Couple of questions pertaining to curved port tubes:
1) How do you measure a port curve? If the "outside" curve is, say, 10", but the "inside" curve is, say, 5" do you just take the average and use that as the port length for that portion of tubing?
2) Are curved ports more likely to result in port noise?
3) Is it acceptible (from an acoustical standpoint) to make a 180 port...i.e a port that is basically the shape of a candy cane?
Lastly, a general question about ports: Is there a particular place in the enclosure that is ideal to place the opening (entrance) of the port? E.g. do you want it near the sub, away from the sub, facing the bottom of the sub, etc...or does it not really matter?
I know I'm asking a lot of questions here but I'd really appreciate any help you guys might have. Thanks!
1: The average of the radii, so, yes. Basically measure the middle radius of the port.
2: I say yes, but I have asked my engineers at Harman this VERY same question, and they say no. The DO, however, recommend using the largest diameter port you have volume for. It is FAR better to make the port longer and the enclosure larger, than to have a smaller enclosure with a shorter but inadequate port diameter. A larger port will always be quieter. WinISD figures Mach speeds in the port, IIRC, and the Harman guys aim for nothing above Mach .1, and some even as low as .05M.
3: Yes. No problem.
4: The general rule is that whatever your port diameter, you always allow at least one radius from any interference: stuffing, woofer frame, box wall, ANY interference... This means a 4" diameter port must be no closer to anything in the enclosure than it's own radius of 2". Anything that CAN be in the way should be made NOT in the way. As far as the terminus, I will always maintain one diameter from the woofer diaphragm.
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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."