Don Pearce wrote:
On Wed, 17 Jan 2007 16:55:33 -0000, "Keith G"
wrote:

"Serge Auckland" wrote in message
...
Keith G wrote:
OK, some techie questions regarding this crossover:

http://www.apah69.dsl.pipex.com/show/crossover1.JPG


1) Anybody care to tell me what order it is (seems pretty basic to me)?
Looks like first order.

OK.


2) Can I slap it between just about any tweeter and similar sized
mid/bass unit with good effect?
Yes to the first part of this question, and possibly to the second part.
It looks like this crossover has a 3.3 ohm resistor in series with the
tweeter, presumably to balance the level with the woofer. I would say this
is done with two specific drive units in mind.

Hmm, well it's in for a shock then....


3) Will a different box size have any bearing on how it works with the
drivers?
Should make much difference as box size effects the bass end, and the
crossover works in the middle.

The box won't be too dissimilar in terms of internal volume, I think....



4) Have I marked up the driver connections correctly?
Yes, it will work this way, but to me it looks upside-down with the +
terminal being the common terminal. By convention, it is the negative
that's common, but it *is* only by convention.

How do we know electrons are negatively charged. That's only relative to
protons..........


I only know it because I tend to believe what I'm told 'til I can *prove*
otherwise!! ;-)


Apologies if these questions are a bit simplistic - I have a bone problem
which prevents me reading reams of techie stuff (and actually *learning*
anything) when a swift thump with a hammer will sort most things out, one
way or another.....

;-)
Particularly effective for setting cartridge tracking.

:-)


OK, another one if you and/or Don are up for it.

What about this one:

http://www.apah69.dsl.pipex.com/show/crossover2A.JPG

http://www.apah69.dsl.pipex.com/show/crossover2B.JPG

http://www.apah69.dsl.pipex.com/show/crossover2C.JPG


It don't look too convincing to me (can't really see any values on the bits
better than in the pix - it's still connected) - which would you use for
messing about with (piling spare drivers into a different box on a 'suck it
and see' basis)...??

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.

d

Completely agree.

S.

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?

--
Eiron.

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?


The difference between ferrite and air is the magnetic flux that each
coil can take before saturating. Ferrite is used as it results in
smaller coils and can use thinner wire for the same resistance or keep
the same thickness and have lower resistance and hence better Q. The
downside is that it takes a lot to saturate air whilst ferrite is
relatively easily saturated. I'll see if I can find my old college notes
regarding the actual differences.

S.

Eiron wrote:

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?

The distortion of ferrite cored inductors is measurable. Air cored coils
don't distort.

Stephen

On Wed, 17 Jan 2007 20:25:18 +0000, 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 think of any, but the signal levels involved are similar to
those in valve output transformers - think how big they have to be to
achieve even their limited degree of linearity. The parallel is not
exact, of course, because these are rods, not closed cores, so in
essence they incorporate a huge air gap. Nevertheless you are dragging
the magnetic flux up and down the standard B/H curve of a piece of
magnetic material, and that just can't be as good as using plain air.

d

--
Pearce Consulting
http://www.pearce.uk.com

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.

"Eiron" wrote in message
...
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?

**There are big differences, but it depends on the specs of the ferrite. In
one case I worked on, the manufacturer shipped a batch of speakers, with the
wrong type of ferrite fitted. Saturation occurred at around 6 VRMS. Since
the speakers were 4 Ohm types, this corresponded to around 10 Watts input
power. Complaints began arriving that the speakers distorted at modest power
levels. A quick sine wave test confirmed the problem. Replacement with
equivalent resistance air core inductors solved the problem.


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

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?

Doesn't look like it to me, they've just use a plastic tranformer former
(there's nothing inside)