John Sayers' Recording Studio Design Forum Archive

i'm in the throes of that acoustic learning curve, trying to puddle together as much good advice as possible to build a simple room with decent sound isolation for loud practise, band, and teaching work. i've only been lurking in homerecording.com and here for a couple of weeks, absorbing ideas, so bear with me!

so far one of the major issues appears to be sealing all air gaps on the inner shell of the room, including power outlets, light fittings and especially door seals...

now, after fitting the room with a decommissioned submarine with fibreglass cladding, i wanna breathe!! shall i cut holes in my seal, or get one of those matter transporters from star trek (including, if possible, that girl with the nice legs)??

my plan for ventilation up until this apparent paradox is outlined in the following high-res artwork (not entirely to scale). i managed to find a couple of identical ventilation fans at the local demo yard for the price of a few chocolate bars =) i'll wire them in reverse so that one blows in and the other blows out.
the inlet and outlet vents are of course ducted to the fans above my false ceiling. without too much talk on internal and external ducting insulation (unless this is actually the way you solve the paradox), can anyone comment on how this will affect my stc?

and if i'm gonna cut these two big holes in my room, why do i have to caulk up all the other half-millimetre gaps?

oh i should also mention my basic plan for the ducting was to create an insulated box isolating two sections of each duct. the ducts attach to the box by rubber seals to reduce transmission:
the principle is to do with standing waves in open columns. the wave is pinned by infuriating physics at each end of the duct (i think in open columns it has to be maximum amplitude at the ends). because the box is a completely different shape to the tube the wave cannot pretend that tube + box = longer tube, so it is pinned at the entry and exit points. by making the lengths of tubing and box as unrelated as possible, no standing wave could be set up throughout the system.

any comments on this ducting design, this general posting, or anything at all would be greatly appreciated.

cheers!
geoff

Basically, you need something as you described in order to keep from ruining the performance of your walls and still get ventilation - I've not dug into this too much as yet, there's one "sticky" on cheapo AC that might help a little.

http://www.johnlsayers.com/phpBB2/viewtopic.php?t=644

Also, see here -

http://forum.studiotips.com/viewtopic.p ... fcd287d816

one more -

http://www.recording.org/postt17684.html

Like I said, I'm really close to being a complete moron about HVAC, which is why I'd rather refer you to people like Rod Gervais who actually KNOW what they're talking about... Steve

hippy wrote: the inlet and outlet vents are of course ducted to the fans above my false ceiling. without too much talk on internal and external ducting insulation (unless this is actually the way you solve the paradox), can anyone comment on how this will affect my stc?

Well, to an extent this is how you solve. And it really isn't a paradox.....

If what you are saying is that your actual seperation to the outside world is above your "false ceiling" - and you are then (for all intent and purposes - penetrating your actual room - then you have a problem - but again - it's all relative.

The way this works (in the ideal world) is that the ducting to the outside world is outside of your room envelope - this way what you then need to acheive is attenuation within the duct itself - which is not so very difficult to acheive......... and any relatively small anmount of noise which makes it through the duct sidewalls is then handled by your wall iolslation.

and if i'm gonna cut these two big holes in my room, why do i have to caulk up all the other half-millimetre gaps?

LOL - that's like asking - if I'm gonna put doors (and windows) through the walls of my home (which i then open and close letting outside air in - and thus inside heat out) then why should I bother to insulate?

The answer is this - each and every penetration through an isolated wall will decrease it's isolation rating........ the more you seal up properly the better you are in the end.

The fact that we need to breathe demands that we provide fresh air to rooms - this will happen regardless of the isolation or not - and the amount of degradation of the system will remain the same -

Let's assume (for a moment) that you have a wall assembly rated at 37 STC and you lose a theoretical 15db of isolation due to duct pentrations in that wall (and this is frequency dependant - so don't take 15db to heart - it would not work that way across the board) but because the remaining walls maintain their rating - then the overall loss is really less than the 15db.

But even if it was the 15db - weighted average across the board - you then would have an STC 22 -

If you increase the wall rating by an additional 30 db - then you still gain the additional 30 of isolation.

Thus the over all rating would be still be STC 52.

oh i should also mention my basic plan for the ducting was to create an insulated box isolating two sections of each duct. the ducts attach to the box by rubber seals to reduce transmission:

the principle is to do with standing waves in open columns. the wave is pinned by infuriating physics at each end of the duct (i think in open columns it has to be maximum amplitude at the ends). because the box is a completely different shape to the tube the wave cannot pretend that tube + box = longer tube, so it is pinned at the entry and exit points. by making the lengths of tubing and box as unrelated as possible, no standing wave could be set up throughout the system.

any comments on this ducting design, this general posting, or anything at all would be greatly appreciated.

The only place this matters is at the fans themself - once the fan is isolated from the duct - everything else is just a matter of air.

What is critical is that you maintain the volume you need with minimum velocity. That - and the need to make certain that the duct and fans are installed with isolating hangers so nothing can transmit back to you through structure.

Using either an acoustical duct board (Like John Mansville Super Duct) or an acoustical duct liner will solve your problem.

Just make certain to turn a few 90's along the way - and to use turning vanes in corners so you do not have a problem with sound buffeting in the process.

By the way - in acoustically lined duct you should never have an issue with standing waves - and in a non-lined metal duct - this would be the least of your issues.

Good Luck,

Rod

hehehe, thanks guys!

but i just found the perfect solution!!! equip everyone with scuba tanks before a session.

hummm

yeah it was a bit over the top to call it a paradox.... but to me, acoustics still seems to be largely based on magic.

in line with the air leak thing, i've noticed that people building double-stud walls will also seal the outer wall completely without really saying why.

this is definitely not the case in my room, where two of the outer walls are weatherboard. with enough caulk i suppose i could seal the 20 odd square metres of gaps... or preferably, i could ignore them and just build inwards. what i'm really wondering is if the outer wall affects attenuation as much as the inner wall. stop me now if i'm being an idiot!

actually don't stop me, it's often my nature =)

i'm not going for perfection here, as my funds are limited! if it's only likely to give me 1 extra dB it might not be worth it...

hope this didn't all come out as gobbledegook. it's probably not the best time for me to post this cos i just missed out on several skips full of free 3+ metre lengths of 4x2, which would have seriously reduced my construction costs my brain's reacting by turning into mush.

disappointed scavenger syndrome.....

g