Failed stuffing experiment

[Carlspeak]

I recently learned of KEF's ACE (Acoustical Compliance Enhancement)technology when reading about their new flagship speaker system retailing for over $100,000. It appears it's been around for 6-7 years now.

ACE involves the use of activated carbon granules as the stuffing medium. The attached press release and white paper explains why KEF thinks it works.

Basically, KEF claims ACE increases the effective volume of a speaker cabinet way beyond the 15-20 percent normally provided by fiberglass stuffing. They write of 200-300 percent!

Their 2001 white paper contains an example experiment where they took one of their bookshelf speakers and created a similar one, only 42 percent smaller in volume and stuffed 44 percent of that volume with activated carbon granules. Their tests showed essentially no difference in bass response characteristics in the 40-300 Hz range.

Ahah, I thought, perhaps the idea could be applied to improving the bass response of AR speakers. After doing some calculations based on the trial in the prior paragraph, I learned the stuffing density was surprisingly high - something in the range of 14 lbs per cubic foot!

I borrowed a pair of AR4x speakers since they might benefit most and my cost of the activated carbon (AC) wouldn't be too great. The density of AC is around 30 lbs per cu. ft. I found some for sale on ebay and ordered 12 lbs which would be more than enough for trialing one AR4x cabinet.

I bought some highly porous, light weight, heat sealable spunbond ticking material from the local fabric store and made up nine 10X10 inch pillows and filled each with 1 pound of AC. I gradually added 2 pillows at a time to the cabinet (after removing the FG) and measured the Fc after re-installing the woofer - after each 2-pillow addition. To my surprise, there was essentially no change all the way up to a total of 9 pounds added. Cabinet with original 18 oz rock wool had Fc of 68 Hz. With the AC pillows, it ranged form 75-76 hz. Most of the pillows ended up right behind the woofer where I thought they would be most effective. I did this with the speaker laying on its back so the piillows would not all sink to the bottom of the cabinet.

Anybody else here heard of this technology? Ken K. perhaps?

Anybody want to buy 12 lbs of AC?

It's all about the music

Carl

Carl's Custom Loudspeakers

[dynaco_dan]

Hi Carl;

Interesting test, thank you, Carl.

I would be interested in buying some custom pillow cases. LOL

Audio Mar/70 had an article for a common sub woofer add-on for Quads.

The enclosure was 35" high x 17 1/2" wide x 15 1/2" deep.

The stuffing material was loosely packed, pure, long-fibered wool.

The wool, back then, was $3.50 per pound, with 1 pound filling 2.3 cubic feet, with a total of 3 pounds for this enclosure.

A practically non-resonant enclosure, with 84 db output, at 22 hz in a 20' x 40' room.

Perhaps we should not be sheepish about using wool. LOL

[soundminded]

>I recently learned of KEF's ACE (Acoustical Compliance

>Enhancement)technology when reading about their new flagship

>speaker system retailing for over $100,000. It appears it's

>been around for 6-7 years now.

>

>ACE involves the use of activated carbon granules as the

>stuffing medium. The attached press release and white paper

>explains why KEF thinks it works.

>

>Basically, KEF claims ACE increases the effective volume of a

>speaker cabinet way beyond the 15-20 percent normally provided

>by fiberglass stuffing. They write of 200-300 percent!

>

>Their 2001 white paper contains an example experiment where

>they took one of their bookshelf speakers and created a

>similar one, only 42 percent smaller in volume and stuffed 44

>percent of that volume with activated carbon granules. Their

>tests showed essentially no difference in bass response

>characteristics in the 40-300 Hz range.

>

>Ahah, I thought, perhaps the idea could be applied to

>improving the bass response of AR speakers. After doing some

>calculations based on the trial in the prior paragraph, I

>learned the stuffing density was surprisingly high - something

>in the range of 14 lbs per cubic foot!

>

>I borrowed a pair of AR4x speakers since they might benefit

>most and my cost of the activated carbon (AC) wouldn't be too

>great. The density of AC is around 30 lbs per cu. ft. I found

>some for sale on ebay and ordered 12 lbs which would be more

>than enough for trialing one AR4x cabinet.

