Hi there Dave, and Welcome!
Please read the
forum rules for posting (click here). You seem to be missing something...
My buddy is an architect and he drew up the blueprints;
Please don't take this the wrong way, but is your buddy also a studio designer, or acoustician?
I have no idea how loud I’ll be monitoring, but I will be recording instruments like drums and bass guitar.
Once again, please don't take this the wrong way, but how in hell did you manage to design the studio to the point where you have started building it, without even knowing how loud you are, how quiet the law requires you to be, or how much isolation you need?
Length: 18.55'
Width: 10.55'
Height: 8' and 9.33'
That's a fairly decent size for a small home-studio control room, but as Greg pointed out, you have a problem with your ratio! You should do some research on that, then figure out how to fix it.
Primarily goal in doing this is to aid in tracking drums -
So it's not a control room? It's a tracking room? Where is the control room going to be?
reflections off the ceiling from cymbals would make getting a solid overhead mic sound very difficult with the existing 8' ceiling space, so I figure I can vault it and suspend some 6" traps above where drums will most likely be recorded.
Higher ceiling is pretty much always better for drums, yes. But you might find that 6" of absorption is too much for cymbals: You want to damp the reflections a little, not kill the entire room stone cold dead!
A concern of mine with this is that I’ll end up putting a 2’ span of the ceiling center point that runs that 10’ effectively a multiple of the length (18.55’ w.r.t. 9.33’). Not sure how to tackle this!!
Is it a live room or a control room? Getting a good ratio for a control room is reasonably important, but not very important at all for a live room.
I’m looking at either ATC SCM25a’s, Focal SM9s, or Amphion Two18s. If I go with the ATC SCM25a’s, can I soffit mount them?
Now you are confusing me again! First you had me thinking that this is a control room, but then you mentioned tracking drums so I switched to thinking it must be a live room, but now you are talking about soffit-mounting studio reference monitors, which flips back to it being a control room again! Very confusing... which is it? Control room, or live room? It can't be both.
Anyway: about your monitors: you choose three rather unusual designs! All of them have "features" that make it difficult to do that, such as side porting, and passive radiators on the rear or top. It MIGHT be possible to soffit mount those, but it would be a challenge. All three of those are designed to deal with room issues, and those design features would not be needed if you soffit mount them (except for the SM9), but preventing them from being a problem inside the soffit is another thing. Things start getting complex when there are ports, drivers, or radiators on the side, top, or bottom of the box. If it really does have to be one of those three ONLY, without any other alternative options, probably the Amphions. What amps would you use to drive those? And they are waaaaay beyond your entire budget: each speaker on its own is about what you plan to spend on your entire build... By the time you add in the amp, you'd be eve further out of your budget. So I'm assuming you already own those? The SM9 has the passive radiator on top. That's a challenge, just form the point of view of mounting the thing in a soffit. The radiator is in the way... but it might be possible.. The ATC SCM25a is side-ported: Less of a problem. I would suggest that you take a look at speakers that CAN be soffit mounted without any trouble: Most front-ported, rear-ported, or un-ported speakers can be soffit mounted, as can some that have rear passive radiators.
If no, can I hang them from the ceiling and angle them down at me?
No. Never. Not ever. Well, assuming that this is a CONTROL room that is, and that you are aiming to make usable as such. If it is a control room, then speakers must ALWAYS be mounted with the acoustic axis around 120 cm or so above the floor, not tilted. There are multiple psycho-acoustic reasons and acoustic reasons why it is a bad idea to raise speakers then tilt them down.
And if I DO soffit mount them, should I be looking at more-involved plans with splayed walls?
Not necessarily. It all depends on which of the many design concepts you decided to use for your room, then also how you intend to actually implement it. Some concepts do require angled surfaces in the room, but it does not have to be the entire wall: even with RFC, or CID, you can still build a rectangular room, then just build additional angled surfaces where needed.
I’m reaching the end of my budget for all this and I’m only going to be living here for about 3 or 4 years.
ummmm... not wanting to seem harsh again, but.... you are only just STARTING the build, you don't actually have a design at all, and your budget is already gone? This does not bode well...
Goal is STC 65 or so. STC 75
You ave been severely mislead! STC is a terrible system for measuring recording studio isolation. In fact, it tells you pretty much nothing at all about how well your studio will isolate! I can explain that in detail if you want, but basically forget STC, and only ever talk about decibels, or transmission loss curves, when deciding on how much isolation you need. STC does not even take into account half of the entire musical spectrum! No use at all or judging studio isolation.
STC 75 would be great, but I don't know if I can get there with the vault + windows.
The vaulted ceiling has no impact on isolation, and neither do the windows, provided that you PLAN and DESIGN the isolation system correctly.
