The Dig Studio Diary (With Questions)

[rockoman]

Hi everyone,
Let me know if you need more details. I've done the best I can with my schematics. My questions will be coloured in blue. Thank you so much for any advice and expertise you may offer. I'm looking forward to learning so much from all of you.

My background
I have been involved with music and home recording for 20 years...got serious about 10 years ago. Since I was the last child at home, my awesome parents let me do whatever I wanted with the empty rooms of my siblings Lets just say I turned half their house into an amateur recording playground. It's where I have been learning recording, producing and mixing for myself and others (at least trying to lol) for the past 10 years. I plan on using this new space (described below) to do the same, although on hopefully on an even more professional level ($$$).

New studio space construction details
What is it? An old garage connected at the end of a shotgun apartment to eventually live in with my family, which I'm also re-modelling. It's in rough-shape but has survived 4 major hurricanes I'm using the outer-shell and re-enforcing as much as possible. It's all wood stud construction. Roughly 16'x22'.
Nearby Obstacles: There is a bathroom directly next to the studio (a foot above grade though my 3D models don't show it) then a bedroom which also shares the same bathroom. The bathroom and studio is separated by a 3 1/2" brick wall. I will have to isolate the bedroom from sound and also 3 neighbour which vary from roughly 50 - 100 feet away. I have marked them in the photos.
Flooring: Sits 1 foot below grade or will once I finish digging. I have 3/4" marine plywood sitting on top of 2x4 triple-braced wood studs sitting a few inches above mud / dirt. I have not encountered any water or moisture issues in the dirt.
Ceiling: Slopes from 9' to 6' towards the rear lengthwise.
Outside Walls: Side facing the alley is plywood and vinyl siding. Other side and rear are just plywood going into another section of attached garage which isn't sealed 100% so it could be considered outside maybe

Intent with the new space
I don't normally do full bands (hard enough to trust just one person let alone 3 or more) but with this bigger space I may explore that avenue in the future if I can, but the majority of my work is I.T.B, track-by-track with a lot of D.I and software sound banks and working with solo artists. I am a big advocate of recording real drums (I am a drummer) so this space will have a live kit setup 99% of the time...would like to get into using and exploring more external gear, amps & effects in the future. Would like to also make it as sound-proof as budget allows - to record late into the night.

List of what I already have, skilset & budget
Already have: Acoustic treatments, Studio furniture, All the tools / equipment needed to build a whole house if I wanted (only costs will be in materials).
Skillset: I do drywall / plastering for a living and have been involved with the building assistance of many DIY house construction projects / additions (mostly as a helper).
Budget: $5k-6k

Progress thus far
It's been 4 months since I started gutting and digging out the space. I had to dig down in order to get any decent ceiling height since extending the roof was out the question.
- Over 10 tons of dirt and broken slab dug thus far, one shovel at a time...by myself with the help of my father every now and then. It's tedious, exhausting work especially being sick all the time but I'm already 3/4 done excavating. Should be wrapping it up this week hopefully!
- 3/4" Marine treated plywood sub-flooring laid on top half the space until I get this other half dug out and framed.
- Reinforced roof with (4) 2x12 beams (doubled each section)

First questions
The subfloor is on top of 2x4x8, 16" apart. Before discovering this forum, I left the cavities open. My immediate concern / question is this:
Should I fill the floor cavities back in with mud /dirt to create mass and prevent resonating instead of leaving them empty? I see so many threads saying fill with sand. Well, I have tons of mud! The reason I did leave them empty was concern with moisture possible affecting the floor some way, but since I haven't encountered seen any issues with moisture, maybe this concern is not valid anymore. I'll get a benefit filling it, correct? Or is it a waste of time / energy? By the way, I will be going with bamboo on top the plywood.

[rockoman]

Got some pictures of progress so far... phew!

[Soundman2020]

Hi there "rockoman", and Welcome!

You probably don't want to hear this, but it seems to me that there are some major issues with what you have done. It looks like you ripped out not just the floor of the old garage, but also part of the foundations, undermining the walls! I see large voids under your sole plates in several places. Also, the slab itself might well have been part of the structural design of the building, or at least it was providing mass and stability. That sounds like a big problem. It might have gone through several hurricanes like that, but I'm not so sure it will survive the next one of you have caused structural damage to the foundations...

I would suggest that before you do anything else, you should call in a qualified structural engineer to look at that, and give you a written report on his findings. He's the only person who can tell you if the building is still safe like that, or not.

