Port Size Correlation? (round ports)

[lbwdog]

Let's say you have a smallish 1x15 cabinet with a 3 3/4" hole for a rear port. The cab wall is 3/4", so you have a port depth of 3/4".

So now you substitute a port tube of the same diameter, but it's 4" long. Does that equate to a bigger diameter hole without using a tube? If so, how much?

I think I'm trying to figure how long the tube should be to equal a non-tube 6" port.

[PhiDeck]

Have you tried modelling it with WinISD?

[billfitzmaurice]

Originally Posted by PhiDeck

Have you tried modelling it with WinISD?

+1. You can use any driver, as Fb and port sizes are independent of driver specs.

[lbwdog]

Originally Posted by PhiDeck

Have you tried modelling it with WinISD?

No....For one, I don't have the program downloaded, and I'm using my work computer.

I was hoping someone could give me a rough estimate.
Am I right in assuming the tube will give me the equivalent of a larger plain hole?

If anyone feels like plugging it into WinISD I'd appreciate it.

[dug dog]

If I'm reading WINISD correctly, a 6 inch diameter port that's 3/4 of an inch deep cannot be replicated with a 3 3/4 inch diameter tube. The 6 inch port tunes a box relatively high and the 3 3/4 tube, even at it's shortest possible length, tunes the box lower.

[lbwdog]

Thanks Dug.....still confused though.

Let's say I have a 4" plain hole. If I change that to a 4" tube several inches longer, would that not equate to a larger plain port?

[NoGraveConcern]

Originally Posted by lbwdog

Am I right in assuming the tube will give me the equivalent of a larger plain hole?

Nope. Completely bass ackwards. The bigger the hole the longer the tube needs to be to maintain the same tuning. A 15" speaker should have a minimum of a 6" dia port tube. If you want to calc the length of tube needed to equal your 3.75 x .75 hole you can use a this web site:

http://www.carstereo.com/help/Articles.cfm?id=31

Looks like you need 6" diameter by 4.5" length to keep the same tuning.