John Sayers' Recording Studio Design Forum

Hey everyone,

Ok so I've been quiet for a while whilst I've been planning and researching and designing this build or should I say "re build" I also finally bought Rods book, it's a bit of a difficult read since we use the metric system here in South Africa and generally our buildings use more brick and concrete construction than in the US but besides from that its really great. Thank you to Rod for such amazing work!

For those of you that aren't familiar with my studio and what I am doing you can have a look here: viewtopic.php?f=2&t=17590 but in a nutshell, it was built with standard single dry wall and suspended ceilings that ran through the walls and over the office areas outside. Obviously not ideal at all for sound transmission loss. It also had a three leaf issue with the wall in between the control room and live room as well as a three leaf issue with the live room ceiling.

So what I did was almost completely tear it down. I had to leave the outside office space untouched but inside the studio I took down the wall dividing the live and control rooms as well as opened up all the perimeter walls on the inside. I also removed the ceilings and cut off the ceiling grid at the studio perimeter walls. So what I have now is a single leaf facing the outside and open walls on the inside with the concrete slab above and below (studio is on the first floor of a high rise office building) An entirely blank canvas to rebuild the studio in. One problem I have found is that the outer leaf wall we are left with has a few tricky cracks and holes in it, for instance where the old ceiling grid used to pass through. I have decided to try my best to seal these up but I'm not sure if I'm going to get this 100% airtight as it is difficult to seal from the inside, any suggestions or thoughts?

The Plan:
I intend to build a new wall structure inside this space, completely decoupled (except for the concrete floor) from the existing and now open outside leaf. In the end this will result in a fully decoupled MSM system wall. The outside leaf is standard dry wall constructed with non load bearing steel C -tracks and studs and only a single gypsum board. This is still filled with the original glass wool insulation. The new wall that will form the inside leaf will also be constructed with the same dry wall system once again filled with 24kg/M3 glass wool insulation and closed off inside with 3 x 12mm gypsum boards.

The problem with the non load bearing dry wall systems is that we can't support a ceiling with it, so what I have done is design a load bearing steel structure that will go inside the dry wall to hold up the new ceiling. This steel framework is made up of 75mm x 50mm rectangular tube. There will be a frame inside the walls on two sides of each room and I will then place 150mm x 38mm timber joists across from one frame to the other. The ceiling boards will then be screwed onto these joists. By doing this I also achieve a full decoupling of the ceiling from the concrete slab above us. And will be able to decouple the two studio rooms ceilings from each other.
The end goal is to build a two room studio (live and control) with completely decoupled and airtight MSM walls and ceilings.

The ventilation will be supplied by a custom built ducted in line fresh air fan system. Each room will have a fan for supply and a fan for return (not anywhere near the rooms obviously). The ducts will pass through properly constructed baffle boxes before entering/exiting the rooms. The air will then be conditioned using a standard wall mounted split unit type air conditioner in each room. The fresh air fans will have the ability to be turned off completely using a switch in both rooms. Thus providing the opportunity to be turned off when recording.This is a fail-safe however since I will be doing my best to get the airflow quiet enough to record with fans on. I also plan to experiment with this configuration, maybe have just a fan extracting from the room and then the air will be pulled in through the supply vent naturally, I believe this is called a passive system?

The studio will also include built in bass trap super chunks at the back corners, flush mounted monitor soffits, all DIY acoustic treatment and some pretty neat little gimmicks like a back lit snake wall box, shadow line LED lights and a custom built desk with isolation cabinets (already built).
I intend to follow my progress in this diary for you all to see with each and every part of the build, not only so that you guys can hopefully stop me from making any serious mistakes but also so that others may learn from my build.

I've been working on this build for two years now and almost all the equipment I wanted (yeah right!) is bought as well as most of the furniture and pretty much 90% of the building materials. As far as budget goes I estimate I will spend another $1000 or so before I finish.

