Port end correction?

[Cannoy]

I recently used torres to build my second box for a friend, I just found out about end correction today and ive found several posts here about it and some say torres calculates this and some say it doesnt. What should i use to know my actually tuning frequency?

[Joe X]

Torres factors in the end correction for slot ports, I mean look at the formula below, you don't need to be told by anyone, unfortunately Torres miscalculates port displacement so you usually still get 1-2Hz off from proper calculations with slot ports.

[Cannoy]

i see how its off on the port displacement, on my next box can i figure out the difference and add that to like the bracing section to see the real frequency?

[Joe X]

There's a way but none that I know from the calculator itself, it involves using Sketchup software to figure out your net volume and port centerline length, you can then enter that as net volume into Torres and enter the port dimensions, that way you bypass the flawed port displacement calculations, that being said the equation predicting tuning are ideal, significantly high or low temperature, port area ratio, any turns and other factors usually alter the theoretically predicted number.

[philrab]

Kinda in the same vein the OP is thinking, my question is how far off is it typically? In statistics, we deal in variance. Everything we do in statistical analysis has a variance, or a margin for error, involved in it. It we're talking 1-2hz difference in port tuning frequency, unless you're chasing numbers competing, just doesn't seam worth worrying over. I'm not saying it doesn't make some difference, just saying I don't think it would drastically effect the final product.

What do you think Joe X? Is there some merrit to that thought, or am I making light of it?

[Joe X]

philrab 1-2 dB or 1-2Hz error is probably not going to make or break a daily system performance. It's a matter of personal opinion to assume or not that any calculator will do as differences in results can be considered negligible.

[SQL50]

1-2 hz higher or lower than the expected tuning frequency? More net volume or less net volume than expected after torres port displacement?

[Joe X]

When Torres released his second revision of the software (2012) it became evident that there were discrepancies and people asked which was correct, here is a report on his thread:

http://www.stevemeadedesigns.com/board/topic/38791-torres-box-tuning-calculator-updated-818/page-27#entry2401303

The flaw is inconsistent for different box layouts so it's not possible to give a constant correction factor (for either version of the calculator), the second flaw is that it will miscalculate tuining for multiple round ports so when working with multiple round ports one should use the PSP.inc online calculator to determine correct tuning.

[philrab]

philrab 1-2 dB or 1-2Hz error is probably not going to make or break a daily system performance. It's a matter of personal opinion to assume or not that any calculator will do as differences in results can be considered negligible.

I guess that was my point. For your average daily system, Torres calculator gets you close enough that the rest is just splitting hairs.

On the other hand, you could always use WinISD and get the port length/diameter info straight from there.

[SQL50]

I was modeling a box on Torres, and after all port displacements, sub etc was 7.55 cu ft net. It said that the port displacement was 3.14. Port dimensions 3 X 40.5 X 29.5= 3,584.25/1728= 2.07. Then for the displacement for the actual wood of the port. 0.75 X 40.5 X 25.75= 782.15625/1728= 0.45. 0.45+2.07= 2.52. Torres displacement was 3.14, so that minus 2.52= 0.62 cu ft more air net. Which interferes with the port area, and I would think the box would be seeing a lower tuning.