Okay, so I'm building some silence cases...

And I need some suggestions/recommendations on the best sound absorber/proofing to use internally. Current the design has a suspended frame inside a sealed plywood (1") case, looking for a treatment to go inside that dead-air space. We'd like at LEAST a 24dB broadband drop with the whole box.

The best STC for the price is where I'm going with this.

I've looked at acoutstic vinyl barrier (also known as mass loaded vinyl barrier), foams, etc. but all I've got is salesmans specs, no real world examples/opinions.

Shout!

W.

duct board?

Any idea on the STC of that stuff?

W.

Is this for a computer? If so, then the ventilation is going to be the real killer. Think heat pipes, and you'll have a winning solution.

For acoustic dampening, there's not much that beats Owens Corning 703 though. I don't buy the hype on that lead loaded vinyl. There's only one real way to stop sound, dead air, and mass. Failing that, adding things like 703 helps to keep resonances down.

Cheers,

Kris

PS: If it is for a computer again, the best solution is to kill noise at the source. Big quiet fans turning slowly....Papst 120mm's running at 7 Volts works quite nicely for me. My PC can barely be heard...even without a case.

It is for computer systems, yes, and the computer is already outfitted with incredibly quiet fans etc., it's just the proximity to the machine that is the main issue. It is, after all, only throwing out about 60-65dB right now...

The ventilation system is automated, with kill switches, etc. to go 'super quiet' when needed, with a visual alarm when temperatures reach critical levels.

Can anyone translate the values at the bottom of this spec sheet into STC for me, or at least explain them as I don't get what they translate to in values respective to dB attenuation?

http://www.owenscorning.com/comminsul/documents/Fiberglas700Series.pdf

W.

look into johns manville too

they make em in 4ft by 2ft bundles of 12

Was looking at them, can't find any STC ratings on 'em though.

W.

Here are some pictures of what I built for my computer.
http://www.avensonaudio.com/isobox

Its mainly MDF with a maze for the air to flow through. I used a 15V-48V variable supply to control the speed of a 48V fan.

What kind of performance do you get out of that?

W.

the stuff you want to use is the vinyl barrier, you want to line the box with a material that has the highest transmission loss coeficcient possible, short of using lead, the vinyl is AMAZING. Two layers of that and you'll be set...

there is a company in mass called sound down, buy it from them, they usually outfit machine rooms on boats and factories, so they dont have their prices adjusted to the pro audio marketplace...

dave

> Can anyone translate the values at the bottom of this spec sheet into STC for me

No. Sound absorption is not the same as sound transmission. "Large" amounts of sound go through fiberglass. If fuzz has 50% absorption, then 50% of the sound is going somewhere else. It may or may not be going through. If 50% goes through, that is sound transmission loss of 6dB, not great. Heavy cardboard can be 10dB, and is a lot nicer to work with.

Absorption is about sound INSIDE the same space as the source.

Transmission is about sound getting OUTSIDE the space with the source.

They have only slight relationship. Mostly the materials that are good for one are not best for the other.

If you need to seal sound inside a box, your first concern is to SEAL ALL HOLES. A small gap or crack leaks more sound than a large panel made of cardboard.

This is a real problem when you also need cooling. To get mass airflow without sound transmission, use ducts, fuzz, and chambers to give the air a long path with room for non-steady flow (sound) to stagnate. A car muffler is an example: in simplest terms, a pipe, a much-bigger pipe (chamber), and a small pipe. Air passes through steady, but pulses expand into the chamber and average-out. The chamber size is related to the lowest frequency it will attenuate. Don't have your inlet and outlet facing each other or highs will shoot right across (car mufflers have baffles to prevent this, and also to give a multi-chamber more-pole low-pass response). A little fuzz in the chamber helps. "Glass Pack" hot-rod mufflers are a single chamber with fuzz lining, take the edge off the high frequency splatt of the exhaust pulses, but pass all the bass and gas-flow. If you don't want the hot-rod sound, a large chamber is better than any fuzz.

After cracks and cooling, you want a heavy wall. For a very small box you also want stiff, but speaker cabinets and room walls are big enough that no practical material makes a big difference, while mass always does. Your cheapest mass for a cabinet is plain old particle board.

Fuzz inside the cabinet is the finishing touch. With a hard interior, rear fan noise will bounce around until it finds the crack you didn't seal well. With fuzz inside, the high frequency noise is weakened before it finds an exit.

