Stand alone “room in a room” studio build ORANGE NSW Australia

[gullfo]

on the runners - i'd suggest lifting the base, and apply generous quantities of caulk and lay a new pressure treated runner on that. then plan to inset the exteriro wall frame by the depth of the mass layers. again, this part is fairly normal construction and it seems likes it harder than it needs to be. no need to try to layer in additional runners inside etc. esp with the price of lumber.

inside of the columns (which are steel, much denser than wood) you can add lumber for nailers to attach the now inset exterior frame to. then with the mass layer now flush to the exterior of the columns (corners included) you can add the moisture and sheathing barriers. this combination will be plenty dense enough and once fully damped by the air cavity insulation, will work fine.

examples shown w/ 2x4 walls and 2" (50mm) frame gap = ~230mm air between mass layers.

[gearjunk1e]

Glenn

Love your work. The timber inside the C section is way better!

In terms of shifting in outer wall frame position to accommodate the mass outside – my first reaction was that I’d have to have to replace the metal sills I’ve got sitting on top of the treated base plate (pic below) – they have been rolled to suit the current frame position – they only just overhang the slab so won’t push inside further.

Metal sill position

BUT THEN I thought about the following:

Moving the frame in to accommodate the external mass

The thing is that if I do that I still have to add a "runner" inside.

So, this means I could avoid:

Option 1. Remove all the nails holding the DPC to the base plate and lift the base plate off. Remove the packers. Cut a piece of 90mm treated pine so that it sits under the base plate (call it the fill), caulk heavily the contact between the DPC and the fill, then drop the fill and base plate back on to the dynabolts and re-tighten. Then re-attach the DPC with nails on the inside.

This is because I reckon I can use the runner as the effective bottom of the outer wall isolation mass if it is installed to isolation standards - ie plenty of sealant/caulk and the base profiled to the slab variations.

If I'm right then the decision on whether to put the outside mass inside or outside the frame just comes down to the cost and ease of execution.

I'll do some sums and have another chat with my engineer to see what drops out.

Thanks again for your input - however this gets done you've got me another ~200mm along the sides of both my control and live rooms!

Andrew

[gearjunk1e]

Hi everyone

I ended up having a PM conversation with Stuart on my wall design off the back of a related issue.
Given it got me some clarity and raised some interesting issues, I thought I'd include the relevant parts of that exchange below

Hi Andrew,

You mentioned trying to figure out your third-leaf loss: You probably already have it, but the full equations for 2-leaf and 3-leaf resonance are:

2-leaf-3-leaf-double-triple-leaf-equations.jpg

There's one caveat to all of this: the equations assume that the cavities are sealed air-tight. If that is not the case, then there will still be some effect, but it will be reduced in intensity (depending on how "unsealed" it is). Extreme example: if you hold a small piece of drywall just one foot square, a few inches away from a good 2-leaf wall, then you might be able to detect some resonant vibration in that piece, but it will have pretty much zero effect at all on the wall. On the other hand, if you built an entire leaf in the same place as your "small piece", covering the complete surface of the 2-leaf wall, at the same distance as your "small piece" was, and you left a one square foot hole in that surface, then you'd get a lot more effect on the overall isolation, nearly as much as having a fully sealed leaf...

Yeah, it gets complicated!

How much isolation are you shooting for in your place?

- Stuart –
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Thanks Stuart

It’s an awfully long time since I've had to do any serious maths so its been a bit of a journey reading academic papers. Thanks for the triple leaf formula - I actually discovered one earlier this afternoon when I found a post from Andre in the green room referencing a paper by Yunikur which outlined the equation - but yours is clearer.

Isolation: I'm expecting inside measurements up to 115dB. My nearest neighbour’s house is 25-30m from my building and I’d like to be at 40dB by the time I hit his back wall. If I take a conservative approach and only use 16m of the gap between the studio and his house and using 4db per doubling of distance I'd need ~60dB at 1m. All planning has been around 70dB TL with the expectation that something will cause an issue somewhere along the way and leave me closer to 60dB.