Next, I'm confused about why you would dig down 12", then put down 2x4's plus 3/4"plywood, plus a few extra inches, thus losing maybe 8" of your hard-dug depth! Not only that, but those 2x4's don't seem to be treated in any way, and there's no sign of a DPM, or gravel and sand drainage, or footings, so I'd give that floor no more than a couple of years before it start rotting as well as sinking, tilting or warping.

If I was going to go to all that trouble of digging out a foot of dirt, I reckon I'd want to keep every last thou of it for head height, and not waste 8 inches for nothing! I'd do the easy thing: pour a new concrete slab on grade, built properly over a sand base with a DPM. You'd lose a lot less headroom like that, and have a much, much better floor, both acoustically and structurally.

Speaking of floors, the problem with a wooden floor is not just the cavity: it is the wooden floor! Wood on joists is resonant, not damped, and transmits impact sound into the rest of the structure.

Should I fill the floor cavities back in with mud /dirt to create mass and prevent resonating instead of leaving them empty? I see so many threads saying fill with sand.

No, you cannot use mud to fill it! When people speak of "sand filled" floors here, they are talking about putting dry graded river sand in a dry, sealed cavity. The sand must stay dry and loose: that is how it achieves the acoustic damping effect. Mud is nothing at all like sand.

The reason I did leave them empty was concern with moisture possible affecting the floor some way,

It very certainly will, if you leave your floor the way you have it now. Untreated lumber in direct contact with dirt... That's a recipe for disaster, especially considering the warm moist climate where you live.

but since I haven't encountered seen any issues with moisture, maybe this concern is not valid anymore.

Just because you didn't encounter any standing water when you dug does not mean that the ground is dry! Not even close. There is plenty of moisture in it, and it will wick into the wood, causing it to rot.

You also cannot build your inner-leaf walls on top of that, because there is no structural support under it, so you cannot have any isolation ("soundproofing"). You'll be stuck with the isolation you can get from that single-leaf that you have now, which I'm guessing is no more than about 20 decibels or so. Even if you were to finish the interior with drywall, you'd still not get more than about 30-something dB of isolation. Not much use when you have live acoustic drums in there... or a thunderstorm outside...

I'll get a benefit filling it, correct?

No, none at all. And whole new bunch of problems if you did!

Or is it a waste of time / energy?

Yes, that's correct. It would be a waste of both time and energy!

By the way, I will be going with bamboo on top the plywood.

Why?

I also noticed from your diagram that one of the entrances to the studio is through your bedroom and the bathroom??? And you want to do professional recordings of full bands? Maybe it's just me, but if I went to a professional studio and had to go through the owner's bedroom, then his bathroom to get to it, I would probably not be interested in going back again... What happens if I need to go out to my car, but his wife is taking a shower in the bathroom and his baby is sleeping in the bedroom? I would also not be too interested in taking my expensive and carefully looked after musical instruments and electronic gear through a steamy hot damp bathroom, to get into the studio...

I'd seriously re-think your access paths into the studio. When musicians come for a recording session, they want the fastest, simplest, safest path for load-in and load-out. Close off that door. I would never have a bathroom opening directly onto a studio anyway.

Please update your drawings to show the inner-leaf walls and doors, plus the layout that you plan to use, as well as the HVAC and electrical plans. It seems so far that this is going to be a single-room studio? In other words, one room that is both control room and also live room? Please show all the details, so we can check that everything is in order, and provide further suggestions on how to proceed.

- Stuart -

[rockoman]

Stuart,

Thanks for the reply! There was some valuable info gained from your post. My apologies for not being more detailed in my original post.

You probably don't want to hear this, but it seems to me that there are some major issues with what you have done. It looks like you ripped out not just the floor of the old garage, but also part of the foundations, undermining the walls! I see large voids under your sole plates in several places. Also, the slab itself might well have been part of the structural design of the building, or at least it was providing mass and stability. That sounds like a big problem. It might have gone through several hurricanes like that, but I'm not so sure it will survive the next one of you have caused structural damage to the foundations...

No, the slab was already broken up in pieces and wasn't connected to the surrounding foundation at all. It wasn't even a solid slab. It was bits and pieces of slab, mixed with dirt. The outside walls are on the original concrete which I never touched. It looks like it in the photos, but it's not.

Next, I'm confused about why you would dig down 12", then put down 2x4's plus 3/4"plywood, plus a few extra inches, thus losing maybe 8" of your hard-dug depth! Not only that, but those 2x4's don't seem to be treated in any way, and there's no sign of a DPM, or gravel and sand drainage, or footings, so I'd give that floor no more than a couple of years before it start rotting as well as sinking, tilting or warping.

