Just finished spending a day experimenting with box cavity damping. The speakers in question are ATC SCM10's which are factory damped with long fiber wool. This ia a small cavity sealed box with an impressive 5.5 inch bass/mid driver that has a very long linear excursion.
A friend of mine attended the Hi Fi Show in Germany this spring and had an invite to spend the nite at a private showing of the new KEF Reference loudspeaker. One of the cool things about the KEF is that it is internally damped with activated charcoal. This is a neat idea as activated charcoal is very porous. Kef claim to have reached a virtually theoretical cavity volume increase of 28 out of 30 % using the charcoal. This got me thinking. Charcoal is messy and expensive. Pearlite is a heat expanded form of rock used in the gardening business usually white but comes in various colours. Pearlite is basically rock heated up like popcoarn or Rice Crispy's and ends up like small kernals of porous soft rock which is soft enough that you can crush it to powder with your fingers. Pearlite is more porus than activated charcoal and is clean and cheap to buy. I replaced all the internal wool damping with the pearlite in the ATC SCM10's. This resulted in a significant improvement across the band with especially improved midrange and more extended bass. You do need to take some precautions however. Pearlite must be sifted first to extract all the fine powder as you only want pieces the size of rice crispy's and larger. Further you need to insure that the pearlite is kept out of the driver/s. This done I would have to say that this is by far the best damping material that I have ever used. This is I think as a result of the fact that pearlite is so very porus and has high resistivity to passage of air and also in that it has tremendous frictional dissapation due to the partical vibrating against one another. Bug screen and fiber batting like polyester or acrylic will keep the pearlite where you want it and permit free air flow about the back side of the driver. For ported boxes you would want to keep a fair size area (should think a minimum of a 1/2 cu. ft.) around the reflex vent free of any damping material to insure correct vent resonance. There you have it cheap and SOTA damping material that works like a charm. You read it hear first. For those who cannot readilly get thier hands on pearlite or who disbelieve a good second choice would be rice crispy's (dont laugh) but they will cost more than pearlite however if you are not fussy you can at least eat the rice crispy's after. You can expect the pearlite to be more effective than the rice crispy's as it is far more porous in structure. BE FOREWARNED you must properly prepare for using pearlite to insure that it only goes where you want it to. This is a real gem of a damping material especially for ultra small cabinet speakers and I should think the absolute bomb for TL's. I am sure that some will laugh till they hurt but do give it a try and for those to busy laughing well that's your loss. Very best regards Moray James.
A friend of mine attended the Hi Fi Show in Germany this spring and had an invite to spend the nite at a private showing of the new KEF Reference loudspeaker. One of the cool things about the KEF is that it is internally damped with activated charcoal. This is a neat idea as activated charcoal is very porous. Kef claim to have reached a virtually theoretical cavity volume increase of 28 out of 30 % using the charcoal. This got me thinking. Charcoal is messy and expensive. Pearlite is a heat expanded form of rock used in the gardening business usually white but comes in various colours. Pearlite is basically rock heated up like popcoarn or Rice Crispy's and ends up like small kernals of porous soft rock which is soft enough that you can crush it to powder with your fingers. Pearlite is more porus than activated charcoal and is clean and cheap to buy. I replaced all the internal wool damping with the pearlite in the ATC SCM10's. This resulted in a significant improvement across the band with especially improved midrange and more extended bass. You do need to take some precautions however. Pearlite must be sifted first to extract all the fine powder as you only want pieces the size of rice crispy's and larger. Further you need to insure that the pearlite is kept out of the driver/s. This done I would have to say that this is by far the best damping material that I have ever used. This is I think as a result of the fact that pearlite is so very porus and has high resistivity to passage of air and also in that it has tremendous frictional dissapation due to the partical vibrating against one another. Bug screen and fiber batting like polyester or acrylic will keep the pearlite where you want it and permit free air flow about the back side of the driver. For ported boxes you would want to keep a fair size area (should think a minimum of a 1/2 cu. ft.) around the reflex vent free of any damping material to insure correct vent resonance. There you have it cheap and SOTA damping material that works like a charm. You read it hear first. For those who cannot readilly get thier hands on pearlite or who disbelieve a good second choice would be rice crispy's (dont laugh) but they will cost more than pearlite however if you are not fussy you can at least eat the rice crispy's after. You can expect the pearlite to be more effective than the rice crispy's as it is far more porous in structure. BE FOREWARNED you must properly prepare for using pearlite to insure that it only goes where you want it to. This is a real gem of a damping material especially for ultra small cabinet speakers and I should think the absolute bomb for TL's. I am sure that some will laugh till they hurt but do give it a try and for those to busy laughing well that's your loss. Very best regards Moray James.
