Log Cabin into a Music Studio...

[ChrisA99]

Hi all,

First off, what a fantastic forum. So much information and help from people, great work everyone!

So... my story. Well I've recently bought a house in Greater London, and it already has a log cabin in the garden. Dimensions are W2740mm, L3780mm, H2040mm, rising to 2510mm in the middle. Made of wood, the entire structure is built on wooden slats, so it is already off the ground, albeit not to the extent required. The walls are pretty thin at the moment so I'd like to get some substantial sound isolation going on. Space does allow for a "room in a room" construction so I think that'll be the best way to go.

The studio is electronic music based, so pretty much just a mixing and mastering space. There will be no live instruments. I wouldn't have thought I'd be louder than a drum kit, and the nearest neighbours are around 20 feet away. And if they're not in their garden, there'll be their brick wall in between! I don't have a sub at the moment but may do in the future.

This is just a hobby studio (if there is such a thing), so there isn't a professional budget. A figure in my head is around £600, which leaves £400 for a good desk to house my equipment. But there is room for movement here...

So my thoughts are :

1) Build a floor by having a felt strip around the room, then a layer of Lamella boards (or maybe boards from a company called ikoustic), then a layer of chipboard.
2) Walls to be made of a layer of acoustic chipboard which is set 100mm from the existing wall, then 100mm or 75mm rockwool, then genie clips, then another layer of acoustic chipboard.
3) Ceiling to have same construction as walls. Ceiling lights will be spotlights, wires to come through holes in the chipboard and sealed with green glue.
4) It does have air con already so I'm planning on re-housing it inside the room. I believe this will circulate air effectively. I will use Green Glue to seal the air con pipes.
5) Room will be a rectangle but with bass traps in the corner.
6) Cover the walls & ceiling with grey carpet, add acoustic slabs to relevant positions on the walls.
7) Floor to have some kind of nice carpet.
Not concerned about keeping the windows. Quite like the idea of a static environment like a Vegas casino.

Questions
Does this sound/look like I'm on the right track?
Do I still need genie clips if the wall is detached from the main wall?
Does the ceiling construction sound correct?
What is the best way to join the walls to the floor to ensure structural integrity? Also the ceiling to the walls?

Few attachments below. A few pics of the log cabin itself, & a sketchup output.

Sketchup file is here : https://dl.dropboxusercontent.com/u/459 ... io%202.skp

Thanks in advance, really appreciate any replies coming though!

[Soundman2020]

Hi there Chris, and Welcome!

Made of wood, the entire structure is built on wooden slats, so it is already off the ground, albeit not to the extent required. The walls are pretty thin at the moment so I'd like to get some substantial sound isolation going on

If the floor is wood, and it is raised above the ground, then that is going to be one of your major weak points for isolation, regardless of how well the walls are isolated. There's also a lot of operable windows and a door in there, which are other major issues for isolation. Lots of weak points!

Space does allow for a "room in a room" construction so I think that'll be the best way to go. ... A figure in my head is around £600,

Well, space might allow for "room in a room", but budget certainly does not! At least not unless you are missing a zero or two on the end of that number...

1) Build a floor by having a felt strip around the room, then a layer of Lamella boards (or maybe boards from a company called ikoustic), then a layer of chipboard.

That would crate the wrong type of "floating floor", in the manner that is described here:

http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

2) Walls to be made of a layer of acoustic chipboard which is set 100mm from the existing wall, then 100mm or 75mm rockwool, then genie clips, then another layer of acoustic chipboard.

That would create a 3-leaf wall, which would be pretty lousy for low frequency isolation, as compared to a proper 2-leaf wall of the same total mass and thickness. You should never, ever build a 3-leaf wall if it is possible to do it correctly, with a 2-laf wall.

3) Ceiling to have same construction as walls. Ceiling lights will be spotlights, wires to come through holes in the chipboard and sealed with green glue

There can not be any holes in any leaves: not the floor, not the walls, and not the ceiling. All holes are major weak points for isolation. There can be one single penetration where the main electrical feed comes into the room, but from there on all the wiring and lighting must be done surface-mount. And Green Glue is not meant for what you want to use it for, either! It is a visco-elastic polymer compound, designed to be used as constrained layer damping between sheets of mass. It is not meant to be used as sealant in electrical pass-through holes.

From the photos, you already have surface mounted electrics in there: all you need to do is to take that all out, and re-install it on the inner-leaf, after you build it. You'll need to hire an electrician to do that: playing with electricity is not safe, and is probably not even legal unless you are licensed to do so.

4) It does have air con already so I'm planning on re-housing it inside the room. I believe this will circulate air effectively. I will use Green Glue to seal the air con pipes.

