Eiron wrote:
Serge Auckland wrote:
Don Pearce wrote:

Without being able to trace the circuits I can't say for definite, but
that looks like a second order crossover. Are those chokes wound on
ferrite? If they are, this crossover has a power limit set by the
magnetic saturation of the ferrite. Your other one is a better way of
making a crossover choke.

Completely agree.

Are there any real test results showing the difference between
air and ferrite cored inductors in a crossover or is it another
evanescent chalk and cheese effect?

I can't find the detail I was hoping to amongst my notes (even Noakes
wasn't a lot of help), but I found the following explanation (I've
edited it for space) on the University of Surrey's website

Saturation

Saturation is a limitation occurring in inductors having a ferromagnetic
core. Initially, as current is increased the flux increases in
proportion to it. At some point, however, further increases in current
lead to progressively smaller increases in flux. Eventually, the core
can make no further contribution to flux growth and any increase
thereafter is limited to that provided by μ0 - perhaps three orders of
magnitude smaller. Iron saturates at about 1.6 T while ferrites will
normally saturate between about 200 mT and 500 mT.

It is usually essential to avoid reaching saturation since it is
accompanied by a drop in inductance. In many circuits the rate at which
current in the coil increases is inversely proportional to inductance (I
= V * T / L). Any drop in inductance therefore causes the current to
rise faster, increasing the field strength and so the core is driven
even further into saturation.

Core manufacturers normally specify the saturation flux density for the
particular material used.

Although saturation is mostly a risk in high power circuits it is still
a possibility in 'small signal' applications having many turns on an
ungapped core and a DC bias (such as the collector current of a transistor).

If you find that saturation is likely then you might -

* Run the inductor at a lower current
* Use a larger core
* Alter the number of turns
* Use a core with a lower permeability
* Use a core with an air gap

or some combination thereof - but you'll need to re-calculate the design
in any case.
............................end................... ..................

Consequently, if you want to avoid the risk of saturation, you use an
air-cored inductor which has a much lower permeability than ferrite or iron.

S.