crossover component formulae

Best way is to look them up in a reference design table as a modification to the standard formulae you mentioned in the first post.

If you want to know where they come from then draw out the transfer function of a series LC lowpass filter, you will get a result with a polynomial on the denominator. This structure is what all more complicated filters are broken down into, because it is the basic filter building block. Ok a 1st order is really the simplest, but with one pole only you can't manipulate it as much.

Once you have the polynomial (coefficient of the s^2 term should be one to be in standard form). The coefficient of the linear term can then give you the Q factor of the filter. So if you want a certain Q and Wo, you reverse engineer from this point to get your L and C. Or you can just look them up as you did!

More reading here, Matlab (or Scilab=free) is very handy for evaluating filter designs and generating nice visual plots. Python is probably quite good too, not used it myself for this purpose.

Edit - Forgot link


Edited by odc04r - 13 March 2017 at 10:32am

Phil
bench with many components here still if you want to try things empirically!
Mik

okay the 2nd order LR components are the same value as the first order butterworth components. obvious when you think about it as LR is two cascaded Butterworth filters. Still stumped on the Bessel values.

Well they will get you into the back row of seats if not the actual ball park...

When I worked for a major speaker manufacturer (long time ago) we would design crossovers using an iterative process. After examining the frequency response and impedance curves of the drivers (and maybe building zobel networks), the starting point would be a "calculated" set of filters built with component substitution boxes.

Then of course, lots of measurements - using either B&K chart recorders or the original TEF analyser (I said it was a long time ago...)

The substitution boxes made it easy to change components just by setting switches, so although it involved a lot of adjustments it was not difficult, just very time-consuming. But I used to get through an awful lot of chart paper...




Edited by madboffin - 09 March 2017 at 12:13am

I'm sure I have seen some online calculators that will give the theoretical filter component values. But the only use for a calculated crossover is as a starting point to get you in the ballpark before doing a proper design exercise - for the reason DJK gives in the previous message.

The component values will need a lot of tweaking before they work properly with real drive units.




Edited by madboffin - 08 March 2017 at 11:34pm

Conanski wrote: snowflake wrote: are there similar formulae for Linkwitz Riley and Bessel alignments? Yes.. there are.