Room in room vs deeper diffusion/absorption?

[tibbon]

Building a control room in my basement. I've got thick masonry walls that are 5ft below grade. The inner walls are at minimum 6" thick brick, and some of them being up to 24" thick (although hollow in the middle as that's where the base of a fireplace is).

The room is roughly 13x18x8. Not huge, but not tiny.

Here's the rub, and what I'm trying to balance. Should I aim for sealing up the room, framing an inner leaf from the masonry (which seems to be aiming for lessening sound transmission) or should I frame it a foot out, and then install 12" deep of rock wool, deeper bass traps, deep QR diffusers, etc... in an attempt to better control in-room frequency response?

Doing both layered the same depths is difficult due to it eating into the area of the room too much to fit my gear and make a comfortable space. And of course the final option is to do just a bit of both and keep them shallower.

I am tracking drums in another area of the basement, but with these walls even with the doors open the STC is pretty decent on account of these super thick walls, or decent enough for me. I don't need silence, i just need to be able to EQ a snare drum without mostly hearing the direct source.

More in depth details about my build are in here: http://www.johnlsayers.com/phpBB2/viewtopic.php?t=22756

[gullfo]

as noted in your other thread - make sure your radon extraction is quiet. some heavy doors will likely meet your need to isolation. i would put the framing in the control room at 1" from the wall, 2x4 frame, fill it with 4" 703 insulation and cover with cloth. same on the ceiling. this way your space is very absorptive.

on the front wall, if you need and are experienced with baffle mounted speakers, spend a bit of time on the site reading up on the triangle you will want to set up, and various aspects of construction for the baffle assembly. most incorporate venting (some for passive, lots for powered speakers), and LF trapping.

once you build this space, you'll likely be happy to spend lots of time there. make sure your HVAC plan is developed early in the process. this is going to be your most expensive and critical part of being in a sealed space.

in the drum room - you can do something similar with the treatment - except make it as floor ceiling frames 24" width, 2x4, 4" 703+cloth and leave spaces around them - this acts to balance the room response but also provides a somewhat diffusive effect to reduce slap echoes without killing the liveness. similar on the ceiling.

[tibbon]

Thank you! I was going to have the radon system moved to another room, but when I had the company out they indicated it really was in the most practical place for the house given the roof line and some other factors. But they recommended heavily insulating around it, building it into the front wall, and just making sure that I had some way to readout the manometer from it (which I've figured out a solution for). Their other recommendation was to put it on a smart-switch (I have a lot of home automation), which I'm going to take one step further and have a sensor which simply turn it off when there's a combination of motion in the room plus sound. I don't need it off when I'm just programming or working quietly on headphones, but if I'm in the room making music I want it off. I've got a good radon meter too, so I can ensure that this isn't lowering the capacity for that to work well.

I'm slowly getting through the front wall, and think I have a good plan on that slowly evolving based on posts here.

The HVAC is going to be a mixture of an air exchanger that I'm going to put together, and a ductless mini split.

As to your answer for my main question, ok cool I'm going to run with that you proposed there as my main plan. I'm not going to try to seal the room except at the doors (and using the copious brick), and will aim for making the wall cavity more "open" with a combination of 703 and stretched fabric. Overall the room is going to have a good amount of LF trapping and broadband diffusion as well.

I really want to get this process as close to "right" as possible which has been somewhat stressful, as I'm doing it all entirely by myself. So many details and so much self doubt, so I really appreciate you double checking what's going through my head.

No matter what, it's probably going to sound, look and behave better than any other room I've used though no matter what.

[gullfo]

on the self-doubt thingie - this type of stuff has been done thousands of times now by people all over the globe, so the general formula for success is pretty well established and generally easy to follow. i think most times people get into trouble when there is some fixation of minutia like GFR between 12K and 21K on 100mm vs 120mm and on and on and on. and sometimes it really matters a great deal and other times, it's what you can readily get your hands on and work with.

another thing people tend to do is start building things before they spend a short period of time thinking about it. honestly, it's a lot less costly and stressful to spend time writing down what you're trying to achieve in a room, the issues with the room, and ultimately the engineering device of all time - the napkin or even sketchup.

it's not unusual for me to draft a given model (after i do the as-is template model) 30-40 times until the structures, finishes, and treatments align such that it's buildable and can be documented. but that means when done, i have a high assurance of success for a client (or myself if its a home project).

so skip the self-doubt phase and start more drawing based on the common solutions/components prevalent/available throughout this site and then have people check it out. but i would suggest that too many people weighing in can be problematic as well. hopefully at that point it will be minor tweaks to get to the build phase.

i know you provided you original model and photos - excellent. next up your refined model for review.

[tibbon]

Thank you! I'm working on getting Sketchup working better and doing another round. Will share results soon!

Next question: In my setup, how critical is it that the wood sub floor have the wood & insulation walls sitting on top of it, vs on the concrete directly? I'm guessing it probably doesn't matter?

[gullfo]

if the wood floor will be decoupled from the concrete - effectively some minimal version of a floated floor, then build your walls on that frame. realistically, if the concrete is earth damped, then build on that. polish and seal the concrete. then if you want to add a hardwood floor over that, plywood (for nailing) and the wood floor.

[Waka]

Thank you! I'm working on getting Sketchup working better and doing another round. Will share results soon!

Next question: In my setup, how critical is it that the wood sub floor have the wood & insulation walls sitting on top of it, vs on the concrete directly? I'm guessing it probably doesn't matter?

Hi Tibbon!

Nice to have you with us. A side note. Like Gullfo alluded to, is the wood subfloor you are talking about fixed to the concrete, floating, with damping material underneath, or an engineered board freely resting (possibly on an underlay)?

A wooden floor will generally not effect the sound character of the room if it is directly fixed to the concrete without any air cavities below it, so it can't vibrate freely (which is harder than it sounds). But if it is "floating" it may take out some mid frequency energy. Which are both fine if you are aware of them and design around them.

I did the majority of my room's tests with the unfinished concrete floor, and the mid frequencies were already about right, so I didn't want to take any more energy from there. I opted to go for levelling compound to smooth it off and tiled over the top. I could do this myself, so I didn't need to pay to have it polished. If you go for tiles make sure you don't leave cavities beneath by trying to "level" the floor using the tile adhesive. This floor should reflect the majority of the sound in the room, so you can treat it properly on your walls/ceiling.

Dan