Starting A New Basement Mix Room

[thedavidlim]

Hey all,

Moved into a new house and am in process of planning a basement renovation that would include a mix room. There is an existing bedroom down there and some additional space that can be opened up, so I've been reading my @$$ off, especially on this forum, about design and have been blown away by the knowledge and especially encouraged by how much I've already learned about what's wrong with typical "Google advice".

So, I don't want to start with too many preconceived notions about what I'm going to do, or what makes sense, etc. because I keep seeing people do whole Sketch Up mockups with "I angled every wall 4x and made them all out of insulation so they'd be bass traps and have 90db isolation" and then be brought down to earth with experienced advice and physics. I do have thoughts, but more questions than anything.

I'm starting with a room that's 11' 10.5"L x 12'W x 7.5'H (to the bottom of the 6" floor joists for the kitchen above). The walls are all hollow (that I can tell) concrete block with brick on the outside facade (it's a basement but the property angles down so the backside of the house is dugout and looks 2-story from the back) . There's an external door, and an internal door to the rest of the basement, and 2 windows that are double-paned with about 4" of space between them. There is an air vent running into the room that is very quiet (unnoticeable), but no return out of the room. The vent can be re-routed, right now its in the ceiling, but can really do whatever. The entire basement has an open ceiling so I can run HVAC as needed.

Here's a pic of my Sketch Up model:

Studio As-Is.jpg

In the main part of the basement is a staircase, I could knock out the cinder block wall and use the space all the way back to that. This would make the length of the room 20' 3.75", but the back wall (if stairs were to my back) would be framed, as wall as part of the right-hand wall.

Studio Could-Be.jpg

Here are my initial considerations:
1. I do not plan to track in here beyond occasional scratch vocals (just in the room) and guitars, it is 99% just mixing. I do not mix abnormally loud, I shoot for the "standard" 82dB on avg. I will often mix louder to start, upwards of 90-95dB, but the majority of the time I'm at 82dB or lower.
2. As mentioned before, the ceiling is the floor of the kitchen and dining room, so ideally I would like to soundproof these as much as possible within space/budget so as to keep especially low-end (I have a subwoofer) from being a bother upstairs, as well as children jumping and running around from getting down.
3. The stud walls in the basement would border the stairs going up to the living room, and the master bedroom downstairs, so I'd want as much isolation as possible there too.
4. I'm near the airport and planes fly overhead frequently. This isn't too much of a bother for mixing (I can wait), but would like to keep isolation as maxed as possible, within reason.
5. I'd probably prefer to NOT soffit my speakers, unless it will be easy to change the soffit later. I have Mackie HR824mkI monitors now, but would like to continue upgrading.
6. I don't mind covering the windows, but would need to keep the outside door.
7. My budget is $5000.

Questions:
1. I'm learning but still not informed enough about LEDE/RFZ/Etc. rooms to make an informed decision about which I'd be aiming for, is there anything you all would recommend given what I've shared so far? Or what will be influencing factors in deciding, what should I think about?
2. In reading the reference thread, I learned about leafs, and that hollow block counts as 2 leafs, which makes sense, so to build frames with insulation and fabric would I attach the stud frames right to the block, with insulation and fabric on them? Or attach/green glue sheetrock to the block to keep it 2 leafs and increase isolation from outside, and frame on that?
3. What's the best way to soundproof the ceiling and the stud walls in back of room?
4. What else do I need to be thinking about?

Thanks all, and I really appreciate all that you are doing on this forum!!

- David

[Soundman2020]

Hi David, and Welcome!

especially encouraged by how much I've already learned about what's wrong with typical "Google advice".

Spot on! And at about the same danger level, is "YouTube Advice". Also beware of that....

I keep seeing people do whole Sketch Up mockups with "I angled every wall 4x and made them all out of insulation so they'd be bass traps and have 90db isolation"

How true! Good one!

I'm starting with a room that's 11' 10.5"L x 12'W x 7.5'H (to the bottom of the 6" floor joists for the kitchen above).

On the small side, yes. And the ceiling is low.... But you already knew that, I'm sure.

The walls are all hollow (that I can tell) concrete block with brick on the outside facade

That's a good start.

In the main part of the basement is a staircase, I could knock out the cinder block wall and use the space all the way back to that.

Are you sure? Better check that the wall is not load-bearing (structural) before you take a hammer to it! Get a structural engineer in to check that for you. You might need to do some things to mitigate taking it out.

This would make the length of the room 20' 3.75",

Much better! That gives you around 240 ft2, which is a nice size for a control room. The ceiling is still low, though.... so that's going to be the part that needs a lot of your attention, in order to keep your final inner-leaf ceiling as high as possible.

