nearing the end of my long build, but along the way I managed to very cleverly not get the same volume in my new box as I had in the old...duhh.
The new box is prob about 10-15% smaller (?), and as I wanted to 'get the same sound' then that is one variable I am a bit concerned about. It may be more of a problem in my case than in others, as I use eq to get the woofer to go lower, and (well at least in my old box) 30-35 hz seems about as low as I can get the woofers to go. With a smaller box that may be harder to achieve.....?
Ok then, stuffing a box with f/glass makes the box 'bigger' to the woofer (of course my current box has f/glass in it too). So does that mean all I do is simply stuff/force/cram even more f/glass into the box to compensate??
I mean it's not some 'never ending' process here is it? more f/glass does not always means 'bigger' box does it? there would be some limit surely where more f/glass produces no more change - or even worsens things?
In any case, can we have too much f/glass? If we have too much, what are the results??
How can we know how much f/glass is optimum, is it just an empiric formula along the lines of kgs/cubic m (and are those formulas only guidelines, or can they be 'modified' as in my case for a certain purpose) , or are there ways to measure and from that determine when we have the right amount.
Indeed, I have seen what appear to be different types of f/glass, some kinda coarse and 'gluggy' or all bonded together, others seem kinda fluffy and free (audiophile descriptions there heh heh). I would presume the fluffy would be the 'best' yeah? ie sort of allows air movement.
just hope the smaller box does not come back to bite me...
The new box is prob about 10-15% smaller (?), and as I wanted to 'get the same sound' then that is one variable I am a bit concerned about. It may be more of a problem in my case than in others, as I use eq to get the woofer to go lower, and (well at least in my old box) 30-35 hz seems about as low as I can get the woofers to go. With a smaller box that may be harder to achieve.....?
Ok then, stuffing a box with f/glass makes the box 'bigger' to the woofer (of course my current box has f/glass in it too). So does that mean all I do is simply stuff/force/cram even more f/glass into the box to compensate??
I mean it's not some 'never ending' process here is it? more f/glass does not always means 'bigger' box does it? there would be some limit surely where more f/glass produces no more change - or even worsens things?
In any case, can we have too much f/glass? If we have too much, what are the results??
How can we know how much f/glass is optimum, is it just an empiric formula along the lines of kgs/cubic m (and are those formulas only guidelines, or can they be 'modified' as in my case for a certain purpose) , or are there ways to measure and from that determine when we have the right amount.
Indeed, I have seen what appear to be different types of f/glass, some kinda coarse and 'gluggy' or all bonded together, others seem kinda fluffy and free (audiophile descriptions there heh heh). I would presume the fluffy would be the 'best' yeah? ie sort of allows air movement.
just hope the smaller box does not come back to bite me...
Re: can you [I]overstuff[/I] a box with f/glass?
If you are speaking of a purely sealed "acoustic suspension" design, 10-15% change will not change performance very much - try doing some box modeling in any of the free programs out there and you'll see.
The best way to "see" how the stuffing is changing things is to run impedance curves with a woofer tester. As stuffing is gradually added, both the system Fs and Qts will drop. At some point of stuffing (when density is too great) the trend will reverse, and box volume is robbed by the stuffing, and the dense stuffing begins to behave more like a solid than absorptive mass.
If you are doing some other design (ported, transmission line, etc) than forget all the above -- added damping will mess with box tuning and Q.
-- Mark
terry j said:
If you are speaking of a purely sealed "acoustic suspension" design, 10-15% change will not change performance very much - try doing some box modeling in any of the free programs out there and you'll see.
The best way to "see" how the stuffing is changing things is to run impedance curves with a woofer tester. As stuffing is gradually added, both the system Fs and Qts will drop. At some point of stuffing (when density is too great) the trend will reverse, and box volume is robbed by the stuffing, and the dense stuffing begins to behave more like a solid than absorptive mass.
If you are doing some other design (ported, transmission line, etc) than forget all the above -- added damping will mess with box tuning and Q.
-- Mark
Hi Terry
I was going to send a link and now I can't find it in my bookmarks, damned old-timers disease; I think that the limit is reached when stuffing exceeds air density by more than a certain percentage, the figure I have in my mind is 30%, but graduated density seems to work better for me.
From memory ( as I said I can't find the link) acoustic fiberglass batts have much finer fibre size and is specially made to have a denser layer on the outside.
That said I always use normal fiberglass as i can walk down to Bunnings and buy a pack any day, but I always try and put that layer of BAM or Polyester between the glass and the woofer.
How's Cinderella going??
I'll go and get the "Cookbook" and get back
I was going to send a link and now I can't find it in my bookmarks, damned old-timers disease; I think that the limit is reached when stuffing exceeds air density by more than a certain percentage, the figure I have in my mind is 30%, but graduated density seems to work better for me.
From memory ( as I said I can't find the link) acoustic fiberglass batts have much finer fibre size and is specially made to have a denser layer on the outside.
That said I always use normal fiberglass as i can walk down to Bunnings and buy a pack any day, but I always try and put that layer of BAM or Polyester between the glass and the woofer.
