Good for you...
AnthonyPT you will want to find a screen to size seperate the perlite so that you start off with only lage particals and remove the dust and small bits. I should think that particle size similar to that of rice crispy's would be excellent. Given my experience with the ATC's I would suggest that you start by totally filling the cabinet interior and listen then back off from there if you think things seem over damped (my guess is that it will not). I look forward to hearing of your results. Regards Moray James.
AnthonyPT you will want to find a screen to size seperate the perlite so that you start off with only lage particals and remove the dust and small bits. I should think that particle size similar to that of rice crispy's would be excellent. Given my experience with the ATC's I would suggest that you start by totally filling the cabinet interior and listen then back off from there if you think things seem over damped (my guess is that it will not). I look forward to hearing of your results. Regards Moray James.
Perlite use
Very interesting. I have used perlite in my speakers, but for the concrete mix, to lighten them up. They are 2 litre sealed enclosuers. I will try the perlite for internal damping and to increase percieved volume and see if the results are positive.
Also, why not use activated carbon, asi done by kef. You can buy this stuff from Farmacies. It is used in case of poisoning as an adsorbent. I will see if I can get my hand on some, shouldnt be too expensive either.
Very interesting. I have used perlite in my speakers, but for the concrete mix, to lighten them up. They are 2 litre sealed enclosuers. I will try the perlite for internal damping and to increase percieved volume and see if the results are positive.
Also, why not use activated carbon, asi done by kef. You can buy this stuff from Farmacies. It is used in case of poisoning as an adsorbent. I will see if I can get my hand on some, shouldnt be too expensive either.
I'd had concerns with the membrane behavior. The other concern is that this is not a porosity issue- it's a chemistry one. The Perlite may work a treat as a damping material, but it's a conventional damping material rather than a chemical action. The dramatic effect of the carbon is that it adsorbs and desorbs air, not so much in the pores acting as a lossy acoustic material.
As far as the membrane is concerned when we're talking pressure rather than acoustics (read: low frequency pressure) , it seems like one would have to have an inflated bag (not in close contact with the carbon) for the membrane to allow compression, and that in itself would displace a significant amount of volume.
I think the most effective implementation of this would be with the carbon wrapped in poly batting (or cotton, or bamboo, just some sort of batting) or cloth. I like the batting idea because it's a good acoustic material in itself, and would form a fairly solid filter against particles. Naturally, one would wish to de-dust the carbon as well as possible.
I've sourced the activated carbon and will give this a shot in the near future. A few extra litres of enclosure volume here and there could be tremendously handy!
As far as the membrane is concerned when we're talking pressure rather than acoustics (read: low frequency pressure) , it seems like one would have to have an inflated bag (not in close contact with the carbon) for the membrane to allow compression, and that in itself would displace a significant amount of volume.
I think the most effective implementation of this would be with the carbon wrapped in poly batting (or cotton, or bamboo, just some sort of batting) or cloth. I like the batting idea because it's a good acoustic material in itself, and would form a fairly solid filter against particles. Naturally, one would wish to de-dust the carbon as well as possible.
I've sourced the activated carbon and will give this a shot in the near future. A few extra litres of enclosure volume here and there could be tremendously handy!
Can't edit the post so I'll repost:
My second point regarding the displaced volume seems to be wrong. I'll be running some impedance sweeps with carbon bagged and in-place, but ultimately, the function of the air is as a spring, and a spring is a spring is a spring. I do think that the bag may change matters slightly, but it should still function largely as intended.
You'd want to use a partially inflated bag, enough so that it can compress without being physically constrained by the carbon, but not so much that it's got significant internal pressure. You'd also want to use a durable, airtight bag- grocery store freezer/sandwich bags probably not ideal here. I'm thinking mylar.
The bag is not just to prevent dust, but also to keep the carbon from reacting with pollutants and wearing out it's efficacy. This would take some time, but a large vented subwoofer enclosure could have enough air exchange as to reduce the strength after a year or three.
