noise attenuator/silencer for Ac system.

[jezzadime]

I have to bring in A/C into the studio I am building. The AC will be hooked up to a large split system that serves the whole floor of the building. My main concern is stopping sound from escaping the studio. I have gone to great lengths sound proofing the room and don't want to shoot myself in the foot with this part of the build.

Does anyone know of any off the shelf silencers that are available? It seems most AC supply stores in Melbourne only make custom built attenuators for my purposes and they are very expensive considering I need a few of them.

If not, it would be great if someone had some basic plans on how to build an effective DIY AC noise attenuator. Is a simple 'z' box stuffed with insulation material the best way to go about this?

Thanks for your help.

[Soundman2020]

Hi " jezzadime". Welcome. Please read the forum rules for posting (click here). You seem to be missing a couple of things!

If not, it would be great if someone had some basic plans on how to build an effective DIY AC noise attenuator. Is a simple 'z' box stuffed with insulation material the best way to go about this?

That's the basic idea, yes, but it's actually quite a bit more complex than that. You need to do some math first, to figure out flow rates, flow volumes, entry and exit duct sizes, insertion loss, static pressure drop, and a few other things, to make sure you are doing it right. We call them "silencer boxes" around here, and the basic principal is that the interior cross section of the silencer is at least twice that of the duct that feeds it, and the transition is sudden (in order to create a sharp impedance mismatch), followed by a series of several "barriers" along the way that force the air to take a long path through the box, with multiple 90° bends along the way, but keeping roughly the same cross section, then finally exiting to either another duct of the same or larger cross section, or exiting directly to a register. Since sound tends to travel in straight lines, it isn't able to follow that twisted path very well, and therefore is greatly attenuated by that, in addition to being attenuated by the impedance mismatch, and to a certain extent by the duct liner.

The box is made of some type of fairly dense material (usually plywood, MDF, or OSB), and is lined on the inside with 1" duct liner, on all surfaces. The surface density of the box should match that of your inner-leaf.

Here are some examples of what people here on the forum have done:

http://www.johnlsayers.com/phpBB2/viewt ... 0&start=45
http://www.johnlsayers.com/phpBB2/viewt ... 9&start=74
http://www.johnlsayers.com/phpBB2/viewt ... 25&start=2
http://www.johnlsayers.com/phpBB2/viewt ... 42&start=5
http://www.johnlsayers.com/phpBB2/viewt ... 61&start=0
http://www.johnlsayers.com/phpBB2/viewt ... 5&start=98
http://www.johnlsayers.com/phpBB2/viewt ... &start=157
http://www.johnlsayers.com/phpBB2/viewt ... =2&t=13821
http://www.johnlsayers.com/phpBB2/viewt ... 8&start=44
http://www.johnlsayers.com/phpBB2/viewt ... 2&start=16



- Stuart -