5. I'd probably prefer to NOT soffit my speakers, unless it will be easy to change the soffit later.

It can be done. Take a look at this thread: http://www.johnlsayers.com/phpBB2/viewt ... =2&t=20471 I originally designed the soffits for some old Genelec speakers that the owner had, but with the same provision you bring up: he wanted to be able to swap them out for any other speaker in the future. So I designed the soffits to have the speaker mounted in a sort of "tray" module that could be slid out easily, then a new module slid in. I made the tray modules large enough that they could accommodate much larger speakers, and that pretty much any speaker could be used, and still have the correct geometry for the mix position. Before long, the owner decided to replace his old speakers with news, that are very different. So he built new trays for the speakers, then one day simply slid out the old modules, slid in the new ones, and carried on working.

1. I'm learning but still not informed enough about LEDE/RFZ/Etc. rooms to make an informed decision about which I'd be aiming for, is there anything you all would recommend given what I've shared so far? Or what will be influencing factors in deciding, what should I think about?

LEDE is pretty much dead. Or rather, the original LEDE concept is dead. RFZ is an extension of that, and there are other extensions that some people still call LEDE, but really aren't. The LEDE concept was that the front of the room should be dead and the rear live, so you'd get initial "clean" sound followed by a reverberate field. It was found to be uncomfortable to work in for long periods, was overly dead, and sounded unnatural. RFZ is an extension, in the sense that it achieves the same goals by different means. Instead of making the front dead (extremely absorptive) it is made extremely reflective, but with the reflections forced to follow a path that leaves the mix position totally clear of all first-order reflections. All of that energy is directed away from the mix position, towards the rear of the room where is both absorbed partially and diffused partially. The goal is that, for the first 20ms or so after the direct sound reaches your ears, there are no reflections at all. Then after that 20ms "window" has passed, you start hearing the diffuse field coming back at you from the rear of the room, but starting at -20dB with reference to the direct sound, then it fades out smoothly and evenly, to nothing at all. That "20-20" criteria is the key: no early reflections in 20ms, then a diffuse field at -20 dB. The final decay happens the same across the entire spectrum, and at a rate that is calculated according to the size of the room, so it sounds "natural".

In my opinion, it's the absolute best design concept out there. Almost all of the rooms I design are based around this concept, with variations as dictated by reality.

2. In reading the reference thread, I learned about leafs, and that hollow block counts as 2 leafs,

Yes..... sort of! It is fully coupled two-leaf, and in reality you can think of it more like one leaf with unusual resonant characteristics (due to the hollow cavities inside). But it does not behave much like a true 2-leaf wall.

so to build frames with insulation and fabric would I attach the stud frames right to the block, with insulation and fabric on them?

Assuming you don't want isolation, yes! But if you DO want isolation, then just pretend that your concrete block wall is single-leaf, and build a second inner-leaf inside that, in the usual manner: stud framing spaced a short distance from the block wall, with sheathing (drywall) on only ONE side, and insulation in the cavity. Tune as necessary to get the isolation level you need.

Or attach/green glue sheetrock to the block to keep it 2 leafs and increase isolation from outside, and frame on that?

I would not do that, no.

3. What's the best way to soundproof the ceiling and the stud walls in back of room?

Treat that framing you show in your model as a continuation of the outer leaf, creating the complete "shell" that you need around you, then build the inner-leaf walls within that then put the inner-leaf ceiling on top of those inner leaf walls.

4. What else do I need to be thinking about?

At a rough guess, about 74,328 other things, all of which are critical...

Some of those would be (in no specific order):

- Room dimensions (room ratio)
- Room layout (where to put the most important stuff that you absolutely must have in the room)
- Room geometry (where to put the speakers and the mix position)
- Doors and window location (if there is a window). Must not interfere with treatment or acoustics, but must still be logical, useful locations that optimize traffic flow, ease of access, etc.
- Soffits (highly recommended).
- Design goals
- Isolation level
- HVAC
- Etc.

That should get you started on the right track.


- Stuart -

[thedavidlim]

Thanks Stuart!

I think I forgot to mention (and didn't think about) the outside of the hollow block wall being covered by brick, so the actual external walls are very thick, 12" (8" block and 4" of mortar/brick). Isolation is good, I'm getting a meter to actually check how much though.

At a rough guess, about 74,328 other things, all of which are critical...

Some of those would be (in no specific order):

- Room dimensions (room ratio)
- Room layout (where to put the most important stuff that you absolutely must have in the room)
- Room geometry (where to put the speakers and the mix position)
- Doors and window location (if there is a window). Must not interfere with treatment or acoustics, but must still be logical, useful locations that optimize traffic flow, ease of access, etc.
- Soffits (highly recommended).
- Design goals
- Isolation level
- HVAC

- Design Goals: I want to make a room in my basement into an accurate listening and mixing environment, with some isolation from my kitchen above and bedroom behind. I don't need to track anything, only mix with occasional voice-over or vocal dubs. I'm not working full-time as a mix engineer but am looking to grow that business. I know the space isn't large enough or suitable to ever be a "world-class" space, and that's ok with me, (by the time I'm working at that level I'd rather not be in my basement) but I want to get the best I can out of what I have instead of just winging it completely.