>

>I bought some highly porous, light weight, heat sealable

>spunbond ticking material from the local fabric store and made

>up nine 10X10 inch pillows and filled each with 1 pound of AC.

>I gradually added 2 pillows at a time to the cabinet (after

>removing the FG) and measured the Fc after re-installing the

>woofer - after each 2-pillow addition. To my surprise, there

>was essentially no change all the way up to a total of 9

>pounds added. Cabinet with original 18 oz rock wool had Fc of

>68 Hz. With the AC pillows, it ranged form 75-76 hz. Most of

>the pillows ended up right behind the woofer where I thought

>they would be most effective. I did this with the speaker

>laying on its back so the piillows would not all sink to the

>bottom of the cabinet.

>

>Anybody else here heard of this technology? Ken K. perhaps?

>Anybody want to buy 12 lbs of AC?

>

>

>It's all about the music

>

>Carl

>Carl's Custom Loudspeakers

What a laugh. So you get a $100,000 pair of speakers and the advantage is that the enclosure is only 1/2 to 1/3 as large as it would otherwise be if they used conventional stuffing. How many pairs did you order? Carl....Psst, shhh, I think at KEF....it's all about the money.

[kkantor]

Carl,

Over the years, there have been many attempts to increase box compliance by using various combinations of solids, liquids and gases. Cerwin Vega was very active in this area; Polk, AR and others also did work in the field. Some of these efforts are documented in an article on bass reproduction technology in the following issue of The Audio Critic:

http://www.theaudiocritic.com/back_issues/...Critic_17_r.pdf.

I'm not really sure what the rationale for "activated carbon" is, though it has been tried several times over the years. I'm not at all surprised by your results.

On a related note... When I was back at AR, I encountered a retired IBM physicist (disk drive guy), name Ralph Marrs, who was working on the use of "Freon" in speaker cabinets.

http://www.aes.org/e-lib/browse.cfm?elib=11631

http://www.freepatentsonline.com/4350724.html

We supported his work for a time, (and I also did some consulting for him, post-AR). As John O'Hanlon (IBM on the other coast...) can attest, the physical acoustics of speaker stuffing is more than meets the eye.

http://auralization.blogspot.com/

-k

www.kenkantor.com

http://kkantor.spaces.live.com

[Guest cdwitmer]

This is a very timely subject for me -- I am definitely interested in trying this myself. I'd like to be able to reduce the size of some sealed subwoofers that I'm building.

Not all activated carbon is equally well suited to this application -- apparently the pore size makes a big difference. It seems that activated carbon used for filtration of liquids will be a poor choice for this application, due to the difference in the pore sizes.

I have been looking at two types of activated carbon made from coconut shells. One is described as being "for general gas adsorption" and the other is describes as being "an activation level adjusted type for gas separation applications" -- does anyone care to take a guess as to which I should try? (The latter one is 50% more expensive than the former.)

Thanks!

Chris Witmer

Tokyo

[kkantor]

I don't get it. What's the activated carbon supposed to actually do? Without any kind of a description of the proposed acoustical mechanism, how can one pick the right material to use?

I mean, you could use PAC or 20x40 GAC or carbon nanotubes or vermiculite or aerogel or cryogenically treated rockwool or hollow sorbothane spheres or a matrix of foamed aluminum pyramids or a delicious blend of Rice Krispies and popcorn or magnetocaloric Gandolinium or R-13 saturated with R-12 or Holofil soaked in Chablis or warm Crystal Pepsi or hot crystal meth or Kingsford soaked in benzene or Mentos and Dr. Pepper (Diet Coke sounds harsh in the mids) or conjugated polymer buckyballs or oxygen-free air or freeze-dried bonemeal or an Ovaltine/Vegemite alloy or live earthworms fed with refried beans or, my favorite, 20 parts charcoal, 10 parts sulfur and 70 parts saltpeter.

