# winIsd port question



## mikey15 (Apr 5, 2008)

Hi all,

I'm using winIsd and I put in 3 2.5" ports. It gives me a length of 30" vs around 12" for one 2.5" port. Is it 3 diveded into the 30" and use that number for each of the 3 ports or is it 3 30" ports. I'm modeling a Dayton designer 12 in 2 ft3.

Thanks

Mike


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## GranteedEV (Aug 8, 2010)

A port is a mass of air whose acoustic impedance interacts with the inside and outside of the box.

One 2.5" x 12" port might give you a specific tuning, but doubling/tripling the surface area changes the pressure relationship with the box/air.

To keep the tuning the same, EACH of the three port will need to be 30" long.


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## ach81090 (Feb 6, 2012)

To put it simple, the more port area you have, the more port volume you need for the same tuning.


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## fusseli (May 1, 2007)

As mentioned, yes the 30" length would be for each of the three ports.

In case you didn't already know: To determine if you need one vs. three, you'd refer to the port velocity graph in WinISD. For ports of that size you wouldn't want more than 16-17m/s of maximum port velocity.


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## paulspencer (May 11, 2007)

I suggest you also look at Collo's "flareit.exe" which is a little free app for determining the max velocity before chuffing. Very useful.


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