Thank you for the tips!
I was hoping that a resonator would do something even in a smaller size, so I made this:
A leftover from some active noise cancelling experiment, where I had some 6,5" woofer mounted on the top. I did some quick calculations on port lengths, and cut some pieces for my relevant frequencies.
Took it home, put it in the corner of the room, and measured just next to the opening like this, I figured that if I could measure something next to it, I could at least tune it a bit, and move on to measure further away.
I did a few sweeps with different port lengths, with and without a sock in the port, and I could not measure any significant difference even that close! Maybe 0.1dB or so, and that could just as well be measurement errors due to background noise or whatever. I studied spectrograms and everything, but could not see any difference.
So, this idea goes in the bin I think.. any 'last orders' before I scrap it?
I even tried dropping the microphone in the resonator, and all I could see was a drop-off at higher frequencies, maybe from tuning frequency and upwards. No clear peak at resonance.
I was hoping that a resonator would do something even in a smaller size, so I made this:
A leftover from some active noise cancelling experiment, where I had some 6,5" woofer mounted on the top. I did some quick calculations on port lengths, and cut some pieces for my relevant frequencies.
Took it home, put it in the corner of the room, and measured just next to the opening like this, I figured that if I could measure something next to it, I could at least tune it a bit, and move on to measure further away.
I did a few sweeps with different port lengths, with and without a sock in the port, and I could not measure any significant difference even that close! Maybe 0.1dB or so, and that could just as well be measurement errors due to background noise or whatever. I studied spectrograms and everything, but could not see any difference.
So, this idea goes in the bin I think.. any 'last orders' before I scrap it?
I even tried dropping the microphone in the resonator, and all I could see was a drop-off at higher frequencies, maybe from tuning frequency and upwards. No clear peak at resonance.
I was a bit lazy, not tightening the lid down. After re-thinking, I had to try it, and I could actually see a few dB's difference. Going low in tuning frequency does less (abt 1dB at 32Hz, and up around 60Hz, there there is a bit more effect, but still, this is measured just by the vent..
I can also se the effect on Q when sliding the damping up in the pipe.
I can also se the effect on Q when sliding the damping up in the pipe.
Doing an experiment with the resonator @60Hz, I got a 2dB reduction at the 'corner listening position'. As far as I can tell, the decay slope is the same (in the waterfall), so the tone dies out at the same rate, it's just 2dB lower. So in my world, this would be the same as using a peaking filter to pull it down 2dB?
Sorry if I'm asking stupid questions, but I'm trying to get my bearings when it comes to this. I have tried EQ:ing for the room in my last apartment, but I was not so happy with the result, so I figured room treatment would be the way to go. When doing the EQ, I thought I lost the attack and dynamics in drums etc.
Maybe resonators work like above, ringing and not removing much energy, and absorption actually gets the energy out of the room quicker?
Sorry if I'm asking stupid questions, but I'm trying to get my bearings when it comes to this. I have tried EQ:ing for the room in my last apartment, but I was not so happy with the result, so I figured room treatment would be the way to go. When doing the EQ, I thought I lost the attack and dynamics in drums etc.
Maybe resonators work like above, ringing and not removing much energy, and absorption actually gets the energy out of the room quicker?
I bought some wood today, plan is to modify the sofa tomorrow (have a day off work), to hopefully improve it's performance as an absorber. It's an easy and cheap mod, so I figure I would start with the easy stuff.
Today it's open from both sides, underside and pillow side. Well, actually it's sealed behind backrest pillows, but just some fabric and springs under the seat, so I consider that as 'open' for bass. I added a bunch of IKEA pillows to the underside under the springs before, so there is maybe 30-40cm of 'absorbing material' counting the pillows on the sofa and the IKEA pillows on the underside. The idea is to extend the edges on the underside to seal the underside to the floor, so it becomes a 'closed back' absorber.
To my understanding, this is better for LF absorption(?). I think of it a little bit like open baffle vs a closed box, the closed box is more effective for producing bass, and I'm thinking a closed back on the absorber should work the same way?
I'm thinking the air flow takes the easiest path, and part of that would be around the edges if it's open from both sides, just like an open baffle as long as baffle is small compared to wavelength, or a car radiator without shrouds. So my assumption is that it will not remove as much energy as if it would have to pass through the porous material?
