ports and noise
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=93854
Printed Date: May 07, 2024 at 1:23 AM
Topic: ports and noise
Posted By: pbguy
Subject: ports and noise
Date Posted: May 12, 2007 at 6:09 PM
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?
Replies:
Posted By: sedate
Date Posted: May 12, 2007 at 8:09 PM
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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"I'm finished!" - Daniel Plainview
Posted By: stevdart
Date Posted: May 13, 2007 at 12:13 AM
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.
Posted By: sedate
Date Posted: May 13, 2007 at 2:05 PM
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? ------------- "I'm finished!" - Daniel Plainview
Posted By: pbguy
Date Posted: May 13, 2007 at 2:59 PM
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.
Posted By: pbguy
Date Posted: May 13, 2007 at 3:02 PM
2 inch port, 1.35 cf, 40 hertz= 2.45 inches port
Posted By: DYohn
Date Posted: May 13, 2007 at 3:20 PM
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. ------------- Support the12volt.com
Posted By: pbguy
Date Posted: May 13, 2007 at 5:32 PM
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.
Posted By: aznboi3644
Date Posted: May 13, 2007 at 9:42 PM
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??
Posted By: stevdart
Date Posted: May 13, 2007 at 10:57 PM
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.
Posted By: sedate
Date Posted: May 14, 2007 at 12:46 AM
aznboi3644 wrote:
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??
I dunno.. I mean I calculated the ports in WinISD first and it didn't have a problem with the setup. I have a pair of 12's with four 1-inch ports that are each about 4inches long. This is why I was originally expressed some original suprise over the problem. If you stand over the trunk and really listen, it does chuff just a bit when the system really gets going, but nothing you hear in the car... certainly not a fart or swish noise. It actually is one of the best sounding boxes I've ever constructed. ------------- "I'm finished!" - Daniel Plainview
Posted By: aznboi3644
Date Posted: May 14, 2007 at 3:44 PM
sedate wrote:
aznboi3644 wrote:
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??
I dunno.. I mean I calculated the ports in WinISD first and it didn't have a problem with the setup. I have a pair of 12's with four 1-inch ports that are each about 4inches long. This is why I was originally expressed some original suprise over the problem.
If you stand over the trunk and really listen, it does chuff just a bit when the system really gets going, but nothing you hear in the car... certainly not a fart or swish noise. It actually is one of the best sounding boxes I've ever constructed.
Ahh icic...well what is the highest port velocity that WinISD says it has?? Have you tried comparing it to a box with more port area??
Posted By: sedate
Date Posted: May 15, 2007 at 8:39 AM
aznboi3644 wrote:
well what is the highest port velocity that WinISD says it has?? Have you tried comparing it to a box with more port area
If I recall, that port velocity was calculated to something like 110feet per second... it was right under what WinISD wouldn't have been happy with... I had to play with it a bit to get the vent mach down into the green. And yes... given my reservations about the smallish ports I was using, I constructed a slightly larger box for the 12's with six 1-inch ports tuned to the same frequency. This box sounded identical to the first box. I probably would have stuck with the six-port enclosure, but when my old Toyota got wrecked, it wouldn't fit into my new car.. so I switched back to that old four-port box. ------------- "I'm finished!" - Daniel Plainview
Posted By: aznboi3644
Date Posted: May 15, 2007 at 4:06 PM
Well what I mean was like a box the same size with two 4 inch round ports or one six inch round port.
In my box right now the maximum port velocity is only about 25ft per second.
Sorry about the thread jackage
Posted By: sedate
Date Posted: May 15, 2007 at 9:59 PM
Whoa that looks sweet. Reminds me of transmission line boxes my ex's dad used to build. You should finish it. Anyway... naww I needed *really* small ports, so that's why I ended up using little 1" ports like that. Four 1"x4" ports were *so* easy to build into the box.. and I'm not really running much power to my 12's anyway.. like ~200watts/sub. I'm liking those TC Sounds subs that keep coming up again and again and I'm thinking of building a new slot-port box specifically for my new car around them... I wanna drop the impedence on my subs down to 2-ohms anyway.. I'm kinda wasting half my sub amp running at 4-ohms. ..Anywho..yea sorry abuot the thread jackage. ------------- "I'm finished!" - Daniel Plainview
Posted By: aznboi3644
Date Posted: May 15, 2007 at 10:34 PM
yeah...Well I graduate Memorial Day weeekend so right now I really have no time to finish it...I still need to glue the baffle board on and fill in all the screw holes...I wanna paint it a glossy black
Carpeting that thing would be a pain in the arse.
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