised on posts here.

What do you mean by "staggered"? What is it that you want to stagger?

Probably just my bad description. I'm taking about having two top plates offset as I saw in another thread here (2nd image down). Is this correct? - http://www.johnlsayers.com/phpBB2/viewt ... 9&start=30

- Floor. A 2 x 4 frame sat on small neoprene pucks

No. You cannot float a floor like that. Here's why not: http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

Ah I see. I'm following what I saw on this post (image at bottom), does this not apply in my case - http://www.johnlsayers.com/phpBB2/viewt ... 9&start=75

- Windows. A major weak point I guess. First a layer of thick perspex inside for security, screwed into place.

Perspex is not much use, acoustically. Very low mass, as compared to glass.

OK got you thanks!

- 2 x 4 framing / base plates- One point I really need clarifying here is do I attach (screw) this to the original floor of the log cabin?

First you'll need to hire a structural engineer to tell you how much extra weight you can put on that floor.

OK will do.

- Separating floor from the wall? Is a strip of neoprene around the side of the floor enough for this?

No. For the same reasons given in the floating floor thread I mentioned above. Floating a wall is basically the same as floating a floor.

OK maybe my bad description again! I'm talking about a separator between the side of the floor I build, so it doesn't touch the new wall? If not neoprene / rubber is caulk enough? Again I was kind of following the advice on the last post I linked above. Also this one here, does this not apply? http://www.johnlsayers.com/phpBB2/viewtopic.php?t=1589

Many thanks,
Kevin

[Soundman2020]

Ah I see. I'm following what I saw on this post (image at bottom), does this not apply in my case

That's from nearly fifteen years ago! Things change in acoustics over time.

Here's a graph that explains the problem in simple terms:

resonant-frequency-of-floating-floor-by-mass-and-gap-Graph---GOOD!!!.-S02.jpg

That shows how much mass you need on your floor, and how much air gap you need under it, to get the right resonant frequency. What I mean by "right resonant frequency" is simply the one that will allow your floor to actually isolate! Your floor is a resonant system. It will resonate naturally at a certain frequency that is governed by the mass (weight) of the floor, and the depth of the air cavity under it. At that frequency, and for one octave above it, the floor will NOT isolate. In fact, not only does it not isolate, it can potentially amplify sounds at that frequency. And because this problem extends to one octave higher, obviously you want your floor's resonant frequency to be at least one octave lower than the lowest frequency you need to isolate. So if you need to isolate kick drums, which are often tuned around 80 Hz, then your floor should be tuned no higher than 40 Hz, which is one octave lower. If you want to isolate bass guitar, which easily goes down to 36 Hz (5 string bass), then you'd need to tune your floor no higher than 18 Hz. Let's assume this is the case, and now we can look at the graph.

The graph shows the frequency up the left hand side. You need something at 18 Hz, so draw an imaginary line across the graph a bit less than 20 Hz. You can now see that no matter how deep your air cavity is, the top two dashed lines are no use: you can never get a low enough frequency if your floor only weighs 5 PSF (pound per square foot) or 10 PSF. Not possible. However, at 30 PSF it is possible (the dotted line, third from the top): it looks like you would need to have an air cavity that is at least 4.5 inches deep, so you can't do it with 2x4's, as they are only 3.5" deep. You'll need to use 2x6's (which are 5.5" deep). Your other option is to go with an even heavier floor: the bottom curve on the graph, labeled 60 psf (solid line, not dashed). With that option, you can get a frequency of 18 Hz. with a cavity about 2" deep, so you could use 2x4s there.

So those are your options: you can build up your floating floor on 2x4s with a 60 PSF floor, or 2x6s with a 30 PSF floor.

So that brings up the question: What would you need to do, to get a 60 PSF floor? Well, we spoke about OSB, and the density of OSB is roughly 610 kg/m3, which works out to about 3.2 PSF for every inch of thickness. So to get 60 PSF using OSB board, you'd need to make it about 19 inches thick! In other words, you'd need to have 31 layers of 5/8" OSB on your floor, to get enough mass. But if you wanted to go with the 30 PSF option, you'd "only" need 16 layers of OSB to get there....