Hi,
I'm not one for knocking some-one who's prepared to
try things based on a series of logical presumptions.
If your fill is effective as KEFs, then the bass driver parameters
may not suit particularly the new effective cabinet size meaning
"improvements" in bass extension may be modest.
(edit : pearlite = vermiculite in the UK, not keen on the rice krispies)
🙂/sreten.
I'm not one for knocking some-one who's prepared to
try things based on a series of logical presumptions.
If your fill is effective as KEFs, then the bass driver parameters
may not suit particularly the new effective cabinet size meaning
"improvements" in bass extension may be modest.
(edit : pearlite = vermiculite in the UK, not keen on the rice krispies)
🙂/sreten.
Here is KEF's white paper on the matter from 2001 in pdf form
http://www.kef.com/technology/pdfs/acewp.pdf
Interesting reading indeed.
J.D.
http://www.kef.com/technology/pdfs/acewp.pdf
Interesting reading indeed.
J.D.
Thanks for running and not laughing!
Good to see people run with the ball! Walton thank you for the reference to the KEF paper. The simple solution to the dust and particle issue (driver contamination) is to place the perlite into sealed plastic bags and then install the filled bags into your speaker box cavity. Regards Moray James
here is a link to other comon garden materials that may also be of use http://www.gchydro.com/information_Growmed.asp
Good to see people run with the ball! Walton thank you for the reference to the KEF paper. The simple solution to the dust and particle issue (driver contamination) is to place the perlite into sealed plastic bags and then install the filled bags into your speaker box cavity. Regards Moray James
here is a link to other comon garden materials that may also be of use http://www.gchydro.com/information_Growmed.asp
Re: Thanks for running and not laughing!
Huh ? I dont think so. Would completely defeat the point.
The vermiculite would need baking and then quickly put
into completely sealed boxes adding hygroscopic crystals
(the little bags that come with cameras / videos etc).
The drivers would also need to be fully sealed, no air path.
the hygroscopic issue is major, rice krispies don't stay
crispy for very long if you leave them out of the packet.
I've also visions of opening up your speakers after a
good pounding to find a pile of dust at the bottom
of the speaker.......
🙂/sreten.
moray james said:
Huh ? I dont think so. Would completely defeat the point.
The vermiculite would need baking and then quickly put
into completely sealed boxes adding hygroscopic crystals
(the little bags that come with cameras / videos etc).
The drivers would also need to be fully sealed, no air path.
the hygroscopic issue is major, rice krispies don't stay
crispy for very long if you leave them out of the packet.
I've also visions of opening up your speakers after a
good pounding to find a pile of dust at the bottom
of the speaker.......
🙂/sreten.
Installing Perlite
I will have to disagree with you on this one with all due respect. The perlite will work just as effectively packaged into plastic bags and sealed. In fact it may well be more effective that way. Have a look at Ted Jordan's work on membrane absorbers. Most all damping materials will hold moisture and I don't see a problem with Perlite being any worse than fiberglass or any other synthetic fiber material even wool. As for the break down of Perlite I guess that the thing to do is to damp a sub woofer box with Perlite and then check it out after a few weeks of good use. If fresh large size particles of Perlite are only used and the contents are placed inside of a sealed bag then it will be eady to determine how much of an issue breakdown will be. Issues of longevity are secondary to the fact that this material works extreemly well as is. Contamination is not an issue if the Perlite is installed inside of a sealed plastic bag. Moisture does not damage Perlite can hold more moisture than do conventional damping materials but the plastic bag method would als deal with that issue as well. Lets try to look on the positive side of things here. I am sure that your valid concers can be dealt with with a little thought. Regards Moray james.
