impedance comp for woofer

[johnmark]

I am wondering how exact the impedance comp needs to be on a woofer for my 2.5 way project.
I am using an 8" woofer for my .5 and a single 5.5 mH coil for a rolloff starting around 200hz.
I can't find the exact manufactures data for my woofer an Audax HM210G0 but I calculated the impedance comp circuit values using the later version HM210G6 for an Re 0f 6.2 and VC induct of 1.47

I wound up with 8ohm resistor and 25 pF cap for the impedance comp circuit.

What if my woofer is not exactly the same the same Re and VC inductance?
I don't have any software to run a "what if"

Thanks for any input

 

[pinkmouse]

The manufacturers data is here

 

[johnmark]

so now my capacitor is way too big

based on that table I should have an impedance comp circuit of r=8 ohms and a capacitor of only 9.4uF

What happens if I use the 25uF cap that I already bought ?

 

[wintermute]

I've only started playing with impedance compensation recently but my advice is that calculated values compared to needed values may bear no resemblance to each other.

Do an impedance measurement with the drivers in the final enclosure both before and after putting in the impedance compensation, and then experiment from there.

Speaker workshops suggested imp comp circuits (assuming you measured the impedance with it) seem to work pretty well as a starting point for fine tuning (much better than formulas that I tried).

Tony.

edit: my first try was with a calculated cap of about 15uF, in reality a cap between 30 and 60 uF is more appropriate (with changes in resistor value as well) for my application.