Do I NEED insulation between my foundation and inner leaf?

[ToneAlive]

Hey everyone, I have a bunch of walls already built up aganst the perimeter of the foundation in my basement. These walls will be the inner walls of the front and left side of my control room. I just checked and found out that there is no insulation in the wall cavities. I am planning on treating the room pretty heavily with absorption to get the acoustics right. So my question is how important is it from an acoustical perspective that these walls have insulation in their cavities? Also, will it affect the isolation capability of the room? I don't think it would be too difficult to cut openings in the drywall, fill with insulation, and close back up, but I don't think I want to do it if it will only improve the thermal characteristics of the room.

Thanks in advance!

[Soundman2020]

I just checked and found out that there is no insulation in the wall cavities.

Oooops!

So my question is how important is it from an acoustical perspective that these walls have insulation in their cavities?

depending on how those walls are built, they might act like panel traps, sucking out energy at whatever frequency they happen to be tuned to.

Also, will it affect the isolation capability of the room?

Yes. Once again, it depends on how they are built, but the lack of insulation in the cavity is costing you at least 5 dB, and maybe as much as 16 dB.

So the first thing you should do, is try to figure out how they are built. If they are separate stud frames, not attached to the outer leaf (whatever that is), a decent sized cavity depth (more than 4"), and done with 5/8" drywall on them, then it would be worthwhile putting insulation in, especially if you need good isolation.

On the other hand, if their stud frames are attached to the outer leaf, there's only that small air gap, and they are done with 1/2" or thinner drywall, then there's not much point to them even existing! That aren't doing anything useful for you for isolation or for acoustics.

So first figure out how they are built, and maybe take some photos too, so we can see what you are seeing.


- Stuart -

[ToneAlive]

So the first thing you should do, is try to figure out how they are built. If they are separate stud frames, not attached to the outer leaf (whatever that is), a decent sized cavity depth (more than 4"), and done with 5/8" drywall on them, then it would be worthwhile putting insulation in, especially if you need good isolation.

On the other hand, if their stud frames are attached to the outer leaf, there's only that small air gap, and they are done with 1/2" or thinner drywall, then there's not much point to them even existing! That aren't doing anything useful for you for isolation or for acoustics.

They are up against the poured concrete foundation with probably only the width of the top and bottom plate layed on its wide side (4") between, and I think it IS 1/2" or thinner drywall. And unfortunately, are coupled the floor joists above.

But I DO want the walls there! There is already electrical wired into them, they will be easy to paint, won't have to tear them down, and most importantly, they will be the support from which the ceiling is installed to.

depending on how those walls are built, they might act like panel traps, sucking out energy at whatever frequency they happen to be tuned to.

that would be a good thing; can't have too much trapping right? ..in that case, would they need to be dampened? If so, that would be a good reason to insulate the insides.

So, the question is.. knowing all of that, is it worth it to slice open in between each stud and install inslation??

[Soundman2020]

that would be a good thing; can't have too much trapping right?

.Welllllll.... not really! Panel traps are tuned devices. They are resonant at very specific frequencies. You normally use them as a last resort to treat particularly problematic modes, and you design them specifically for that. Yours are random: You have no idea what frequency they are tuned to, and you have no idea of that just happens to correspond to one of your major modal issues, by shear lucky chance. The chances are overwhelmingly against you that a random device might happen to exactly hit one of your modal issues. It is much more likely that the tuning of your "panel trap" walls will coincide with a frequency that is NOT a problem, thus destroying the EQ for that one, and at the same time your walls WONT treat the problems that really are there!

Yes, bass trapping is a good idea, but we are talking about broadband bass trapping, not tuned bass trapping. Broadband covers a wide range of frequencies, damping all of them but not specifically targeting any of them. Your walls do the opposite...

But I DO want the walls there! There is already electrical wired into them, they will be easy to paint, won't have to tear them down, and most importantly, they will be the support from which the ceiling is installed to. ... So, the question is.. knowing all of that, is it worth it to slice open in between each stud and install inslation??

Well, you don't say how much isolation you need, but assuming that you need a lot, then if that was my room, what I would do is to take off the drywall, seal the wall behind it absolutely air-tight, put resilient channel (or RSIC clips and hat channel) across the studs, put insulation in the cavity, and put a new layer of 5/8" drywall on. If the old drywall is 1/2" or less, I'd trash it, and if it is 5/8" then I'd save it and use it to beef up the sub-floor above you, between the joists. I'd also hang the new ceiling from resilient channel (or clips plus hat channel), since there's no real purpose in using those existing walls, if they are already fully coupled to both the outer leaf and the floor overhead.

But that's just me, assuming that you do need decent isolation and a good sounding room. Others might have different opinions...

- Stuart -