Couple questions on this box design

[sprkn_ranger]

Ok, I worked up this design on sketchup an would like some input on it. I was originally going to do a port 13" tall an 1.5 inches wide, but I decided that having a port that skinny wouldn't be optimal. So I came up with a design that uses a 7.5" tall by 2.5" wide port.

While using Torres to get it figured out it comes up with a port volume of .56ft^3 but I calculated it several times to be only .41ft^3. I'm not sure where the discrepancy is but I can't figure it out. Im shooting for a net box volume of about 1.25ft^3 and a tuning of around 35ish. My sketchup works out to about what I want my net volume and tuning to be but Torres is a bit different because of this discrepancy.

If anyone can tell me what I did wrong I would greatly appreciate it! And if anyone has input on the box design as well I would love to hear it too. Thanks!

[Joe X]

Your calculations are correct, The torres add to port displacement the external area of the port per the length of the end correction, for a given gross volume the net volume will lose the same amount the port volume will gain.

[sprkn_ranger]

Not quite sure I understand...I trust the Torres calc but would like to understand why my numbers come up different than on the calc.

I'm thinking I'll just tweak my design to fit whatever Torres comes up with cause many boxes has been built with that calc lol.

[Joe X]

Not quite sure I understand...I trust the Torres calc but would like to understand why my numbers come up different than on the calc.

I'm thinking I'll just tweak my design to fit whatever Torres comes up with cause many boxes has been built with that calc lol.

The difference is minimal.

[sprkn_ranger]

Well the difference changes my tuning from 35ish to almost 38, that seems like a lot to me.

[Joe X]

I checked that yesterday and it was Fb = 35.645 Hz and port displacement was 0.41 as you stated. That number is more like 36 and the other was les than 38, I don't think this is a big deal...