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location of port inside of box


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MikeHusain 
Copper - Posts: 139
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Joined: April 10, 2003
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Posted: July 15, 2010 at 5:18 PM / IP Logged  

I am designing a ported enclosure for 2-12 inch W6V2 subwoofers and had a question regarding port location.  First, this is a common enclosure of 3.9 cubic feet internal space which I will be using a single port diameter of 7 inches and 30.5 inches long.  This should tune the box to/around 32 hz.  Due to the enclosure design, i have to use a round port.  I know the port outside of the box should face the same side as the woofers, but does it matter where the other side of the port is?  In other words, can the port be closer to woofer #1 than woofer #2?  Can it be in any direction inside of the box, lets say perpendicular to the subs? Or should the inside port be as close as inbetween the subs as possible in a certain direction?  Any help is greatly appreciated.

Thanks.

stevdart 
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Joined: January 24, 2004
Location: Pennsylvania, United States
Posted: July 16, 2010 at 12:08 AM / IP Logged  

The direction of the port inside the box is of no consequence whatsoever.  It is important, though, to leave a few inches of free air at the port terminus (both inside and outside the box).  Inside, there would be no difference at all that the port terminated closer to woofer one than to woofer two. 

This design is very sensitive to port length, as you have it spec'd out with a 7 inch port.  Just an inch in length will make a noticeable difference is Fb, so try to design this box so that you can adjust the port length for best sound in the actual car environment.  Use the calculator and put in different and varying tuning freqs to see what I mean about the critical port length in this enclosure.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
MikeHusain 
Copper - Posts: 139
Copper spacespace
Joined: April 10, 2003
Location: Pennsylvania, United States
Posted: July 16, 2010 at 7:30 AM / IP Logged  
Thanks for the information.  I see what you mean by length in port changes with respect to tuning frequency.  I spoke to a rep from JL audio and those are the specs he provided.  I noticed that when plugging in the 7 inch diameter with 3.0 net(excluding sub displacement and port) the calculator says to have a 28.6 inch port length.  This is about 2 inches short of what they spec'd.  Regardless, I will do what you said. Once completed, I can modify the port length to achieve desired sound performance. Thanks again for your help.
stevdart 
Platinum - Posts: 5,816
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Posted: July 16, 2010 at 8:14 PM / IP Logged  
...And you will rock!   ;-)
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
MikeHusain 
Copper - Posts: 139
Copper spacespace
Joined: April 10, 2003
Location: Pennsylvania, United States
Posted: July 19, 2010 at 12:20 PM / IP Logged  
Well, i completed the enclosure but came across a problem with the port design.  I can no longer work with a 7 inch diameter port as I would have liked to.  Being that I need a 40 square inch opening, can i use any dimensions to meet those specifications? For example, a 4" x 10" or 5" x 8" port?  THanks
stevdart 
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Posted: July 19, 2010 at 9:14 PM / IP Logged  
The square inch opening of a 7" port would have been 38.5 rather than 40, but I know you can fudge the dimensions a little to get where you want to be.  So sure, either of those square port openings would fit the bill.
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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