I see many people putting free standing absorbers in a corner (for example standing on the floor and leaning toward the wall), but with the ends open. Is this really the best way, or are they doing it wrong?
Thank you all for the good input so far, keep it coming! As I said, I have no experience from acoustic treatments, just reading and watching some youtube videos. There are a lot of limitations since it's a living room, and in a rental apartment. It has to be practical, and not intrude to much on the living space, look 'good' etc. I can't be gluing on the wall paper, or drilling too many holes, or I will be in trouble when the landlord finds out.. It also needs to be easy to remove, and hopefully re-usable if we move. Too bulky, and it will be hard to move as well. So, there are a lot of limits, oh, I forgot cost, that's definitely a factor too!
Today it's open from both sides, underside and pillow side. Well, actually it's sealed behind backrest pillows, but just some fabric and springs under the seat, so I consider that as 'open' for bass. I added a bunch of IKEA pillows to the underside under the springs before, so there is maybe 30-40cm of 'absorbing material' counting the pillows on the sofa and the IKEA pillows on the underside. The idea is to extend the edges on the underside to seal the underside to the floor, so it becomes a 'closed back' absorber.
To my understanding, this is better for LF absorption(?). I think of it a little bit like open baffle vs a closed box, the closed box is more effective for producing bass, and I'm thinking a closed back on the absorber should work the same way?
I'm thinking the air flow takes the easiest path, and part of that would be around the edges if it's open from both sides, just like an open baffle as long as baffle is small compared to wavelength, or a car radiator without shrouds. So my assumption is that it will not remove as much energy as if it would have to pass through the porous material?
I see many people putting free standing absorbers in a corner (for example standing on the floor and leaning toward the wall), but with the ends open. Is this really the best way, or are they doing it wrong?
Thank you all for the good input so far, keep it coming! As I said, I have no experience from acoustic treatments, just reading and watching some youtube videos. There are a lot of limitations since it's a living room, and in a rental apartment. It has to be practical, and not intrude to much on the living space, look 'good' etc. I can't be gluing on the wall paper, or drilling too many holes, or I will be in trouble when the landlord finds out.. It also needs to be easy to remove, and hopefully re-usable if we move. Too bulky, and it will be hard to move as well. So, there are a lot of limits, oh, I forgot cost, that's definitely a factor too!
For acoustical treatment, a thick 6' x 3' wool rug hung on the wall works very well, especially on the wall behind you.
Otherwise, hang the rug between the speakers, or at one of the the first reflection points on the side walls.
You can buy wool rugs with various colors and patterns, and they can look reasonably good on a wall.
Build a rectangular wood frame that is somewhat smaller in size, with the rug nailed to it only along the top edge.
The frame is hung on the wall like a picture, with two hooks because of the weight and long width.
The rug should overlap the wood frame on all sides by around 4" so the frame is not visible. You could also paint
the frame white (or the same color as the wall) so it is less visible.
Otherwise, hang the rug between the speakers, or at one of the the first reflection points on the side walls.
You can buy wool rugs with various colors and patterns, and they can look reasonably good on a wall.
Build a rectangular wood frame that is somewhat smaller in size, with the rug nailed to it only along the top edge.
The frame is hung on the wall like a picture, with two hooks because of the weight and long width.
The rug should overlap the wood frame on all sides by around 4" so the frame is not visible. You could also paint
the frame white (or the same color as the wall) so it is less visible.
Last edited:
I have been thinking about that earlier, and looked at some rugs in thrift stores, but never actually 'pulled the trigger'. It does appear much easier for covering larger areas of the walls..
I cant cover the rear wall because of windows, so I have to make do with curtains that can be easily opened to let light in, water flowers etc.
I cant cover the rear wall because of windows, so I have to make do with curtains that can be easily opened to let light in, water flowers etc.
So, I did my sofa mods today..
The pillows were there before, I just added the 'fairing' between the legs on the sofa and some felt to act as a seal to the floor.
Measurements show no improvement, and possibly a deeper null, but the measurements vary a bit, so I would say the result is the same or slightly worse. Not a good result for a days work..
I did a -4dB 'notch' at 36Hz in the DSP, and that made more difference in the measurement, and took maybe 1min.. But, then again I'm into room-EQ territory that I was not completely positive about last time I tried it.
The pillows were there before, I just added the 'fairing' between the legs on the sofa and some felt to act as a seal to the floor.