You will have to design silencer boxes on the air ducts, and once again Green Glue compound is not a sealant: that's not what it is meant for.

6) Cover the walls & ceiling with grey carpet,

Umm.... carpet is about the worst possible "treatment" you can put in a studio. It does the exact opposite of what is needed, acoustically. Which is why you practically never see it used on walls, floors or ceilings in professional studios! If you do see carpet in a pro studio, you can pretty much bet that it isn't normal carpet at all, but rather is acoustic carpet that is hiding the real treatment behind it....

7) Floor to have some kind of nice carpet.

Ditto! See above. If you carpet your room, it will end up sounding dull, honky, cavey, "thin", lifeless, and very unpleasant.

Does this sound/look like I'm on the right track?

No.

Do I still need genie clips if the wall is detached from the main wall?

Not only do you not need the genie clips, you also do not need the third leaf! You need two leaves, only two leaves, and nothing but two leaves.

Does the ceiling construction sound correct?

No. The ceiling needs to be 2-leaf construction too.

What is the best way to join the walls to the floor to ensure structural integrity? Also the ceiling to the walls?

You'll need to get a copy of your local building code to answer that. It will describe what methods are permitted, and those are the methods you'll have to use, or it won't pass inspection. It won't even get approval if the materials and methods don't meet code. And since this is already an elevated structure, you are going to need to hire a structural engineer to tell you what you can and cannot do safely, and what type of reinforcing will be needed under the building to support the huge amount of extra weight you'll be adding to it.

I'd also suggest that you buy two books: "Master Handbook of Acoustics" by F. Alton Everest (that's sort of the Bible for acoustics), and "Home Recording Studio: Build it Like the Pros", by Rod Gervais. Those will set you on the right track to do what you want to do, safely, correctly and properly. Between them, those two books will eat up about 10% of your budget, which is another reason why you seriously need to reconsider that. If buying a couple of books so you can learn the most basic concepts and methods is going to take a large chunk out of your budget, then that should tell you right away that the budget is very much inadequate.


- Stuart -

[ChrisA99]

Hey Stuart,

Thank you so much for taking the time to write such a detailed replied. It's been quite fascinating to read. Since I wrote this I've done a lot more research and completely agree with you on a lot of the points! Especially the underestimation of the budget... So I just have a couple of questions

1) So the best thing to do is go for a 2 leaf system. Do you keep an air gap between the rockwool and the outside wall? Or should it all be compressed together as much as possible?
2) I understand from an acoustic view that 2 leaf is better. I hate to say this on such a forum but one of my main reasons for doing this is to keep the neighbours happy. So would choosing 2 leaf over 3 have a significant difference in sound isolation? The main outside wall of the log cabin is really not thick at all...
3) If not carpet, what does an internal studio get decorated with? Once this is done, I should essentially have a room which is just plasterboard. I think it needs softening up somehow! Is it simply a paint job that's required? I'm still planning to mount some acoustic tiles when finished.

Many thanks for the extremely helpful info

[Soundman2020]

So the best thing to do is go for a 2 leaf system. Do you keep an air gap between the rockwool and the outside wall? Or should it all be compressed together as much as possible?

The more the gap is filled, the better damping you have, so it's best to fill it all the way to the outside. HOWEVER! You should NOT "compress" the insulation to get it in! Just put in enough to fill the cavity, but without forcing it in. If it is compressed, you run the risk of creating a "flanking path" that can transmit sound across the gap.

I understand from an acoustic view that 2 leaf is better. I hate to say this on such a forum but one of my main reasons for doing this is to keep the neighbours happy. So would choosing 2 leaf over 3 have a significant difference in sound isolation? The main outside wall of the log cabin is really not thick at all...

Oh yes! 2 leaf is very significantly better than 3-leaf. Here's how much:

2-leaf-3-leaf-classic-walls-diagram-MSM-walls.gif

Going from left to right: the first diagram shows a typical house wall with no insulation inside, and the one next to it shows that you'd get a roughly 3 dB increase in isolation from adding insulation. The next one across shows what happens if you were to build another identical wall right next to the first one: you only get a 4 dB increase, even though you doubled the mass and thickness of the entire system, because of the 4-leaf resonance effect. If you were then to take off the drywall from the interior of one of those two walls, then you'd have the next situation: a sudden large jump of 10 dB! And you got that by REMOVING mass from the wall. The reason for that large jump is because you converted the 4-leaf wall to a 3-leaf wall. If you then take off the internal drywall from the other original wall, so that you now have just a 2-leaf wall, once again you get a massive jump in isolation, even though here again you removed mass from the wall. The final diagram (on the right) shows what the situation would be if you were to take the drywall sheets that you removed from the middle, and put them on the outsides. In other words, adding mass to the leaves. You get yet another big jump. The ONLY difference between this one, marked STC-63 and the third diagram, marked STC-40, is that the drywall has moved from the inside to the outside, converting it from a 4-leaf to a 2-leaf. The total mass is the same, and the total thickness is the same, yet there's an enormous difference in isolation. This one is 23 dB better, meaning that it blocks over one hundred times more energy, and it would be over four times quieter, subjectively.