I'm pretty sure you could find an internet reviewer to praise "the sound" of each of these. And I think I just blew my next few consulting gigs. Lord, make it stop!

-k

www.kenkantor.com

[soundminded]

I have read the paper and in my opinion, it is technically incorrect. The change in the dynamic tuning of the enclosure has nothing to do with the adsorption of air by activated carbon, it is due to increased surface area for a given volume of material. This leaves more space for air in a given size enclosure for a given damping factor B reducing the K in Newton's second law of motion. In other words there is a favorable tradeoff increasing B while reducing K choosing this material instead of traditional stuffing.

As I mentioned in other postings, the performance of all oscillating devices including lousdpeaker/enclosure systems is described perfectly by Newton's second law of motion as the classic second order ordinary differential eqation;

F(t) = M*d2x/(dt)squared + B*dx/dt + K*x

I'm not going to look up the approximate solution for forced oscillation now but it's all over the internet and in every basic textbook of college physics and mechanic/dynamics. It's been around a few hundred years and correlates just about perfectly with observed phenomena every time. The answer gives the frequency response as a function of M(mass of the moving object), B (damping factor) and K (spring constant.) B is a velocity related friction component which depends on the physical characteristics of air (or whatever gas is being worked against by the moving mass) and the surface characteristics and area of the material the air is being pushed and pulled through. You can get a comparable advantge by increasing M but of course the price is efficiency becasue the motor has to move a heavier object.

The advantage of the acoustic suspension principle which should really be called pneumatic suspension over ported designs is obvious from looking at K. In an AS design, K is not frequency dependent because it is almost entirely the result of the ideal gas laws (Charle's law, Boyle's law etc.) In a ported design, the magnitude of K due to compression/rarifaction of air is highly frequency dependent being almost zero at the tuned resonant frequency of the port at which point air slides easily throug the port and reaching local minima at exact multiples of the resonant frequency F, 2F, 3F, etc. and high at frequencies halfway between where it is difficult to push air through the port and at one octave intervals 1.5Fc, 2.5Fc, 3.5Fc etc. You also have to add the often frequency dependent mechanical suspension K of the driver itself. Therefore the FR of a ported design will oscillate where an AS design will not. The FR of the AS design also has the advantage of the relatively moderate 12db/octave falloff below resonance compared to 24 db/octave for ported designs. This makes AS designs usually equalizable for at least half an octave to an octave to extend their bass response. Original Bose 901 is extended 3 octaves that way although not correctly in his circuit (only a 6db/octave boost.)

[Pete B]

I have to give you credit for trying Carl.

Coming from KEF I like to hope that it is not a total

crock if you know what I mean.

I skimmed the article looking for the mechanism through

which this claim might work. I notice adsorption, so

let's take a look:

http://en.wikipedia.org/wiki/Adsorption

So, it would seem that their claim is that something

strange happens on the surface of the activated charcoal

where I suppose the air molecules form a layer where

the total volume of the activated charcoal and air is

greatly reduced. Seems remotely possible through some

sort of surface tension effect. Their chart shows that

different forms of activated carbon have different

characteristics, are you sure you got the best type?

On the other hand, it's not clear if they performed any

experiments to prove their hypothesis.

I'd expect that they obtained patents for this, if there

claims are valid, might look for them.

[dynaco_dan]

Hi KenK;

From the extensive list of other stuffing materials that you noted, you must have been lucky with more than a few, to your credit.

You definitely know what you are talking about.

I own NHT SuperZero's and they are fantastic.

Chablis stuffing, I believe. LOL LOL

I can relate to the Hollowfill, if each fibre was crimped at each end, forming a hollow, slightly compressible tube.

The wool that I mentioned earlier was a sheepish excuse to mention one more less well known stuffing material.

To fellow members, if we heed Ken's advice, we will not go wrong, he is the only person on this site with many personal or team effort winner's in the hifi field.

Popcorn, Heh?

Cheese, plain or buttered? LOL

I exited this topic and as usual, I had another thought.

What if the cabinets were filled with round balls sized such as marbles or ping pong balls.