Measurements show no improvement, and possibly a deeper null, but the measurements vary a bit, so I would say the result is the same or slightly worse. Not a good result for a days work..
I did a -4dB 'notch' at 36Hz in the DSP, and that made more difference in the measurement, and took maybe 1min..
But, then again I'm into room-EQ territory that I was not completely positive about last time I tried it.
Nice hands on stuff, thanks documenting it here!
You could think wavelength as some kind of guide. I bet if an object, absorber or a rock or anything has very little effect if wavelength is 10x bigger. There probably is noticeable effect when wavelength is 4x, perhaps very noticeable (absorber in velocity node). Max effect is reached when wavelength is size of the object.
Although its not very accurate because sound reflects in room (modes!) and hits an object multiple times but perhaps it can still act as simple rule of thumb.
A cubic meter pillow is probably effective to say 4 meter wavelength (85hz) but has not much effect for 10 meter wavelength (35Hz). Same for the helmholz resonator, sound probably just went around like it wasn't there at all.
This is analugous to bafflestep, which peaks around 1wl baffle size and minimum is reached perhaps 3 octaves below. Wavelength is so long the box has no effect on it and radiation is same to all directions like the box wasnt there at all, while above bafflestep the box is big enough to reflect and diffract.
You could think wavelength as some kind of guide. I bet if an object, absorber or a rock or anything has very little effect if wavelength is 10x bigger. There probably is noticeable effect when wavelength is 4x, perhaps very noticeable (absorber in velocity node). Max effect is reached when wavelength is size of the object.
Although its not very accurate because sound reflects in room (modes!) and hits an object multiple times but perhaps it can still act as simple rule of thumb.
A cubic meter pillow is probably effective to say 4 meter wavelength (85hz) but has not much effect for 10 meter wavelength (35Hz). Same for the helmholz resonator, sound probably just went around like it wasn't there at all.
This is analugous to bafflestep, which peaks around 1wl baffle size and minimum is reached perhaps 3 octaves below. Wavelength is so long the box has no effect on it and radiation is same to all directions like the box wasnt there at all, while above bafflestep the box is big enough to reflect and diffract.
Last edited:
Yes, I'm with you on the wavelength. I did not really expect the sofa mod to do much to the 36Hz resonance, but I was hoping to see some changes from maybe 60Hz or so. I understand absorbers are most effective from !/4 wavelength and up, and absorption falls off below that. Then I guess it's about how the sound hits the absorber too. Here the 'entry point' is the seat pillows, and that is probably not the best place.. I'm thinking maybe I should try to open up the gap to the floor on the back (against the wall), not sure if it's a good idea or not..
Thinking about absorbers at low frequencies, they are between the high pressure node (the wall/corner etc) and the velocity maximum, I'm thinking the pressure difference is driving the air through the porous material and slowing it down, and converting it to heat. So, if that is the case, the absorber should sit at 1/4 wl from the pressure node, and the air should be forced to go through the absorber (not around) to get to the pressure node, where it obviously wants to go -because it's a pressure node, for maximum effect. Does this seem logical?
Thinking about absorbers at low frequencies, they are between the high pressure node (the wall/corner etc) and the velocity maximum, I'm thinking the pressure difference is driving the air through the porous material and slowing it down, and converting it to heat. So, if that is the case, the absorber should sit at 1/4 wl from the pressure node, and the air should be forced to go through the absorber (not around) to get to the pressure node, where it obviously wants to go -because it's a pressure node, for maximum effect. Does this seem logical?
Ok, today work has begun on some absorbers. I changed the plan a bit after re-thinking. I had the plan to use the hemp-based insulation in the ceiling, but today after 'listening to it' a bit, I think it's almost useless as an absorber. Fibers are to coarse and far between, and it's light, so the whole thing is very 'sound transparent'. The 'recycled cloth'/denim is a lot heavier, and sounds a lot more 'dead' when I put my ear close to it, very similar to rockwool I think. It's also heavier and has no rigidity, which is a problem, as it collapses on itself by it's own weight. It needs support to keep it's shape when used in a frame.
Ok, so based on what I have learned lately, I also think I need a lot more area covered than I had planned form the beginning, so instead of making a pair of absorbers at listening height, I decided to go floor to ceiling, and make some adjustable feet or similar, so the absorber can be 'jammed' between floor and ceiling. No need for drilling holes, and it will be easy to move around if needed. I used the denim on the outside, and the hemp based just as a backing against the wall instead of an air gap. It helps hold the denim insulation in place, and I get some use for it. Total thickness is abt 9cm, The plan is to order more material and make at least one more for the opposite side of the room. Something for ceiling absorbers too, and possibly a rug for the front wall behind the TV.
