In article ,
chris wrote:
"Richard D Pierce" wrote in message
...
In article CEkYa.56109$cF.20345@rwcrnsc53,
chris wrote:
Richard

Would a zobel network have any value placed outside of a xover unit on a
modern speaker?

What do you presume is the purpose of such?

I was asking if using a zobel to correct any imperfections in the impeadance
curve could possibly be of any use. I have no knowledge of zobel devices
in real use, and I was .enquiring as to if you had any experiance of them.

The main purpose, in the context of speakers, for such conjugate
networks, aka "Zobels," is to provide a resistive load for the
passive crossover. Using standard ladder-type passive filters,
there are entire classes of useful transfer functions which you
simply CANNOT get unless your crossover has a resistive load. So
a "Zobel" is used to make sure that the non-resistive load
typically presented by a driver is converted to a resistive
load.

On the other hand, one often sees a passive network on the
output of power amplifiers. Common forms are a parallel
combination of a resistor and inductor in series with the load,
or a series combination of a resistor and capacitor shunting the
output. These are NOT "Zobel" networks, in that they are NOT
intended as a conjugate circuit for some load. They are there
for the prupose of either decoupling the amplifier or providing
filtering at some very high frequency to increase stability well
outside the audio bandpass.

A lot of people call such circuits "Zobels." They aren't. It's
as simple as that.


and if so would it not be best placed near or at the amps o/p terminals ?
ie
to correct the total impeadance of lead and speaker ?

The impedance imposed by all but the most pathologically bad of
speaker leads is such a TINY part of the total impedance seen by
the amplifier as to be insignificant.

Further, I would submit that if such a network IS needed, it is
correcting for a defficiency in the amplifier, and one might
argue that applying external means of solving the internal
defficiency of an amplifier is the wrong approach to addressing
the problem.

I wasnt really thinking of amplifer defficencies but in that respect I agree
(poss best to ditch the amp), but more of where would be the best place to
put the correctig device should one be required.

But exactly WHAT are you correcting?

so what are the (overpriced?) "network thinggys" that I hear people put
at
the speaker terminals?

Often, they are nothing more than passive tone controls.

So what are they less often ?

Effective. Useful. Needed. Properly designed.

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