I'm building a compact Sonosub with a freebie 18" tall x 15" wide fiber bin and I'm looking for ways to get the port tune low so i can eq down low without over excursion.
Basically I want to fit a long port in a small cylinder.
Some ways i've thought of would be slanted ports and some extra mdf on the top plate for added length or using the tube as a natural port by sealing off 1 side of the tube in the inside and extending it above the tube with mdf at a right angle like this:
Is there any point making the part of the port that's inside the tube larger than the mdf part of the port?
I can't have the port exiting on the driver side if that's what you mean, it's a 15" wide tube and a 12" driver.
How much does direction change effect port noise?
No reason you couldnt have the port opening on the top like a SVS sono sub? As long as you measure it out so the driver is clear, and the internal opening is unobstructed by at least as much as the port diameter you're good to go.
Why would you propose an angled slot port, and then question an angled tube port?
I usually try to keep it under 25 m/s. The threshold for audibility is considered 17 m/s.
How loud you actually listen to the sub will be the biggest variable. For example, you may model 30m/s at 112 db, but in actuality you never go louder then 106 db in which case your velocity would never exceed 16 m/s.
Isn't it ideal to have the port opening facing the driver though?
No, that's actually less ideal due to the possibility of sound leakage through the port. A port is simply an air mass that resonates with the air spring of the enclosure. The frequency of which it resonates is based on the enclosure volume, and the port dimensions. It is not there to pump out sound directly from the rear of driver.