The balls would be only full of atmospheric pressure air, or another gas, and be made of a very soft flexible material to actually be able to compress slightly.

I just took my meds. LOL

[RoyC]

Given the idea originated with KEF it was worthy of experimentation, and I share the appreciation for Carl's effort and report.

I'm also thinking that Ken's charcoal/sulfer/saltpeter suggestion is worth a try as we head into the 4th of July. If the speaker sounds bad, just stick a fuse in it and light it at the appropriate moment during Tchaikovsky's "1812 Overture". It could bring new meaning to the term "dynamic range".

As for KEF's claims, and in light of Carl's experience...the best science fiction always seems plausible on the surface.

Happy 4th of July,

Roy

[soundminded]

The idea should work and it is quite ingenious. According to Wikipedia, one gram of activated charcoal normally has a surface area of about 500 square meters and can actually be manufactured to have a surface area of 1500 square meters. A tennis court by comparison has an area of 260 square meters. The reason I criticized the paper is that I don't believe it can possibly work through adsorption which is an attachment of molecules to the surface of the charcoal. If that happened and the box was sealed, the pressure inside would slowly reduce compared to the outside. If it were not sealed, the activated charcoal would eventually reach its capacity to adsorb any more nitrogen and would have to be recharged by removing it and heating it to drive off the nitrogen, that or replaced. In fact, it may be necessary to have a very small air leak to allow more nitrogen to enter as the nitrogen in the box is adsorbed. Installing activated charcoal which has already adsorbed as much nitrogen as it can may be the best way to take full advantage of the idea because it is stable. Instead whether nitrogen has or hasn't already been adsorbed, the enormous surface area creates high frictional losses for its volume to increase damping B substantially and because it takes up so little volume itself, the actual amount of air inside is greater reducing K quite a bit. Look at the structure described in the second reference. The micropore configuration is perfect for this application. This can be tuned using a particular driver to have a much lower Fs at critical damping with a given sized enclosure. But the idea isn't worth $100,000 to the consumer. Maybe $100 or $200 instead. The difference is only the size of the box and the amount of stuffing needed, the audible results are entirely equivalent.

http://en.wikipedia.org/wiki/Adsorption

http://en.wikipedia.org/wiki/Activated_carbon

[RoyC]

Soundminded,

Maybe you should relieve Carl of his excess activated carbon and give it a go....

Roy

[kkantor]

There are many woofer tunings that will behave almost identically in two different sized boxes. What I want to see is the woofer in the smaller box, with and without the carbon. This would seem to be the simplest and most logical demonstration. Also, why wasn't the standard box compliance given, so that anyone could understand the benefit achieved. At least a definition of what "2X" improvement refers to would be helpful.

If anyone can find this information, it would be easier to determine whether there is something interesting here, or not. But, as I have said, this is not the first time that competent engineers have tried activated charcoal, and tried different varieties, of course.

-k

www.kenkantor.com

[johnieo]

Wikiscience

Beware Wikiscience. Sorption is a very complex subject that has been studied for a century and for which there is no one model to explain all the experimental data – people spend their entire careers studying how molecules attach to solids. Sorption has nothing to do with surface tension or Newton’s law.

Highly-porous fiber stuffing attempts to keep the cabinet gas isothermal by heat exchange between gas and fibers - absorbing and releasing heat as the woofer cone cycles, in order to make the cabinet appear acoustically larger than its physical volume.

It appears that sorption materials attempt to do the same thing by binding gas to a surface. That reduces the gas density a bit and removes the heat of sorption. The effect at atmospheric pressure is small, and why I did not think it to be important.

Charcoal can sorb gas on activation sites to a depth of one monolayer by polarization and van der Waals forces on the vast surfaces of the huge number of microscopic cavities. At cryogenic temperatures, these become powerful high vacuum pumps; at room temperature, charcoal’s use is limited to specific tasks. The one other material useful as a gas sorbent is molecular sieve (hydrated alumino-silicate) made by Linde.

