John Sayers' Recording Studio Design Forum Archive

Just getting started on a journey towards building my own studio, and I have a few questions before I head too far down the rabbit hole. I’m spoilt, and looking to create an isolated mixing (7x5x3.5sqm) and 2x live rooms (10x6x4 & 2x4x3) I haven’t yet found a space, and am also considering building, so these questions are to help me narrow down my choices...!

Here in West Australia the predominant building types is double brick (brick cavity), giving me a “double leaf”. As I understand it, without considering the roof or windows, this gives me around 55 STC on the external walls.

And so the questions:

What about flashing on external brickwork? Does that open up a hole to the “outside”?

So what I need to understand is how I would go about isolating the mixing room from the live room (seems like I need double leaf?), inside of the double leaf external walls, without creating a triple or quadruple leaf?

All this makes me lean towards building from scratch... Or am I just really off the mark...?

Hi "crayziecarl", and Welcome!

I have a few questions before I head too far down the rabbit hole

Too late! If you are already considering building a studio, then you are already in the rabbit hole... no going back now! You took the pillllll....

an isolated mixing (7x5x3.5sqm)

Did you check those dimensions to make sure they give you a good room ratio?

and 2x live rooms (10x6x4 & 2x4x3)

10x6 is a nice size for a live room, but 2x4 is more of an iso booth, not a live room! And only 2m wide makes it a smallish iso booth, with a perfectly rectangular cross section (length is exactly twice width), implying a lousy ratio and modal problems. Also, I'm wondering why you have a higher ceiling in the CR than the iso booth?

this gives me around 55 STC on the external walls.

Forget STC. It is no use at all for telling you how well your studio will be isolated. STC was never meant to measure such things. Here's an excerpt from the actual ASTM test procedure (E413) that explains the use of STC.

“These single-number ratings correlate in a general way with subjective impressions of sound transmission for speech, radio, television and similar sources of noise in offices and buildings. This classification method is not appropriate for sound sources with spectra significantly different from those sources listed above. Such sources include machinery, industrial processes, bowling alleys, power transformers, musical instruments, many music systems and transportation noises such as motor vehicles, aircraft and trains. For these sources, accurate assessment of sound transmission requires a detailed analysis in frequency bands.”

It's a common misconception that you can use STC ratings to decide if a particular wall, window, door, or building material will be of any use in a studio. As you can see above, in the statement from the people who designed the STC rating system and the method for calculating it, STC is simply not applicable.

Here's how it works:

To determine the STC rating for a wall, door, window, or whatever, you start by measuring the actual transmission loss at 16 specific frequencies between 125 Hz and 4kHz. You do not measure anything above or below that range, and you do not measure anything in between those 16 points. Just those 16, and nothing else. Then you plot those 16 points on a graph, and do some fudging and nudging with the numbers and the curve, until it fits in below one of the standard STC curves. Then you read off the number of that specific curve, and that number is your STC rating. There is no relationship to real-world decibels: it is just the index number of the reference curve that is closest to your curve.

On the other hand, when you measure the isolation of a studio wall, you want to be sure that it is isolating ALL frequencies, across the entire spectrum from 20 Hz up to 20,000 Hz, not just 16 specific points that somebody chose 50 years ago, because he thought they were a good representation of human speech. STC does not take into account the bottom two and a half octaves of the musical spectrum (nothing below 125Hz), nor does it take into account the top two and a quarter octaves (nothing above 4k). Of the ten octaves that our hearing range covers, STC ignores five of them (or nearly five). So STC tells you nothing useful about how well a wall, door or window will work in a studio. The ONLY way to determine that, is by look at the Transmission Loss curve for it, or by estimating with a sound level meter set to "C" weighting (or even "Z"), and slow response, then measuring the levels on each side. That will give you a true indication of the number of decibels that the wall/door/window is blocking, across the full audible range.

Consider this: It is quite possible to have a door rated at STC-30 that does not provide even 20 decibels of actual isolation, and I can build you a wall rated at STC-20 that provides much better than 30 dB of isolation. There simply is no relationship between STC rating and the ability of a barrier to stop full-spectrum sound, such as music. STC was never designed for that, and cannot be used for that.

Then there's the issue of installation. You can buy a door that really does provide 40 dB of isolation, but unless you install it correctly, it will not provide that level! If you install it in a wall that provides only 20 dB, then the total isolation of that wall+door is 20 dB: isolation is only as good as the worst part. Even if you put a door rated at 90 dB in that wall, it would STILL only give you 20 dB. The total is only as good as the weakest part of the system.