How's Cinderella going??
I'll go and get the "Cookbook" and get back
Just quickly reading ; maximum size increase seems to be at the 2lb per cubic foot mark when using standard 100% fill.
When using 50/50 fill there is a significant increase in apparent box size when using 2lb cubic foot against the walls and 1lb per cubic foot as the rest of the fill, Qtc shows big drop equal to 30%+ increase in box size.
So use normal stuff against the walls and fluff up the rest and hope it works, or try and get the proper acoustic stuff from ACI for the fill;
Owens-Corning 205 is the real stuff, I don't know if it is available in OZ
Regards
Ted
When using 50/50 fill there is a significant increase in apparent box size when using 2lb cubic foot against the walls and 1lb per cubic foot as the rest of the fill, Qtc shows big drop equal to 30%+ increase in box size.
So use normal stuff against the walls and fluff up the rest and hope it works, or try and get the proper acoustic stuff from ACI for the fill;
Owens-Corning 205 is the real stuff, I don't know if it is available in OZ
Regards
Ted
Re: Re: can you [I]overstuff[/I] a box with f/glass?
How silly of me to leave that bit of data out. Yes it is sealed. Always 'knew' that 10-15% was no biggie, except as in my case I use tons of eq to get it low. Think in the box au naturale it starts rolling off at 70-75 hz or so, so to get it low in room requires a bit of eq. Dunno if that changes the situation of a minor percentage change or not.
Yeah, that articulates well what I was trying to say was my gut feel. At some point you have added so much or compressed it so much that it is no longer 'porous' and ends up just like adding bricks to the chamber, ie robbing volume.
Now I don't have woofer tester, but I vaguely recall seeing a post at the shack where he somehow used REW (maybe measuring across a resistor???) to get impedence plots. maybe not exact or calibrated, but enough to guage changes as we add f/glass....will try and find it, if I do I'll link to it here.
thanks for your help
I can get how thinner would help (more surface area), but on the flip side would not the denser cover inhibit?
Is that to keep fibres away from the woofer? does it matter, or some sort of health thing?
yeah that is what this is about, going well since my revitalisation recently. Prob next week can start the veneering of the baffle, the finishing will take a bit longer and then I guess that's it!
start planning for bathurst this year yeah?? you're running out of excuses you know.
Tubamark said:
How silly of me to leave that bit of data out. Yes it is sealed. Always 'knew' that 10-15% was no biggie, except as in my case I use tons of eq to get it low. Think in the box au naturale it starts rolling off at 70-75 hz or so, so to get it low in room requires a bit of eq. Dunno if that changes the situation of a minor percentage change or not.
Yeah, that articulates well what I was trying to say was my gut feel. At some point you have added so much or compressed it so much that it is no longer 'porous' and ends up just like adding bricks to the chamber, ie robbing volume.
Now I don't have woofer tester, but I vaguely recall seeing a post at the shack where he somehow used REW (maybe measuring across a resistor???) to get impedence plots. maybe not exact or calibrated, but enough to guage changes as we add f/glass....will try and find it, if I do I'll link to it here.
thanks for your help
Moondog55 said:
I can get how thinner would help (more surface area), but on the flip side would not the denser cover inhibit?
Is that to keep fibres away from the woofer? does it matter, or some sort of health thing?
yeah that is what this is about, going well since my revitalisation recently. Prob next week can start the veneering of the baffle, the finishing will take a bit longer and then I guess that's it!
start planning for bathurst this year yeah?? you're running out of excuses you know.
thanks malcoHm
BUT, it took me years to finally get a nice looking box (so frankenstein can morph into cindarella dontcha know?) so at this stage no more bodgying yeah?
And BTW, you gotta start planning for bathurst too, you are coming aren't you???
cheers moondoggieboy, think I'll just use f/glass yeah? I can easily rob it from the house rather than buying special stuff.
BUT, it took me years to finally get a nice looking box (so frankenstein can morph into cindarella dontcha know?) so at this stage no more bodgying yeah?
And BTW, you gotta start planning for bathurst too, you are coming aren't you???
cheers moondoggieboy, think I'll just use f/glass yeah? I can easily rob it from the house rather than buying special stuff.
Denser on the outside to trap the "Adiabatic to Isothermic" heat inside the batt. used a lot in window treatment of pubs and discos to keep the "Noise" inside.
The health issue is a consideration too but remember that the fibers from the glass is so fine that as the woofer pumps in and out ( I assume voice coil venting here ) some fibers get inside and apparently can build up to the point where the voice coil can jam/pole when it gets hot, never happened to me but why take the chance when poly is so cheap/ free even, I just use old pillows if have run out of the bonded sheet.
Bonded sheet is also free, I get mine from air-conditioning duct off cuts, factory just down the road.
Bathurst? love to, gotta get a job first so I can pay for the petrol, unless I hitch-hike.
And the get together WAS my idea wasn't it, damn i gotta buy that church in the country
The health issue is a consideration too but remember that the fibers from the glass is so fine that as the woofer pumps in and out ( I assume voice coil venting here ) some fibers get inside and apparently can build up to the point where the voice coil can jam/pole when it gets hot, never happened to me but why take the chance when poly is so cheap/ free even, I just use old pillows if have run out of the bonded sheet.