So yes, I'd call that a substantial difference!

If not carpet, what does an internal studio get decorated with?

The floor is usually laminate flooring, linoleum, ceramic, or solid hardwood. The walls usually have acoustic treatment panels on them, and for a small room like that, those panels would be mostly very thick absorption, such as 10cm to 20cm of mineral wool or fiberglass, in a wooden frame and with fabric over the front. The ceiling is usually similar to the walls, with thick absorption. But you need to calculate how much absorption has to go in, and what frequency range you want to treat, in order to design the panels and figure out where to place them. In a much larger room you could also have diffusers, but that room is too small to be able to use them.

Once this is done, I should essentially have a room which is just plasterboard. I think it needs softening up somehow! Is it simply a paint job that's required? I'm still planning to mount some acoustic tiles when finished.

Acoustic tiles are basically useless for studios. That's not what they are designed for. Forget that. You can build your own acoustic panels at low cost, or buy some commercial ones ready-made (much more ... plus shipping.. and they are BIG!).

Search the forum for things like "DIY acoustic panels" and you'll find numerous examples of how people have built there own, and the results they have obtained.


- Stuart -

[ChrisA99]

That's great, thank you so much for the advice Stuart, much appreciated.

[ChrisA99]

For those interested on how this has turned out... :

http://chriskipsterstudiobuild.blogspot.co.uk/

[Soundman2020]

Cool! It's always nice to see a studio completed.

Could you do us a big favor, and run a REW acoustic test in there, so everyone can see how it worked out for you? You can download REW for free from here:

http://www.roomeqwizard.com/

It's very simple to use, and all you need to do afterwards is to upload the file that it creates to some place like DropBox, then post the link here so we can download it. I'd he happy to analyze it for you, and perhaps suggest things you can do to make it even better.

- Stuart -

[ChrisA99]

No worries. I'll borrow a mic in the week and put the results up. Would love to hear your views...

[ChrisA99]

Okey dokes, I hope I've done it correctly!

https://dl.dropboxusercontent.com/u/459 ... ement.mdat

Would love to know what you think, let me know if there's anything more I can supply...

[Soundman2020]

Great! Thanks.

The response is reasonable, considering that is is a very small room. However, there's still room for improvement!

Here's your situation:

First, the full spectrum frequency response:

ChrisA99-FR-Full.jpg

You have swings of +/- 12 dB, which is a bit much. Also, there's a rise in the low end and the mids, which makes it look like there's a dip in the low mids, but that's actually not the problem: the bass rise and mid rise makes it look that way. And there's a large rise/drop-off in the high end as well.

Now, concentrating on just the low end, which is the most important part, this is what you have:

ChrisA99-FR-Low-end.jpg

The bass rise looks to be about 4 or 5 dB, so I'm guessing that's due to the position of the speakers, and the incorrect adjustment of he speaker controls. More about that below.

This is the waterfall plot for the same low end part of the spectrum:

ChrisA99-WF-Low-end.jpg

There's some very clear modal problems there: 49 Hz, 64 Hz, 85 Hz, 97 Hz, 131 Hz, 170 Hz, and a few other minor ones. This is indicative of insufficient bass trapping in the room. Looking at the photos, it seems like you have no bass trapping at all!

Here's the spectrogram for the low end, which represents the same data in a different way:

ChrisA99-SP.jpg

You can clearly see that the low end response is not very smooth: there are large variations in both level and time.

Next up: decay times at 1/3 octave intervals, across most of the spectrum:

ChrisA99-RT-.jpg

Overall, it seems to be around 250 ms. That's a bit too live for such a small room, and it isn't even. It should be almost flat, with very little variation between adjacent bands, except at the low end where it can rise a bit.

And finally the actual impulse response graph:

ChrisA99-IR-dB.jpg

Also not very smooth, and with clear early reflections.

Focusing in on the first few milliseconds, we get this:

ChrisA99-IR-percent.jpg

There's a lot of early energy, and several obvious early reflections within the first coupe of ms, and several more just a few ms later. My guess is that those are coming off the desk or video screens, which would also explain the mid-range rise.