I'm chasing this triple leaf issue to ground really just to be cautious - this pic should contextualise..

Soundman PM240821.png

Glenn and I have been bouncing around alternatives for my outer wall but for a host of reasons I'm going to stick to the "metal cladding outside" option with my outer isolation leaf on the inside of the same frame as pictured. Intuitively, I'm comfortable that the very low mass of the metal cladding together with the open airflow behind it will cause me no great issues from a triple leaf standpoint but I wanted to try and put some numbers around it even if the formulas I use would produce a worse case than I'd have in practice.

If there was any meaningful impact I was considering whether I should add more mass to the outer leaf vs the inner - I'd seen somewhere else you'd recommended that in similar circumstances.

Andrew
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"If there was any meaningful impact I was considering whether I should add more mass to the outer leaf vs the inner - I'd seen somewhere else you'd recommended that in similar circumstances."

It's in the Wyle report at some point. I don't have the reference on hand, but basically their conclusion is that the optimum performance for a 3-leaf system is when the mass on the middle leaf is the same as the combined mass of the other two leaves, and both air-gaps are equal: In other words: d1=d2, and m2=m1+m3, where m1 = m3. I also seem to recall that this is the arrangement required for the equation to be valid, but I'm not 100% certain about that. It makes sense, though.

70 dB isolation is a tall order: it’s about as much as you can hope for in a typical project studio / home studio. so if you are in any doubt as to what mass to use, I would suggest increasing it as much as you can. And I would also suggest using Green Glue between at least two layers on each of the walls. That stuff is pricey, but very much worth it, if you need high isolation. Also, your seals will be critical, and your HVAC system is going to need some careful design... especially the silencer boxes and duct runs. It can be done, though! Not impossible.

- Stuart –

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Hi Stuart

As you can see, I do have some wriggle room on the 70dB
- I really need 60dB – 59dB actually,
- I only used 16m of the 20-25m to my neighbour’s house for decay; and
- The room that has the 115dB max is a further 6m from my neighbour’s house than where I’m measuring from

From having viewed so many projects on this and johnsayers forum I’m acutely aware that studio building is a series of compromises and I'm fully expecting something to come along that forces me to have to give some up TL.

I did see that “doubling the middle leaf mass” observation in Wyles - my problem is that any studies I’ve found assume
- Sealed air gaps; and
- Leaves of reasonably similar mass

In my case I’m working to an MSM of inner leaf of 37.5kg/m2 – 200mm air (sealed) – outer leaf 37.5kg/m2 – 90mm air (unsealed) – 4kg/m2 “leaf”. There is not much research that covers one unsealed air gap and a 3rd leaf that is ~10% surface mass of the others!

If I use the analogy in your original reply, my case is like building a barrier of 1/8th" wide drywall (if that existed) 3 ½” outside the fully isolated structure. ….and my hypothetical “drywall” is corrugated.

I suppose that in the context of my TL wriggle room if I knew that the worst case was a loss of 6dB in TL I’d just accept the impact and move on.

Andrew

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Hi Andrew,

I wouldn't be too worried about your third "leaf", to be honest. There might be some loss from that, but I can't see it being large. What I would suggest is that you find some way to damp it, so that any vibrations that are induced in it will not be a big issue. Maybe some insulation pressed up against it, or perhaps some type of spray-foam product that doesn't harden and remains soft and rubbery when cured. There's actually a type of "acoustic damping paint" that has some useful effects there: https://www.atsacoustics.com/quietcoat.html I used that once on a place in North Carolina, and it seems to work, although not as wonderfully as the marketing hype claims! (Surprise!) If you could spray the inner face of your metal siding with that, and put some mineral wool (not fiberglass) in the gap, you should be fine. I don't see this robbing you of a lot of isolation.

