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Old 03-09-2015, 09:55 PM
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Default Quick Port Question

If making a center port box and you want to make the port 4.25 inches longer and im already the port width away from the back wall do I just L them off toward the sides of the box on each side 2.125 inches on each side? Hope this makes since. Lol.
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Old 03-09-2015, 11:31 PM
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Extend it the entire length of the extension, so both sides will be 4.25", but half the width to keep port area consistent. Example: you need a port 6"wide by 15" tall and 4.25" more in length. Each leg will be 3" wide, 15" tall, and 4.25" in length.

Also keep in mind that if the port runs along the back wall you'll get more of a slot loading effect than you would with a center port who's terminus just hangs in the middle of the enclosure.
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Old 03-10-2015, 10:27 AM
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Originally Posted by SPLEclipse View Post
Extend it the entire length of the extension, so both sides will be 4.25", but half the width to keep port area consistent. Example: you need a port 6"wide by 15" tall and 4.25" more in length. Each leg will be 3" wide, 15" tall, and 4.25" in length.

Also keep in mind that if the port runs along the back wall you'll get more of a slot loading effect than you would with a center port who's terminus just hangs in the middle of the enclosure.
To make sure i read right, I make both legs 4.25" long. What do you mean by slot loading affect? How would this affect the enclosure?
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Old 03-10-2015, 11:35 AM
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That's right. Both legs 4.25" long but half the width.

Slot loading happens when one edge of the port is longer because it uses the enclosure wall as one of it's walls. This effectively extends the port length beyond what you have calculated for. The typical adjustment you make is to account for an extra 1/2 width of the port and assume it's going to be added to the physical length you have in the enclosure.

I attached a picture. In the top box, if the port was 4" wide and 6" long, you could calculate tuning like normal. The port walls are in red and the effective port length is in green. It would act like a 6" long port. In the second picture if the port was 4" wide and 10" long, the green line that represents effective port length goes beyond the physical port length in the box because the air mass "drags" along the back wall. You can see that the two red lines representing the port are different lengths, with the back wall acting like a longer port leg.

If you want more info you can google "port end correction".
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Old 03-10-2015, 11:41 AM
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Quote:
Originally Posted by SPLEclipse View Post
That's right. Both legs 4.25" long but half the width.

Slot loading happens when one edge of the port is longer because it uses the enclosure wall as one of it's walls. This effectively extends the port length beyond what you have calculated for. The typical adjustment you make is to account for an extra 1/2 width of the port and assume it's going to be added to the physical length you have in the enclosure.

I attached a picture. In the top box, if the port was 4" wide and 6" long, you could calculate tuning like normal. The port walls are in red and the effective port length is in green. It would act like a 6" long port. In the second picture if the port was 4" wide and 10" long, the green line that represents effective port length goes beyond the physical port length in the box because the air mass "drags" along the back wall. You can see that the two red lines representing the port are different lengths, with the back wall acting like a longer port leg.

If you want more info you can google "port end correction".
Oh end correction. I am familiar with that. Effective port length vs physical port length. I gothcha. Thanks bro.
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