# crazy port noise



## mikemareen (Apr 20, 2006)

can anyone help me get rid of port noise ?

I have a ported box for two 6w0's and it sounds great, the only problem is the crazy port noise.

the noise goes away completely when I cover the port.

the noise gets louder when I put my hand above the port and feel the air coming out of the port.

keep in mind the port is only a 3" by 1" vent.

what do u guys think I should do ?


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## DonutHands (Jan 27, 2006)

sounds like its too small of a vent. maybe but some poly fill in the opening.


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## strong*I*bumpin (Oct 3, 2005)

...or too small of a box


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## mikemareen (Apr 20, 2006)

ok thanks guys

I will try polyfil.

hopefully I can get rid of the noise because I really really like the sound of this set-up


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## Tommythecat (Apr 6, 2006)

I used the stock WinISD files to look at port velocity.

As soon as you put 75 watts into them, the port velocity gets above the safety zone (which I believe is around 30-35 m/s, anyone want to correct me?). If you bumped up to a 3" port (you're at about a 2" port) then that would halve the port velocity. And they'd still be at acceptable levels up to 150W->rated power together.

What kind of power are they seeing now? Over 100W?


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## mikemareen (Apr 20, 2006)

Tommythecat said:



> I used the stock WinISD files to look at port velocity.
> 
> As soon as you put 75 watts into them, the port velocity gets above the safety zone (which I believe is around 30-35 m/s, anyone want to correct me?). If you bumped up to a 3" port (you're at about a 2" port) then that would halve the port velocity. And they'd still be at acceptable levels up to 150W->rated power together.
> 
> What kind of power are they seeing now? Over 100W?


I haven't re-adjusted the gains on the amp yet so they are both probably seeing about 320 watts rms (2 channels bridged off a arc 4150xxk)

but yeah when I turn it up, the velocity of the air coming out of the port is insane, it almost feels like air from a hair blow dryer.

so your saying increasing the port size by 50 percent (2" to 3" ) should decrease port noise? that's gonna be hard to do cuz the box is already built.  what about adding polyfill ? you think it will help ?


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## mikemareen (Apr 20, 2006)

well guys, I've been told to use a subsonic filter, lower the lowpass xover point and stuff more polyfill.

hope it works.

any other suggestions in it doesn't work ?


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## notacop (Jan 27, 2006)

subsonic and lowering the lowpass just means they will play less of the audio spectrum, this may reduce port noise, but will effect other ways that they integrate with everything else. 

You can also try rounding the edges of the port, and eliminating any ridges where the baffle meets the port.


The best answer is not the easiest, your box is not optimal for them, you need more port area.


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## chuyler1 (Apr 10, 2006)

If you increase the port area you will also have to change the length of the port...just making sure you know that. 

I'm just playing around with this quick box calculator...
http://www.carstereo.com/help/Articles.cfm?id=31

It recommends a port diameter of 3" for a pair of 6.5" speakers if you were to tune the box at 35Hz. If you tune it to 20Hz you could go as small as 2.3".

Now on the bottom of the page I entered in 1 port, 0.5cuft enclosure, tuned to 35Hz, with a 1" diameter port. This gave me a port length of 2.7". That's pretty close to what you have now. Let's say I change that port diameter to 2" and leave the rest the same. The calculator now says you need a port length of 12.36". If you increase the port diameter to the recommended 3" the length would have to be 28"! Ouch!

Ok, back to the drawing board. Increase the size of the box to 1 cuft with one port and tune it to 35Hz. With a port diameter of 2.5" you can get by with a 9" long port. That is at least reasonable.


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## mikemareen (Apr 20, 2006)

I'm maxed out on air-space. the box is ON TOP of my rear deck (acura sedan) and is only 3.5" thick, any thicker and it will distrupt my rear view visual clearance.


It sounds absolutely wonderful, it's not as loud as a 10" in the trunk but it is loud enough (no weak sauce bass and I've had some decent amp-sub set ups in my trunk) , I don't feel the need to have to pump it louder because it is so nicely balanced. It sounds nothing like a subwoofer in the trunk, no sloppy over-extended low end.

now I'm wondering how a pair of ED eu700's or Tang Band w6 subs would do.

but hey, I'm gonna try a few things that u guys suggested with the polyfill and subsonic filter, etc. Hopefully it will do the trick.









chuyler1 said:


> If you increase the port area you will also have to change the length of the port...just making sure you know that.
> 
> I'm just playing around with this quick box calculator...
> http://www.carstereo.com/help/Articles.cfm?id=31
> ...


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## notacop (Jan 27, 2006)

The eD 700's will likely be too deep they are near 3.75" deep by themselves. 


If you are laying it on the rear deck make sure it is secured!!! Otherwise in an accident it will be flying right at the back of your head. 


Using a slot port you can get port lengths much longer than you can with pvc by simply folding the port back and forth inside the box. If you give the maximum dimensions you have available I am sure there are people here who could help see if there are better options for you.


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## mikemareen (Apr 20, 2006)

my available dimensions are:

45.5" length
3.5" depth
8" height

currently the port is actually 1.25" x 2.5" x 9.25" 







notacop said:


> The eD 700's will likely be too deep they are near 3.75" deep by themselves.
> 
> 
> If you are laying it on the rear deck make sure it is secured!!! Otherwise in an accident it will be flying right at the back of your head.
> ...


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## notacop (Jan 27, 2006)

mikemareen said:


> my available dimensions are:
> 
> 45.5" length
> 3.5" depth
> ...



Those dimensions work out to an internal volume of 0.45 cube if you use 0.5" MDF, that is _before_ woofer and port displacement. A port of 1.25*2.5*9.25" long will displace around 0.02 cubes, the woofers without looking it up are probably going to bring your gross volume down to 0.4 or less cubes, that is getting pretty small for ported. 


Your best bet for those dimensions is to go sealed, as that is about optimal. It would sound better and fit perfect, however your output may be down a little.


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## mikemareen (Apr 20, 2006)

notacop said:


> Those dimensions work out to an internal volume of 0.45 cube if you use 0.5" MDF, that is _before_ woofer and port displacement. A port of 1.25*2.5*9.25" long will displace around 0.02 cubes, the woofers without looking it up are probably going to bring your gross volume down to 0.4 or less cubes, that is getting pretty small for ported.
> 
> 
> Your best bet for those dimensions is to go sealed, as that is about optimal. It would sound better and fit perfect, however your output may be down a little.


wow your right on the money, that's the exact specs I got when I put in the order for this box.


Ya I've tried it sealed with no satisfactory output.


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## mikemareen (Apr 20, 2006)

wow this is the first time everything consecutively worked out my way

the poly fill did the trick.

I stuffed the box and the port with polyfill. I wasn't affraid to generously stuff it seeing that JL audio and Kicker both tightly stuff their prefab boxes like crazy.

at first I just stuffed the box which decreased port noise by about 50 percent but not completely. I then stuffed the port which completely removed port noise.

it definitely slowed down the turbulence in the port opening.

sound quality is actually better identical to when it was sealed; however I did notice a slight loss in DB (in comparison to before the polyfill stuffing) , probably about 1 db.

the only slight noise I get is when the 6w0 subwoofer cones start to reach it's limitations.


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