Well, I actually dug down 24". Where the floor sites now is 12" below grade. The original floor was at two different heights so I had to dig down to meet to bottom level. Yes, the 2x4s are treated. I haven't used anything untreated except for a couple boards used as a guide / measuring check. The 2x4s are sitting on top of 4x4 treated lumber which are on top of concrete footings poured below that.

If I was going to go to all that trouble of digging out a foot of dirt, I reckon I'd want to keep every last thou of it for head height, and not waste 8 inches for nothing! I'd do the easy thing: pour a new concrete slab on grade, built properly over a sand base with a DPM. You'd lose a lot less headroom like that, and have a much, much better floor, both acoustically and structurally.

I wish I could, but to pour a slab like that would have been considerably more expensive and time consuming.

Speaking of floors, the problem with a wooden floor is not just the cavity: it is the wooden floor! Wood on joists is resonant, not damped, and transmits impact sound into the rest of the structure.

Considering I have had success mixing in an old home who's room was on Piers, I'd figure I can do the same here. I have been pretty happy with the results I am getting. I definitely am concerned with impact sound but I guess I'll have just have to deal with best I can, like before. This isn't a permanent studio....just something better than where I'm at now which is a smaller room, next to a street, in the middle of a house.

Should I fill the floor cavities back in with mud /dirt to create mass and prevent resonating instead of leaving them empty? I see so many threads saying fill with sand.

No, you cannot use mud to fill it! When people speak of "sand filled" floors here, they are talking about putting dry graded river sand in a dry, sealed cavity. The sand must stay dry and loose: that is how it achieves the acoustic damping effect. Mud is nothing at all like sand.

I understand. That makes sense.

The reason I did leave them empty was concern with moisture possible affecting the floor some way,

It very certainly will, if you leave your floor the way you have it now. Untreated lumber in direct contact with dirt... That's a recipe for disaster, especially considering the warm moist climate where you live.

Treated lumber was used which is currently not in direct contact with the dirt (due to that concern even though it's treated). I guess I will leave it empty.

By the way, I will be going with bamboo on top the plywood.

Why?

I really like it. Water Resistant, easy to maintain, cheap price and durable. I installed bamboo flooring in the current space I am and have been so impressed with it.

I also noticed from your diagram that one of the entrances to the studio is through your bedroom and the bathroom???

No, in my diagram there is a Side door in the studio which opens to an alley. Access would be from that alley. The bathroom would be shared, not an entrance. I need a place for them to use a bathroom without going in my house.

Please update your drawings to show the inner-leaf walls and doors, plus the layout that you plan to use, as well as the HVAC and electrical plans. It seems so far that this is going to be a single-room studio? In other words, one room that is both control room and also live room? Please show all the details, so we can check that everything is in order, and provide further suggestions on how to proceed.

I will do that. HVAC - I was planning on installing a split-system. I have used them with success in the past. Yes, this will be a single room. I will improve the diagrams as I get more practice in using the software. Thanks again for your reply.

-R.

[rockoman]

A better view of subfloor

[Soundman2020]

A better view of subfloor

That lumber does not look treated to me. What type of treatment is it? Not CCA, for sure, and it doesn't seem to be ACQ, SBX, MCQ or MCA either, although it's hard to tell for sure from the photos.

But regardless of the issue of rot, fungus, mold, and insect attacks, what you have there is a thin, light-weight floor over an undamped cavity: it WILL resonate. The fundamental resonant frequency is given by the equation F=60/ (sqrt (m.d)), where m is the surface density of the deck in kg/m2 and d is the depth of the cavity in meters. That is going to resonate at several frequencies in the range of the bass guitar, the low end of keyboards and electric guitars, and probably some drum pieces too.

Considering I have had success mixing in an old home who's room was on Piers, I'd figure I can do the same here.

If you have a resonant floor then you have two problems. First, the floor will transmit and amplify any note that happens to coincide closely with one of its resonant frequencies, and second it will either greatly enhance or greatly attenuate that same note inside the room, and in both cases will do so with "ringing" that lasts beyond the duration of the note itself. Thus, what you hear in the room will NOT be what the music is actually doing. Some notes will be louder than they should be, others will be quieter, and others will be correct. The natural tendency when mixing in such an environment is to compensate for those room problems by adjusting the EQ or dynamics of the "offending" tones, or by adding effects to mask them. The result is that the mix ends up sound decent in that room... but then does NOT sound decent when played in other places. The mix does not "translate". That's a very common issue with home studios that are not built or treated properly. Mixes sound good in that specific studio, but don't sound good elsewhere, since all other locations where they are played do not share the same acoustic faults. The brain is pretty good at picking up on the fact that the sounds it is hearing do not match the acoustic space they are being heard in. It's usually hard to put your finger on exactly what the problem is when listening to such a mix in a different room, but most people notice that it just does not "sound right" or it sounds "strange".