Plan is to build in super thick shutters so I don’t have to lose all of my daylight.
That won't work. Sorry. Just plan to keep the windows where they are, but re-build them correctly: IE, with the correct thickness and type of glass for the amount of isolation you need. Yu cannot leave them as they are and still expect decent isolation.
Budget is approximately >$3,500. Could go more, I guess, but ideally would not. Currently about $2,700 deep.
So you have maybe US$ 800 left in your budget, and you have not yet even considered ventilation, electrical, windows, or doors?
As Greg said:
"It appears that you've made the mistake most people do. You started building without consulting this forum" 
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TOTALLY bummed me out, actually!! but not enough to make me give up
That's good! A positive attitude is a really good sign that you can make this work! If you design carefully...
i'd only be able to get up to 50 STC max without removing the old wall!!!
... and once again, STC is no use at all for measuring studio isolation.. Here's why: 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.
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.
has r11 in the walls,
That's wonderful!... for THERMAL insulation, but pretty meaningless for ACOUSTIC isolation...
Then throwing in r13 or r14 in my new wall once I get that situated.
Why did you choose that insulation? What acoustic propitiates does it have that made you choose it for your wall? What coefficeint of absorption does it have for each frequency band, and does that tie in with the MSM resonance that you calculated when you designed your wall?
Floor is not just plywood. It's going to be: joists + insulation > 3/4" plywood > carpet > 7/16" plywood > vinyl hardwood imitator on top at the end. Just laying the plywood over the carpet as a subfloor,
Why? What isolation will that offer? Did you check with a structural engineer to make sure that your floor joists can handle the load? It's just a shed floor, so it likely does not have much spare live-load capacity. You DID check that, right?
Ceiling also has insulation on top of it already. Likely just going to leave that as is.
What type of insulation? What density? IS it suitable for MSM damping?
For treatment, I agree - planned on LEDE principles.
LEDE hasn't been used in decades... That's a very old concept that proved to be uncomfortable to mix in for long sessions, as it sounded unnatural, and fatiguing. Nobody designs pure LEDE rooms these days. Extensions of LEDE and other design concepts are far, far better. Personally, I'm a big an of RFZ.
but place 4" Rockboard hanging 4" from the ceiling as a cloud,
Why 4" Rockboard? What are the acoustic absorption characteristics of that, as compared to the spectrum of sound put out by cymbals and snares? Are you SURE that's the correct stuff for that application?
has an ASTM C423 performance of 1.03 at 125 hz,
Cymbals put out very little energy at 125 Hz... Kicks, toms, and snares do, but not cymbals or high-hats. Also, is that for A mount, or E-405 mount? Yours is neither of those, so the specs you quote are probably not applicable at all.
and the frequency whose wavelength is 9.33' is 105 hz.
Now you lost me! How does that relate in any way at all to the energy spectrum put out by cymbals? I'm not following your logic at all...
so I'll just have to experiment with things to see how I can get the most accurate response in the listening position.
Now you lost me even more! I though the purpose of that 4" rockboard was for the CYMBALS, to help deal with reflections off the ceiling, so what does that have to do with the listening position ???? Unless you plan to put the overhead mics at the mix position, I don't see any connection at all. I guess I must be missing something here...
Also, "experimenting" is a really bad way to approach studio design. If you want the most accurate response in the mix position, then download the ITU BS.1116-3 document, and take a look at chapters 7 and 8, so you can see what you should be aiming for, and how to get it. The room should be designed from the start with that response in mind, the fine tuned to get it once it is built. Here's a thread that shows you how the process of tuning a control room should go:
http://www.johnlsayers.com/phpBB2/viewt ... =2&t=21368 .
I'm mostly just expanding a bit on what Greg already said, adding my voice to his. It seems that you have run a bit ahead of yourself, and gotten beyond where you should be. It would be a good idea to stop right now, re-evaluate your goals, the read a couple of books, such as "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. The first one will give you the background in acoustics that you need to be able to design a studio, and the second one will give you the basics for actually designing it and building it. Once you have read those, then you can sit down and start actually designing your studio properly, and once the design is in place, then you can build it. If you carry on with your current plain, the results will NOT be what you are hoping You will have wasted a lot of time, money, and effort, and the studio won't be usable. I'm really sorry to have to be the bearer of bad news, and I'm sure you did NOT want to hear me say it, but that is the sad truth. The good news is that you are not too far along that it can't be fixed! If you stop now and learn how to do it right, re-resigning it properly, then you can just undo a bit of what you did wrong, then carry on from there.
- Stuart -
It appears that the original walls of the shed have some sort of sheathing on them (plywood? drywall?) and then you have framed up an inner leaf wall.
