Adding Polyfill to port
12-04-2006, 10:54 AM
#1
50 Watt CAFz'r
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Join Date: Nov 2006
Posts: 145
Adding Polyfill to port
If my port is not quite as long as it should be, could i line 1 of the wall (its a slot port) with polyfill and trick the sub into thinking the port is loner? If so, how would I calulate the new length of the port?
12-06-2006, 06:55 AM
#2
Originally Posted by s14_240sx
If my port is not quite as long as it should be, could i line 1 of the wall (its a slot port) with polyfill and trick the sub into thinking the port is loner? If so, how would I calulate the new length of the port?
why polyfill? how is that going to work?
if it's a slot port, I assume an MDF box, can you add another section of MDF to make the port longer?
Mark
12-06-2006, 05:37 PM
#4
I like to use cowprint mac tac,did it before with dramatic results low deep clear bass, best sq ive ever heard.
j/k put the polyfill iside the box it will make the box seem "bigger" and tuning will in effect be lower a little.
Do a search on polyfil and you'll find tonnes of info on it.....
Maybe you can cut a peice of 5/8 mdf the size of the port wall too and glue it in,smaller opening=shorter port
j/k put the polyfill iside the box it will make the box seem "bigger" and tuning will in effect be lower a little.
Do a search on polyfil and you'll find tonnes of info on it.....
Maybe you can cut a peice of 5/8 mdf the size of the port wall too and glue it in,smaller opening=shorter port
Last edited by 92zed34; 12-06-2006 at 05:41 PM.
12-06-2006, 06:23 PM
#5
Originally Posted by Dukk
Dammit Mark, quit deconfusing it 
Mark
12-06-2006, 07:14 PM
#6
in practice Id hazard a guess that if anything stuffing fill into a port would make it seem shorter...
checking out tuning is almost as simple as hooking up a dmm to your sub and playing some test tones so it could be worth trying out...
but on the otherhand you are probably going to kill some of your output....
checking out tuning is almost as simple as hooking up a dmm to your sub and playing some test tones so it could be worth trying out...
but on the otherhand you are probably going to kill some of your output....
Last edited by Haunz; 12-11-2006 at 02:12 PM.
12-06-2006, 07:28 PM
#7
if you take a section of the port and fill it with polyfill, you will slow down the velocity of the air, which makes the port sound like it's a longer port, because a lot of the tuning is affected by the velocity of the air leaving the port, also, if you have the port end very close to a wall, so that it restricts the amount of airflow, it will make the port seem longer.
by seeming longer, I mean lowering the tuning note of the box.
by seeming longer, I mean lowering the tuning note of the box.
12-06-2006, 08:22 PM
#8
50 Watt CAFz'r
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Join Date: Nov 2006
Posts: 145
Thanks sassmaster, Thats what I thought would happen too (slowing down the air). I decided im just going to make my slot port thinner, therefore i won't need to have such a long port. The port velocity is still respectable, at around 20m/s.
12-06-2006, 08:42 PM
#9
sass you can look at the velocity of sound in two ways which work independently from one another.....
since we are dealing with long wavelengths the velocity of air inside the ports we are talking about can be seen as a function of the rate of pressure change inside the port.... greater rate ~ greater pressure ~ greater velocity........ and true enough adding fill will reduce this.... which will effectivley reduce the amplitude of the pressure wave leaving the port....
The other velocity we are interested in is propagation of a wave through space....
I strongly doubt that the port will seem longer to a pressure wave... and to boot as direct resistriction to airflow increases, the box will begin to approximate the response of a sealed box.... and that will also likley raise fb.....
That said I encourage you to test it out for yourself before you take my word for it...
since we are dealing with long wavelengths the velocity of air inside the ports we are talking about can be seen as a function of the rate of pressure change inside the port.... greater rate ~ greater pressure ~ greater velocity........ and true enough adding fill will reduce this.... which will effectivley reduce the amplitude of the pressure wave leaving the port....
The other velocity we are interested in is propagation of a wave through space....
I strongly doubt that the port will seem longer to a pressure wave... and to boot as direct resistriction to airflow increases, the box will begin to approximate the response of a sealed box.... and that will also likley raise fb.....
That said I encourage you to test it out for yourself before you take my word for it...
Last edited by Haunz; 12-11-2006 at 02:14 PM.
12-06-2006, 09:01 PM
#10
The fill isn't a solid though, it's a whole lot of randomly shaped solids that force the air to reflect and change it's path around the tiny solids. True, it will reduce the output slightly, but the low end ouput will be better. adding a resonance chamber in the middle of the port can achieve the same thing without the restriction...
