Port calculations

[Austin Duggan]

Thanks for the great responses guys. Learning a lot. I think my final question before cutting all the holes and making this box a done deal is...how do I calculate the minimum diameter of a flared port? Or, how do I calculate the diameter equivalence between a flared port and a straight port? I ask this question again because precision ports claims a minimum diameter of 7.25" is equivalent to a 4" flared port. If this is the case, then making room for ports just got a lot easier. Thanks.

[Austin Duggan]

p.s. I have scoured the internet, including this message board for an answer to this question. There's obviously an equation for this. It just hasn't been posted anyplace that I can find.

[Brett]

Use the sims to get an approx, then tune via Z curves.

[Inductor]

Originally posted by Austin Duggan
p.s. I have scoured the internet, including this message board for an answer to this question. There's obviously an equation for this. It just hasn't been posted anyplace that I can find.

It's based on experience and off course Flare-it must have it nailed. So, it's based on the velocity (of the air in the port) of the driver. What driver did you say you have and it's T/S specs??? size of the enclosure and tunning frequency? (Try to work w/your head a little... npi, I know it can be confusing but don't give judgements if you don't give the details...)

[Austin Duggan]

I'm using the eminence kappalite 3015. All the date can be found here: http://www.eminence.com/pdf/kappalite-3015.pdf After factoring in the displacement of the speaker and the bracing, I'm working with about 102 liters. Tuning frequency is 45hz. Don't know what you mean by giving judgments. I'm just getting different answers from different programs, so would like the equations to work with myself. Trust me, I'm grateful to have all these resources.

[Brett]

AD, the Eminence serving suggestions should be pretty close. Don't forget to factor in port volume too. Then build, then tune.

[Inductor]

Ok Austin. Let's make a first approach. (I don't know what you have?)
First I went to NotaxNotes and it said a working diameter of 212,8mm (this is based on T/S-derived and experience as he said). The formula is there for you to see. I am not working with the formulas as I use the software(s). This is my methodology. Ok, then I went to WinISD, did you checked it(?). All the softwares might have the formulas somewhere or then email their authors asking for that imformation. I don't know what your objective is, but you decide if you want to go the scientific way.
In WinISD it gave me a first alignment of 81L. I'm going to insert here:

[bjorno]

Hi,
Port/ Driver placement is crucial if low ripple FR is a goal and IMO if XO: ed above 250 Hz, all the internal walls should be covered with at least a ¼” wool felt or similar in order to prevent internal reflexes to leak through a short wide port at high signal levels causing vertical image shift and larger MAA.

OTOH if XO: ed below 250 Hz (>= 20 dB/octave) the MAA or Location issue can be ignored as long as the driver is a low distortion type.

b

1(1)

[Inductor]

I used a second alignment, that you told me (102L) here:

As the first is with one vent of 10cm, I used a second try with 2 vents to be close to NotaxNotes 20cm.
Also note that this is for flared tubes on one side, because we can choose it, as this parameter was set first (assumed by the software) - one, two or none.

[Inductor]

and the air velocity: