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Old 06-26-2015, 11:09 PM
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Default Question regarding port and dual subs

If I have two subwoofer in a common enclosure, I only need one port correct? Because a port tunes the enclosure, not the subs?
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Old 06-26-2015, 11:15 PM
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Quote:
Originally Posted by Vmax911 View Post
If I have two subwoofer in a common enclosure, I only need one port correct? Because a port tunes the enclosure, not the subs?
you can have two ports, three ports, or one port, depending on what you want to tune the enclosure to.

If you're using aero's, you may need more than 1 for your desired tuning and port area requirements. Typically, you want to be able to do everything with 1 port for efficiency purposes.

And yes, the port tunes the enclosure. Subs SLIGHTLY change the tuning of the enclosure due to displacement
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Old 06-26-2015, 11:29 PM
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Thanks for the quick reply. Though you kind of blew my mind with the multiple port thing. Do the ports sum together, or act independently?
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Old 06-26-2015, 11:39 PM
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Port Length Calculator
Play with this a bit and it will all make sense. Just start pluggin in numbers
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Old 06-27-2015, 12:04 AM
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Thanks for the link. Looks like the more ports the longer they need to be, why would anyone want more than one port?

Also, does the port volume subtract from the net volume of the enclosure?
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Old 06-27-2015, 01:00 AM
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Yes it does. As an avg 9-12sq in of port area for round and 12-15sq in per cubic foot of box volume for a slot port.
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Old 06-27-2015, 08:46 AM
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Thanks again for the info. Looks like I need to add with some numbers now.

Lastly (hopefully), does it matter where the port openings are located?
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Old 06-27-2015, 09:43 AM
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Quote:
Originally Posted by Vmax911 View Post
Thanks again for the info. Looks like I need to add with some numbers now.

Lastly (hopefully), does it matter where the port openings are located?
It can. The concept is referred to as "end correction". Ports rely on a very specific amount of air that is contained within the boundary of the port volume. Imagine a square port that goes through the middle of the enclosure wall and the inside port opening (terminus) isn't near a corner or nearby wall. The volume of air in the port will be consistent with the port dimensions. If the same sized port is moved over so that it is against one of the enclosure walls, the enclosure wall acts like a port extension on one side. In the attached drawing you can see a "normal" port on the left. The green lines represent the walls of the port and the yellow area is the volume of the port. The picture on the right represents the same port width and depth but you can see that the enclosure wall on the right acts like a really long port wall. The yellow area of the port volume is extended out a bit and becomes larger due to that longer wall. The longer the port the lower the tuning, so as you can see the port of the right will be tuned lower than the port on the left even though the port length is exactly the same.

This is called "slot loading", which you will probably see listed in most online port tuning calculators.

Also note that anything which is around or next to the port opening on the inside or the outside of the enclosure can result in a lower tuning. Pushing a ported enclosure up next to the side wall of your trunk so that the port fires off of the side of the trunk will cause effective tuning to lower because of the same concept; the calculated volume of the port will "couple" to some additional air volume that is squeezed in next to the port due to the close proximity of a loading surface near the port terminus.

Note that the larger the enclosure (and/or port) the bigger the role this concept plays. For averaged sized ports the enc correction might only account for a couple hertz difference in effective tuning, but for large enclosures with short port lengths there could be a difference of 10 or more hertz between the calculated tuning and the effective tuning after accounting for end correction.
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Old 06-27-2015, 10:31 AM
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Awesome, you guys really know your stuff! And thanks for taking the time to explain that.

I know the port is tuned to a specific frequency, but does the sound actually emanate from the port? If so, should put on the same side as the drivers to keep the same phase?
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Old 06-27-2015, 11:04 AM
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Yes you can put it on the same side
That is where you get vehicle dependent though

Some cars like sub and port back
Some like sub up port back
Some port forward subs back
Some both forward
Some like port firing to one side or even a specific corner

The options for testing are limitless

What vehicle is this going in people will be able to give you a great general idea
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