- Room Dimensions - Right now, the room is 20' 3" x 12' by 7' 6". If I build inner walls, to isolate further, it'll obviously be smaller, but I'll get into the Bolt area, according to the Amroc room calculator. If leave a 4" gap and use .5" drywall then I end up with about 18' 10 1/2" x 10' 9" x ~7' (depending on how I do the ceiling). This does take me below the ideal 220sf though.

- Room Geometry - This is the thought. Soffit's are just thrown on for the sake of showing the idea, not calculated or placed, etc.

Studio Could-Be 3.png

- Isolation Goal - measuring tomorrow, but probably 40-50dB. As I originally posted, I mix at avg 82-85, with a subwoofer. I'm more concerned with music going up through the ceiling to the kitchen and through the wall to the bedroom than the other way around.

- HVAC - Hands are more tied here. It will probably come into the room above and to the right of my proposed mix position, in the corner. I am still exploring how to do the return though.

But if you DO want isolation, then just pretend that your concrete block wall is single-leaf, and build a second inner-leaf inside that, in the usual manner: stud framing spaced a short distance from the block wall, with sheathing (drywall) on only ONE side, and insulation in the cavity. Tune as necessary to get the isolation level you need.

When you say "a short distance", where do you typically start? Is there a minimum in order to be effective? Or, maybe a better question, what would I use/where would I go to calculate what that gap should be? Followup is, would you build the wall "inside out"?

---
The isolation I'm most concerned with are the 2 interior walls that will separate the mix room from the bedroom and stairs, and then the ceiling, which separates me from the kitchen. Obviously my ceiling height is already limited, with the bottoms of the joists at 7'6", so there isn't a lot of wiggle room. That said, would there be a big disadvantage to insulating between joists and then hanging a couple sheets of drywall on RC from the joists, versus framing an inner ceiling on top of inner walls? With even an inch air gap, 3.5" joists, then 1/2" drywall I'd lose ~5", and if double-drywall my ceiling would sit at ~7', that's why I'm asking. If I hung drywall on RC from the existing joists I'd keep the ceiling up around 7'4" or so. Already low, but then if I hung a cloud it might not be touching my head

---
I've been reading all afternoon about soffit design, is there a minimum depth that is ideal? I sketched out a thought using John's soffit, and using a couple things I saw you say in other threads (at least 4' wide, speakers not centered), but they aren't very deep. I also saw a couple places where you mentioned you favor a different design than he does, what do you like?

---
My room is rectangular, and so are the inner walls I've sketched as of now. I see other designs on this forum with some angles, but I don't want to throw an angle in arbitrarily. Would it be better in my situation to keep the walls rectangular and treat them? Or calculate (how?) and frame in the angles to start?

---
What kind of treatment would you recommend? I don't think I want the room as dead as possibly, but am not sure how to start planning trapping and other treatment, outside of first reflection absorption.

I'll quit now, thanks for all the help!

[Gregwor]

I'll try to answer with my limited knowledge, and I'm sure one of the pros can tell us where I'm wrong.

I am still exploring how to do the return though.

Did you consider the size and placement of the silencer boxes? I ended up having to fit my return silencers inside of my inner leaf in somewhat of a bulkhead design. Remember, you need a silencer for each leaf, and for both the supply and return. That = 4 per room.

what would I use/where would I go to calculate what that gap should be?

I just made a calculator to figure out that exact problem. Here's the thread:

http://www.johnlsayers.com/phpBB2/viewt ... =3&t=21373

You'll just need some info regarding the surface density of your outer leaf. From there, you can enter different amounts of drywall and gap.

would there be a big disadvantage to insulating between joists and then hanging a couple sheets of drywall on RC from the joists

First off, it won't provide as much isolation as a true two leaf system. Secondly, RC is only rated to hold a certain amount of weight. So hanging a cloud off of it may be an impossible feat. The only real disadvantage of going the two leaf route is the fact that you probably won't be able to use JUST 2x4's for your ceiling framing. You should check with a structural engineer to find out the minimum type of material to use and build a skeleton type of frame in which you will install your inside out modules. This will probably end up being some sort of rim board/LVL type wood. Either way, it is the best solution. Yes, visually, you may have what seems to be a lower ceiling, but acoustically, it will be as high as if you used RC. The ceiling joists can be filled with insulation and covered with fabric so that pretty much acts as a cloud. You may want to have an angled front portion of your ceiling to create that RFZ room, but that will be from your critical listening distance to the front of the room, not really affecting the height under where you walk/stand. So don't let that sway your opinion of what is proposed here.

soffit design, is there a minimum depth that is ideal?