The performance of a sorption material is characterized by its sorption isotherm and by its activation energy. The isotherm describes the sorbed quantity versus pressure at one temp. Back of envelope calculation from activated coconut charcoal’s room temperature isotherm says it would take about 3-to-4 kg of charcoal to sorb the air displaced from a 1-cm inward motion of an AR-3a woofer voice coil, provided the charcoal had seen only clean dry air.

The reason this technique does not seem practical relates to how the activation energy of adsorption depends on gas species. Binding energies are weakest for helium, nitrogen is a bit more strongly bound, then oxygen, water vapor, and lastly organic compounds, which have the strongest binding energies. The primary issue is displacement. Organic compounds displace water, which displaces nitrogen, etc., in succession. There are differences in the isotherms of various kinds of charcoal, but the pecking order will not change - e.g., organics will displace air in all types.

If the charcoal were saturated with water vapor from sitting in the room for a few hours, then it would not pump nitrogen or oxygen. If organic compounds fill its activation sites, then it needs to be baked or discarded. Displacement is why charcoal is exceedingly effective at removing organic odors from tap water, some stuff in cigarette smoke, gas masks, airplane cabin air, and cooking vapors over the stove. If water and organic vapors have filled all its activation sites, activated charcoal would not show any increase in capacity for nitrogen, as the cone moves inward, hence it would not provide any acoustic increase in cabinet volume. Carl’s data agrees. Lot’s of concepts don’t survive in the real world.

[soundminded]

>Wikiscience

>

>Beware Wikiscience. Sorption is a very complex subject that

>has been studied for a century and for which there is no one

>model to explain all the experimental data – people spend

>their entire careers studying how molecules attach to solids.

>Sorption has nothing to do with surface tension or Newton’s

>law.

>

>Highly-porous fiber stuffing attempts to keep the cabinet gas

>isothermal by heat exchange between gas and fibers -

>absorbing and releasing heat as the woofer cone cycles, in

>order to make the cabinet appear acoustically larger than its

>physical volume.

>

>It appears that sorption materials attempt to do the same

>thing by binding gas to a surface. That reduces the gas

>density a bit and removes the heat of sorption. The effect at

>atmospheric pressure is small, and why I did not think it to

>be important.

>

>Charcoal can sorb gas on activation sites to a depth of one

>monolayer by polarization and van der Waals forces on the vast

>surfaces of the huge number of microscopic cavities. At

>cryogenic temperatures, these become powerful high vacuum

>pumps; at room temperature, charcoal’s use is limited to

>specific tasks. The one other material useful as a gas sorbent

>is molecular sieve (hydrated alumino-silicate) made by Linde.

>

>The performance of a sorption material is characterized by its

>sorption isotherm and by its activation energy. The isotherm

>describes the sorbed quantity versus pressure at one temp.

>Back of envelope calculation from activated coconut charcoal’s

>room temperature isotherm says it would take about 3-to-4 kg

>of charcoal to sorb the air displaced from a 1-cm inward

>motion of an AR-3a woofer voice coil, provided the charcoal

>had seen only clean dry air.

>

>The reason this technique does not seem practical relates to

>how the activation energy of adsorption depends on gas

>species. Binding energies are weakest for helium, nitrogen is

>a bit more strongly bound, then oxygen, water vapor, and

>lastly organic compounds, which have the strongest binding

>energies. The primary issue is displacement. Organic compounds

>displace water, which displaces nitrogen, etc., in succession.

>There are differences in the isotherms of various kinds of

>charcoal, but the pecking order will not change - e.g.,

>organics will displace air in all types.

>

>If the charcoal were saturated with water vapor from sitting

>in the room for a few hours, then it would not pump nitrogen

>or oxygen. If organic compounds fill its activation sites,

>then it needs to be baked or discarded. Displacement is why

>charcoal is exceedingly effective at removing organic odors

>from tap water, some stuff in cigarette smoke, gas masks,

>airplane cabin air, and cooking vapors over the stove. If

>water and organic vapors have filled all its activation sites,

>activated charcoal would not show any increase in capacity for

>nitrogen, as the cone moves inward, hence it would not provide

>any acoustic increase in cabinet volume. Carl’s data agrees.

