newbie question.WinISD and port tubes

[PTM]

I'm using WinISD beta to do some box and port calculations. Funny thing is that as I increase the diameter of my round tube dimensions, the length of the tube "increases".. Model a smaller dia. tube and the length "decreases"..
This seems backwards to me. Should a larger tube require less length to tune?

Thanks for any help you can give me..

Phil

 

[454Casull]

No. The larger the cross-sectional area of the port, the longer the port must be to maintain a given tuning frequency.

It's in the math.

 

[muhy3]

How would you recommend to measure the length of a vent accurately when it has bends? Measure the length using a piece of string through the inside, or add up the lengths of the smallest paths?

 

[PTM]

I see. I guess I need to learn more about this. Thanks for clearing that up for me.
By the way.. Is WinISD accurate with vents, if you have the correct driver information and volume calculated?

Does the vent tuning length include the area to the front face of the speaker baffle? It would seem that it would, but I am not sure.

Thanks for the help..

Mag...

 

[slartibartfast]

It should be useful if you get a vent with adjustable length, because all the calculations can't be that accurate we would like to. Also the form of the boxes gives an amount of standing waves you could not correct precalculate. The program uses the length of the tube itself and the cross-section area of it. It's better when you have a spectrum analizing software, so you could measure what finally have you built.