I'd like to find where I can get this done so that I know what to tune my port when I make my next box.
For the Van area people: I hear there's an electrical engineering dept in BCIT that could do this for me. Any suggestions?

It's for a Dodge Omni FYI. No dynamat currently.
I'm guessing my car's Re is between 46 and 50.

umm, trial and error really. u can use the formula that's there but it envoles a use of a ruler, speed of sound and a calculator. it's a mess in short.

make a box tuned to 40hz, burp it at 50 and and go from there.

Well, it is currently tuned to 40. At 46/47 it seems to make the loudest reverb after I cut the note.

Use a RTA, then play a test one sweep, then record the highest spl. That will be the fr your looking for.

I have a note by note test CD, with its tuning it gets loudest at 40/41 and peaks a bit at 45/46. Hmmmm.

Thats it. I think I am going to borrow my shop's RTA meter and have a test and tune at my house. I'll set it up, you can play some pink noise, and I will be able to find your loudest note. This is how I found my 149-150 sweet spot.

Hit me up dude.

^You could have told me that over the phone yesterday, Mike. Ha

that wont find your res. freq. it'll just find what your box peaks at..

1/4 wave theory...
measure from sub to mic in feet, take 1130 divided by that #, and then divide by 4.

or...

use a sealed sub

1/4 wave will not work in a car...there are way to many variables and it is completly useless. The PROPER way to find your resonant frequancy is to build a box that will have a Q of 0.707 for your sub, then put the sub in the exact place that you will have your ported box and see which frequency is loudest.