I also started making a smaller/thinner absorber from the basotect I had left. Plan is to put the basotect on some fibrous board as backing and cover it with some band poster and put it over the sofa on the wall to the left of the listening position. I have noticed some subjective improvement when placing pillows there.
Ok, so based on what I have learned lately, I also think I need a lot more area covered than I had planned form the beginning, so instead of making a pair of absorbers at listening height, I decided to go floor to ceiling, and make some adjustable feet or similar, so the absorber can be 'jammed' between floor and ceiling. No need for drilling holes, and it will be easy to move around if needed. I used the denim on the outside, and the hemp based just as a backing against the wall instead of an air gap. It helps hold the denim insulation in place, and I get some use for it. Total thickness is abt 9cm, The plan is to order more material and make at least one more for the opposite side of the room. Something for ceiling absorbers too, and possibly a rug for the front wall behind the TV.
I also started making a smaller/thinner absorber from the basotect I had left. Plan is to put the basotect on some fibrous board as backing and cover it with some band poster and put it over the sofa on the wall to the left of the listening position. I have noticed some subjective improvement when placing pillows there.
Where are you located? Hemp is to "light" for being used as a "thin" absorber (<40cm), also are your IKEA pillows. You need more dense material for that.
What you need ist the flow resistivity of the material. And then you can easily calculate (read estimate ;-)) what's going on:
http://www.acousticmodelling.com/porous.php
http://www.acousticmodelling.com/multi.php
Your idea of floor to ceiling is very good! Way to often people forget about the area >2m height and get bad flutter echoes there.
Basotect is good but expensive. I like to use Caruso Isobond, sheep wool or "wood wool". But simple rock wool is also great for that purpose, probably best with a thin plastic layer around it cause of fibers.
I would not had sealed the sofa to the ground, at least let it oben in front or back so sound pressure from the floor can get into it. But most important is the absorbing part AWAY from the wall (so where you sit - it's there anyway) and less the space you improved. So it's no wonder this doesn't do a lot.
What you need ist the flow resistivity of the material. And then you can easily calculate (read estimate ;-)) what's going on:
http://www.acousticmodelling.com/porous.php
http://www.acousticmodelling.com/multi.php
Your idea of floor to ceiling is very good! Way to often people forget about the area >2m height and get bad flutter echoes there.
Basotect is good but expensive. I like to use Caruso Isobond, sheep wool or "wood wool". But simple rock wool is also great for that purpose, probably best with a thin plastic layer around it cause of fibers.
I would not had sealed the sofa to the ground, at least let it oben in front or back so sound pressure from the floor can get into it. But most important is the absorbing part AWAY from the wall (so where you sit - it's there anyway) and less the space you improved. So it's no wonder this doesn't do a lot.
I'm located in Sweden, which should be 'insulation land', but have not found any denim based insulation here, and I have not been able to find anybody in Europe who sells the denim based insulation in small quantities and ships it. I sent an email to eurokustik where I got this, and asked if they stopped selling it, and if they know somewhere where I can get it.
I kind of liked it, and I would like to make one more of those high absorbers to put on the other side wall first reflection point.. If I can't get more, maybe I have to split it in two and just place them at listening height anyway.
I have seen some wool-based insulation while searching I think, but by description it was very loosely packed, and that is why I did not investigate it further, thinking it would be a pain to 'pack' and it would push the fabric covering the absorber, making it swell like a pillow..?
I want to avoid the rockwool.. wouldn't wrapping it in air tight plastic make it something different than a porous absorber? More like a membrane-type, since it will not 'breathe'?
I'm thinking I should re-visit the sofa mods, but at the moment I'm just stuck sitting in it listening to music Opening the underside to the back to the rear seems most logical to me (makes a bigger 'baffle' ref to the discussion before), but my acoustic intuition seems to be mostly wrong so far!
When it comes to basotect, I'm thinking of using it in the ceiling, maybe four 60x120x5cm pieces around the first reflection point. I don't want to have too much thickness there, since it might intrude too much and make the ceiling feel/look too low.
