# Port question, round vs rectangular

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#### kvk

I promise I'm almost done with my noob questions.

If a port is spec in a raound, dia x len, is there a conversion to rectangular?

Intuitively, I'd guess to keep area and length the same but my guess is that you might need also change area a tad, maybe like up it a few %.

I found this cool calculater but it only does round ports, not slot--
http://www.mhsoft.nl/Helmholtzabsorber.asp

#### vinylkid58

kvk said:
If a port is spec in a raound, dia x len, is there a conversion to rectangular?

Intuitively, I'd guess to keep area and length the same but my guess is that you might need also change area a tad, maybe like up it a few %.

You're on the right track, so to speak. Just compare area to area, all you need to know is the diameter of the port to calculate it's area. Just keep the length the same for either.

Jeff

#### kvk

Alright, let's muddy the water.

Keep the area the same put flares on the ends of the port. Do you measure the length the beginnings or ends of the flares or somewhere in between?

My guess would be about 1/2 in between the beginning and end of the flares but that's just intuition. I'm the noob here.

#### vinylkid58

kvk said:
My guess would be about 1/2 in between the beginning and end of the flares but that's just intuition. I'm the noob here.

I can't give you a definitive answer, but there is an "end correction" function which deals with this issue when modeling boxes. Obviously, the correction factor will grow as the port gets larger, but I don't know how to calculate an exact number.

What you suggest makes sense, as long as you are dealing with only one (1) vent.

Jeff

#### cabbagerat

Try WinISD Pro. It supports simulation of both round and rectangular ports. The help file also has a lot of interesting info about ports, end correction, and other topics.

#### Commsandsound

Port length

Hi
Dont forget to check the port length unless it is just a hole.

regards

www.commsandsound.com

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