So forget STC as a useful indicator, and just use the actual TL graphs to judge if a wall, door, window, floor, roof, or whatever will meet your needs.

Your first order of business should therefore be to come up with a real number that accurately represents how much isolation you need. Do that with a proper hand-held sound-level meter (not an app on your iPhone!), set to "C" and "Slow". Measure how loud you are in a typical session, and measure how quite you need to be. The difference is how many decibels of isolation you need, and that's your starting point for the entire design process.

What about flashing on external brickwork? Does that open up a hole to the “outside”?

Yes it does. Any penetration through the wall even the size of a small crack or a nail hole, is a loss of isolation. The larger the hole, the larger the loss, but even very small holes still cause sizeable losses of isolation. Think of it this way: If air can get through the hole, then so can sound, because sound is nothing more than waves moving through air.

So what I need to understand is how I would go about isolating the mixing room from the live room (seems like I need double leaf?), inside of the double leaf external walls, without creating a triple or quadruple leaf?

You build one single outer leaf around the entire building, perhaps using something like concrete blocks (what you call "Besser blocks" in Aussie), sealed air-tight, then you build one single leaf for each internal room, using standard timber framing with sheathing on only ONE side of it. "Sheating" refers to things like drywall, OSB, MDF, plywood, fiber-cement board and similar. You can have several layers of sheathing if you happen to need it, but all of them must be on the same side of the framing, and in direct contact with each other, without glue between them (except if you want t use Green Glue, which isn't glue anyway despite the name).

All this makes me lean towards building from scratch...

If you need high isolation (which you seem to be implying), and the best possible studio you can have, then yes, a ground-up build is the way to go. It gives you the freedom to design the entire thing for optimum performance, without being limited by existing construction. Of course, it costs more, but the results will undoubtedly be better, if you design it correctly and have the time and money to do it right.

Or am I just really off the mark...?

Hey, you already decide to build a studio, so you are way of the "mark"! Only crazy folks decide to build studios at home... so welcome to the club of crazy "off the mark" folks!


- Stuart -

Thanks Stuart,

Yikes what a start. Thanks to John and everyone else in this place the world ahead seems like a happier and easier place.

Well... with all that help, the good news is I’ve pretty much settled on a build from scratch. Nothing is doing to start for at least twelve months so now to the planning!

Re: the small room, you are right - I meant vocal booth. I have run all the room dimensions through a bolt calculator and they all seem to sit ok. Hence the ceiling height changes.

Once I’ve had a play around in the next few weeks I will post a few mock ups of my intended floor space.

What I do need to check is if the room sizes “change” when I add in absorbers/diffusers and/or soffit mount speakers . Put more simply, do these fixtures detract from the room size?

And lastly, if I were to design an RFZ room - splayed walls/not “perfectly” rectangular - do the bolt laws still (mostly) apply?

Well... with all that help, the good news is I’ve pretty much settled on a build from scratch.

If you want the best, and have the budget to do that, then I'd say that's a really smart move.

Nothing is doing to start for at least twelve months so now to the planning!

Sounds about right, if you plan on designing it all yourself. That's realistic. It will take you maybe 3 or 4 months to learn the basics of acoustics to the point where you are able to design the place, another couple of months to learn the basics of studio design and construction techniques well enough that you can actually design it intelligently with structural integrity so it won't fall over and kill you, then another month or so to learn the design software itself (I'd recommend SketchUp at present, but that might change with their recent decision to stop producing the free product "SketchUp Make", and do a rather silly move to a browser-based version, which is plain nuts if you ask me... but I digress). And then you'll need about four to six months of actual design work to get to the point where you can start building.

So yes, if you start the process now, realistically you could have your design completed and be ready to start building by December 2018.

.... dimensions through a bolt calculator and they all seem to sit ok. Hence the ceiling height changes.

You only really need to worry about room ratios for the control room, as that's where it matters most. The control room must have neutral acoustics across the entire spectrum that you need to work with (both time domain and frequency domain, as well as phase, reflections, etc.), so it's important to get your low end modal issues as smooth as possible, and choosing a good ratio can often help with that. But for live rooms, it's not so much of an issue. A live room is not supposed to be neutral, like a control room is. A live room is supposed to be... welll... ummm.. "live"! It is supposed to have life, and character, and "vibe", and an acoustic response that makes it attractive for musicians to play in, making them want to come back and play some more, because the room "sounds warm, nice, engaging, groovy, insert-your-favourite-musican-term-here". So if it would help to have some modal stuff going on in order to get a nice "vibe" in the room that musicians like and records well, then that's fine.