I think the white basotect would melt right in with the white ceiling and save a lot of extra work wrapping with fabric etc. Wooden frames, fabric etc costs money too, so it might not even cost more in the end. It is a bit sensitive, so I'm not so keen on using it on walls where stuff might fall against it etc and rip it.
I made a small basotect absorber and put it in the end of the sofa today. I put the self-adhesive basotect on a fibrous board and then some wooden legs on that and stuck the legs between the sofa and the wall. Covered with the 'flag-poster' of one of my childhoods favorite records
Here is the high absorber, still in the garage, can't get it in my car, and still need to solve the fastening.
I kind of liked it, and I would like to make one more of those high absorbers to put on the other side wall first reflection point.. If I can't get more, maybe I have to split it in two and just place them at listening height anyway.
I have seen some wool-based insulation while searching I think, but by description it was very loosely packed, and that is why I did not investigate it further, thinking it would be a pain to 'pack' and it would push the fabric covering the absorber, making it swell like a pillow..?
I want to avoid the rockwool.. wouldn't wrapping it in air tight plastic make it something different than a porous absorber? More like a membrane-type, since it will not 'breathe'?
I'm thinking I should re-visit the sofa mods, but at the moment I'm just stuck sitting in it listening to music
Opening the underside to the back to the rear seems most logical to me (makes a bigger 'baffle' ref to the discussion before), but my acoustic intuition seems to be mostly wrong so far!When it comes to basotect, I'm thinking of using it in the ceiling, maybe four 60x120x5cm pieces around the first reflection point. I don't want to have too much thickness there, since it might intrude too much and make the ceiling feel/look too low.
I think the white basotect would melt right in with the white ceiling and save a lot of extra work wrapping with fabric etc. Wooden frames, fabric etc costs money too, so it might not even cost more in the end. It is a bit sensitive, so I'm not so keen on using it on walls where stuff might fall against it etc and rip it.
I made a small basotect absorber and put it in the end of the sofa today. I put the self-adhesive basotect on a fibrous board and then some wooden legs on that and stuck the legs between the sofa and the wall. Covered with the 'flag-poster' of one of my childhoods favorite records
Here is the high absorber, still in the garage, can't get it in my car, and still need to solve the fastening.
I have a pair of 'absorbers' I made from towels some time ago, and they have been sitting behind the speakers waiting for modifications, since I thought they would not work, but yesterday I tried moving them around a bit, and put them at an angle facing back towards the speakers around the first side reflection points, and there was actually some improvement in upper mid/treble clarity, so There is for sure some improvements to be had there.
Try to put it in here: http://www.acousticmodelling.com/porous.php
50mm, for Basotect maybe a little higer flow resistivity, 15.000.
When your reflection should be 20dB lower in Level - you need an absorption of 0,9! So that's 1kHz with 5cm .... and the really bad frequency area of 100-300Hz sees no serious dampening at all.
The room needs AT LEAST as much love as the speaker! ;-)
50mm, for Basotect maybe a little higer flow resistivity, 15.000.
When your reflection should be 20dB lower in Level - you need an absorption of 0,9! So that's 1kHz with 5cm .... and the really bad frequency area of 100-300Hz sees no serious dampening at all.
The room needs AT LEAST as much love as the speaker! ;-)
I know it's a compromise, but I can't put >20cm thick absorbers hanging from the ceiling at the first reflection point.., tall persons would basically hit their heads.. and it's just too much aesthetically even for me. Maybe I could leave some air gap above the 5cm panels to make the reach a bit lower in frequency, but that's about it..
I'm considering adding something in the front wall corners with some more thickness to do something for lower frequencies though. There is some 'dead space' anyway, and it would not intrude on the 'living space'.
I'm considering adding something in the front wall corners with some more thickness to do something for lower frequencies though. There is some 'dead space' anyway, and it would not intrude on the 'living space'.
Your room is small and tricky, as you don’t have that many options with placement of furniture and speakers due to doors and windows and the large L-shaped couch doesn’t make it easier. As a start, one option would be to lift out the “foot rest” from the room. You could then move the couch forward, further away from the back wall. Some things should then improve: A) Mode problems should be lessened further away from the wall, 1st and 2nd length modes are hard for you to “fix” with absorbers which aren’t deep and large. B) Each foot / 0,34 m away from the back wall will delay the specular reflection from it with 2 ms. Specular reflections within the first 5 ms (or so) are the worst and should be avoided if possible. Try about 1,5 m distance if that is practical for you, otherwise the further the better. C) Moving out the couch from the back wall should improve your listening angle as well.