>Lot’s of concepts don’t survive in the real world.

>

John, I've thought about Villchur's thermodynamic model of how the stuffing works and frankly I still don't see it. Thermodynamics studies the interconversion of energy between directed energy such as mechanical motion or electricity and random energy, heat. Far more heat is generated by the VC resistance of even the most efficient speakers than by conversion via mechanical energy of the moving mass to heating the stuffing and enclosure and virtually none of it is turned back into mechanical energy. It's not that this idea is wrong, it's quantitatively insignificant and just doesn't explain why an AS speaker is different from any other speaker of comparable efficiency. Thermodynamics is a misnomer, it should really be called comparative thermostatics because it usually compares various quasi stable (thermodynamic equalibrium) intermediate and end states rather than describing the motional processes between one state and another. That's where Newton's laws of motion come in.

I did not get my understanding of adsorption from "Wikiscience" :-) It's been awhile ago, a long while ago. I agree, adsorption is a monomolecular surface phenomeon. Activated charcoal is a good choice IF it is manufactured in a way which gives it a very large surface area, otherwise it will become "denatured" very quickly in use. Also, it is best when whatever substance is to be adsorbed comes into greatest contact with it such as through micropores which are open at both ends so that the material to be adsorbed passes through them. My best understanding of how it works is that carbon will form both polar and non polar covalent bonds with many substances but frankly, the nitrogen in air (80%) and oxygen in air (20%) are not good candidates without a catylist present such as the enzymes in some bacteria. Isn't this how termites can digest cellulose and why wood rots? Carbon has far greater affinity for other organic compounds and some inorganic compounds especially in the presence of a suitable catylist, acid, or base. Were activated carbon filters to have any strong affinity for the constituents of air, it would become denatured quickly once exposed because of the high surface contact with the large number of N2 and O2 molecules passing over it. This and what I said above are the main reasons I am confident adsorption is NOT the mechanism by which this activated charcoal works. Instead, it is the physical structure which creates the frictional losses as air passes through the pores which increases the damping factor B in Newton's equation. The effect IMO would be exactly the same with an identical physically structured material which is not adsorbant. That this can be done with a quantity of material which is physically small reduces the volume of air it displaces in a sealed enclosure and therefore increases in air volume reduces K in the same equation.

[kkantor]

Pearls before swine, Doctor, pearls before swine.

[kkantor]

Hey, if you have any "meds" left over, you can try putting them into the SuperZeros as stuffing material.

Valium gives a relaxed kind of sound. Prozac smooths out the midrange depression. Pot is great for the highs, but it can get you into treble. And, or course, a touch of Lomotil will tighten up the low end.

-k

www.kenkantor.com

http://kkantor.spaces.live.com

[tysontom]

> And, or course, a touch of Lomotil will

>tighten up the low end.

>

>-k

>

Therefore, professor, will a touch of Colace do the opposite?

--Tom Tyson

[kkantor]

>Therefore, professor, will a touch of Colace do the opposite?

>

>--Tom Tyson

Only if taken with a shot of port. (Oh, such bass humor.)

-k

www.kenkantor.com

http://kkantor.spaces.live.com

[Carlspeak]

Thanks all who commented on this post. I wrote it and dashed off to the Cape for a week's vacation.

Here's a little more info.

The specific AC I bought for the experiment is coal based, not coconut shell based (spec sheet attached below as a word doc). KEF's white paper had a bar graph that showed coconut shell's pore volume distrubution vs coal-based as having more pores at the 5 angstrom width level but fewer than coal-based at larger pore widths. They didn't explicitly reveal which type of AC they use, however. Would coconut shell make all that much difference? I don't know. The AC I bought appears to have been designed for water filtration - not for air. Would that explain the failure?

Here is the ebay address for the seemingly endless ad for the AC I bought:

http://cgi.ebay.com/12-Lbs-Premium-Activat...1QQcmdZViewItem

The price and quantity was right because most other web sellers want over $50/lb in larger batch sizes for either type of AC.