If you have any questions or comments please feel free. I am a construction project manager by day so I have really planned this thing to death. There is a highly detailed and accurate to the millimeter sketch up model for the entire studio and everything in it please don't hesitate to ask, if you'd like a link to any of the models I will put them up.
I have broken the build down into 12 phases, the first 7 are attached in pictures, I will post the rest once we get to them
Thanks to all of you on here that have played such a crucial role in helping me get to this point, now let's finish it!

Gareth

Here is the floor plan with inside room measurements and pics of where we are now. Clearly still in Phase 1! Still need to clean up the ceiling cavity and seal up those walls as airtight as possible.

Gareth

Hello,

Just a quick update. I met with the engineer today so he could give me the go ahead for my steel ceiling support system. Basically he was happy except for the fact that my design didn't call for any bracing. He advised me to add one or two diagonal braces and cross tie beams to join the two frames together, I will take the new design to him tomorrow for his approval hopefully.

This has had a slight impact on how I had planned to put up the framing for my walls but after a few hours I've come up with a plan that I'm happy with and haven't lost an awful amount of floor space. Id much rather lose floor space than have the ceiling coming down on my head anyway

I carry on with phase 1 tomorrow night and plan to be starting with phase 2 by the weekend.

Attached find a view of the old vs the new steel work.

Gareth

I'm just wondering why you want to do that with steel. why not just do it with plain old 2x4 wood studs? Or if you really prefer working in metal, why not do it with plain old structural metal studs? I just don't understand the need for this complex and expensive steel structure.

Also, what research do you have on the acoustic response of steel-framed walls? How much does this unusual framing method change the isolation characteristics of the wall ,and in what way?

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Hey Stuart, thanks for the reply.



Because its cheaper



Because its cheaper



Believe it or not but building it this way is much much cheaper than both 2x4 timber and deffinately cheaper than load bearing dry wall studs.

Probably the dry wall companies that push the prices up on those studs but they are extremely expensive here. Where as you can go buy any type of steel tube, angle or plate even have it cut, bent or fabricated to your custom requirements just about anywhere and for a reasonable price. There are thousands of steel merchants and work shops in this country. Timber on the other hand is quite expensive as well, we usually only use timber in our roof trusses here as far as general construction goes.

I have no data on this but I would guess that my walls will behave similar to walls built with load bearing studs. But that's just a guess. Do you think I should look into alternative ways to raise the cieling then? Do you have any specific concerns as far as the steel frame goes when it comes to isolation?

Thanks again for the help man

Gareth

Hey Stuart,

After your post earlier I considered what you said quite seriously and did some calling around to get some estimates in doing this with timber or with load bearing dry wall. To further answer your question this is what I found out.

Timber:

I called my local timber city branch which is probably the biggest nationwide chain of timber suppliers here in south africa. According to them they dont keep a 2 x 4 as standard stock at all and neither do other suppliers, the closest they have is a 2 x 6 and if I wanted a 2 x 4 I would have to have it specially cut.

The total cost of the framework using 2 x 6 for the two rooms would be roughly $2000 USD

Load Bearing Dry Wall:

I checked with the steel merchants and unfortunately they do not supply this stuff as its not really a standard structural steel section. So the only place to get it is from gyproc.

The total cost of the framework using Load Bearing Dry Wall Tracks and Studs for the two rooms would be roughly $2500 USD

The system I have designed (hybrid of structural steel and non load bearing dry wall frame)

The total cost of the framework $890 USD

You can see the difference in price is huge. I do have a budget but its not very big, so hopefully that gives you a better idea of my local economics and why I want to do it this way.

Your comments do have me concerned though, I am worried that this will have a negative effect on the isolation of my wall, I don't know how it would but I've been doing this long enough to know that doesn't count and it could be something I never even imagined. One positive I considered is that rigidity helps with isolation does it not? I was even considering placing stringers between my studs for this purpose, If it does help the structural steel will definitely make my dry wall frame much more rigid all round, but I'm just speculating here. My logic tells me that it shouldn't perform any less than a load bearing steel framed wall though, since the steel frame is part of the inner leaf wall and is still decoupled from the outer leaf. But I eagerly await your thoughts on it

Thanks again

Gareth

I'm surprised that you can't get plain old 2x4s in Jo'burg. When I lived there (nearly 30 years ago) I didn't have the need to go looking for them, so I really don't know if they were available back then, but I did see plenty of wood-framed garden sheds, garages, and other assorted outbuildings on plots and small-holdings when we lived out on the East Rand, and also in Halfway House, so I just assumed that it would be available.