As you can see, it is physically impossible to float a light-weight deck consisting of just a couple of sheets of OSB on 2x4 studs. If you did that, the resonant frequency would be around 42 Hz, so the floor would amplify kicks, toms, bass guitar, electric guitar, and keyboards! It would only isolate from about 84 Hz upwards.

So how do you get such a high mass? If you can't do it with OSB, then what do you need? Simple: Concrete. The density of concrete is around 2400 kg/m3, which is roughly 12 PSF for each inch of thickness. So a concrete slab just 3 inches thick (36 PSF) would let you do it with a 3.5" cavity, and if you went up to 5" thick concrete slab, you could do it on a 1.5" air cavity.

That's the plain, hard, cold facts. You cannot float a light-weight deck and expect to get good isolation for low frequencies. The laws of physics prevent it.

Now, all of the above assumes that the "deck" is fully isolated from the underlying subfloor, and that the only "spring" in there, is the air in the cavity. In real life, that is not possible: you need some type of resilient mounting to decouple the deck: it might be rubber pads, or metal springs, or something else, but there has to be something that disconnects the deck from the subfloor, mechanically. Which makes things worse! That rubber or metal spring works in parallel with the air spring, and that REDUCES the total "springiness". So you actually need a deeper cavity to get the same frequency...

Now for the kicker that really dooms this whole light-weight deck concept: Whatever it is that you use as the srping to decouple the deck (rubber, metal springs, snake oil), you have to ensure that it will will float! If you put too much weight on a spring, then you flatten it out completely, and it is not "springy" any more: it bottoms out, and does not float. On the other hand, if you don't put enough weight on it, it is also not "springy"! It "tops out" and does not float. So you have to ensure that you put the right amount of weight on each spring, such that it has the optimal amount of compression, and really does float. For each type of spring, there are tables and equations that allow you to do that, but for most springs, you need to compress it about 10 to 20% to make it "float". Less that 10% "tops out" and more than 20% "bottoms out".

Great So let's go back to the light-weight deck (pretending that the above graph does not exist, and imagining that it might be possible to magically get the right frequency with just two layers of OSB). We already know that two layers of OSB weighs about 6 pounds per square foot, so let's say we do some calculations for magical rubber pads, made of purest snake oil, and arrive at the conclusion that we need four pads of two square inches each for every square foot of floor, and with a load of 6 PSF, that will float just fine, with exactly 15% compression. Great! Amazing! The floor floats! ... Until you stand on it.... Assuming you weigh about 180 pounds, and that your weight will be spread across four square feet of floor, just by stepping on that floor you increase the loading from 6 PSF to 51 PSF Gulp! I think you see where this is going.... You just flattened your rubber pads into oblivion! They are now squashed flat, and don't float.

So you think creatively, and decide that you don't need the floor to float when you are not in the room, so you re-design it to float when the load is 51 PSF. Fantastic! Wonderful! It floats! .... until you bring in your guitar, amp, a couple of pizzas and a crate of beer... now the load is 65 PSF, and the floor doesn't float....

So you wrack your brains, and re-design the rubber pads yet again, so they float at 65 PSF.... But then you invite your buddy over to join you for a jamming session, an he brings his girlfriend, another amp, more pizza, and a suitcase, since he's going to stay the night.... and now you have a load of 90 PSF....

OK, I can keep on adding scenarios here, such as the desk, chair, couch, your DAW, other gear, etc. etc., but you can see the problem: The load on a light-weight deck varies so enormously that it just is not practical. But with a concrete deck, that has a much, much higher density, this is not a problem. Putting all that extra load on the floor, or taking it off, only changes the total mass by a few percent, and the floor still floats: the springs are still inside their optimal range.

So that's the issue. Floating a light-weight floor is not a viable solution. You need huge mass to float a floor successfully. It is certainly possible to float a floor, and companies like Mason Industries make devices to do that, but it only works with very high mass for the floor deck, such as 3 or 4 inches of solid concrete.

OK maybe my bad description again! I'm talking about a separator between the side of the floor I build, so it doesn't touch the new wall? If not neoprene / rubber is caulk enough?

Ahhh! OK. Now I get it. Yes, if you do float your floor, then you absolutely must leave a gap around the edge, up to the walls, and you can indeed fill that gap with suitable high-flexibility caulk. You need the type of caulk that never hardens, remains very soft and rubbery even when it is completely dry.