I will have to disagree with you on this one with all due respect. The perlite will work just as effectively packaged into plastic bags and sealed. In fact it may well be more effective that way. Have a look at Ted Jordan's work on membrane absorbers. Most all damping materials will hold moisture and I don't see a problem with Perlite being any worse than fiberglass or any other synthetic fiber material even wool. As for the break down of Perlite I guess that the thing to do is to damp a sub woofer box with Perlite and then check it out after a few weeks of good use. If fresh large size particles of Perlite are only used and the contents are placed inside of a sealed bag then it will be eady to determine how much of an issue breakdown will be. Issues of longevity are secondary to the fact that this material works extreemly well as is. Contamination is not an issue if the Perlite is installed inside of a sealed plastic bag. Moisture does not damage Perlite can hold more moisture than do conventional damping materials but the plastic bag method would als deal with that issue as well. Lets try to look on the positive side of things here. I am sure that your valid concers can be dealt with with a little thought. Regards Moray james.
WARNING:
When working with perlite in dry form a face-mask MUST be used. Since perlite is a form of natural glass those tiny paricles is hazardous to lungs.
Perlite when used in horticulture is mixed with water before mixing it with soil to avoid the dust.
Be safe!
When working with perlite in dry form a face-mask MUST be used. Since perlite is a form of natural glass those tiny paricles is hazardous to lungs.
Perlite when used in horticulture is mixed with water before mixing it with soil to avoid the dust.
Be safe!
Re: Installing Perlite
I'm afraid I don't understand something here. I tried googling for Edward Jordan Membrane Absorbers. No dice. Maybe you can provide a link. How is the air supposed to penetrate the sealed plastic bag? Or does it not have to? I must say I don't like the idea of rustling rice crispies inside my speakers. Maybe some bricks of porous lava rock or similar would work, or does this method rely on the frictional movement of small grains?
Max
moray james said:
I'm afraid I don't understand something here. I tried googling for Edward Jordan Membrane Absorbers. No dice. Maybe you can provide a link. How is the air supposed to penetrate the sealed plastic bag? Or does it not have to? I must say I don't like the idea of rustling rice crispies inside my speakers. Maybe some bricks of porous lava rock or similar would work, or does this method rely on the frictional movement of small grains?
Max
vermiculite.
yeah i agree... be careful with this stuff.
do not breath it in. I think a manufacturer was actually sued here in the USA by ppl getting lung cancer from breathing in this stuff.
but good idea anyways
yeah i agree... be careful with this stuff.
do not breath it in. I think a manufacturer was actually sued here in the USA by ppl getting lung cancer from breathing in this stuff.
but good idea anyways
Works like this...
the air pressure generated by the driver motion presses against the plastic film and that moves the air inside the bag which squirts through the perlite and turns the acoustic energy into heat and so disipates the energy (particle friction also plays a disipative role here). The thinner the film of the bag the better. Ted Jordan published a series of articles in Wireless World back in seventies I think all about sealed membrane absorbers which used fiberous batting in a low 5 sided box with a sealed membrane on the 6th side, the batting has to be inside the box in contact with the membrane to work effectively. You will not hear a sound from the perlite inside the cabinet but you will hear clearer cleaner sound from your speaker. Regards Moray James.
the air pressure generated by the driver motion presses against the plastic film and that moves the air inside the bag which squirts through the perlite and turns the acoustic energy into heat and so disipates the energy (particle friction also plays a disipative role here). The thinner the film of the bag the better. Ted Jordan published a series of articles in Wireless World back in seventies I think all about sealed membrane absorbers which used fiberous batting in a low 5 sided box with a sealed membrane on the 6th side, the batting has to be inside the box in contact with the membrane to work effectively. You will not hear a sound from the perlite inside the cabinet but you will hear clearer cleaner sound from your speaker. Regards Moray James.
