Activated Carbon Stuffing

[kipman725]

Few quick questions about using activated carbon as stuffing to increase apparent box volume:
1. where do you get large amounts of activated carbon?
2. how tightly packed should the enclosure be for a closed aplication?

[speaker dave]

I don't know where you get it but we discussed it in a thread at Classic Speakers

Failed stuffing experiment - The Classic Speaker Pages Discussion Forums

I have some measurement results on the second page. As far as I know it, it is heavily patented and only available to KEF. The stuff(ing) worked and was 3.7 times the compliance of air, but it is harder to fill a cabinet with it than you would think.

Regards,
David

[speakerdoctor]

I am the author of the 'failed stuffing exp.' thread at CSP.

IIRC, there are two types of AC available. I bought the less expensive kind for my trials. KEF probably uses the more expensive kind. I doubt that KEF has any patent on how to mfg. AC, but certainly have the patents on used it in speakers as speakerdave pointed out.

In any case, for the DIY hobbyist who has the money, there shouldn't be any problem.

So, give it a try and let us know how it goes.

[kevinahcc20]

Activated carbon is a highly engineered product (granule/pellet size, pore structure and micropore geometry) designed for a particular application. There are two broad classes, the first is designed to trap and hold (trapped compounds more tightly bound) while the second is designed to be able to be regenerated after loading (trapped compounds more loosely bound) by flowing uncontaminated air across the carbon bed. The largest volume application by far is for municipal water treatment. My experience was in activated carbon used to trap fuel system evaporative hydrocarbon emissions in motor vehicles, where the carbon is loaded with fuel vapors when the vehicle is parked and regenerated when the vehicle is driven. In the U.S. that market represents about 20 million litres of activated carbon sales annually. In my experience MeadWestvaco is by far the most technically competent supplier, but they are unlikely to be able to focus on a niche as small as speaker stuffing.

[speakerdoctor]

Here's one you might want to consider getting to play with. It's packaged similar to the way KEF did it.
What I did was use a small, closed box speaker so I didn't need so much AC. Stuff with FG first, measure Fc then repeat with different amounts of AC whilst measuring Fc each time.
Have fun!

REEF AQUARIUM ACTIVATED CARBON CHARCOAL FILTER MEDIA - eBay (item 150569499776 end time Mar-05-11 14:48:38 PST)

[mayhem13]

All activated carbons aren't the same as pointed out. The higher porosity varieties will cost more but if you can afford it, the highest grades are indeed used in the Reef Aquarium Hobby. I'd be really surpised if there was an appreciable difference over polyfill though considering both media will also consume some physical volume only to give back in the form of heat absorbtion.

[speakerdoctor]

Originally Posted by speakerdoctor

Here's one you might want to consider getting to play with. It's packaged similar to the way KEF did it.
What I did was use a small, closed box speaker so I didn't need so much AC. Stuff with FG first, measure Fc then repeat with different amounts of AC whilst measuring Fc each time.
Have fun!

REEF AQUARIUM ACTIVATED CARBON CHARCOAL FILTER MEDIA - eBay (item 150569499776 end time Mar-05-11 14:48:38 PST)

Incidentally, my rule of thumb for stuffing cabs with fiberglass is use 1 lb per cu. ft of volume. I use Owens Corning Pink stuff like you buy for wall insulation and just strip off the vapor barrier paper.
My belief is the key to FG and AC's good results lies in the total surface area.
FG diameter is around 5 microns. You can do a calculation to see how that compars with AC's 500 sq. meters per gram.

BTW, do you have a copy of KEF's original white paper on ACE? I may still have a copy of it. Let me know if you want one because it's no longer available on their web site.

[Bill F.]

A couple years ago, I was talking with a chemistry PhD friend about using GAC (granular activated carbon) adsorption to increase apparent enclosure volume. I asked him whether polar or non-polar molecules would be more efficiently adsorbed, and IIRC, he said non-polar. Does anyone here have more insight about this?

At the time, I wondered how well sulfur hexafluoride (non-polar, I believe) would be adsorbed onto GAC. I've heard it theorized that the high molecular weight of sulfur hex (lower speed of sound) has its own effect on apparent enclosure volume. It's also inert and its molecular size would make it less prone to leak out of enclosures.

[kipman725]

I have seen Kef's white paper:
http://www.kef.com/resources/whitepapers/ace.pdf

Incidently I have just had a thought, why don't we stuff cabs with sand? it's very good at turning sound into heat...

[kevinahcc20]

Originally Posted by Bill F.

A couple years ago, I was talking with a chemistry PhD friend about using GAC (granular activated carbon) adsorption to increase apparent enclosure volume. I asked him whether polar or non-polar molecules would be more efficiently adsorbed, and IIRC, he said non-polar. Does anyone here have more insight about this?

At the time, I wondered how well sulfur hexafluoride (non-polar, I believe) would be adsorbed onto GAC. I've heard it theorized that the high molecular weight of sulfur hex (lower speed of sound) has its own effect on apparent enclosure volume. It's also inert and its molecular size would make it less prone to leak out of enclosures.

The activated carbons I am familiar with were designed to work primarily with non-polar HCs in gasoline vapor. That said they would readily adsorb either polar or non-polar compounds...the problem was that it was much more difficult to get them to desorb (purge) the polar species, requiring either heating of the carbon bed or many many bed volumes of purge flow and significant time. The polar species in particular in this case were either water or ethanol.