There's another option here, which is even better: build your inner-leaf walls on top of the floor! In that case, the entire room is floated. The calculations for the springs are a bit more complicated like that, but the total floated mass es even greater, so variations from people standing on the floor an moving gear in and out are even lower, as a percentage of the total floated mass. That's a lot more expensive, of course, and more complex, but if you really do have a need for extra high isolation, that's as good as it gets.


- Stuart -

[KevinG]

Ah I see. I'm following what I saw on this post (image at bottom), does this not apply in my case

That's from nearly fifteen years ago! Things change in acoustics over time.

haha! okay noted. I'm actually glad, it simplifies my task.

Thank you so much for the detailed info about floating floors / walls.

31 layers of 5/8" OSB on your floor, to get enough mass.

Thats hilarious. In a parallel universe I'd do it just for the laughs

So it seems pretty obvious I'm not gonna float in any way whatsoever. Thank you!

So just to clarify- I need to attach the wall and floor framing solidly to the original log cabin floor? i.e. with screws and caulk to make it a firm immovable contact? (Of course, only after I've checked that the weight I intend to add is structurally possible).

One other question if you don't mind. I planned using Rockwool RW5 throughout, do you think it is really needed? Or could I get away with a basic fluffy type insulation? I've read the FAQ but also seen a few conflicting opinions in other threads, saying that I don't need the expensive insulation like RW5. Or is that only when combining with RC?

Many thanks again!
Kevin

[KevinG]

Hey all, update on this and a quick question about neoprene if anybody can help?

I've nearly completed the 4x2 timber framework for the inner wall. There is a gap all the way round for decoupling, roughly 20mm between stud and outer log cabin wall.

However just to be safe, would it be crazy to put a few neoprene / rubber pucks on the studs? Just in case anything moves over time, or the wood swells and stud / wall makes contact?

Please don't say I have to make the gap bigger, the thought of starting again would kill me off!

many thanks guys....

[Soundman2020]

However just to be safe, would it be crazy to put a few neoprene / rubber pucks on the studs? Just in case anything moves over time, or the wood swells and stud / wall makes contact?

I can't imagine that the wood is going to swell by 2 cm. If it swells that much, then you have much bigger problems than leaves touching each other! With that much swell the drywall nails/screws would probably be popping...

Also, if you put rubber pads on there, then you have LESS space for swelling to happen, before the walls make contact.... let's say you put a rather thing 12mm pad on one side... that only leaves 8mm before the touch... And unless there's exactly the right amount of deflection ("compression") on the rubber, it won't isolate at all!

You might want to read this: http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173 That's about floors, but the same principles apply to walls. (Yep, I know I already gave you that link before, but just to remind you about it, and to point out that it also applies to walls).

- Stuart -

[KevinG]

OK thanks. That puts my mind at rest.

However just to be safe, would it be crazy to put a few neoprene / rubber pucks on the studs? Just in case anything moves over time, or the wood swells and stud / wall makes contact?

I can't imagine that the wood is going to swell by 2 cm. If it swells that much, then you have much bigger problems than leaves touching each other! With that much swell the drywall nails/screws would probably be popping...

Also, if you put rubber pads on there, then you have LESS space for swelling to happen, before the walls make contact.... let's say you put a rather thing 12mm pad on one side... that only leaves 8mm before the touch... And unless there's exactly the right amount of deflection ("compression") on the rubber, it won't isolate at all!

You might want to read this: http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173 That's about floors, but the same principles apply to walls. (Yep, I know I already gave you that link before, but just to remind you about it, and to point out that it also applies to walls).

- Stuart -

[KevinG]

Hey all - another quick question, regarding Green Glue and choice of insulation..

I'd planned to use 75mm RW5 Rockwool, to target low frequencies. But now I'm coming across info saying not to use such dense material, as it can have a detrimental effect. e.g. this from the Green Glue site

'Don’t be tempted to use dense insulation thinking it will work better at isolating sound. It is more expensive and actually raises the resonance of low frequencies.
Source - http://www.greengluecompany.com/benefit/how-to-use-it-

It defies my basic understanding of isolation, so I'd be really grateful if anyone here has any thoughts
thanks
Kevin

[Soundman2020]

'Don’t be tempted to use dense insulation thinking it will work better at isolating sound. It is more expensive and actually raises the resonance of low frequencies.

