Howdy. I'm working on porting the 1.70 ft3 volume in which I've housed a PE Reference 10 inch sub. Thanks to Chris R.'s replies here, I understand that he recommends a 4 inch port over a 3 inch diameter one.

Here's the confusing part. It seems that when you increase port diameter, you need to increase the port length... by a lot. Insane amount. That just doesn't make sense.

Let's say that for a 25 hz tuning for that 1.70 ft3 volume, a 3 inch diameter port has to be 16 inches long. So, the total volume of that port's = 113.1 square inches.

Then, if I increase the diameter to 4 inches, keeping the length the same at 16 inches, the total volume = 201 square inches. That's 88 additional square inches. So, if it's more cubic displacement, then the port should be shorter, right? For the same cubic displacement, the 4 incher should be about 8 inches long.

But, it turns out that if you go from a 3 inch diameter port for 25 hz to a 4 incher, you need to increase the length to about 30 inches! Wow. That's nuts. Why?

Why do you need to almost double the length if you're increasing diameter? It seems that the opposite should be true. Baffled.

Here's the confusing part. It seems that when you increase port diameter, you need to increase the port length... by a lot. Insane amount. That just doesn't make sense.

Let's say that for a 25 hz tuning for that 1.70 ft3 volume, a 3 inch diameter port has to be 16 inches long. So, the total volume of that port's = 113.1 square inches.

Then, if I increase the diameter to 4 inches, keeping the length the same at 16 inches, the total volume = 201 square inches. That's 88 additional square inches. So, if it's more cubic displacement, then the port should be shorter, right? For the same cubic displacement, the 4 incher should be about 8 inches long.

But, it turns out that if you go from a 3 inch diameter port for 25 hz to a 4 incher, you need to increase the length to about 30 inches! Wow. That's nuts. Why?

Why do you need to almost double the length if you're increasing diameter? It seems that the opposite should be true. Baffled.

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