Overall conclusion: the room is under-treated, and the geometry is not correct. The biggest issue is the lack of bass trapping, and the lack of mid-range absorption.

There's lots you could do to fix that:

First, get the speakers out of the room corners! That's a biggie. Get them positioned at about 28% and 72% of the room width, tight up against the front wall except for the absorption panels that need to go in between the speakers and the wall (move those panels that you have in the middle of the front wall, so they are centered behind each speaker). Then move your mix position such that your head is about 35% of the distance between the front and rear walls. Now aim both of your speakers for a point about 25 cm behind your head. Get rid of that desk, and replace it with something smaller that is flat, and that does not have "humps" on the top. Get your video screens down below the level of the speakers. Replace the speaker stands with something far more massive, solid, and rigid. Then install large, deep bass traps in both of the rear vertical corners, as well as the rear horizontal corner (wall/ceiling), but cover them with plastic so that they do not suck out too much of the high end.

That will get you started. Then do another REW test, and post that here so we can see what else might need doing.

It's a very small room, so it can never be made fantastic, but it can still be improved quite a bit.


- Stuart -

[ChrisA99]

That's awesome, thank you so much for analyzing the readings, I do find this all quite fascinating.

First, get the speakers out of the room corners! That's a biggie.

No worries. I thought as they were front ported that putting them in the corners would be OK. I shall get them moved.

Get them positioned at about 28% and 72% of the room width, tight up against the front wall except for the absorption panels that need to go in between the speakers and the wall (move those panels that you have in the middle of the front wall, so they are centered behind each speaker). Then move your mix position such that your head is about 35% of the distance between the front and rear walls. Now aim both of your speakers for a point about 25 cm behind your head. Get rid of that desk, and replace it with something smaller that is flat, and that does not have "humps" on the top. Get your video screens down below the level of the speakers.

This is going to be interesting! I can take the top "hump" off the desk so the video screens are lower. That would allow me to bring the speakers in. Almost going on top of them I'd imagine. Will have to try it out as I'm slightly worried that if the monitors go down, my posture and back will suffer (I am quite tall...). Will try out some options.

Then install large, deep bass traps in both of the rear vertical corners, as well as the rear horizontal corner (wall/ceiling), but cover them with plastic so that they do not suck out too much of the high end.

OK, I should be able to create custom traps with some Rockwool I have left over. I'd imagine I will move the four panels on the back wall to a more central position. Maybe lose two of them to make room for the traps.

That will get you started. Then do another REW test, and post that here so we can see what else might need doing.

Will do! Thanks for the help, much appreciated.

[Soundman2020]

I thought as they were front ported that putting them in the corners would be OK. I shall get them moved.

Front porting only means that it is easier to soffit-mount them. Speakers should never go in corners, since all room modes terminate in corners, so having a speaker right there is sure to trigger all of them! There's also the issue of massive bass buildup, beyond the ability of most "room correction" controls to fix, and also the problem with geometry. Corners are not nice. I'm trying to figure out how to build the perfect room: it would be rectangular, but it would have no corners at all... (not even rounded ones).... If I could figure out how to do that, I'd make a killing building perfect studios! Alas, the laws of physics don't seem to want to cooperate with me...

- Stuart -

[ChrisA99]

Hah, yeah those laws always get in the way!

OK, so I've changed things around a bit. The monitors are out of the corners! I've brought them inward so they're sitting on the table. The table is actually designed to house the monitors but I couldn't get both my 24" screens on there too. So they have been moved back and now sit on the monitor stands.

I've also built a couple of bass traps. Covered them in plastic - Well, actually it's this stuff : http://www.wickes.co.uk/Wickes-Seasonal ... 2/p/210014. I then covered them in felt. A couple of pics of this below. I then removed all of my audio panels and ran some measurements. Then I added each audio panel back in and took another measurement. I positioned them with a view to emulating the London 12 Room Kit (http://www.primacoustic.com/london12.htm). So as you can see from the REW file, there is one untreated, then with the bass traps, then with additional panels at the back, then with side panels, then with panels in the front corners. The REW file is here : https://dl.dropboxusercontent.com/u/459 ... ments.mdat. Would love to hear your views

[Soundman2020]

I'm not sure I understand the question, Anton. I'd have to see a diagram of what you are trying to describe.

Also, if the ceiling is sloped (~6,6 degrees) - do you build the leaf as a square or allign it to the ceiling?

You can do it either way, provided you understand the consequences and deal with them. The MSM resonant frequency is defined by the smallest depth of the air gap. So if the cavity ends up as 9" on one side and 6" on the other, then the 6" side is the one that defines the MSM resonance.

- Stuart -