John Sayers' Recording Studio Design Forum Archive

Ahhh, I was referring to F1, not F0. That makes all the difference

And if the brick DOES make the wall a double leaf already then I can just frame it to hold insulation and not put extra drywall up. Cheaper for me and saves space! Haha.

The density of concrete is around 2400 kg/m3, give or take. Brick is a little less, around 2300. So weigh one block and one brick, and/or measure the thickness of each, and figure out the SURFACE density from that.

As Rich pointed out, blocks are hollow, which adds an unknown factor into the mix, and you might also have an additional cavity in there between them, plus veneer walls usually have solid ties (wire) running between the brick and the block, for structural reasons, to that also adds to the complexity. But you can still get a very rough idea from the math. It's a starting point.

I'd need 90" of air gap between leaves to get isolation starting at 50hz

Then there's something wrong with the calculator, or with the data you are giving it. With my own calculations, assuming that you your wall is equivalent to 4" of concrete, and with a cavity gap of 4.5" (1" framing space plus 2x4 studs), then two layers of 5/8 drywall, with suitable insulation filling the gap, you should be getting an MSM frequency of 27 Hz, and good isolation starting at 54 Hz. Increase the gap to 8", and you get 20 Hz MSM, with isolation starting at around 40 Hz. Your overall isolation would be around 63 dB in that case, theoretically. More like 55-60 in real life.

So there's something wrong with either the calculator you are using, or the data you are using.


- Stuart -

something wrong with either the calculator you are using, or the data you are using

I was reading the number for F1, not F0. What does the F1 number correlate to?

But you can still get a very rough idea from the math

I'd be sorting the surface density and then adding the 2 together, correct? Taking my lead from how the 2x 5/8's are calculated, but thought I'd check.

So there's something wrong with either the calculator you are using, or the data you are using.

I'm 99.9999999999% confident that the calculator is correct.

I was reading the number for F1, not F0. What does the F1 number correlate to?

If you look at the second sheet of the Excel file, you will see the information that really matters.
You'll see that I even labeled what F1 is. It is labeled as "Constant based on wall properties". It is calculated by: F1 = 55/depth of cavity

The reason I say that the second sheet is what matters, is because you will achieve different amounts of isolation at different frequencies. The blue column says that for frequencies lower than your resonant frequency, you will achieve x amount of isolation. As an example, if your resonant frequency (without insulation) is say 50 cycles, than look at the decibels for 50 Hz and less. The pink column says for frequencies between the resonant frequency and F1 (which again is the constant based on the wall properties, and clearly written for you to check out), it will have x amount of isolation. Once you hit the value of F1, the isolation flat lines and will never be higher. Again, this is pretty broad assuming the chart that Stuart posted as it is up and down way more than this math indicates.

If I were more of an Excel wizard, I would figure out a way for the chart to automatically only show the valid data, but for now, just look at the numbers and figure out which fall within the specified range.

I hope I clarified any confusion. Since the values are pretty linear, I only stuck with 1/3rd octave bands which hopefully make looking at the results easier!

Greg

I should maybe use my screenshot to explain it better:

Blue column dB apply to frequencies below 22.9Hz. In probably every situation, we will always use insulation, so that's why I'm using that frequency instead of the 31.9Hz.
So, it's saying at 20Hz we will have 11.6dB of isolation. After that, we look at the second column:
The pink column says that we have to look at the values between 22.9Hz and 166.6Hz. So, at 25Hz, we get 54dB of isolation and it increases up to 160Hz where it says we achieve 70.1dB of isolation. Quite the jump from crappy 11.6dB at 20Hz to pretty awesome isolation at 25Hz of 54dB. Crazy, but I guess that's what the math says!
Then, after F1, which is 166.6Hz, the isolation flat lines at 70.6dB.

If I made the file wrong, I sure hope someone tells me so I can fix it! It is pretty simple math though.

Greg

That’s great! I missed the second sheet, it’s my fault. The only thing I can think of that could be helpful for blind newbies such as myself is throwing those labels on the first sheet (saying what f0 and f1 are) with a reminder to check the second sheet. But your explanation here works for me, especially of f1 and what it means. My confusion before was reading f1 as the resonant freq, having missed the second sheet.

Thanks!

In probably every situation, we will always use insulation,

True, but there's a caveat here: That constant applies to wall cavities that are completely filled with excellent absorption. Many people don't fill their entire cavities, either through ignorance or cost, or some other factor (eg, the gap is 5" but insulation only comes in 2" and 4" thickness....), so it would be good to add some method for allowing for that. In the case of windows, for example, there is no insulation at all in the cavity (until someone manages to invent completely invisible insulation.... ), so you need the option to leave it out. Double-doors also usually have very little insulation in the cavity (if any).

Also, not all insulation is "excellent"! The equation assumes acoustically perfect insulation, and of course in real life there is no such thing.

So if you could add an adjustment factor, that would be great.... however, the relationship is not linear! Half-filling the cavity does not mean that the constant is half way between "empty" and "full". Somewhere I have a graph that shows the relationship, I think... not sure... I'll see if I can find it....

- Stuart -

So I removed some door jambs (to frame in a different part of the basement) and took a couple pics of the block and brick construction. It looks like there is a small gap, no insulation, but a lot of mortar in the gap, attaching the brick to the block.
Should I still count this as one leaf?