I remember searching for days, literally, to find the answer to this. I never did find a written answer, but it did solve itself once I started ray tracing my RFZ room. Basically, to have my head at the ideal 38% point in the length of the room, in order to have the sphere area around my head only have the direct sounds hit it, I had to slide my entire front acoustic walls of my room into the room a bit. Ultimately, THAT is where your soffit walls need to live. Having some space between your inner leaf drywall and the front of your soffit walls is ideal purely so that you can get effective bass trapping with hangers on the lower portion of them. Your room will get smaller and smaller feeling (because of this and a deep rear treatment wall), but ultimately, who cares because you're not going to be playing dodge ball in there, you're going to be sitting in your chair mixing!

soffit, and using a couple things I saw you say in other threads (at least 4' wide, speakers not centered), but they aren't very deep

From me digging around for countless hours, I came across some instructions that say to have your speakers situated ~ 28% of the room width away from the inner leaf side walls. 25% is BAD as that will land your speaker within frequency null point. Also, don't put your speakers on the 45 degree line from the corner. Your soffit wall should be ~ 30 degrees. Between 25 and 35 degrees will work well.

I also saw a couple places where you mentioned you favor a different design than he does, what do you like?

The difference between John and Stuarts flush mounting designs is that John mounts his speakers very solidly into the wall structure. Stuart likes to "float" his speakers so to speak. He has a proprietary design that he has never shared to the public. As far as I've seen in his designs though (and I'm taking a wild guess here, so don't even let this next part enter your brain), is that he rigidly mounts the speaker into a box. Then, he sets that box on top of some sort of sorbothane type material. Since each speaker/box combination will be different weights, and it's probably impossible to have a specific type of rubber material made, he pre-loads the material using a threaded type system (in layman's terms, picture a long bolt with a washer and a nut on top mounted on each side of the box. Crank that nut down until the rubber is squashed. Of course, this entire system is damped by more sorbothane at all connection points.

My room is rectangular, and so are the inner walls I've sketched as of now. I see other designs on this forum with some angles, but I don't want to throw an angle in arbitrarily. Would it be better in my situation to keep the walls rectangular and treat them? Or calculate (how?) and frame in the angles to start?

The best thing you can do in your room is to flush/soffit mount you speakers. In order to totally utilize that design, you should go for an RFZ style control room. With that comes angled walls. Your rectangular drywalled inner leaf is awesome (keep it rectangular because then you can use websites like Bob Golds and the Amroc one to calculate how your room will perform). In order to calculate the angles of your walls:
- set your soffit walls to the average/recommended 30 degrees. Make them as big as possible.
- the wall in between the soffit walls, in front of you, will be straight.
- the "soffit wing" or "partial" wall angles between the soffits and your side walls can really only be determined by ray tracing.
- the side walls can be whatever works out with your ray tracing, treatment needs, what works with doors/windows/furniture, and visually makes your room sexy.
- the rear wall is the same as your side walls. Typically, you want to utilize this rear wall for bass treatment, so it should be at least 20" thick and maybe even have the corners of it angled to make it even deeper there!
- your ceiling/cloud, like the side and rear walls can only be determined through ray tracing.

What kind of treatment would you recommend?

- I'm still learning this part, but from what I've read, you want your front, soffit, and soffit wing walls to be very rigid/dense. They deflect the sound from your speakers away from your head. They become extensions of your speaker baffles. The lower portions of these walls can be open and used for bass trapping (hangers in the front and soffit walls), and the soffit wings can be whatever... let's say slat resonators or broad band absorption.
- The side walls, from what I've seen, are either broad band and/or tuned helmholz type slat resonator walls.
- The rear walls typically seem to filled with hangers and used purely as bass trapping. Problematic modes (where two modes line up really close together - you can find out from the room mode calculator sites) can be treated on this rear wall too... look at lots of John's designs where he has a triangular type slat wall in the middle of the rear wall. Often you want to keep some high end from being sucked away, so you can add some more reflective type surface to the corners of the rear wall.
- The ceiling is usually a broadband absorber (because you have a hard floor surface), but the upper side of clouds is a hard material (wood/drywall) which will deflect sound towards the rear wall and become diffuse. Above that hard surface is more bass trapping such as hangers.

The key is to plan ahead as much as possible (which is possible with rectangular rooms) but put up one piece of treatment at a time and take measurements using REW to see what problems still exist so you can make adjustments to the following treatments. Maybe you want to add some plastic to the front of your insulation to give some high end back to the room. Maybe you have a major problem with 92Hz in the middle of your rear wall. Using the helmholtz calculator available on john's recording manual site, you can easily calculate then build appropriate treatment devices to fix these problems.

I don't think I want the room as dead as possibly

You most certainly do not want a super dead sounding room. Balanced/flat should be your goal, and with proper care, you can get a killer sounding room.

I'd recommend following this post. I learned a lot from it so far, and it's on going!

http://www.johnlsayers.com/phpBB2/viewt ... 8&start=30

Greg

[thedavidlim]

Thanks Greg! Everything you said makes sense, and I need to learn more about how to ray trace in SketchUp. Any resources you know of? I'm using the Search here also.

[Gregwor]

The biggest issue I had with ray tracing was that when I drew a line, without making the line a "group" or "component".. which you can't when it's just a line, you can't assign it to a layer. So when you draw another one, it cuts the first one where it crosses it, etc, etc. Nightmare.