For many years I've been working on a spreadsheet that predicts isolation for various 2-leaf and 3-leaf assemblies. It isn0t accurate yet, but it is decent for ball-park estimates. With your 37.5 kg/m2 mass on each leaf, plus your 20 cm air gap, and good seals everywhere, it says you should get 70.5 dB, assuming everything is perfect. It also estimates a "real world" value, based on typical imperfections and workmanship issues, and it says 63 dB for your case. So with a bit of care, you should certainly be able to get over 60 dB. It also estimates f to be around 20 Hz, considering just a 2-leaf system (ignoring your outer siding), and for that 3-leaf system, it estimates F- = 21 Hz and F+ = 28 Hz. As I said, it isn't accurate at all, but it does give you a reasonable indication. It also says you should be getting 41 dB, just from the mass alone, without considering the MSM effect.

So, overall, I'd say you are fine! Good quality materials and attention to detail in the build should get you where you want to go.

- Stuart –

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Thanks Stuart

On the dampening, the most common approach here would be what I have under the roof - something I'm sure you'd be familiar with - Bradford Anticon https://www.bradfordinsulation.com.au/h ... ng/anticon. It obviously has the aluminium foil on the backing which theoretically adds to the isolation equation but I've pulled that apart and the 2 aluminium layers are tissue paper thin - hence my adding the term "theoretical". However that is classified as glasswool insulation - I'd have to check first whether that is what you call fibreglass.

Andrew

If anyone can unbundle for me the issue of what constitutes mineral wool versus fibreglass that would be great - I see glasswool advertised as mineral wool down here when its made from recycled plastic bottles - I thought mineral wool was made of fibres of stone or iron ore waste. Unfortunately, mineral wool made of fibres of stone or iron ore waste is way less common down here than the recycled glass stuff.

Andrew

[Soundman2020]

Source of the post I thought mineral wool was made of fibres of stone or iron ore waste.

Right! That's the stuff you need. Anything else is not mineral wool. Yes, fiberglass is sometimes sold as "mineral wool", but there is a difference, acoustically and also practically. You can use either fiberglass or mineral wool for various acoustic applications (as long as you choose the right characteristics), but I recommended mineral wool for your specific application for a practical reason: you are using it on an exterior wall. If fiberglass insulation gets wet, it usually ends up as a soggy mess, and doesn't recover its original shape well after it dries out. Mineral wool, on the other hand, is basically just rock: if it gets wet, then all that happens is that it gets wet! After it dries out again, it is fine. Of course, I'm assuming that it is made with non water-soluble binders, but mineral wool usually is.

In Australia: Knauf, James Hardie, Tombo, Paroc, Bradford, and others do make true mineral wool. You should also be able to find the Rockwool brand. Careful with that! "Rockwool" is actually the name of a company, and a trade name, but some suppliers call anything made from stone "Rockwool", even though it isn't..... But whatever you get, do confirm with the supplier that it really is mineral wool, made from stone (commonly from smelter slag).

And, of course, choose the product that has the right Gas Flow Resistivity for your application! Don't get high-density...

- Stuart -

[gearjunk1e]

Stuart

Thanks. I've done some digging - real mineral wool is way, way more expensive than glasswool insulation down here. Like 4:1.

I take your point on risk of getting wet but I'm very confident of the water-tightness of my structure - both in design and execution.

Notwithstanding this confidence I'm thinking of putting mineral wool in the most risky places - bottom of walls and corners and using glass wool elsewhere.

Andrew

[Soundman2020]

Source of the post real mineral wool is way, way more expensive than glasswool insulation down here. Like 4:1.

Wow! That's pretty steep! Yup, with price difference like that, for sure fiberglass is the way to go. Acoustically, they both do the job rather well. Mineral wool has the water advantage, but apart from that, there's no important differences acoustically.

