Help with notch filter

[nobody special]

I have an idea for a crossover design, but I am having trouble finding info on how to calculate the notch filter I need. I can't find my copy of the Loudspeaker Design cookbook, so I am asking for some help here.
I have a woofer that has a fairly smooth frequency response and a nice, predictable rolloff, with the exception of a peak (cone breakup mode, I presume) at 3250 Hz. The peak is about 6 db, and is fairly narrow. I need the information on how to calculate a notch filter to reduce this peak. Also, please specify whether the filter has the RCL in series, paralleled with the woofer, or if it has the RCL in parallel- inline with the woofer.
My goal is to reduce this peak and then use the natural rolloff of the woofer to crossover @12db/octave to a tweeter at around 4600Hz. If the filter is a little too broad, that isn't too big of a deal, because the tweeter has a couple db lift around the 3000-4000 range that would complement it.
It is kind of interesting- the woofer is almost exactly 180 degrees out of phase right where it is down 6db, and it's rolloff is almost exactly 12db/octave, maybe a little shallower- closer to 10/11db. It looks like a really easy and simple crossover using a second order high pass on the tweeter. I just have to get rid of that peak! I hope it works as well in practice as in theory (does that ever happen?).
Anyway, if you guys can help me out with the notch filter info, I would really appreciate it!.
Steve

[filippo22]

Hi

here you can find a good on-line calculator

http://lalena.com/audio/

ciao
Filippo
www.audiofanatic.it