So, what I did, was create 1/32" circle, then push/pulled it out making it resemble a cable. Since the circle has many faces, I was able to triple click it, make it a group or component and then assign it to a layer. I labeled my traces like "L35" for left speaker 35 degrees. Or "V20" for vertical 20 degrees. I did them in 5 degree increments. I also did close wall traces on one speaker, and the opposite (throwing towards the center of the room) on the other speaker. It seemed to tidy up the project visually. Also, it gets pretty chaotic, so I'd recommend using layers like I did and hide them once they're done so they're not in your way.

Basically, draw a straight cable as I described (circle, then pull it out), then make it a group or component, assign it to a layer, then use the rotate tool to angle it. Hit a wall, use the protractor to calculate the angle, then draw a new line straight out from that wall, then repeat the above procedure to angle it, etc, etc. Lots of work sadly.

I personally was kind of stuck with my wall angles (due to some crap) and therefore I just drew my traces and they did unfortunately hit my head. I just grabbed my entire front wall/speakers/ray traces and pull them all towards me nearly a foot and all of them now missed my head just perfectly. That may help you determine your wall angles/front wall (or rear wall as I've seen people call it) distance from your inner leaf drywall. Remember, having that extra room between your inner leaf drywall and your front/soffit wall isn't a bad thing as it will provide better bass trapping!

I've enjoyed following your thread so far and look forward to seeing your progress!

Greg

[thedavidlim]

So, I'm continuing to work through this, and having fun. I've been reading this forum like crazy, and also inhaled Rod Gervais' book, and have been referring back to it.

So, questions!

On ceilings:
- Rod recommends loading up the bottom of the subfloor with drywall, in-between joists, then pink insulation, then RC-2 with 2 layers of 5/8" drywall of those. I would need to get a structural engineer to come make sure I could safely hang that much weight, but it would be ideal because I'd only lose 1.75" off my 7'6" ceiling. To hang a ceiling off my inner walls, spanning 12' and carrying weight would require at least 2x8's (according to the span calculator I found) and would put my ceiling very low, inches under 7'. Am I off on these calculations? The other option may be a semi-independent ceiling.
- What would be (or is there) a good way to construct the ceiling to maintain the max height possible, and add ~30dB isolation?


On room dimensions:
- When I'm measuring, if my inner leaf is inside out, would I then measure the room from the inside of the drywall (as opposed to the studs)?
- As of now, if I leave a 1" air gap between leaves, with double 5/8" drywall on the inside, the interior of the room is 18' 11 1/2" x 11' 1/2". With a 7' ceiling those dimensions put me outside of the Bolt area, with some heavy modal overlap at key frequencies, like 60hz, 80hz and 100hz. On the other hand, it maximizes the volume of the room. If I reduce the length by 2 1/2', to 16' 3", my room ratio is good, but would I be better off leaving it long and trying to treat that low end? I'd be putting at least 2' of hangars against the back wall either way.
- When I'm measuring the air gap between leaves, am I measuring between studs? Or drywall? For instance, if I have 2 walls with 1" between the studs, is my air gap actually 8.5" (the gap between drywall), or is it 1"?


On isolation:
- I did some measurements with pink noise and found that when I'm starting at 97C/85A in the room, I get 73C/57A in the kitchen above, and ~65C/50A (lots of outside noise and also readings start to get too low), so existing structure is already giving me about 24dB of isolation. To land in the "quiet" range of 40dB upstairs, I will need to isolate by an additional 25-30dB (40-50dB total). Does this seem realistic?

Alright, I'll leave it there for now. Thanks!

[Soundman2020]

The biggest issue I had with ray tracing was that when I drew a line, without making the line a "group" or "component".. which you can't when it's just a line, you can't assign it to a layer.

You can, actually... Draw each line as two line segments, then make them into a component... Also, select the layer you want them to be on before you start, in the "layers" window.

To hang a ceiling off my inner walls, spanning 12' and carrying weight would require at least 2x8's (according to the span calculator I found) and would put my ceiling very low, inches under 7'. Am I off on these calculations? The other option may be a semi-independent ceiling.
- What would be (or is there) a good way to construct the ceiling to maintain the max height possible, and add ~30dB isolation?

Ahh, but not really... It would put the lower edge of the joists at 7', sure, but the CEILING can still be at the same height it would have been. All you have to do is to build your ceiling "inside-out", just like the walls. That maximizes the acoustic height of your ceiling, which is what really matters. The joists will be lower, yes, but that's only a visual issue.... plus it allows you to use the bays between the joists for acoustic treatment... Win! Win! Win!

- When I'm measuring, if my inner leaf is inside out, would I then measure the room from the inside of the drywall (as opposed to the studs)?

Correct. Measure to the face of the hard, solid, massive, rigid boundary surface of the room, ignoring the studs as if they were not there.

