Hi Dave, and Welcome! Sorry I missed your post originally. Better late than never!
10'w x 29'l x 7'h
The area is fine, but the ceiling is very low... There are techniques that might allow you to get a higher ceiling, especially considering that the relationship between your dimensions ("room ratio") is not very hopeful...
and a drop ceiling made up of armstrong acoustic tiles over R-13 filled joists.
Forget the drop ceiling: it has no use in a studio. Acoustic tiles are no use, acoustically (despite the name!) for studios. Fine for offices, shops, schools, etc. but not for studios. Also, if you are measuring your ceiling height up to the tiles, than that is NOT the acoustic height of your room: it's just the visual height. There is definitely a better way of doing that!
The walls are 5/8" sheetrock on metals studs with R13 for the walls along the underground foundation and a new double wall against the existing basement with two layers of sheetrock on the outer walls (5/8" & 1/2"), acoustic sealant, backer rod and R-15 insulation in each wall.
Please show a diagram of that. The explanation is confusing, as it seems that you are describing a 4-leaf wall...
The ceiling may change in the future, but it's what I have for now - but, it will still be low...
What is the height from the concrete floot up toe the bottom of the joists of the floor above? That's the important dimension here.
I’m essentially splitting the room in half using that dual frame wall to create this 29x10x7 room.
That's why you are not getting good isolation! You misunderstood what Rod was saying. You CANNOT isolate a room by building an isolation wall on only one side. This is similar to trying to build an aquarium by only putting glass on one side... A room isolated on only one side will "hold sound" about as well as that fish tank will hold water...
The other reason why you are not getting any isolation, is the ceiling.... Acoustic tiles in a drop ceiling do not isolate! That's not what they are meant for at all...
HVAC is being taken of.
It is? How? HVAC design for studios is a big deal. VERY big. Way bigger than most first-time studio builders think. Please describe in what way it is "is being taken of".
I’ll look up Bob Gold’s info, but there really wasn’t much choice here, unfortunately.
I beg to differ! You say you have a drop ceiling in there, with ordinary acoustic tiles: You also say that this is one room within a much larger room: therefore you have MAJOR options for adjusting the room dimensions, in length, width, and most importantly, in height.
I won't know exactly what until the construction is finished but, I did want to start looking into a way to have better vocal isolation for voiceover, vocal recording and acoustic instrument recording.
It's not clear what the purpose of this room is: You mention both tracking and also mixing, but a room cannot be treated to be good for both. It can either be good for tracking, or it can be good for mixing. And with a very low ceiling, it's never going to be good for tracking, so I'm assuming that the primary purpose of the room is mixing? If so, then it should be designed for mixing, and have the correct acoustic response for mixing (refer to ITU BS.1116-3), and then the treatment devices that give you environment, can also be made "movable" in some sense to modify the acoustics. "Movable" in the sense of being able to be slid, flipped, rotated, opened, closed, or some other such movement, to expose a different type of surface to the room.
Yes, gobos can modify the acoustic response to a certain extent, but if you really do want the room to be somewhat usable for both, then variable treatment on the walls and ceiling would be the best option.
I was thinking of building three large, rolling gobos (4' wide x 6.5' high) to use for this purpose - having the ability to use them for isolation, mostly.
Gobos do not isolate. That's a common misconception of how they work, and what they do. They can be used to reduce the "bleed" between instruments that are being tracked at the same time in the same room, but gobos can't actually isolate instruments from each other.
I was thinking 1x hardware as the external frame, Rockwool AFB or OC 703 (2' x 4' in the top and two "bays" in the bottom making it 4' x 4') and then using a nice sheet of plywood or pallet-type wood across the back for a reflective/absorptive design. I'd mount them on wheels for easy movement and storage.
That's a typical design for a gobo, and it would work fine.
Looking at the site I found a few plans but I was hoping to get some more information before building. If I'm specifically looking to keep low frequency noise (street, air, motors, etc) out of my recordings, :
Not gonna happen! Sorry. You cannot accomplish that with gobos. That's sort of like saying "Umbrellas are good for keeping rain off, so next time I'm swimming in the ocean I'll put four umbrellas around me to stay dry while I swim....". You can see the fallacy, I hope! Yes, umbrellas keep you dry in the rain, because rain is little drops. Yes gobos reduce bleed because bleed is mostly mids and highs. But a gogo will no more block low frequency sound than an umbrella will block a flood. Think in terms of the wavelengths, and you'll understand it better. There's a basic principle of acoustics that says an object can only affect sound waves that are smaller than the dimensions of the object. Your gobos will be 4 feet high, it seems, and thus will have an effect on wavelengths of around 4 feet and smaller, which means about 300 Hz and up. Frequencies lower than that (longer wavelengths) will simply not be affected by the gobo: they will just pass by it as though it wasn't there for wavelengths that are considerably longer, or diffract around the edges for wavelengths of similar length.
