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View Full Version : does adding polyfill change port tuning?



87regal
08-05-2009, 12:04 AM
If the volume of the box plays a role in the port tuning, and adding polyfill makes the box seem larger to the sub...does that mean the tuning would be affected by adding polyfill?

KyleBechtold
08-05-2009, 12:06 AM
usually don't add it to ported boxes but it doesn't actually increase space so i would say no.. it just slows down the waves..

michaellane
08-05-2009, 12:07 AM
hhhmmmm i dont know that ppl use it for ported boxes......but wait and see

KyleBechtold
08-05-2009, 12:09 AM
hhhmmmm i dont know that ppl use it for ported boxes......but wait and see

some do.. Idk what it would do... I would think it would lower the tuning if anything..

Sarthos
08-05-2009, 12:20 AM
doesn't the polyfill take up space in the box, making it smaller? Or is it an insignificant amount? I guess it depends on how much you use.

Jroo
08-05-2009, 10:11 AM
I dont usually see poly in car audio ported boxes, but home audio guys use it on their ported boxes all the time. You may want to ask the question on some of the home audio forums and see why they use it and how it changes porting and response.

dappa5
08-05-2009, 10:15 AM
i thought it only changed the tunning in that split seond it was ejected from the port like a cat upchucking a hairball ????

SubNit
08-05-2009, 10:15 AM
I've never really had luck in ported boxes with polyfill. It just seemed to soften the hit...and it can get messy

WrenchGuy
08-05-2009, 10:20 AM
http://www.soundsolutionsaudio.com/forum/index.php?/topic/7168-a-technical-understanding-of-polyfill/

Nut Hair Trick
08-05-2009, 10:27 AM
From what I understood, Polyfill makes the box seem bigger. If that's the case, it would be pointless to put polyfill in there because you will be changing the port tuning ie, port stays the same, but box get's bigger. Totaly defeats the purpose of designing the port for a specific tune to a specific box size. Unless you f'd up on the box build in the first place, that would be the only reason why I could see anyone using it for a ported box.

shizzzon
08-05-2009, 04:51 PM
There's another reason i'm bout to start testing.

I started an advanced thread about this over on SSA because i have a wall that i am currently building for next season comps and just ran into a.. well a wall(obstacle) on port tuning.

I have finally found the best port for my wall but if i want anymore output, i'm gonna need more internal volume.

I'm about to order a load of Acousta-stuf.. the expensive stuff and start doing testing with it in the box and in and around the port with a meter.

Basically, when sound passed through it, it will heat the surrounding air up making the air less dense which will allow the sound to flow quicker.

This phenomenon makes the sub think it's in a larger box.

I have theories but must be tested to conclude results-
Sound must pass through first or nothing will happen...

so what happens when it's in a port? Does it increase volume of a port and if it does... are all 3 dimensions increased proportionally resulting in the same tuning or does tuning go up since sound is flowing faster?

If packed too tight, it will make the sub think the volume has shrunk so be careful!

You also do not want this stuff touching speakers.

For my testing, if it does succeed in increasing volume, then i should see an increase on the meter when i rebuild the port to peak at my note...

These tests will commence in about a week from now.

rumblebee2
08-06-2009, 12:18 AM
very cool

dappa5
08-06-2009, 12:26 AM
T
This phenomenon makes the sub think it's in a larger box.

I WANT SOME SUBS THAT THINK !!! and where's my flying car d@mn it the Jetsons lied

Volenti
08-06-2009, 07:29 AM
There's another reason i'm bout to start testing.

I started an advanced thread about this over on SSA because i have a wall that i am currently building for next season comps and just ran into a.. well a wall(obstacle) on port tuning.

I have finally found the best port for my wall but if i want anymore output, i'm gonna need more internal volume.

I'm about to order a load of Acousta-stuf.. the expensive stuff and start doing testing with it in the box and in and around the port with a meter.

Basically, when sound passed through it, it will heat the surrounding air up making the air less dense which will allow the sound to flow quicker.

This phenomenon makes the sub think it's in a larger box.

I have theories but must be tested to conclude results-
Sound must pass through first or nothing will happen...

so what happens when it's in a port? Does it increase volume of a port and if it does... are all 3 dimensions increased proportionally resulting in the same tuning or does tuning go up since sound is flowing faster?

If packed too tight, it will make the sub think the volume has shrunk so be careful!

You also do not want this stuff touching speakers.

For my testing, if it does succeed in increasing volume, then i should see an increase on the meter when i rebuild the port to peak at my note...

These tests will commence in about a week from now.

The bottom line on dacron (or anything else that provides resistive damping) is that it will reduce resonance, reducing resonance can make an enclosure sound better, but it will never, ever increase absolute output, you need to increase resonance if you want more output with the same driver and power.

But don't take my word for it, play with different packing setups, and see the results for your self.

(edit to clarify) there are 2 effects happening, one is the thermal effect that makes the box "appear larger", this is a real effect and does actually happen. However, it is actually pretty subtle, in a sealed optimally packed enclosure the difference can amount to only 3-4hz difference between packed and empty. What swamps this is the second effect, which is resistive damping, that can have quite a dramatic effect and can reduce the amplitude of a resonant peak by half or more.

So yes you can indeed increase the apparent enclosure volume, but at the same time you cut your resonant peak in half, that will murder your spl score.

Immacomputer
08-06-2009, 08:39 AM
Home audio users use polyfil in their enclosures to reduce peaks around resonance (port tuning) and to smooth out upper frequency response. You shouldn't just pack it in a ported box all random because it will really kill the main function of the port. Most home audio ported enclosures just have polyfil lining the walls. Polyfil doesn't have the same spring loading properties that air has and so the enclosure can't really drive the port.

Polyfil doesn't really "make the box seem bigger" but rather just lowers the total damping of the system. It also doesn't "slow the sound wave down" either. I agree with Violenti in that the thermal effects are very minuscule.

Also, adding polyfil INTO the port is a terrible idea. That will change the port tuning drastically but not at all because of it making it appear bigger. It will load down the port with a much larger mass and drop the tuning significantly as your tuning frequency is based on the mass of the resonator (usually air or passive radiator).

shizzzon
08-06-2009, 09:27 PM
After polyfill testing is complete.. i will be doing another type of testing-

Bellmouth port testing. It's like aeroports for square vents.

I got a guy in my area that will custom make any size of Bellmouth port for my wall REAL CHEAP...

The bottom pic is an example of a Bellmouth port for my wall-

http://www.subwoofer-builder.com/port-flares/bellmouths.jpg

They have to be slightly modified to kill potential resonance for acoustical uses but besides that, in a few weeks i'll be testing these for more results.

dappa5
08-06-2009, 09:29 PM
After polyfill testing is complete.. i will be doing another type of testing-

Bellmouth port testing. It's like aeroports for square vents.

I got a guy in my area that will custom make any size of Bellmouth port for my wall REAL CHEAP...

The bottom pic is an example of a Bellmouth port for my wall-

http://www.subwoofer-builder.com/port-flares/bellmouths.jpg

They have to be slightly modified to kill potential resonance for acoustical uses but besides that, in a few weeks i'll be testing these for more results.
sombody has been to the HVAC store lol G/L w/that