- As of now, if I leave a 1" air gap between leaves

Do you mean that there is only one inch across the cavity inside the wall, form the surface of the outer leaf to the surface of the inner-leaf? Ignoring insulation, studs, and anything else in there? If so, that's too small. The MSM frequency will be too high, and isolation will suffer. You need a gap of at least 4", and you then need to fill that gap with suitable insulation. Even when filled with insulation it is stall considered to be the "air gap", since insulation is mostly air anyway.

If I reduce the length by 2 1/2', to 16' 3", my room ratio is good, but would I be better off leaving it long and trying to treat that low end?

Reducing the length would be a mistake. Maximize volume and treat accordingly. As long as you have no dimensions that are direct multiples of each other, or within 5% of being direct multiples, then you should be OK. There's a couple of numbers that are often thrown out as being the minimum for a high quality "critical listening room": 220, and 4,700. That's 220 square feet of floor area (acoustically speaking), and 4700 cubic feet of room volume. With your current dimensions, you are really close with both of those, but if you make the room any smaller, you get further away. Go for volume.

I'd be putting at least 2' of hangars against the back wall either way.

Right. At least!

- When I'm measuring the air gap between leaves, am I measuring between studs? Or drywall? For instance, if I have 2 walls with 1" between the studs, is my air gap actually 8.5" (the gap between drywall), or is it 1"?

Forget the studs, and the insulation. The "gap" is from face to face across the cavity. That's what the sound waves "see", since they are much larger than any stud, and much deeper than any insulation. It's the hard, solid rigid, massive boundaries that matter. Those are what determine your MSM frequency.

On isolation:
- I did some measurements with pink noise and found that when I'm starting at 97C/85A in the room, I get 73C/57A in the kitchen above

Pink noise is not a good way to measure isolation, since it is basically the same as background noise. Also, dBA is not the correct weighting. Measure using bass-heavy music played through full-range speakers, and measure using "C" weighting, with "Slow" response. "A" weighting completely ignores the low end, which is where all your problems will be. Here's what the two weighting curves look like:

SPL-DB-Weightings--A-and-C--GOOD!!!!.gif

So if you measure with "A", you are NOT measuring all of the low end! Use "C".

so existing structure is already giving me about 24dB of isolation.

Only with "A" weighting! With "C" it will be considerably less.

I will need to isolate by an additional 25-30dB (40-50dB total). Does this seem realistic?

Yes, but use realistic measurements to get there! I would assume that you are likely getting around 20 dB right now (measured using "C"), and if you want 50, then you'll need an additional 30 above and beyond where you are now. In other words, you need to block one thousand times more energy than you are blocking at present. (dB is logarithmic: 30 dB = 10x10x10 intensity, = 1000 times).

- Stuart -

[thedavidlim]

Thanks for the quick reply! I happened to be online, so I'm hitting replying right away... ha.

All you have to do is to build your ceiling "inside-out", just like the walls.

If I start with 7'6", leave a gap (say 1" for ease) then hang 2x8 trusses with 5/8" drywall, how would I be at 7'? Wouldn't I be at max 6' 8 3/8"? Or are you thinking 2x4 trusses? My framing experience has been with other people, not designing the construction myself, so I didn't know if 2x4's could hold up the weight at 24"oc. But I guess that's how walls are...

Do you mean that there is only one inch across the cavity inside the wall, form the surface of the outer leaf to the surface of the inner-leaf?

No, I meant from sill to sill on the floor. That's why I was also asking if I should ignore the studs, which was my hunch and you answered in the affirmative. If I built the walls inside out I'd move the wall to be 4" away from the outer leaf, but for the purpose of my question, 1" was just sill to sill. The ACTUAL air gap in my current design, then, would be 4 1/2".

That leads to a different question. I don't want to overly deaden the room, and it's small, so which walls would I be wise to build inside out, and which should I keep with drywall facing in?

Reducing the length would be a mistake.

Understood. I've seen you advise that before, so thought I should check.

Pink noise is not a good way to measure isolation, since it is basically the same as background noise.

Got it. It's what I use to tune PA systems (I'm a fulltime FOH engineer also), so it's what I'm familiar with, but I mix hip hop, so bass-heavy music in very available

dBA is not the correct weighting. "A" weighting completely ignores the low end

I measured both, because of that. Again, in my other life as an FOH engineer I use both A and C weightings. 99% of venues with dB limits use A weighting, slow response, over x amount of time. Venues with C weighted dB limits are usually protecting their building from me Anyways, I measured (and posted) both measurements because I was interested in ow much isolation I was getting without low end. For the purposes of isolation though, I'm using the C weighting for sure.

Only with "A" weighting! With "C" it will be considerably less.

Actually, on the meter I was using, which granted is not the world's best but is what I had on hand, the numbers I posted were what I was seeing. 24dB less C-weighted, and 28dB less A-weighted. I started with a 12dB difference between the two weightings, but had a 16dB difference upstairs, so high end had 4dB more TL.

In Rod Gervais' book, the double-leaf wall done correctly improved isolation by 27dB, or at least improved STC by 27dB, which I know is not a useable measurement in this case. So then, would I use the spreadsheet "gap" calculator above (from Greg) to figure out estimated isolation gained? Or is there another equation I should be using?