You do mention wood joists for your ceiling: what are you planning to use there?

But if price is the issue, then I understand where you are coming from. spending two or three times the money seems a bit heavy...

That's the thing, isn't it? All the research literature I can find is about wood-framed or metal-framed walls, or concrete, or brick. I can't find much at all about steel framed. Like you, I suspect that it should behave well and isolate to decent levels, but that's just a hunch with no scientific basis to go on. You might well be fine with that, but if there's one thing I've learned about acoustics it would be that making assumptions based on no data is a dangerous thing, since small details can have large effects. I really don't see how welded steel channel framing would be greatly different from wood framing or ordinary metal framing, but there WILL be some differences, simply because the properties of the supporting structure will be different. Whether those differences will be favorable or, big or small, good or bad, and at what frequency they will make themselves known, is the big question.

For isolation, the audio spectrum can be broken down into several "regions", each of which is controlled by a different characteristic. At the very lowest frequencies, the stiffness of the wall (rigidity) is what controls isolation the most. In this region, mass and damping are not very important at all, and stiffness is the most important factor. Go up the scale a bit, and you get to the region where MSM resonance controls the isolation, with stiffness no longer being so important. In this region, it is the tuning of the MSM system that matters most. Higher still, once you get to several times the lowest resonant frequency, mass starts taking over, and that region of the spectrum is controlled mostly by mass, with stiffness and damping not being involved much. Next, at even higher frequencies you get the region where isolation is controlled mostly by the "coincidence effect". That one is kind of hard to explain, and is related to bending waves in the wall itself, the speed of sound in different materials, and the angle of incidence (among other things). But in this region, damping is probably the most important factor for isolation. And finally, once you get beyond the coincidence region and the critical frequency, stiffness start to play a big role again.

So the question is this: does steel framing affect any of those factors? Does it make the wall any more or less stiff at very low frequencies? Does it change the factors that govern the coincidence dip? Does it modify the resonant behavior of the wall? My guess is that there will be differences, but that they won't be a huge deal. But I stress: That's just a guess, and I can't point to any research or equations that would support it. So take it for what it is worth. You might be fine with your plan, but you might also discover something that you were not expecting. Basically, you become your own guinea pig, and your own acoustic test lab.

Bottom line? I'm guessing your plan will work, but I don't know how well it will work. But I'll be very interested to see the results, if you do decide to build it that way!

By the way, how much isolation are you aiming for in the end, in terms of decibels?

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Hey man,



I have no idea I was also shocked when they said they didn't keep 2 x 4, Ill try somewhere else tomorrow and see what they say. Either way its still going to cost double the price so It might not be an option for me at all at those prices.



The joists for the ceiling will be standard roofing/ceiling joists 38mm x 150mm. So that's like 1 1/2 x 6 inches?

I see what you mean with the "regions" and as far as rigidity goes I had just edited my last post when you posted that reply. If anything I am 100% sure that the structural steel will stiffen the dry wall frame work, without a doubt. Maybe I should add some stringers too? So I'm hoping that is actually a positive in controlling that lower region. But as you say there is no science to say whether its pro or con.



I think were going to go ahead with the hybrid, who knows maybe ill start a new trend in studio construction (just kidding) I too am interested and also petrified of any negative effects. But my bottom line is will this design not at least give me a huge increase in isolation to what I had previously? I mean that is the end goal I suppose.



150db at 20hz! ha ha. No being realistic I would reluctantly settle for 50db minimum but id be really happy with 60db or more if at all possible. Obviously I wont achieve this much on the low end but generally around that area would be good to me? What do you think? Is more possible for me?