You probably already know this, but it bares mentioning again: the physical characteristic of any insulation that best defines it's acoustic performance, is GFR, or "Gas Flow Resistivity" (sometimes also called "air flow resistivity"), which is measured in the strange units of "MKS Rayls" (technically, the units are kPa.s/m2, or "Kilopascal seconds per square meter". Yup). That is a measure of how the material impedes the movement of gas (air) through it, and in fact is directly related to acoustic impedance (after all, sound is just vibrating air...). So GFR is the number you need to know. Then, for any specific acoustic application, all you need is a material that has the right GFR number. In general, lower numbers are better for absorbing low frequencies, and higher numbers are better when you only want to absorb higher frequencies, not lows. Fortunately, you don't need to be exact: there's a fairly broad range of GFR numbers that will work for any specific application.

The trouble is, insulation manufacturers often don't publish the GFR number for their product, and often don't even measure it! It has no relationship to the primary use of insulation: thermal insulation. It is only meaningful in acoustics, so they don't usually bother. Only when they also want to market the product acoustically, do they measure and publish the numbers. Fortunately, there's an approximate relationship between the GFR and the density of each type of insulation, so you can use the density to help find the right product. Once again, higher densities (heavier) are better at absorbing just high frequencies, and lower densities (lighter) are better at absorbing down into the low end of the audio spectrum.

The relationship between GFR and density is different for each type of insulation (mineral wool, fiberglass, polyester, recycled fabric, cellulose, etc.)m but fairly consistent within the family. Here's a graph showing the aprox. relationship for mineral wool:

And here's graph that shows the difference between mineral wool and fiberglass:

Hopefully, that is of some use to you in choosing the right product!

- Stuart -

[gearjunk1e]

Stuart

Great info - I've been looking at Bradford Soundscreen as my "go to" for insulation - it goes as follows

Soundscreen specs

and is generally pretty price competitive. Love their transparency on the acoustic specs.

Andrew

[Soundman2020]

Looks good to me! That's a decent GFR number for your application, too. If it is reasonably priced, I'd say go for it!

- Stuart -

[SoWhat]

Kilopascal...

...the name of the next Bond villain.

[gearjunk1e]

Hi everyone

Lots going on here on the building front - see my build post https://www.digistar.cl/Forum/viewtopic.php?f=5&t=915

Also - a fair bit on design in the background

I'll be posting a revised wall structure once I pull the last bits together but to do that I need one piece of feedback. (I've decided to use green glue between layers and am just working through alternatives to drywall etc etc)

The QUESTION I have relates to gap filling

All the posts I read about the insulation between inner and outer rooms says to the effect of "use the cheapest, fluffiest but fill the space"

So...
I'm looking at filling my 200mm wall gap with insulation that is rated at 5000 mks rayls/m - IS THIS TOO LOW? My understanding is that the "between wall" insulation is there purely to dampen an excitement in the mass layers.

Andrew

[gearjunk1e]

May have answered my own question here - I was working through Starlight's project posts tonight and found

Source of the post Then the gaps were filled with low density mineral wool, 10.7kg/cu.m.

That's pretty much in the ball park of what I'm looking at for dampening

[gearjunk1e]

Hi everyone

Design update

After working through wall designs with input from Glenn and Stuart in particular and digging deep into the world of green glue and the test results, I’ve revised my wall structure.

The pics cover it…but a few notes first:

1. I’m going to test the isolation from the outer room walls before settling on the inner room wall mass – for now its 2 layers of 16mm Fyrchek (drywall) with green glue in between;
2. I plan to make the outer wall mass larger than the inner. While feedback has been that my steel sheet cladding shouldn’t pose a material 3rd leaf issue, I know that the best way to deal with 3 leaf issues is to bump up the mass on the middle wall;
3. I haven’t closed my mind to the outer layer being 1 layer of structafloor and one of mdf or 16mm drywall but structafloor is cheaper per m2; and
4. The insulation I’m using behind the metal sheet cladding has a lower GFR than I was proposing in earlier posts – I’d stuffed up the price comparison so the Bradford Soundscreen I was looking at will have to wait until its broadband absorption time.

I do have a specific question on top of any general observations anyone may make.