In summary, you cannot do what you are wanting to do with gobos. Isolating external sounds is a function of the ROOM, not a function of things inside the room. Your walls, ceiling, windows, doors, and HVAC system must be built specifically to isolate, and in that case should have been designed correctly to isolate the specific problems that you are facing. In other words, the walls should have be tuned correctly to isolate the problematic frequencies, with the MSM frequency of the walls themselves being tuned at least an octave lower than the lowest frequency you need to isolate.
How thick should the gobos be? How many inches of rockwool or oc703 should I be looking to put in to them?
If you want them to isolate low frequency sounds, then that's impossible, so it doesn't matter how think you make them. Even if you made then two feet thick, they still wont isolate, because thickness is not the issue: wavelength is. However, if you want to use them as gobos are typically used in recording studios, then 4" to 6" is common. ie, a 2x4 or 2x6 frame with 3/4" ply or MDF on the "hard" side, and 4" to 6" of insulation on the "soft" side. I have seen thinner gobos too: just an inch of insulation and a half inch of ply.... but they are not very effective.
For the specified uses above, is it preferred to have an air gap within the panel, or should I just build an enclosed wood "cabinet" with wrapped insulation inside?
I already showed that you cannot do what you are hoping to do, so your "specified uses above" is off the table. So that just leaves normal gobos. One of the definitions of "gobo" is that it "GOes BOth" ways, implying that ti has two very different sides: hard and reflective on one side, soft and absorptive on the other. That's the usual way of making a gobo, with many variations. Another method is to make it diffusive on one side, and either reflective or absorptive on the other. That also works, but is more complex to build.
Related to the first question, should I be looking to add diffusion to the top section of the Gobo so that vocals are not too dry?
That depends on which side you have facing the singer's back! It is yet another common misconception that what matters most for a singer is what he "sees" in front of him, as he's facing the mic. Garbage. What matters most is what the MIC sees BEHIND the singer. Typical vocal mics have cardioid or super-cardioid patterns, and are therefore rather insensitive to what happens behind the mic (in the direction the signer is facing). They are designed to have maximum sensitivity TOWARDS the singer (duh!), so what matters to the mic is what the mic "sees" in addition to the singer's voice, and that means also what is behind the singer: that's the most important surface in a vocal booth, or any setup where vocals are being recorded. And since there's not much of the singer's voice going out behind his head and bouncing off that surface BEHIND him, it's clear that the vocals themselves won't be "dry" if that surface is absorptive. What's coming off that surface behind him, is reflected sound that has already bounced around the room a bit: it is ROOM sound, not direct voice sound. So in that sense, you do NOT normally want a highly reflective surface behind the singer: vocal booths commonly have deep absorption back there, or MAYBE some type of diffusion. Diffusers are not common in vocal booths, though, for another reason. Actually, several reasons, among them: diffusers are large, and vocal booths are small: you have to be at least ten feet away from a typical diffuser that is tuned to a useful frequency range, to avoid the temporal artifacts that it creates directly in front of it: diffusers on the wall behind the singer are not diffusing his voice very much: only the reflected reflections of his voice. If you do want to use diffusers for vocals, put them in FRONT of the singer (the direction he is facing), or maybe out to the sides, but not behind him.
Yes, diffusion is a good thing, and can help improve the sound in general, but it has to be placed far enough away from the sound source, and from the mic.
Finally, the typical dry, boxy, dull sound that you often hear on vocals recorded in poorly designed studios, is not due to lack of diffusion: it is due to the small size of the room, mostly, and partly to low ceilings. Small rooms will ALWAYS create a "boxy" sound, and there's nothing that you can do about it: it's a fact of acoustics. So small rooms have to be dead in order to be usable for vocals. Rather dead than "boxy". But setting up a bunch of gobos around a singer to reduce some of the bleed from instruments, is not the same as a small room, so you should not have that problem anyway. Your room is a reasonable size for vocals, and as long as you don't have drums in there, or an instrument cab turned up to 11, there's a chance you can get decent vocals by having the gobos in front of and behind him with their "soft" sides facing him, and the ones to the sides could have either soft or hard sides facing him, as needed. I would not use diffusion on those, unless you can set them up at least ten feet away from him...
This is also the reason why the so-called "reflection filters" that some places want to sell you, to hang on a mic stand in FRONT of the singer, actually have no effect at all! Pure marketing hype, with zero actual use in real life. Total waste of money.
To avoid having to much specular reflection from your gobos, you could curve the plywood slightly, or as Greg suggested, make it perf panel. Or both! Perf panel does give true diffusion, but it can help to break up the hard reflections at high frequencies. Curved panels can be truly diffusive at low frequencies, to a certain extent (especially if the curve is not cylindrical!). The combination of both can work across a wide range.
So, in short: Gobos don't isolate, and won't do what you are hoping they might. Your ROOM is what isolates, not gobos. If the room is not providing enough isolation, and outside sounds are getting into your mics, there's nothing you can do about that inside the room: you would need to modify the walls, ceiling, doors, windows and HVAC system to isolate properly, at the frequencies where you need it. Variable treatment on the walls is the best option, but gobos can also help.
- Stuart -