Separate question, when I'm filling the space between studs and cavities between walls, is OC703 or mineral wool the best, to get the most density? Or is pink fluffy ok? Or what is recommended?

Should I still count this as one leaf?

Yup, I would call that one leaf.

is OC703 or mineral wool the best, to get the most density?

Myth! Mistake! You do NOT want high density insulation in your wall cavity. High density insulation is only good when you need to treat high frequencies without touching the lows very much. It's a common mistake to assume that, because bass notes are low and loud and "big", you must need dense, heavy insulation to treat them. In actual fact, you need LIGHT insulation to treat low notes, and HEAVY insulation for highs. And it is different for each type of insulation.... To be fully correct, you need the RIGHT insulation for the job. And for the job here, damping wall cavity resonance, you need EITHER mineral wool with a density of around 50 kg/m3, OR fiberglass insulation with a density of around 30 kg/m3.

is OC703 or mineral wool the best, to get the most density? Or is pink fluffy ok? Or what is recommended?

OC703 is the most recommended, usually. What you want is stuff that has a very high coefficient of absorption for the frequencies that will be most prominent INSIDE the wall cavity, and that's your MSM resonant frequency, along with the other resonances that will be going on in there. So anything that is similar to OC703 for low frequency coefficients of absorption would be fine.

- Stuart -

Stuart,

Somewhere I have a graph that shows the relationship, I think... not sure... I'll see if I can find it....

Right now I have the resonant frequency for empty and with insulation included, but you're right, it would be ideal to be able to adjust it accordingly. I could make a user input for the constant. So, if you can find the graph, maybe I can just embed it into the Excel file and people can adjust the constant according to their situation.

Greg

Yup, I would call that one leaf.

Great, thanks!

You do NOT want high density insulation in your wall cavity

Ah, that makes sense, thank you.

anything that is similar to OC703 for low frequency coefficients of absorption would be fine.

I noticed in Rod Gervais' book that he consistently recommends fluffy insulation (like R13 batts? Is that considering fluffy?) in wall and ceiling cavities. In other forums people have asked about mineral wool and 703 and he answers, saying only if you need it to stand up. Obviously 703 is quite a bit more expensive, and that may be ok, I am just interested in how much difference it would make.

Thank you!

Obviously 703 is quite a bit more expensive, and that may be ok, I am just interested in how much difference it would make.

Here's the specs for 703. Compare that to whatever other options you are considering. If you find something that has better properties for a lower price, then use that.


- Stuart -

Alright, so I've been working in Sketchup a bit. Here's what I've got so far. Thoughts? Black rectangle is a sofa, back wall behind it would be cloth covered wall in front of hangars.

Is there enough depth on the soffited wall? How deep does that wall need to be?

I've also been looking at a lot of John's small room designs, and reading back through his construction and acoustics pages. Would slot walls be what I'd want to use on the angled walls?

Those walls are all angled at 12 degrees at the moment.

Is there enough depth on the soffited wall? How deep does that wall need to be?

Deep enough to hold your choice of speakers and box built around them.

Would slot walls be what I'd want to use on the angled walls?

Maybe. The side walls are typically used to tune frequency response as where your front and rear wall have major effect on the time domain response.

Have you done ray tracing yet?

Greg

Well, plans changed completely, as they do, and I'm moving the whole room to a different part of the basement, with a whole different set of questions, although it will be a much simpler build, and 2 of the walls (in the pic they are the right and rear walls as you face the speakers) are below grade, so it's dead quiet in there already.
Dimensions have improved also, but the main service panel for the house is in the back corner, and codes dictate I have 36" of space in front of it, so I'm thinking of putting a hallway right off the stairs, with a door leading into it, and then another door leading into the studio in-between rear wall bass traps.

My first questions are really about that layout. I left the rear stud wall as a single leaf so that the door to the stairs would be the 2nd leaf between studio and upstairs, is that line of thinking correct? I'm not concerned with sound leaking in/out through that cinderblock wall, as almost all of it at that point is below grade, only from leakage through the hallway to upstairs through the doorway.

To reiterate my number from my initial post (and old design), I'll only be mixing in here, not tracking, and not tracking drums even if I do dub something. I don't mix loudly, probably 95dB max, and that's only for short periods of time or with guests. Usual is ~82-85dB, so I'm looking to try and achieve 40-50dB of isolation, that seems ideal to keep the family upstairs only hearing things at 40-50dB.

Next is about the ceiling. I'm in the same situation as before, the bottom of the studs sit at 7' 5", so i really don't want to sit an inside out ceiling sitting on outer studs, since the span would dictate 2x8 joists (right?). My acoustic ceiling would be higher, but my practical ceiling would be well below 7', which i know would bother me and feel even more like a cave than it already will. I would prefer to do a ceiling like Rod Gervais suggests, beefing up subfloor and then hanging 1" of drywall of resilient channel. I know that there is a trade off with isolation with this method, so my question then is: if I beef up between joists with 1.25" of drywall, stuff the space with fluffy insulation, then the RC and 1" of drywall, do I calculate the MSM in the same way, even with ceiling and subfloor not being isolated from each other on the joists? I'm not sure how to calculate in the resilient channel in that equation either. Does that make sense?

Lastly, maybe there's a better way to do the whole thing, and I could even put a door on the left wall if that would be smarter, but since I think I need the space in front of the service panel anyways, it seemed to make sense to put a hallway there and use it as the entrance.

Thoughts?

Thanks!!