Curious. Now, what would happen if the plastic bag were at a different pressure than the surrounding air?
Max
Max
Well...
if the bag containing the perlite was inflated with air then that would reduce the effectivness of the system. I would think that drawing out excess air from the bag would be of benefit. Remember that you want the membrane (wall of the bag) to press against the perlite inside the bag but you do not want it so firm as to prevent the particles from moving either. Does that answer your question? You could take the opertunity to replace the air inside of the bag (inbetween the perlite particles and inside the little holes in the perlite) with say sulferhexaflouride gas which is heavier than air (and really seal the bag so it cannot leak) that way you would further fool the speaker into thinking that it is in an even larger volume than just the perlite alone would do. Good trick but a bit of a PITA I should think but you could and it would and that's cool. Regards Moray James.
if the bag containing the perlite was inflated with air then that would reduce the effectivness of the system. I would think that drawing out excess air from the bag would be of benefit. Remember that you want the membrane (wall of the bag) to press against the perlite inside the bag but you do not want it so firm as to prevent the particles from moving either. Does that answer your question? You could take the opertunity to replace the air inside of the bag (inbetween the perlite particles and inside the little holes in the perlite) with say sulferhexaflouride gas which is heavier than air (and really seal the bag so it cannot leak) that way you would further fool the speaker into thinking that it is in an even larger volume than just the perlite alone would do. Good trick but a bit of a PITA I should think but you could and it would and that's cool. Regards Moray James.
Another question.......
How heavy is this stuff? Will it also add some significant mass to the speaker or is it like Rice Crispies, and mostly made of air? 😉
How heavy is this stuff? Will it also add some significant mass to the speaker or is it like Rice Crispies, and mostly made of air? 😉
Re: Installing Perlite
Hmmm......
Well I have a concern that a process thats supposed to (up to) triple
the effective volume will be limited by plastic membranes and the
physical restrictions of the absorber preventing membrane movement.
In principle the plastic bags at < 100Hz would have no effect as long
as movement was not restricted, at higher frequencies the bags will
reduce absorbtion of midrange frequencies.
Hygroscopic issues appear to be a major issue when attemptiing to triple
the effective volume according to the KEF paper, and simply saying its
not an issue with BAF, Fibreglass etc. is not particularly relevant.
🙂/sreten.
moray james said:
Hmmm......
Well I have a concern that a process thats supposed to (up to) triple
the effective volume will be limited by plastic membranes and the
physical restrictions of the absorber preventing membrane movement.
In principle the plastic bags at < 100Hz would have no effect as long
as movement was not restricted, at higher frequencies the bags will
reduce absorbtion of midrange frequencies.
Hygroscopic issues appear to be a major issue when attemptiing to triple
the effective volume according to the KEF paper, and simply saying its
not an issue with BAF, Fibreglass etc. is not particularly relevant.
🙂/sreten.
This is an extremely interesting principle. And the ability to control/test it is quite handy, toss a bag or two in, take them out, cakewalk! Just make sure the bags hold up 🙂 The idea of acting as a mechanical damper as well as an acoustic absorber is nice as well.
I think I'll have to test this with my sub 🙂 Most of my bassboxes are already volume-optimized, with moderate stuffing, and low Q alignments, but the sub has some fiddleroom left, and one can use a fairly hefty bag (IE: no breaking and spilling dust into my driver!) given the bass is all <60Hz.
Let's keep this one alive, see some testing, etc!
I think I'll have to test this with my sub 🙂 Most of my bassboxes are already volume-optimized, with moderate stuffing, and low Q alignments, but the sub has some fiddleroom left, and one can use a fairly hefty bag (IE: no breaking and spilling dust into my driver!) given the bass is all <60Hz.
Let's keep this one alive, see some testing, etc!
perlite :
These are made from processed granules of volcanic rock.
Perlite has excellent capillary properties and doesn't compact
which makes for good aeration.
http://www.users.globalnet.co.uk/~chegeo/perlite.htm
vermiculite :
formed from heating mica
http://www.hoben.com/vermiculite/index.htm
Have to say the perlite looks most suitable.