Bonded sheet is also free, I get mine from air-conditioning duct off cuts, factory just down the road.
Bathurst? love to, gotta get a job first so I can pay for the petrol, unless I hitch-hike.
And the get together WAS my idea wasn't it, damn i gotta buy that church in the country
thanks for the link, had seen it before but no way would I have found it again easily.
re measuring impedance, I guess at the end of the day there is no real difference between doing that and simply (close mic) measuring the woofer is there??
If you are going to the effort of finding the exact amount (which would entail removing the woofer multiple times) then just re-measure the FR each time and you should end up at the same place surely?
re measuring impedance, I guess at the end of the day there is no real difference between doing that and simply (close mic) measuring the woofer is there??
If you are going to the effort of finding the exact amount (which would entail removing the woofer multiple times) then just re-measure the FR each time and you should end up at the same place surely?
dunno the date malcolm, usually early october. I'm sure andrew will start a thread on it. you can give moondog a lift heh heh, as well as chickenman
You serious moondog?? the fibres can build up enough to sieze the drivers??
Still, get your point, why not put a barrier? Taking those idea forward a bit, what's to stop the f/glass eventually slumping/vibrating enough to physically touch the woofer?? Surely that is a more probable eventuality?
You serious moondog?? the fibres can build up enough to sieze the drivers??
Still, get your point, why not put a barrier? Taking those idea forward a bit, what's to stop the f/glass eventually slumping/vibrating enough to physically touch the woofer?? Surely that is a more probable eventuality?
Terry I have no idea, but it was a serious warning in the book by Weems; so as it adds zero to the cost I have always done it.
It helps that I cannot stop scrounging, I once filled a big transmission line ( boy was that a mistake--- long story ) with an couplepof down Doonas that were thrown out by Myer
It helps that I cannot stop scrounging, I once filled a big transmission line ( boy was that a mistake--- long story ) with an couplepof down Doonas that were thrown out by Myer
The old rule of thumb was to only slightly compress the fibreglass or tontine.
Adding extra to compensate for a smaller volume may reduce the sensitivity. Why not place something in the larger enclosure to reduce it's volume?
If the driver is vented a piece of muslin or stocking material over the vent will help keep the fibres out of the gap.
Adding extra to compensate for a smaller volume may reduce the sensitivity. Why not place something in the larger enclosure to reduce it's volume?
If the driver is vented a piece of muslin or stocking material over the vent will help keep the fibres out of the gap.
Re: Re: Re: can you [I]overstuff[/I] a box with f/glass?
Hi,
KEF, England invented a second opportunity to virtually boost the enclosure volume. The fibre stuff aims to bring the compression from adiabatic to isothermal. Factor is 20% at it's ultimate maximum. Well, KEF aims for a temporal absoption of air molecules in active coal. For that purpose active coal is packed into small sacks. These are found in the eclosure to boost the acoutical volume by a greater margin than acievable before. You have to google it Yourself, sorry, I forgot the exact link.
so long
btw: perhaps You take the "sack" idea for itself. It wouldn't harm if the fibres are contained in an airtight (!) sack. If only the sack is flexible and lightweight enough. Appropiate foil is available nearly everywhere.
terry j said:
Hi,
KEF, England invented a second opportunity to virtually boost the enclosure volume. The fibre stuff aims to bring the compression from adiabatic to isothermal. Factor is 20% at it's ultimate maximum. Well, KEF aims for a temporal absoption of air molecules in active coal. For that purpose active coal is packed into small sacks. These are found in the eclosure to boost the acoutical volume by a greater margin than acievable before. You have to google it Yourself, sorry, I forgot the exact link.
so long
btw: perhaps You take the "sack" idea for itself. It wouldn't harm if the fibres are contained in an airtight (!) sack. If only the sack is flexible and lightweight enough. Appropiate foil is available nearly everywhere.
Re: Re: Re: Re: can you [I]overstuff[/I] a box with f/glass?
I know you will be there, your life would not be worth living if you weren't!
old was about 110, new I would not think more than 85-90.
did you mean active charcoal? I've heard of that kinda, but don't know anymore than that.
will do a search on active charcoal
edit, not a lot, and not toooo much useful info
http://74.125.153.132/search?q=cach...ers&cd=1&hl=en&ct=clnk&gl=au&client=firefox-a
Brett said:
I know you will be there, your life would not be worth living if you weren't!
old was about 110, new I would not think more than 85-90.
xpert said:
did you mean active charcoal? I've heard of that kinda, but don't know anymore than that.
will do a search on active charcoal
edit, not a lot, and not toooo much useful info
http://74.125.153.132/search?q=cach...ers&cd=1&hl=en&ct=clnk&gl=au&client=firefox-a
Re: Re: Re: Re: Re: can you [I]overstuff[/I] a box with f/glass?
http://www.kef.com/technology/acoustic/acework.asp
terry j said:
http://www.kef.com/technology/acoustic/acework.asp
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