Moving the PC to another room (on long wires) is usually more practical than boxing it. The doors between a studio and an adjacent room may already be fairly crack-free, low-leakage. The other room is in effect a very large volume of air, a muffler to average-out the sound before it reaches a crack. A room has enough thermal mass and leakage that you could seal it and a PC would not overheat soon, maybe never.

Biggest issue is of course, space. I only got one room (one room apt.) so moving the machine elsewhere won't do.

I've thought most of this through, got the box (sealed), got the airflow (and some new ideas for better airflow, thanks guys), got the mass and the dead air space, the biggest issue here is what to use for the 'fuzz' internally (what'll work the best without spending several hundred bucks a box?), as we wanna kill them bouncing sound waves.

Soundguy, know anyone in Canada doing the same? Shipping from the US can get, well, crazy after duties, etc..

W.

I agree. If I was faced with the same problem--and luckily I'm not, since I don't record with a computer--I'd put the PC in another room and use a KVM extender.

Key point: no other room

W.

>Soundguy, know anyone in Canada doing the same?
>Shipping from the US can get, well, crazy after duties, etc..

If you are in Montreal area send me a private message. I am not ready yet but will need to find a solution as well as both my PC and my MAgnum's Power Supply are LOUD!

Maybe we can help each other.

jim

Fibre glass and Rockwool

:sad:

I stopped using these for any areas where people could come into contact.

Speaker boxes. air vents and ducts ... near fans etc.
I now use a polyester wool that is often found in pillows and sleep wear and some furniture. Doesn't work quite as well but the company/ and other copiers do have products that try to emulate some of the famous brands and products.

As PRR said, these things are not really about absorption.
Create a barrier with weight and seal the sound in. This does mean that air is now also sealed in and this may give rise to heat issues.

If you must vent then use a long baffled vent that points away from your listening position. The above poly product can help in the vent system.

There are no magic answers to this sort of stuff.

good luck

Get Santa to bring you an equipment room next Christmas.

> what to use for the 'fuzz' internally (what'll work the best without spending several hundred bucks a box?)

"Dead cats" are an old joke. Their fur sucks sound, and "a few more dead cats" in a room never hurt the sound.

Seriously: fiberglass attic insulation, old wool (not poly) blankets and socks, or 7xx-series acoustic fiberglass in medium density half as thick as your free air space.

Attic insulation is not really dense enough to do much in thin layers (and peeling even 3" stuff into thinner layers is itchy business). If you have a foot of free space, 6" or 8" of attic insulation is about as dead as it gets.

I've had very good experiences with wool stuffing in speakers. But these days, to get enough wool to go around a PC, you'd probably have to find WWII east-europe military surplus at clear-out prices, which usually means stink, mold, and moths.

7xx-series fiberglass is available in proper sizes and predictable performance. In bulk it is not overpriced, but getting just a couple sheets from a distributor will cost you, both mark-up and hassle.

Nothing works better than medium density fiberglass. I think wool sounds better in speakers, but I'm probably just hating the feel of fiberglass. Thick layers of low-density insulation work nearly as good as 7xx-panels, and are WAY more available and competitively priced. Insulating a large attic needs a LOT of fiberglass and is going to be significant money; Home Depot, Lowes, and Joe's Lumber all try to under-price each other to get the business, and you benefit even if you just want one roll. (And if you need a half-roll, you or somebody you know has a thin-spot in the attic to put the leftover on.)

Get a mike and headphones. Go over the outside of the box and see where the sound is loudest. (On a recent room-leakage job, I gave my helper an 8 foot tube. Boombox in adjacent room, One end of tube to ear, run the other end over wall ceiling floor joints, outlet plates, heater pipes, to see where the sound was worst. These rooms had cracks above the tops of the walls. We used closed-cell foam pipe-wrap to get the bulk of the gap closed, with canned-foam for ends and around joists.)

if you get the right vinyl mass and overlap your edges and put a lot of attention into getting it into the box right, double the stuff up and you might not even need the wool inside the box, which is really only going to gelp with higher freq. noise anyway. Youd be suprised how well the vinyl works for keeping stuff in.

dave

Bluzzi,

I'm in Alberta, so not very close to Montreal, but I may be making a few of these units in order to keep the cost down, and selling the extra ones off at cost (plus shipping if that's involved).

I'll try and keep you informed.

Been doing some testing on a prototype without any specialized materials or insulation and it's already nixed more than half the volume, so just going for that 'little extra' now.

W.

Has anyone tried removing the PSU to the computer and making it remote? As in hopefully it would allow you to make a more heatproof/soundproof box for the rest of it? Never tried it, but hey...why not?

Bjorn