In other words, you don't need to be too worried about ratios for your iso booth and live room. Modes are only really important for the CR (Control Room). Therefore, you can make your other two rooms pretty much any dimensions that look good, and sound good, provided that you have suitable treatment.

run all the room dimensions through a bolt calculator and they all seem to sit ok.

I'm not sure which calculator you used, but it should have given you some pretty large large red flags, waving madly! Your control room length is exactly twice the height: 3.5m high, 7m long. In other words, all the second-order axial modes in the vertical axis will line up perfectly with the first order axial modes in the front-back direction. To be even more precise, you'll have a very major issue at 49.2 Hz, which is the 0,0,1 mode (first lengthwise axial), and also the 2,0,0 mode (second height axial). Then another major issue at 60.1 Hz, where your 0,1,1 tangential mode perfectly matches your 2,1,0 tangential mode. Then again at 68.9, where your 0,2,0 axial lines up almost spot on with your 2,0,1 axis at 69.6 Hz... Similar at 84.7 Hz, 98.4 Hz, 104.3 Hz, and quite a few others in the low end...

Your iso booth suffers from the same issue: the length is twice the width.

It looks like you are not using a useful room mode calculator, or maybe not reading the results correctly. A good mode calculator should have highlighted those major issues and flagged them in several ways. I'd say you can abandon whatever it was you used, and switch to somethign a bit better. I'd suggest that you use one of these Room Ratio calculators to figure out the best dimensions for your room:

http://www.bobgolds.com/Mode/RoomModes.htm

http://amroc.andymel.eu/

Both of those are very good, and will help you to decide how best to build your room. They give you tons of information that is really useful to help figure out the best dimensions, in addition to just simple mode calculations.

What I do need to check is if the room sizes “change” when I add in absorbers/diffusers and/or soffit mount speakers . Put more simply, do these fixtures detract from the room size?

No. Treatment does not change the room dimensions. At least, not for room mode calculations. It is the hard, solid, massive, rigid, sealed boundary surfaces of the room that you are interested in: the floor, ceiling, walls, doors, and windows. Since modal issues are all in the low frequency end of the spectrum, where wavelengths are very long (much bigger than any device you could hang on the walls or ceiling), the waves don't even really "see" such devices, and only "see" the room boundaries. For example, your 49 Hz modal issue has a wavelength of 7 m, and a half wave of 3.5m, so any object smaller than roughly 7m is pretty much ignored by such a wave, as far as dimensions, wavelength, and frequency changes are concerned. So for all your calculations regarding modal response, use just the room boundaries, and ignore any treatment devices hanging there.

However (and this sounds contradictory and non-intuitive, but is true), for the actual calculations regarding how an device works, and what it does to the sound that hits it, you normal use the surface of the device, not the surface of the wall behind it. So if you want to know what the peak absorption frequency would be for a 10cm thick panel of OC-703 that you have spaced another 15cm away from the wall, you would do your calculations based on the surface of the panel being 25cm away from the wall. At least, you'd do that for the "normally incident sound" (waves that hit it head on, at an angle of 90°). For waves arriving at other angles, you'd have to get into the trig functions to calculate the depth, since the wave would be taking a longer path through the device if it happens to arrive at an angle of 30°, rather than 90°... or 27°.... or 43.8° ... or 81.2° or whatever...

Not trying to scare you! Just pointing out that things can be a little more complicate than they seem at first glance! Much of acoustics is not "logical" or "intuitive" at first glance... until you understand the theory behind it, then it all makes perfect sense. For example, logically you would expect that if you have a wall that is isolating reasonably well but needs improvement, and it has two leaves of mass, then adding a third leaf in the middle should "intuitively" and "logically" make it isolate even better... but of course that isn't necessarily true. It is quite possible that the third leaf could make the isolation substantially worse! Not intuitive... until you understand the power of acoustic resonance. There's lots of stuff like that in acoustics, and it does take a while to get your head around all of it.

Anyway, getting back to the basic question: Just use the dimensions of the room itself (wall face to wall face) when figuring out modal response.

And lastly, if I were to design an RFZ room - splayed walls/not “perfectly” rectangular - do the bolt laws still (mostly) apply?

