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
Thanks
Sardonx
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
Grey
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,
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,
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.
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??????
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??????
dont use fibreglas as a fill....go to a poly or wool fill...you doont want to be breathing in thatMember
Joined 2002
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.
I've alway heard as was originally mentioned- that it is the mass of the fill absorbing heat, albeit a very small amount.
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?
I would love to use wool... does it work as well as fiberglass for expanding volume? And where can i get wool?
The equation for the compliance of the air in a box is the same for a closed and a vented box. So nothing changes.
I am not sure I understand your second question. If you stuffed a vented box to reach a 20% virtual increase in volume, then I think one of the results would also be that the box is not very resonant any more. This would require a lot of stuffing. The QL would be very low and the motion of the air in the port would be significantly attenuated. It would be a very weak bass reflex design and not perform as expected.
This link shows the results of a practical experiment to determine the amount of change you can get with various densities of stuffing.
http://www.win.net/audtatious/audio/fiber.html
http://www.win.net/audtatious/audio/fiber.html
mwmkravchenko, sorry about the delay. I remember trying to post up and something came up and just left...anyway the post that was intended for you never reached you. If you use MSN then add me to your list please: voodooman_1000@hotmail.com
Also, insulation+fiberglass is not supposed to be safe either...doesn't stop me though..anything to kill those nasty resonances and "increase" enclosure size.
Also, insulation+fiberglass is not supposed to be safe either...doesn't stop me though..anything to kill those nasty resonances and "increase" enclosure size.
Nuuk said:
Erm..... I sorry but they don't.
you need a clear aipspace arround the port to allow it to work,
the maximum stuffing you can use is ~ 50% of the aipspace,
either by lining the walls or by stuffing the top half where the
driver is & leaving the bottom half unstuffed where the port is.
So maximum increase for a reflex is ~ 10%.
🙂 sreten.
I used fibreglass stuffing in my tempest subs, they were sealed and I just used standard baf around the driver to stop the 'nasty' stuff getting near me when I fitted the driver.
If you stuff it outside and use a mask, gloves , long sleeves etc then you should be fine.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=20091&perpage=15&highlight=&pagenumber=6
Cheers,
Rob
If you stuff it outside and use a mask, gloves , long sleeves etc then you should be fine.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=20091&perpage=15&highlight=&pagenumber=6
Cheers,
Rob
Everyone is talking about a seeming increase in size, a decrease in Qtc and a decrease in Fc.
But isn't there a corresponding reduction in sensitivity as well? Don't you go down a dB or two along with your Fc and Qtc?
But isn't there a corresponding reduction in sensitivity as well? Don't you go down a dB or two along with your Fc and Qtc?
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