By how much can fiberglass actually 'increase' enclosure volume?? - diyAudio
 By how much can fiberglass actually 'increase' enclosure volume??
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 14th January 2004, 12:15 AM #1 diyAudio Member   Join Date: Jun 2003 Location: Canada By how much can fiberglass actually 'increase' enclosure volume?? I've read that by using fiberglass as stuffing in a speaker you can make the driver 'see' a bigger enclosure (something to do with its thermal properties). Does anyone know approximately how much 'virtual' volume you can gain by using this to its full advantage? Thanks Sardonx __________________ The End
 14th January 2004, 12:44 AM #2 diyAudio Member   Join Date: Feb 2001 Location: Columbia, SC I've seen different values in different books, but the upper limit seems to be about 1.4 x nominal enclosure volume. How tightly you have to pack it is open to question; they never seem to get around to telling you that part. Lotsa places admit to more modest figures like 1.2. Grey
 14th January 2004, 12:46 AM #3 Account disabled at member's request   Join Date: Feb 2002 Location: Clifton Park, NY Hi Sardonx, The compliance of the air in a box is calculated using the following expression : Cab = V / (rho x c^2) where V = volume rho = density of air c = speed of sound in air For a given box, the volume V and the density of air are constant. The speed of sound is related to the type of expansion and compression of the air in the box. If the air compresses adiabatically (the box is empty) then c^2 is proportional to the adiabatic ratio of the specific heats which is 1.4. If the air compresses isothermally (best possible fiber present to absorb the heat) then c^2 is proportional to the isothermal ratio fo specific heat 1.0. In this second case the box has a lower compliance and looks 40% bigger then the empty box. The most a box can be made to look "bigger" by adding fiber is about 40%, this is the upper limit. This assumes the fiber volume is small compared to the box air volume. In real world applications, my guess is that the most you can gain in "virtual" volume is about 20%. Hope that helps,
 14th January 2004, 01:57 AM #4 diyAudio Member   Join Date: Dec 2001 Location: Ottawa, Ontario, Canada MJK, would the equation that you posted change for a vented enclosure? Considering you now have three air masses instead of two. Rear wave inside enclosure, front wave outside enclosure, and the air-mass inside the port. __________________ ERTW 4 life! "the day has 24hours. If that is not enough take the night."-Roemhild
 14th January 2004, 02:19 AM #5 Mark Kravchenko diyAudio Member     Join Date: Jan 2002 Location: Perth Canada Filled up and still more space The max you can get in the real world is about 25% greater seen volume by the woofer suspension system. It's been described rather well. The air flowing in to the box through the port or air within a closed box will literally be slowed down when it is forced through the filler. Not the whole truth but it works. This makes the woofer think that it is inside a bigger box because with the filler it behaves like it is inside a bigger box. Mark Ps. BoseO where do you live so that I can check out your enclosures?????? __________________ Mark www.kravchenko-audio.com
 14th January 2004, 03:56 AM #6 diyAudio Member     Join Date: Apr 2003 Location: Brantford, ON dont use fibreglas as a fill....go to a poly or wool fill...you doont want to be breathing in that
 14th January 2004, 04:25 AM #7 Banned   Join Date: Apr 2002 it is also not Cotton candy. : O ) but looks like it : O)
 14th January 2004, 04:51 AM #8 diyAudio Editor     Join Date: Dec 2001 Location: San Francisco, USA San José, Costa Rica I think the air being slowed is a different thing-an aperiodic port. I've alway heard as was originally mentioned- that it is the mass of the fill absorbing heat, albeit a very small amount. __________________ "The geek shall inherit the earth" 2016 S.F. Burning Amp Festival To Be Nov. 13 Burning Amp thread here on diyAudio [/B]
 14th January 2004, 05:50 AM #9 diyAudio Member   Join Date: Jun 2003 Location: Canada Wow... Thank you, Grey and MJK. 20% is not bad at all. I didn't know it was that much! __________________ The End
 14th January 2004, 05:53 AM #10 diyAudio Member   Join Date: Jun 2003 Location: Canada and thanks everyone else! The server was down for a while.. i didn't realize there were more posts. I would love to use wool... does it work as well as fiberglass for expanding volume? And where can i get wool? __________________ The End

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