ports and noise

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pbguy

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Joined: April 27, 2007

Posted: May 12, 2007 at 6:09 PM / IP Logged

My sister has 2 punch 8' P1 subwoofers in a dual enclosure. Rockford recommends .65 cubic feet ported. The box is 1.35 cubic feet, so basically 2 subs are perfect for that enclosure. Well the port is soppose to be 2' dia and almost 6 inches long (I made both ports 2' and 6 inches long) So all the specs are right, but everytime they hit the air coming out of the ports makes a swissshh or a fart sound. What is wrong? I was thinking the ports need to be bigger or longer. Also is was impossible to make the port 2 inches away from the side and the bottom, so its near the walls as well.

Help please?

sedate

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Location: Colorado, United States

Posted: May 12, 2007 at 8:09 PM / IP Logged

Huh. That looks like plenty of port for those woofers. I mean *plenty* of port. That's really strange. I have a pair 12's I run with less port and I don't have that problem.

I dunno man. Build a new box? Perhaps something with a slot-port design?

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stevdart

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Joined: January 24, 2004

Location: Pennsylvania, United States

Posted: May 13, 2007 at 12:13 AM / IP Logged

The tuning freq is very high. Lower the Fb by using longer ports. You can replace the current ports with these flared port tubes from Parts Express. Length should be along the lines of about 9 to 10 inches. Here is a port calculator that will tell you what the flared length should be for desired Fb, and the port tubes come with instructions for the calculation as well. I would look at lowering tuning to around 38 Hz, and see how it sounds.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

sedate

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Posted: May 13, 2007 at 2:05 PM / IP Logged

stevdart wrote:

The tuning freq is very high.

Why does this matter? Wouldn't port noise strickly be a product of too much air in too small a port?

Not trying to argue, just expand my working knowledge.

stevdart, can you please elaborate on this?

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pbguy

Member - Posts: 17

Joined: April 27, 2007

Posted: May 13, 2007 at 2:59 PM / IP Logged

Well I did the calculating for 40 hz and it said like a 3 inch port. Tryed that, same prob. Then I went to 6 inches same problem. I asked around and people told me the ports needed to be rounded off , because it creates wind noise.

Im just using standard pvc pipe to port it if that helps.

pbguy

Member - Posts: 17

Joined: April 27, 2007

Posted: May 13, 2007 at 3:02 PM / IP Logged

2 inch port, 1.35 cf, 40 hertz= 2.45 inches port

DYohn

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Posted: May 13, 2007 at 3:20 PM / IP Logged

If you are getting port noise then the port diameter needs to be increased. Try 4". If the tuning frequency is too high that makes it easier to hear port noise, since most of the sound output at the tuning frequency comes from the port and our ears pick up on 48Hz a lot better than they do on 24Hz, for example.

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pbguy

Member - Posts: 17

Joined: April 27, 2007

Posted: May 13, 2007 at 5:32 PM / IP Logged

4' diameter ? Thats half the size of the sub, you think that inst too big?

I want to make sure so i dont have to make the hole bigger ,and cant go back.

aznboi3644

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Posted: May 13, 2007 at 9:42 PM / IP Logged

too big??? haha...nah it isn't too big. It will be a lot better than the ports you have now.

Sedate...I'm curious. How do you have a couple 12s with less port area than two 2 inch round ports and not have any port noise or extremely high port velocity??

stevdart

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Posted: May 13, 2007 at 10:57 PM / IP Logged

sedate, DYohn elaborated for me. My first instinct was to suggest a larger diameter port as well, but length will grow very long with such a port. The most reasonable compromise is to lower tuning freq. pbguy, do you understand that I suggested flared (rounded off) ports? You didn't say so...and 4" is normal port size for a sub. Calculate square inches of a 4" circle (12.56) compared to a 8" circle (50.24) and you quickly see that the port is not half the size of the sub, (as if that matters anyway). It is 1/ 4th the size.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

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