Thanks again, everyone, for all the help. This is already such an inspiring and educating experience that I'm applying to many other engineering gigs!

[Soundman2020]

If I start with 7'6", leave a gap (say 1" for ease) then hang 2x8 trusses with 5/8" drywall, how would I be at 7'?

Like I said: buld the ceiling INSIDE-OUT, just like the walls! In other words, in the scenario you describe, the drywall would be ON TOP of the joists, not below them, so it would still be 1" below the 7 '6" floor joists above you, exactly as it would be if you used clips and hat channel. Think about it...

Or are you thinking 2x4 trusses? My framing experience has been with other people, not designing the construction myself, so I didn't know if 2x4's could hold up the weight at 24"oc. But I guess that's how walls are...

The dimensions of the ceiling jousts (not trusses: this is not a roof), is irrelevant. With an inside-out ceiling, the height of the drywall above he floor would be exactly the same, regardless of how deep the joists are. Even if you used 2x12 joists, the drywall would still be at 7' 5", one inch below the outer-leaf joists above you.

Don't confuse the visual height of the ceiling with the acoustic height of the ceiling....

1" was just sill to sill. The ACTUAL air gap in my current design, then, would be 4 1/2".

That's fine. As long as you have enough mass on each leaf, you should be able to get your MSM low enough to get good isolation.

That leads to a different question. I don't want to overly deaden the room, and it's small, so which walls would I be wise to build inside out, and which should I keep with drywall facing in?

There are two approaches to tuning a control room: one is to start with an extremely live, loudly reverberant room (also hard reflective surfaces, all around) then hang thick absorption panels to get that dulled down to a usable level. The other is to start with a very dead, lifeless room, then add reflective and/or diffusive devices to get that back up to the needed level. I prefer the latter, for a simple reason: it saves space, and is much easier! It saves space because the then that makes the room "dead" takes up zero space inside the room: it is between the studs, and does no project out into the room at all, and the things you need to put on top of it are relatively thin, maybe an inch or so. But of you start with the "over live" approach, then you need to hang absorption to get the decay times down, and that absorption is very thick: many inches. So it sticks out from the walls a lot further, taking up space inside the room.

Refer to Franks' control room tuning thread ( http://www.johnlsayers.com/phpBB2/viewt ... =2&t=21368 ), currently in progress, to see how it is done, starting with the dead room.

Got it. It's what I use to tune PA systems (I'm a fulltime FOH engineer also), so it's what I'm familiar with,

Right, but ringing out the room to adjust the EQ is not what you are doing here! Very different. I'm a live sound guy too: events pretty much every week, so I absolutely get what you are saying, but measuring room isolation is very different from measuring room response, which is basically what you and I are doing when we ring out the room.

99% of venues with dB limits use A weighting, slow response, over x amount of time.

Right. Basically Leq measurement, but by another name. And you can be very glad that they measure "A"! If they measured "C", you'd have to pull the level down by about 10 to 20 dB, then the crowd would complain.... if the limit is 95 dBA, that's about 15 dB louder than a limit of 95 dBC for typical contemporary music with a good bass beat (and about 500000 dB louder for hip-hop! ). The reason venues do that is because "nuisance noise" regulations and laws are almost always specified as dBA, since they were originally written with low-level distant noise in mind, where the "A" weighting is more suited, and "C" weighting would be too sensitive to local sources. But to measure the actual way that human ears perceive loud music, "C" weighting is the correct method.

the double-leaf wall done correctly improved isolation by 27dB, or at least improved STC by 27dB,

Don't get me started on STC!!! It's a terrible system for measuring studio isolation, since it only considers about one third of the total audible spectrum... Improving isolation by 27 dB is not the same as getting an increase of 27 points STC. STC and decibels are not the same thing: only very vaguely related, as long lost distance second cousins in the third generation by a dubious marriage that not even the family recognized as vlaid!

So then, would I use the spreadsheet "gap" calculator above (from Greg) to figure out estimated isolation gained? Or is there another equation I should be using?

Calculate the mass law isolation for each leaf, calculate the MSM resonant frequency, then figure out the isolation in each region. I think that's what Greg's spreadsheet does, but I'm not certain....

- Stuart -

[thedavidlim]

Like I said: build the ceiling INSIDE-OUT

Sorry, I did understand you meant that, I wrote it unclearly. I was thinking the bottom of the joists (not trusses, not even sure why I wrote that?) being really low. But totally get the acoustic ceiling part. And I'll work with that.

Refer to Franks' control room tuning thread

Thanks!

Basically Leq measurement, but by another name

Exactly.

Don't get me started on STC!!!

Hahaha, I've seen your opinions on STC many times now, so had to drop the bait But thanks for the info on figuring isolation. I'll work on all this and post where I'm at tomorrow.