Some other thoughts I had,

The existing outer leaf wall is not airtight at all. As I said in an earlier post there are numerous breaches where aircon ducting passes through and where the old ceiling grid used to come through (all of these are above the ceiling height of the studio you can see some in the pics above) I plan to start sealing these up as best I can tonight, ill be using caulk and mud to do it but I'm very worried the effect this will have on my isolation. My inner leaf will be as airtight as a submarine Ill make sure of that.

Also I had the opportunity to speak to a acoustics specialist today who has built numerous radio studios here in Joburg and he recommended that I put in a few layers of glass wool and chipboard on the live room floor for extra isolation. Not floating but just pack it up a bit to reduce any transmission. What do you think?

Thanks mate, your always such a great help!

Gareth

Wood will dampen the source, lightweight steel will minimize transfer and structural steel is rigid, doesn't sound travel faster in steel than in concrete?

_________________
Brien Holcombe
_____________________________________________
Sound: You can't stop it, you can only try to contain it.

Yep. Nearly twice as fast, in fact. Roughly 6100 m/s for steel, vs. 3200 m/s for concrete. (Interestingly, the speed for wood is pretty much the same as for concrete, at around 3300 m/s.)


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Well now you guys have gone and made me doubt this design again. What could be the possible negative effects of having the sound traveling faster through the frame?

Gareth

So in looking for a solution to seal up my existing outer leaf wall I came accross a supplier of DIY polyeurethane spray foam kits. My idea is to use the spray foam to seal up all the holes and joins to make the wall airtight. I will then put the the glass wool insulation back in the frame before constructing the inner leaf wall frames. What do you guys think? I will post up the data sheet for the foam kit tomorrow when I'm at my pc. Bear in mind that my plan is to use the foam only to seal any holes and joins for airtighness of the wall and NOT to coat it with the foam for insulation purposes.

Back on the topic of the steel, I read somewhere tonight that steel stud walls perform better than timber because of resilience, but on the same token we know that rigidity helps in the TL of lower frequencies. So im quite confused since does rigidity of the framework not lesson the resilience? Am I grasping the concept of resilience wrong?

I allso read that the speed of sound in gypsum is allso around 6000 m/s. Similar to steel. I've allso been reading about coincidence effect and critical frequency. My understanding is that for optimum isolation I need get the resonant frequency as low as possible and the critical frequency as high as possible. So far my reading suggests the best way to lower resonance and raise critical is to reduce rigidity. So once again I am left confused since I thought rigidity was important for controlling the lower end transmission as well as the higher end. Still my question is how should I go about evaluating what effect my steel system has on my resonance and my critical frequency? If that is at all possible. Am I over thinking it?


Thanks for the help

Gareth

Ok so after doing some looking around I have decided that I'm going to take Stuarts advice and not build the steel structure to support the cieling. I just can't risk building a wall that might compromise my isolation. There just isn't enough data on the subject of using structural steel in this application and the only studies I have found show that thicker gauge load bearing steel reduces the isolation. So...

The new plan (still in the making)

I intend to carry on with my efforts in sealing up the existing outer leaf walls airtight using dry wall plaster or caulk depending on the hole. I will then go over every join and breach with a layer of spray foam to make extra sure the wall is airtight.

The new inner leaf will still be constructed out of non load bearing light gauge steel tracks and studs. The cielings (inner leaf) will be supported by suspending it from the concrete slab above (outer leaf) I will use spring hangers from Masson Industries to suspend the cieling and hopefully this will decouple it sufficiently. I am meeting with the guys from Masson tomorrow so that they can help me with the design.

The hangers I will use will probably be the W30N or their local equivalent as specified on page 22 here: http://www.acoustiquepn.ca/PDF/acs102v2.pdf

I'm happy with this plan for two reasons, it sets my mind at ease knowing that I will be using tried and tested technologies and techniques (doing it the right way so to speak) and because I gain some floor space back now that I won't have to accommodate the steel structure inside my walls. Which brings me to my next question...

How big must the air gap in my walls be? I was aiming for 100mm leaf to leaf on average except for where my CR walls splay out and about 200mm for the wall between the LR and CR. Any help on this is much appreciated as always.

Gareth