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
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
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.
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.
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.
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)
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)
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.
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.
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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.
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.
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...
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...
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.
In this application as a volume stuffer it's unclear to me that adsorption can be the prominent mechanism. To the extent that the carbon can adsorb air (N2) it would be in an N2 saturated equilibrium state from exposure to air in the speaker. Adsorption and desorption requires time to transport the thermodynamic energy deposited on adsorption and required to drive desorption through the bulk of the carbon bed. It seems unlkikely to me that these processes can act on the timescale of audio frequencies. More likely it seems is that it is the viscous fluid flow of air into and out of the branchlike volume of the pore structure that accounts for the apparent volume increase.
I don't know how many of you guys are still interested, but I just recently saw a video of an interesting idea for activated carbon for use with a speaker/sub.. Here's a link to their video, it just got posted a couple of days ago..
A.C.E. – Acoustic Fields
It has two videos, one is a repeat of Kef's, but there's another video with another concept, also using Activated Carbon in a box that the speaker cabinet fits inside of. They are prototypes, but still something interesting.
The company is Acoustic Fields. They, from talking to them, make their own Activated Carbon they feel is optimal specifically for low frequency absorption and they have their own way of mfg. the pellets. they also do have patents, but they do more low frequency absorption with diaphragmatic cabinets or build within the wall structure.
I have been in a test room they had set up and I can honestly say, I was floored as to the sound quality of their room treatment products, so I can vouch for their treatment in being quite good. Have had or have been in rooms with other products and materials and none of them came close to the QoS as the AF room did, FWIW. Plus, they work with DIYers which is a plus.
A.C.E. – Acoustic Fields
It has two videos, one is a repeat of Kef's, but there's another video with another concept, also using Activated Carbon in a box that the speaker cabinet fits inside of. They are prototypes, but still something interesting.
The company is Acoustic Fields. They, from talking to them, make their own Activated Carbon they feel is optimal specifically for low frequency absorption and they have their own way of mfg. the pellets. they also do have patents, but they do more low frequency absorption with diaphragmatic cabinets or build within the wall structure.
I have been in a test room they had set up and I can honestly say, I was floored as to the sound quality of their room treatment products, so I can vouch for their treatment in being quite good. Have had or have been in rooms with other products and materials and none of them came close to the QoS as the AF room did, FWIW. Plus, they work with DIYers which is a plus.
Yes, but the AC that is commonly used for water filtration apparently doesn't work as well. That's what AF told me a few years ago, which is why they had to create their own unique pellets and they told me they have a totally unique way of mfg. them. Give them a call, if your interested. They do help DIY'ers for making your own bass traps, wall construction, etc.. I think they sell the AC filters (which they make) separately if you wanted to make your own bass traps, walls using their designs using AC, because they have to create the filters a certain way and with a certain amount per filter. They pack them pretty tightly. But if you're interested, I'd give them a call. I do know how well their bass traps, etc. works from being able to visit a room they had them in. I just thought others would be interested since they just posted a video of cabinets they made as a project they are working on which is kind of sort of similar, but a little twist on the A.C.E. version Kef was doing.
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