That is what will happen with your mixes unless you design, build and treat the room properly, to get as close as possible to the ITU, EBU, and AES specifications for critical listening rooms.

I guess I will leave it empty.

Normally I would recommend filling that cavity with acoustically suitable insulation, but seeing as there is no DPM, air barrier, moisture barrier, or vapor barrier or any kind anywhere in that floor assembly, I would NOT recommend doing that, as it would just create even more ideal conditions for bugs, insects, rodents, mold, fungus and rot to set in, and could end up slowing down the appearance of those problems on the actual floor. So you would not notice them until it was too late if you put acoustic treatment in there. Better to have an early indicator of the problem on the floor itself, so you can tear it up and fix it fast, rather than have the presentation delayed until there are major structural issues. So yes, leave it empty, as long as you are OK with the room not being up to par acoustically.

There is also the other major issue here that I already mentioned but that you did not comment on: you will NOT be able to build the inner-leaf walls on that flimsy sub-floor, so your isolation (soundproofing) is limited to what can be accomplished with a single leaf, or a coupled two-leaf. I hope your family and neighbors enjoy listening to your sessions!

The only way you can get good isolation at low cost is with a proper two-leaf MSM system, and the only way you can build that is if there is good structural support for the inner leaf. You won't even be able to add any useful mass to the single leaf that you have, due to the structural limitations that are already evident in the photos. So you are pretty much stuck with about the same level of isolation you are getting right now. You won't be able to increase that by more than about 5 to 10 dB, max.

to pour a slab like that would have been considerably more expensive and time consuming.

From someone who has done both: I disagree! It's a piece of cake for a couple of people to do a slab like that by hand in one day, or two days max. Rent a small concrete mixer, get all your materials ready, and work from dawn to dusk. This I can tell you first hand, because I have personally done slabs like that, with just myself and one helper. It is back-breaking, exhausting work, yes, but it's not complicated and not expensive. One guy mans the mixer, loading the bagged dry stuff into it in the correct proportions, adding the right amount of water, running the machine for a few minutes until it well mixed, then dumping it into the form for the other guy to spread and level. Switch jobs a few times during the day, to avoid boredom. Done! It give you a MUCH better floor, both structurally and acoustically, and one that wont rot, or have issues with fungus, mold, insects or rodents. And you can put your bamboo on top, if that's the final finish you want.

Of course, if you call for a load of ready-mix delivered by a mixer truck, then it goes even faster; you can be done in a few hours. You'll need more people, though, to work the concrete before it cures too much, and it will be more expensive like that, but it will be better quality and more uniform than you can achieve by hand mixing. And much faster. I've done a 200 m2 (2100 square feet) floor in a few hours with 20 people like that. Pouring a slab is not as daunting as it sounds, and the result is far superior to a flimsy, resonant, rotting wood base. You would also gain back all of that headroom that you are losing with that wooden patchwork, and studios need headroom. Having a high ceiling is one of the best things you can do to a studio, if you want it to sound good. Recordings done in rooms with low ceilings never sound good, and that applies particularly to drums, as well to acoustic guitars and vocals.

The bathroom would be shared, not an entrance. I need a place for them to use a bathroom without going in my house.

Then put the entrance to the bathroom on the side of the building, so that it does not open directly into the studio. You do NOT want the sudden drastic swings in humidity from opening and closing the door. Humidity affects the tuning and tone of some instruments, and also the tone of some mics. If you don't want problems from instruments and people sounding different as the sessions progresses and humidity changes, then don't expose the room to water vapor. You also do NOT want the sounds and smells from the bathroom getting into the studio during sessions. Running water, toilet flushing, hair-dryer running... you can do without all of those when you are trying to record. Bathrooms are noisy, messy, smelly, moist, nasty places, that have no place at all inside a studio.

I will do that. HVAC - I was planning on installing a split-system.

That's only a small part of HVAC. You still need the ventilation. That implies ducts, silencer boxes, fans, and dampers. They all take up space, and they all breach the isolation system. HVAC needs careful planning.

--

My number one advice here would be to take out that wood floor, bite the bullet, and pour a proper concrete slab. That immediately solves a bunch of the issues you will be facing if you carry on down the current path...


- Stuart -