Also worthy of note is the absence of patents on this technology at KEF's web site. If this actually worked in this application, I'd expect they would have gotten a few.

It's all about the music

Carl

Carl's Custom Loudspeakers

[kkantor]

Carl,

I looked the data on your activated carbon. Did you bake it before you tried it? Because of the origin and intended use of your material, there's a good chance that it had accrued moisture, which would render it ineffective.

I'm not suggesting it would be effective if it were dry; just that being moist will pretty much guarantee failure. Perhaps you can bake the pillows you have?

Or send them to JO and he can leave them out in the Arizona sun for a few seconds.

-k

[soundminded]

"Also worthy of note is the absence of patents on this technology at KEF's web site. If this actually worked in this application, I'd expect they would have gotten a few."

To merit a patent, an innovation cannot be "obvious" to someone "skilled in the art." Given that pneumatically loaded acoustic suspension speakers have been around for 50 years now, using a different stuffing material for adjusting damping and air spring loading can't be all that startling an idea, at least for a mechanical engineer. Basically IMO this is a mechanical engineering not an electrical engineering problem. In fact, the electrical problem is trivial by comparison consisting merely of an appropriate filter network once the optimal mechanical parameters have been established.

Personally, were I going to experiment, I'd buy some filters designed for safety breathing masks like those miners would wear. You'd know that the charcoal would have to allow air to flow through them and that there would be a large surface area. Since they are usually round cans and threaded, they might allow for easy mounting in different configurations such as on a sheet metal form forcing the speaker to pull and push air through them and they should also be fairly cheap although I've haven't priced them. They should be widely available anywhere they sell industrial safety equipment.

[Carlspeak]

No, I didn't bake it before packaging it. In fact it sat in my cellar for a few days before I could get to fabricating the pillows and filling them (sigh). Don't have a clue how much moisture could have crept in or how much was there to start with.

The pillows have all been destroyed and the AC is back in the original carton. They were extremely fragile and one split while still in the cabinet. Vacuum to the rescue!

Like I wrote before, anybody interested in 12 lbs of AC???

It's all about the music

Carl

Carl's Custom Loudspeakers

[dynaco_dan]

Hi Carl;

I was hoping to buy those cute little pillowcases for my bed, Carl. LOL LOL

The humidy level issue reminds me of, dessicant (spel), for removing moisture from air in packaging.

I believe it needs 1/2 hour at 150 degrees F in an oven to dehydrate.

[Guest rythmikaudio]

>I have read the paper and in my opinion, it is technically

>incorrect. The change in the dynamic tuning of the enclosure

>has nothing to do with the adsorption of air by activated

>carbon, it is due to increased surface area for a given volume

>of material.

I agree the change in impedance does not mean an improvement, rather it is the transfer function of acoustic output vs input voltage (not even power), which can be done by a simple nearfield measurement. Personally I am interested in whatever method that the make smaller enclosure "sound" larger, while not sacrificing efficiency. The reason is I am interested in servo application. Because of FR can be totally controlled by servo, all I care is the "raw" efficient which should be as high as possible. So not long ago, someone recommended to use the enclosure vent such as those sold by Dynaudio or Scan-speak in small enclosures (aperiodic enclosures). So I did the experiment. First measure the raw efficiency without the vent, then add the vent. Although I can see the impedance change after addding the vent, the efficient was never as good as the one without the vent for the frequencies above 10hz. I gave up that idea completely. What the vent did is lowering the Q value of the roll-off at the same time moving the corner frequency lower. The net result is just lower efficiency above 10hz. Of course, this may not be a fair statement because larger enclosure would have lower Q. But the additional loss of the vent makes the Q value even further lower. The experiment was done on a 15.5" cube and a 15" driver. Based on the paper publish by KEF, it has similar effect. I am not saying the activated carbon will turn out to be the same as the aperiodic vents. However, I would encourage anyone did the experiment start with output transfer function meausrement using close-mic technique.

-Brian