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,
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 thatBanned
Joined 2002
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
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