If moving the couch into the room considerably is an option for you, you can build / place a bench, say 60 cm deep behind the couch and below the windows. Preferably along the whole back wall. It could serve 2 purposes: A) To put stuff on and B) under the top you fill it up with insulation with low air flow resistivity. 60 cm with 5 kPa x s / m will make a difference in the bass and low mids. 5 kPa x S / m² would in Sweden be Isover Piano or URSA 37 from Byggmax: https://www.byggmax.se/media/catalo...012/Ursa_multiskiva37.pdf-1645443115.1204.pdf If you must go for a slimmer depth you should go up a bit in air flow resistivity, Rockwool Flexibatts is around 9 kPa x s / m² (say < 20 cm) Isover Byggskiva 37 is around 13 kPa x s / m² (say <= 10 cm). The IKEA pillows have a filling of dacron / polyester hole fibre, If not densily compressed and as a sheet, air flow resistivity is around 3 kPa x s / m². (It doesn’t surprise me you found them to more or less useless under the couch cushions).
You can also build compound absorbers with insulation material having different air flow resistivities. Check up: https://jhbrandt.net/wp-content/uploads/2022/11/Broadband-Absorption.pdf There are also several other articles and papers on John Brant´s page https://jhbrandt.net/resources/ which are well worth reading. The 3 kPa x s / m² material he mentions for the compound absorbers would be dacron / polyester but as a fabric / weave. You can buy this as various fabric stores, it is used for jackets and furniture, usually comes in 12 – 20 mm thickness (täckjacksfoder in Swedish, yes I’m Swedish too), https://www.selfmade.com/sv-se/p/polyester-foder-vit-3595/8001 ) If you use this as front material towards the room, you need not to worry about loose fibres from the Isover or rockwool insulation. (There is actually no health hazard with them. Yes they irritate and itch on the skin, but the fibre diameter is so large they don’t present a health risk like lung cancer. Numerous thorough investigations over decades have shown that. The fibre diameter has to be 6 mikrometers or smaller to be a serious health problem, asbestos fibre are in that range, smaller than 6 mikrometers.)
If moving the couch into the room considerably is an option for you, you can build / place a bench, say 60 cm deep behind the couch and below the windows. Preferably along the whole back wall. It could serve 2 purposes: A) To put stuff on and B) under the top you fill it up with insulation with low air flow resistivity. 60 cm with 5 kPa x s / m will make a difference in the bass and low mids. 5 kPa x S / m² would in Sweden be Isover Piano or URSA 37 from Byggmax: https://www.byggmax.se/media/catalo...012/Ursa_multiskiva37.pdf-1645443115.1204.pdf If you must go for a slimmer depth you should go up a bit in air flow resistivity, Rockwool Flexibatts is around 9 kPa x s / m² (say < 20 cm) Isover Byggskiva 37 is around 13 kPa x s / m² (say <= 10 cm). The IKEA pillows have a filling of dacron / polyester hole fibre, If not densily compressed and as a sheet, air flow resistivity is around 3 kPa x s / m². (It doesn’t surprise me you found them to more or less useless under the couch cushions).
You can also build compound absorbers with insulation material having different air flow resistivities. Check up: https://jhbrandt.net/wp-content/uploads/2022/11/Broadband-Absorption.pdf There are also several other articles and papers on John Brant´s page https://jhbrandt.net/resources/ which are well worth reading. The 3 kPa x s / m² material he mentions for the compound absorbers would be dacron / polyester but as a fabric / weave. You can buy this as various fabric stores, it is used for jackets and furniture, usually comes in 12 – 20 mm thickness (täckjacksfoder in Swedish, yes I’m Swedish too), https://www.selfmade.com/sv-se/p/polyester-foder-vit-3595/8001 ) If you use this as front material towards the room, you need not to worry about loose fibres from the Isover or rockwool insulation. (There is actually no health hazard with them. Yes they irritate and itch on the skin, but the fibre diameter is so large they don’t present a health risk like lung cancer. Numerous thorough investigations over decades have shown that. The fibre diameter has to be 6 mikrometers or smaller to be a serious health problem, asbestos fibre are in that range, smaller than 6 mikrometers.)