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MAM Frequency / Resonance Confusion!
Old 11th June 2019
  #1
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MAM Frequency / Resonance Confusion!

Hi.

I'm building a studio and I've been following advice from both Rod's book and John Brandt's youtube videos but I'm running myself around in circles.

I've got a 9" thick brick outer wall (also rendered on the inside) which as I understand it would be pretty good at dealing with low frequencies on it's own. My plan was to build a room inside a room, but as soon as I put an isolated stud wall in front of it though, according to John's videos, I might actually be making the existing wall less effective. I need to have a finish on the walls (can't leave as rendered brick) as well as some insulation (for building code) but I'm short of space in the rooms so can't afford a larger air gap.

My plan was:

1) Wooden stud 20mm from the outer wall filled with fibre glass in the cavity
2) Two layers of 15mm Fire drywall with Green glue in between.

The distance from the outer wall to the inner wall gypsum would be around 160mm in total. Using John's calculator, the resonant frequency of the new wall would be around 27Hz which means that the lowest working frequency would be 38.5Hz.

Does that mean that this stud wall is completely ineffective in dealing with frequencies lower than that and am I also making the outer wall less effective too? I could add another layer of drywall to the stud but I'm still only getting down to a lowest working frequency of 32Hz.

As i said, I can't make the air gap any bigger as I don't have room. Does anyone have any solutions that might help? Don't want to go to all of this trouble and end up with something worse than I started with. Presumably this new construction would help a lot with higher frequencies?


Thanks!

Chris
Old 11th June 2019
  #2
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What are you playing that goes below 38 Hz and why do you think around 25 dB is insufficent issolation at fmam? For low frequencies that is huge.

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Old 11th June 2019
  #3
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Thanks for the quick reply. Good point!

My only concern after watching John's videos was that I might be degrading the low frequency isolation of the brick wall by adding a stud wall so close to it. I've got a neighbour at about 10ft away so just don't want to bother them and also keep out general garden noise (kids playing , mowers etc). I'm writing for Film / TV so not playing drums or anything but there is the occasional sub bass which I don't want annoying them. I monitor around at around 70dB from what I've tested. Is there a way of finding out the amount of low end isolation I need and at what frequency?

I understand that adding the room inside a room construction will help with the higher frequencies so are you saying that construction will probably be ok with the lower end?

Many Thanks!
Old 11th June 2019
  #4
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From what you have written the wall construction will be fine
Old 11th June 2019
  #5
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Thanks. That's really helpful.

Can I ask a couple of other questions if you've got time?

Is there any point in using resilient channel on the walls? The studs will be independent from the outer walls and the ceiling apart from Sway braces to the brick wall. (I'm going to use some of the Mason sway Braces that Rod recommends) I can't have a fully isolated ceiling due to height restrictions so I'm having to use isolation clips / channels from the existing joists. The walls will be in contact with the ceiling but only by backer rod and caulk. I'm on a concrete slab on the ground. Not sure whether I'm already sufficiently isolated?

I've also got a corridor outside the isolated room which needs some kind of wall insulation (again for code) so I'm probably going to use a similar construction to the main room but with only one layer of drywall. It's 1m away from the isolated walls. Is that distance going to effectively going to give me a triple leaf wall or is it far enough away not to matter?

Many Thanks for the advice!
Old 11th June 2019
  #6
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If thete is nocontact rc etc are not required.

That width does not create mam..
Old 11th June 2019
  #7
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OK, great. Thanks for your help!
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