Yes and no! (Don't you just love the simple, unequivocal, accurate, easy answers to simple acoustic questions??!!!). Yes, Bolt's conclusions still apply to rooms, but no the simplified equations for room mode calculations do not apply. Room mode calculators, such as the two I linked you to above, can only produce valid, accurate answers if the room is perfectly rectangular, consisting of 6 boundary surfaces that are mutually perpendicular and parallel to each other. Ie, four walls, one ceiling, one floor, with 90° angles all around. As soon as you change that, the calculations are no longer accurate. However! (Ahh..... yes... the wonderful clarity of acoustics... where every simple, clear answer has a cloudy, muddy "however" attached to it....) ... if you angle one wall just a tiny amount, say 0.1°, then the effect is infinitesimally small, to tiny to even measure. And if you angle it a bit more, then the effect is still tiny, so the precision of those calculators is still good. It makes sense when you think about it: If we are talking about a wave that is 7 meters long, and you angle a wall by a couple of cm, you only changed things by a tiny fraction of 1%. But if you angle your wall at 45°, obviously that's a much bigger change, and you would totally screw up the calculations: they would not be accurate at all.... However... (yup... even the "howevers" have "howevers" attached to them....) If you only angled a small part of the wall, then you get back to "practically no effect". So lets say you take your 7m wall and decide to angle just the first 10cm at an angle of 45°... well, that would basically do nothing. But if you angled half of the wall at 45°, yes, that's a hell of a change.

So there's no simple "one size fit all" answer to your question.

What you are basically asking is, if you have a room that is not entirely rectangular, are the calculators producing valid results? Compare your room to the closest rectangle: If there are major differences, with large parts of all walls angled at large angles, then no, forget the calculator: it will not be accurate. But if you are only angling some parts of some walls, and the angles aren't too large, then the calculator can still be useful to give you an idea of how the room will behave. And the walls that are NOT angled will still be calculated perfectly. What I mean is, that if you look at a typical RFZ room, you notice that the maybe a third of the side walls is angled inwards at the front of the room, but the rest of the side walls are not: they are still parallel. Therefore, there will still be axial modal stuff going on between the parallel parts, at the frequency predicted by the calculators, but for the angled parts of the wall the frequency will be higher, and the axial modes will have been changed into tangential or oblique modes... so you can assume that the predicted mode will be there, but it will be somewhat "blurred" since only part of the wall is parallel to its companion, and there will also be tangential modes at a slight higher frequency that are NOT predicted by the calculator.... and you can also assume that the calculator will predict the vertical modes perfectly, since the ceiling and floor are still parallel.

Now maybe you can see why I said "Yes and no". It's not as simple as giving you a precise, clear answer.

Rule of thumb: if your room is close to rectangular, then you can get a reasonable impression of how it will be have by using the average dimensions in a standard calculator. It won't be 100% accurate, but as the say "it will be good enough for government work"!

If you go with an RFZ style room, with proper flush mounted speakers in angle modules at the front of the room ("soffit mounts"), then you can still use a mode calculator to get a rough idea, but don't count on it being accurate.

(I just realized that I probably didn't help you much at all with that long waffling reply, and likely left you more confused than when you asked the question! All I can say is ... welcome to the rabbit hole! Don't you wish you had taken the OTHER pill? Maybe you are wishing you had taken up something much simpler as a hobby instead of acoustics, such as rocket science, or deciphering DNA, or brain surgery? )

- Stuart -

Believe it or not this is actually starting to make sense.

For the time being I’ve realised there’s a million different ratios out there but if I keep within the Walker range I’ve got a fairly good chance of a nice sounding room. Interestingly, I had used the bobgolds calculator you suggested and it seemed to give me ok results. but I now realise I was reading it wrong - it gives you such a large list of variables!! I guess that’s the point though, and why control rooms aren’t all the same. I’m currently leaning toward 8*5.2*3.5, but not set.

I’m glad the treatment doesn’t affect the calculations, else things were going to get realllly silly.

It makes sens the live rooms don’t need as careful planning - it didn’t make intuitive sense to me to be mathing them out. Some of the best sounding rooms I’ve played in are really odd shapes. I take it the method here is to go with the space available and treat if necessary / variable treatments.

I guess that’s the point though, and why control rooms aren’t all the same. I’m currently leaning toward 8*5.2*3.5, but not set.

In general, make it as big as you possibly can, in terms of total room volume, even if that means moving slightly away from a "perfect" ratio. There are no perfect ratios anyway, and it's usually better to have more air in the room, as long as that doesn't take you close to a bad ratio.

Some of the best sounding rooms I’ve played in are really odd shapes. I take it the method here is to go with the space available and treat if necessary / variable treatments

Same general rule applies here: Make it as big as you can (air volume), as long as that doesn't mess up something else. Yes, it can have strange angles if that would help to maximize space, but there's no need to angle walls to "improve" the acoustics.


- Stuart -