Yup. Green Glue is correct.

This is a rather common myth, or mis-belief, or call it what you will: it just seems "right" to think that .deep, "heavy" bass notes must need "heavy" insulation to deal with them. But as with many things in acoustics that are not intuitive, this is not true. Higher density insulation does NOT work better for low frequencies: in fact, it works better for high frequencies. Lower density is better for low frequencies. There's an optimal point, actually: obviously, if you go TOO low, then that's no good either. The optimal point depends on what TYPE of insulation you are using. If it is mineral wool ("Rockwool"), then the optimum point is around 50 kg/m3, and if you are using fiberglass insulation, it's more like 30 kg/m3. Actually, it's not even the density that matters, but rather an obscure metric called "Gas Flow Resistivity", which is measured in the even more obscure units of MKS Rayls. Ideally, you need something in the range of around 9,000 to 18,000 MKS rayls, roughly. But since insulation manufacturers don't usually bother measuring or publishing that parameter for their products, the second-best option is to go on the density for each type of insulation, as there's a vague relationship between GFR and density.

I'd planned to use 75mm RW5 Rockwool, to target low frequencies

What is the density of that product? Check with the manufacturer,or if you already have some, then weigh a large sample so you can figure out the density yourself.

75mm is probably OK, but how deep is the cavity inside your walls? Filling the cavity completely is better than filling it partially.

It defies my basic understanding of isolation,

There's a lot of strange, non-intuitive things like that in acoustics!

- Stuart -

[KevinG]

OK thanks again for such great info. So Rockwool RW5 would be too dense as it is 100kg m/3. The best would be Rockwool RW45 which is 5kg m/3.

75mm is probably OK, but how deep is the cavity inside your walls? Filling the cavity completely is better than filling it partially.

The cavity is 95cm plus air gap 15mm. So I guess I should go for 100mm RW45 then?

There's a lot of strange, non-intuitive things like that in acoustics!

Yes! But I'm so glad to get your help on them. If there is any kind of testing I can share afterwards, do let me know.

[Soundman2020]

Rockwool RW5 would be too dense as it is 100kg m/3

Right. That's more than twice the optimal density.

Rockwool RW45 which is 5kg m/3.

.... and that's only one tenth of the recommended density!

As I mentioned: "

If it is mineral wool ("Rockwool"), then the optimum point is around 50 kg/m3

,". 5 kg/m3 is way too low.


- Stuart -

[KevinG]

Rockwool RW5 would be too dense as it is 100kg m/3

Right. That's more than twice the optimal density.

Rockwool RW45 which is 5kg m/3.

oops sorry, that was a typo, I missed a character! Rockwool RW45 is 45kg m/3


Kevin

[KevinG]

So this job is practically done. Thanks again for all the advice, especially Stuart. If there is anything I can do to help the forum, tests etc, do let me know.

I'm just at the stage of acoustic treatment and I have a quick question about that & leaves. I'm making broadband absorber panels (with Rockwool etc) and not sure if I should leave a small air gap inside the back of them and the wall? Would this create a triple leaf effect? i.e. damaging the soundproofing aspects?

Many thanks
Kevin

[Soundman2020]

So this job is practically done. Thanks again for all the advice, especially Stuart

!

I have a quick question about that & leaves. I'm making broadband absorber panels (with Rockwool etc) and not sure if I should leave a small air gap inside the back of them and the wall? Would this create a triple leaf effect? i.e. damaging the soundproofing aspects?

No. It won't do any harm to your isolation, since it absorbers are not massive, not sealed, not rigid, etc. Not a problem.

Leaving a gap between the insulation and the wall can extend the absorption down lower, so that's a good thing. As long as the absorption itself is fairly thick, then leaving a gap is beneficial. Sometimes you hear people say that the gap MUST be the same size as the thickness of the insulation (eg 2" insulation and 2" gap, 4" insulation and 4" gap), but that simply isn't true. You can ignore that advice, and make the gap whatever size it needs to be to cover the frequency range that needs to be covered at that spot in the room.

- Stuart -