The STRUCTAfloor sheets have a groove cut along the edge – when you lay them as a floor it is used to line up the sheets so that they join flat (hence the nickname “yellowtongue”). My question is whether I should join the boards in this manner or cut the boards back to the base of the slot (about 7mm) to square them up, shelve the plastic joiners and leave a 1/8th inch gap between sheets for backer rod/sealant (caulk) as you see on OSB walls.

The plastic joiners have a surface mass of 2.5kg/m2 – the surface density of the section that includes the plastic joiner is 12.9 kg/m2 versus straight yellowtongue at 13.2kg/m2. The answer has to be that I trim the slots out but I’d love to hear a counter argument to save me the fiddling around!!

Andrew

[endorka]

Source of the postThe STRUCTAfloor sheets have a groove cut along the edge – when you lay them as a floor it is used to line up the sheets so that they join flat (hence the nickname “yellowtongue”). My question is whether I should join the boards in this manner or cut the boards back to the base of the slot (about 7mm) to square them up, shelve the plastic joiners and leave a 1/8th inch gap between sheets for backer rod/sealant (caulk) as you see on OSB walls.

The plastic joiners have a surface mass of 2.5kg/m2 – the surface density of the section that includes the plastic joiner is 12.9 kg/m2 versus straight yellowtongue at 13.2kg/m2. The answer has to be that I trim the slots out but I’d love to hear a counter argument to save me the fiddling around!!

I've no idea if you could get away with it unfortunately As well as other unknowns, I would be concerned about these joins creaking as the material expanded and contracted with temperature changes.

The two layers of this material and also the drywall should be staggered so the joins do not overlap. Last time I checked the building code here has fairly specific ways in which this should be done. No doubt you've already thought of this, but it is not shown explicitly in your drawings so thought I'd point it out just in case.

Cheers!
Jennifer

[Starlight]

Source of the post3. I haven’t closed my mind to the outer layer being 1 layer of structafloor and one of mdf or 16mm drywall but structafloor is cheaper per m2; and

MDF in an outer wall rings an alarm bell in my head. Only marginally less dense is OSB at 640kg/m3 compared with MDF at 720kg/m3. OSB will withstand damp and water far better than MDF which is about as water-resistant as Weetabix (UK), Weet-Bix (Aus). Painting OSB with exterior paint will make it even more weather-proof.

[gearjunk1e]

Source of the postMDF in an outer wall rings an alarm bell in my head. Only marginally less dense is OSB at 640kg/m3 compared with MDF at 720kg/m3. OSB will withstand damp and water far better than MDF which is about as water-resistant as Weetabix (UK), Weet-Bix (Aus). Painting OSB with exterior paint will make it even more weather-proof.

Starlight

Great advice - appreciate your input!

MDF = mush once it gets wet - love the weetbix analogy. I'd love to use OSB but down here they only seem to sell it to 6mm thickness - structafloor is the closest product we have down here in any width. (My engineer had a piece covering a hole on a site for 18 months where it was subject to water, water and more water and it hadn't lost structural integrity when he pulled it up.)

I've insured against water egress to about 250% according to my brother-in-law who is a builder and is helping me at the mo.

I have a damp course on the slab that folds up behind the base plate, then a metal sill on the first base plate and the external wall frame sits on that. The join between where the damp course folds up (behind the base plate) and the slab is sealed with quality sealant. The acoustic sheathing on the outer wall sits on another double base plate running inside the original one and that one will be protected with a damp course below and between itself and the one that supports the outside cladding. The height of this "inner" base plate means that the structafloor/MDF only starts at a level above the top of the metal sill of the outer wall.
On top of all that I have a breatheable membrane underneath the metal outer cladding over the timber frame that covers the whole of the outer wall area which allows moisture out but not in. It works really well - before I clad the outer walls we had some serious storms and it was as dry as a bone inside.

(Having written that its probably confusing with me having all these base plates but pic 5 is the best view without all the detail around sealant)

Andrew