The carbon I've sourced is for use in aquarium filtration systems. 20lbs in 1 pound mesh bags for $50 shipped off ebay. It's also in pellet form, which they claim to reduce the "compacting" of the pebbles and maintain greater exposed surface area and flow-through characteristics.
Still working on what I want to do with the mylar.
Also interesting should be any secondary acoustic effects. Most frequencies should pass through the membrane reasonably well and I'd expect there to be some decent acoustic loss in the pellets, due to the overall porous nature of the "pile" of pellets. The microporousity probably doesn't do us any good due to the wavelength vs. pore size.
I'll run some impedance sweeps once I get the process pinned down and report back. Hopefully we can 'fake' a bigger box. The mechanism appears to be primarily effective below 150Hz, so we'll have to see what we get
My second point regarding the displaced volume seems to be wrong. I'll be running some impedance sweeps with carbon bagged and in-place, but ultimately, the function of the air is as a spring, and a spring is a spring is a spring. I do think that the bag may change matters slightly, but it should still function largely as intended.
You'd want to use a partially inflated bag, enough so that it can compress without being physically constrained by the carbon, but not so much that it's got significant internal pressure. You'd also want to use a durable, airtight bag- grocery store freezer/sandwich bags probably not ideal here. I'm thinking mylar.
The bag is not just to prevent dust, but also to keep the carbon from reacting with pollutants and wearing out it's efficacy. This would take some time, but a large vented subwoofer enclosure could have enough air exchange as to reduce the strength after a year or three.
The carbon I've sourced is for use in aquarium filtration systems. 20lbs in 1 pound mesh bags for $50 shipped off ebay. It's also in pellet form, which they claim to reduce the "compacting" of the pebbles and maintain greater exposed surface area and flow-through characteristics.
Still working on what I want to do with the mylar.
Also interesting should be any secondary acoustic effects. Most frequencies should pass through the membrane reasonably well and I'd expect there to be some decent acoustic loss in the pellets, due to the overall porous nature of the "pile" of pellets. The microporousity probably doesn't do us any good due to the wavelength vs. pore size.
I'll run some impedance sweeps once I get the process pinned down and report back. Hopefully we can 'fake' a bigger box. The mechanism appears to be primarily effective below 150Hz, so we'll have to see what we get
Activated Carbon
Ok, Just got a hold of some Activated Carbon from a company that sells Filters. I was able to buy 5 kilos of local production (around 24litre bucket) for about 75 argentine pesos (20 US dollars). Will be doing some experiments. Read up on a patent by Panasonic that also uses activated carbon for bass extension. Worth the read. Interesting system used to to maintain the activated carbon dry.
I hope my sealed speaker is good enough at maintaining the carbon dry. Here in buenos aires humidity really is a problem. If not i will have to use some type of sealed bag. Will try both systems.
My speaker has two litres in volume. I will try adding 1 litre up to 1.7 litres and see what happens.
Ok, Just got a hold of some Activated Carbon from a company that sells Filters. I was able to buy 5 kilos of local production (around 24litre bucket) for about 75 argentine pesos (20 US dollars). Will be doing some experiments. Read up on a patent by Panasonic that also uses activated carbon for bass extension. Worth the read. Interesting system used to to maintain the activated carbon dry.
I hope my sealed speaker is good enough at maintaining the carbon dry. Here in buenos aires humidity really is a problem. If not i will have to use some type of sealed bag. Will try both systems.
My speaker has two litres in volume. I will try adding 1 litre up to 1.7 litres and see what happens.
I tried it with a few lbs. worth, , maybe a little under 2Litres, in enclosures somewhat big, 23-25 litres or thereabouts. Probably a very poor test environment, in retrospect. The little spherical fullrangers should be a much better indicator as I can get a significant portion of them filled.
EDIT
I tried it in some smaller enclosures last night with minimal effect. I think it may have been the FR125 mounting, so out comes the file and we'll re-try tonight with some material removed from around the driver mounting.
EDIT
I tried it in some smaller enclosures last night with minimal effect. I think it may have been the FR125 mounting, so out comes the file and we'll re-try tonight with some material removed from around the driver mounting.
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