[thedavidlim]

I'm working with the spreadsheet calculator that Greg posted for MSM calculations (http://www.johnlsayers.com/phpBB2/viewt ... =3&t=21373) and have a few questions.

1. My outer leaf is 8" hollow block and 3.5" brick on the outside. In the calculator, would I use 11.5" then for "Depth of Stud 1"?
2. I believe the calculator is adding a double course of 5/8" drywall to that leaf automatically, which I can remove, but where would I find the surface density of the block?
3. F1 is the resonant frequency, but what should I be aiming for here?

[richroyc]

I'm not an expert but I think I may be able to offer some guidance:

but where would I find the surface density of the block?

It may be challenging since there are voids inside the block (hollow not solid) which you may have to calculate, but basically you take the objects weight and divide it by the surface area.

So with a typical 8" x 8" x 16" block that weighs 36 lbs, the surface density would be 40.5 psf (36lbs/.88 sq.ft.) if the blocks are arranged typically (length wise). (197kg/m2)
or 81 psf if you were to stack the blocks the short way making the thickness of the wall bigger (not typical construction). (395 kg/m2)

For your purposes, it's probably safe to assume the hollow block is roughly 1/3 as heavy as a solid block. Maybe assume 60kg/m2?? So the surface density should still be very high compared to the gypsum or any new materials.

F1 is the resonant frequency, but what should I be aiming for here?

My understanding is that you get great isolation at twice the resonant freq. so if you want isolation at 50Hz and above, you would aim to get your resonant freq around 25Hz.

1. My outer leaf is 8" hollow block and 3.5" brick on the outside. In the calculator, would I use 11.5" then for "Depth of Stud 1"?

No. for this you would put 0. The purpose of the stud depth is to determine the air space between leaves. If you have blocks, that is the leaf, and there is no framing or studs, the airspace starts right at the surface of the block. The depth of stud is NOT the thickness of the leaf. the stud is just the framing member that the leaf is fastened to.

1. My outer leaf is 8" hollow block and 3.5" brick on the outside.

this is the one thing that may be a concern, because if these two materials (brick and block) are separated by any airspace or cavity, then it's technically TWO leaves. Adding another inner leaf could possibly make a 3-leaf system. You need to check how the wall is constructed; typical brick over block has a gap that is usually filled with insulation and such but usually not closed cell or in a way that would make the brick and the block one single leaf.

see photo of typical block and brick construction:

01.030.0312 - brik2.jpg

[thedavidlim]

I'll take a look and see if I can figure out the construction. I know there isn't a 2" air gap for sure, the total wall width isn't wide enough for that.

if you want isolation at 50Hz and above, you would aim to get your resonant freq around 25Hz.

I'm a little confused by this. Stuart mentioned in a earlier reply that with a 4.5" air gap I should be able to get MSM low enough to get good isolation, and elsewhere that the block wall with brick was a good leaf. Standard leaf construction seems to be studs with 2x 5/8" drywall on one side, but according to the calculator, and using the surface density you gave for the blocks (which I'm not questioning), I'd need 90" of air gap between leaves to get isolation starting at 50hz! To do that on every leaf would mean the room would have to be enormous, much larger than the minimum 220sf even. With a 4.5" air gap, isolation wouldn't be good until 1kHz?

This seems off to me because most of the designs I've seen on this forum, especially the small rooms that John has done have 4.5" air gaps, and many with block walls and then a "standard" inner leaf, so is he only aiming at great isolation above 1kHz?

Please don't take this as me saying you are wrong, richroyc! I'm just asking questions!

[richroyc]

Please don't take this as me saying you are wrong, richroyc! I'm just asking questions!

Not a problem at all, I'm in the same boat, still figuring all of this out myself, not an expert by any means. I see a lot of similarities between both of our designs/basements so hopefully we can learn from each other.

I'll take a look and see if I can figure out the construction. I know there isn't a 2" air gap for sure, the total wall width isn't wide enough for that.

It may not be 2" but any air gap at all would constitute a 2nd leaf. Definitely something you want to confirm.

Yes..... sort of! It is fully coupled two-leaf, and in reality you can think of it more like one leaf with unusual resonant characteristics (due to the hollow cavities inside). But it does not behave much like a true 2-leaf wall.

this is what Stuart said. I'm not sure if he is aware of the brick on the other side though? But if the brick is tight up to the block with no airspace as you said, then I guess, yes that would be just 1 leaf with the caveats as Stuart mentioned above.

Your results for the MSM calculation should look something like this. this is assuming you are building your stud wall 1" from the face of the existing block.

IMG_9481.JPG

(P.S. I tried 3 times to get this image upright - i give up lol, sorry for the neck strain)

I put in 60 kg/m2 for you block wall.


That gives you 32 Hz as your resonant frequency with good isolation starting at 64 Hz - not too bad yeah?

I'm not sure what the F1 = 481.19 Hz is for ? I'm sure Stuart or Gregwor can tell you. But I'm pretty certain that is NOT the resonant freq. 32 Hz is your number with cavity filled with insulation.