🙂/sreten.
An externally hosted image should be here but it was not working when we last tested it.
These are made from processed granules of volcanic rock.
Perlite has excellent capillary properties and doesn't compact
which makes for good aeration.
http://www.users.globalnet.co.uk/~chegeo/perlite.htm
vermiculite :
An externally hosted image should be here but it was not working when we last tested it.
formed from heating mica
http://www.hoben.com/vermiculite/index.htm
Have to say the perlite looks most suitable.
🙂/sreten.
Perlite isn't only used for aeration of gardening soil but also to keep snails from reaching your plants: the perlite sticks to their body and shifts when they try to move over it, it's like a treadmill for snails 😀
Definitely worth considering as dampening material
Simon
Definitely worth considering as dampening material
Simon
Hi
I found various grades of Perlite & Vermiculite at my big
hardware store. AUD$8.00 for a small 5 litre bag and Aud$16.00 for a big 20 litre sack. After reading the Kef paper on activated charcoal, it looks like my 3 litre enclosure can be upped to maybe 4.2 litres if we guess that 44% Perlite stuffing will work. Since Perlite is not Activated Charcoal and the use of thin bags for the material would perhaps be preferable a lot of testing will be necessary. I also purchased a cheap mask to handle the stuff but it should have been a mask suitable for handling Asbestos to be entirely safe.Maybe wetting a mask and using two together might be enough to get the amount I need in 2 bags. Going further with this project in Fremantle where I live is out of the question to the wind drops a bit and I can work in the garden.Clear skies forcast for Saturday this week for the Footie.
Perhaps this idea is similar to what Anthony Gallo claimed he was doing to enhance those little spheres he makes. He has some sort of Foam spagetti in his enclosures I believe.
Also I saw aerated clay balls in packs. Wonder if they might work too. Certainly less dust !
Regards
AnthonyPT
I found various grades of Perlite & Vermiculite at my big
hardware store. AUD$8.00 for a small 5 litre bag and Aud$16.00 for a big 20 litre sack. After reading the Kef paper on activated charcoal, it looks like my 3 litre enclosure can be upped to maybe 4.2 litres if we guess that 44% Perlite stuffing will work. Since Perlite is not Activated Charcoal and the use of thin bags for the material would perhaps be preferable a lot of testing will be necessary. I also purchased a cheap mask to handle the stuff but it should have been a mask suitable for handling Asbestos to be entirely safe.Maybe wetting a mask and using two together might be enough to get the amount I need in 2 bags. Going further with this project in Fremantle where I live is out of the question to the wind drops a bit and I can work in the garden.Clear skies forcast for Saturday this week for the Footie.
Perhaps this idea is similar to what Anthony Gallo claimed he was doing to enhance those little spheres he makes. He has some sort of Foam spagetti in his enclosures I believe.
Also I saw aerated clay balls in packs. Wonder if they might work too. Certainly less dust !
Regards
AnthonyPT
Hi to everyone,
several years ago, this article appeared as a paper in JAES. Since then I`ve been interested in practical results obtainable with activated carbon granules. Now I read about Perlite, and now you really got my attention.
The moisture problem can be "solved" using well sealed closed box, thus not allowing the moisture from the outer world to get to damping material. I was thinking of solving the particle breaking by putting the damping in a bag of polyester damping polyester or other stuffing metrial. But if this other damping material acts like a sieve and allows the smallest particles to pass through it, then we do nothing about protecting the speaker.
several years ago, this article appeared as a paper in JAES. Since then I`ve been interested in practical results obtainable with activated carbon granules. Now I read about Perlite, and now you really got my attention.
The moisture problem can be "solved" using well sealed closed box, thus not allowing the moisture from the outer world to get to damping material. I was thinking of solving the particle breaking by putting the damping in a bag of polyester damping polyester or other stuffing metrial. But if this other damping material acts like a sieve and allows the smallest particles to pass through it, then we do nothing about protecting the speaker.
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