John Sayers' Recording Studio Design Forum Archive

First, I wanted to thank everyone who contributes, and after lurking for 2 years, I'm ready to start building and want to answer some questions first.
Hopefully my drawings will help some others, too.

Here's the deal - basic American basement (5" slab, 8" partial ht conc walls, limited ceiling height - 7' 8"). It's new construction and there is no moisture, luckily. Living space above the studio.

My questions involve the floor and ceiling conditions. I've attached detailed drawings of 3 schemes and the ceiling/floor assemblies are different in each and interchangable. The main questions:

Floor

Scheme A - 1/4" floating Pergo over continuous 1/4" sheet rubber
Scheme B - 1/2" hardwd floor over 3/4" plywd over 1/2 rubber pucks (16" OC)
Scheme C - 1/4" Pergo over 3/4" Ply over 2x4's on 1/2" rubber pucks(16"OC)

Ceiling

Scheme A - 5/8" gyp bd over 1/2" homasote over existing 5/8" gyp bd (existing 19" batt insul)
Scheme B - pull down existing gyp bd and hang 2 layers 5/8" gyp bd on RC1 / add 2" rigid and leave existing 19" batt insul
Scheme C - pull down existing gyp bd and hang 2 layers 5/8" gyp bd on RC1 / add 2" rigid tigh to subfloor and remove existing 19" batt insul

Any advice is much appreciated, and I hope these drawings are useful to some of you.

jpmanis

schemes b and c

Your floor WILL flank noise thru the slab, thru the stemwalls, then thru the framed upper basement walls, rim joists, upper wall frames, wallboard, and re-radiate into any and all living areas - for this reason, "C" will be best (not for headroom, obviously) -

Ceiling - "B" is the winner, put the rigid fiberglass on the bottom so it won't crush the fluffy stuff; if necessary, add more fluffy stuff so you get a bit of compression on the fill; this will help damp the subfloor leaf (including the added gyp inserts, which should have ZERO air space between them and subfloor) and the rigid will rest on the inner bottom leaf for the same function.

If you're concerned with Impact noise reaching you from above, about the only thing that will make much diff is heavy pad and carpet on the floor above.

BTW, welcome to the board; and VERY nice drawings, I'm sure we'll be referring to them as examples from time to time... Steve

Knightfly-

Thanks for the reply.

When you discuss "adding the gyp inserts" are you referring to pulling out all of the existing batt insulation and adding some gyp directly to the subfloor from below? I'd really LOVE to not do that to avoid messing with the ROMEX and pipes running through the joists.

Thanks alot for your help!

John

Yeah, I know it's a PITA - difference is, if your joists are 2x6 then using 2 layers of 5/8 rock on RC will net you about 26 dB TL at 50 hZ - translates to, any low bass over about 80-85 dB will start to become audible upstairs.

Same scenario, but adding the two 5/8 under the subfloor - raises the LF TL from about 26 to around 35, which is VERY noticeable improvement.

It's kinda like, PITA now, or PITA FOREVER - keep in mind though, that any flanking paths have to be taken into consideration or it's all moot... Steve

Steve-

Are those numbers any better or worse any given that the joists are 2x10?Also, any recommendation for the dimension for the airspace between the rigid insulation and the concrete retaining wall? As usual, there is not much room in the space to spare, so every inch counts...

Thanks
John

About the same difference, 25 vs 33 dB @ 50 hZ, gradual rise to STC 58 vs. STC 61 - the 33 dB low end would mean about 90 dB spl in the room before it's audible upstairs, vs. about 82-83 dB for audibility upstairs (both assuming no worse paths, and complete silence upstairs)

HTH... Steve

Thanks Steve.

...and the airspace dimension...?

That was with 2x10's, figuring total air gap of 240mm - but it just dawned on me that I screwed up; I didn't subtract the extra inserts' thickness from the air gap when figuring - new #'s are around 32 dB @50 hZ for inserts, 25 dB without inserts, both based on 2x10 joists and STANDARD house insulation light fill - this would improve a couple of dB with the rigid/standard mix... Steve

I'm sorry, Steve - I was asking about the dimension for the space between the rigid insulation on the WALLS and the existing concrete retaining wall...

Sorry for the confusion.

J

OK, we didn't discuss the walls at all yet; I see potential problems there depending on which plan you use. The solid concrete won't be a problem, especially if it's mostly backed with earth outside - however, above that BOTH of your plans show 3 separate masses instead of just mass-air-mass - this will actually worsen your isolation at lower frequencies. IF you were to use the separate frame version, your best isolation would be gotten by removing the inner gypsum on the original frame above the concrete, and just having the outer sheathing, then lots of insulation, and finally the innermost layers of gypsum. That would actually GAIN isolation in lower ranges, possibly as much as 10-15 dB in some cases.

Doing that would make the concrete and inner double layer of gypsum your mass-air-mass for the lower part of the wall, and the outer sheathing and innermost double layer of gypsum would be your mass-air-mass for the upper half of the wall. The increased distance on the upper half will go quite a ways toward making that part of the wall as good as the bottom half.

If your drawing is to scale, it looks like you have 2x6 outer wall frames with an 8" thick stemwall - if so, the concrete alone will give roughly STC 62, with about 35 dB TL at 50 hZ - when you include the inner double gypsum, leaving a 3" air gap from concrete to wallboard would yield somewhere around STC 83, with TL @ 50 coming in somewhere around 40 dB.

The top half of the wall, keeping those same dimensions, would work out to an air gap of 11 inches (assuming those ARE 2x6's and the concrete is 8" - this would give roughly STC 68, with the TL @ 50 hZ falling at about 36-37 dB -

What this means, is that the entire wall would end up at the worst case which is still pretty good.

If you needed a bit more (right now it looks like drums at 90 dB would just start to be audible right outside the wall, if you build with no mistakes or air leaks allowed) you could use the gypsum that needs to come off the inside of the top framed wall as inserts against the inside surface of the outer sheathing (no air gap between sheathing and gypsum) - that would get you another 3 dB, maybe only 2, at the low end where it's really needed.

If I'm off on dimensions, you could always supply them ... Steve

BTW, the way that wall is drawn you'd need to build the frame and add the two layers of wallboard while the wall is still horizontal on the floor, epoxy impaling clips onto the concrete, etc, impale the insulation, then tip it up and fasten in place -

Steve-

Your assumptions are correct - 8" stem wall with compacted earth behind, and 2x6 studs above.

Now, I'l go read your post for the 10th time to try to understand it...you are a fountain of good info!

Thanks again
John