Port Length Calculations ?

[Alex2507]

In my case I am dealing with a JBL GTx10. The first thing I would like is an accurate source for the T/S parameters, either from JBL or measured. I have in hand 2 sets of numbers. One set is supposedly from JBL and the other has a substantially different Vas and an erroneous basket displacement which sort of makes everything suspect.

The formula I have for length is:

L = (2117xD^2) / (fb^2xVb) - (0.732xD)

fb = 0.39 x fob

fob = fs / Qts

I've had a couple of cabinet suggestions handed to me. With the first one I was unable to meet the Vb requirements. The second one is fine in that regard but I can't make the numbers line up with these formulas which came out of a book published 10 years ago. Has something changed?

TIA,
Alex

Edit: BTW is a higher Vas good or bad?

To convert a slot port area into circle area dimensions I found a formula which works:

radius = square root of ( a / pi )

 

[annunaki]

In my case I am dealing with a JBL GTx10. The first thing I would like is an accurate source for the T/S parameters, either from JBL or measured. I have in hand 2 sets of numbers. One set is supposedly from JBL and the other has a substantially different Vas and an erroneous basket displacement which sort of makes everything suspect.

The formula I have for length is:

L = (2117xD^2) / (fb^2xVb) - (0.732xD)

fb = 0.39 x fob

fob = fs / Qts

I've had a couple of cabinet suggestions handed to me. With the first one I was unable to meet the Vb requirements. The second one is fine in that regard but I can't make the numbers line up with these formulas which came out of a book published 10 years ago. Has something changed?

TIA,
Alex

Edit: BTW is a higher Vas good or bad?

To convert a slot port area into circle area dimensions I found a formula which works:

radius = square root of ( a / pi )

Alex,

Here is a great link. Lots of great info. http://mobile.jlaudio.com/support_pages.php?page_id=165

The Vas number will vary along with other parameters of the woofer. VERY Generally speaking a lower Vas froduces a lower enclosure volume.

 

[Alex2507]

Went and got me a better calculator. Radio Shack $20.

 

[Alex2507]

That is a great link. Those guys pooh-pooh particle board pretty hard cause it's too "flaky". I have a sheet of it that has melamine on it and am tempted to use it. At this point it has turned into rock, paper, scissors with that. I'm starting to lean toward some well braced free material and a finish of some really good looking free formica.

For referance here is a link for more formulas.

http://www.carstereo.com/help/Articles.cfm?id=21

Enough of the numbers with the different formulas work out amazingly close which has re-inspired my confidence in the design.

 

[ErinH]

Have you checked out some box modeling programs such as bass box pro? That particular one is free.

 

[Alex2507]

Have you checked out some box modeling programs such as bass box pro? That particular one is free.

I tried a free winISD(?) and quickly found that I was beyond my depth. Couln't figure out how to use it in the time I put into it. Partsexpress sells a BassBox 6 Pro for Windows for $119. Part # 500-927. Must be a bigger better version of the free one. In any event TLS guy was good enough to model these drivers for me so I'm good to go in that regard. At least I have a plan, right? Just for a goof I got JBL to send me their T/S parameters via e-mail but I can't get the file opened because it's excel and #1 I don't have that and #2 I wouldn't know how to use it if I did.

Tough Monday. LOL. Hey, if it was easy I wouldn't be interested.