"Bob-Stanton" wrote in message
om
"Arny Krueger" wrote in message news:vPadnb-

Zobels and other networks can make the tweeter impedance constant.

Not necessarily perfectly constant in both magnitude and phase at all
frequencies without a ton of work. For example, modelling the
inductance of a tweeter as being a pure inductance, which is
essentially what simple zobel calcuations do, is not a particularly
good approximation for most tweeters.

See http://users.ece.gatech.edu/~mleach/...oads/zobel.pdf
for additional caveats. Notice that his plots only show the
magnitude of the impedance and not its phase angle. There's a slight
dip and a downward slope in most of his magnitude plots, and that
suggests non-zero phase.

So, the only difference in the filter response will be due to the
finite Q of the inductors and capacitors.

Hopefully.

You are right that making a high-pass filter compensate for the
impedance changes of a driver, is a *hell of lot* of work.
Fortunately, it is unnecessary. The problem can be obviated by starting
the test with the L-pad set to 10 dB (or 15 dB!). That way, the
impedance the filter sees, will always be 8 Ohms. (You probably would
want to do it anyway. Than you wouldn't need to use ear plugs.)

Oh, I guess so. This is, I provided a more straightforward methodology some
posts back.

No. L-pads don't change the impedance at all. Here are the values
for 8 Ohm L-pads, for various attenuations.

Attenuation R(series) R(parallel)
in dB in Ohms in Ohms

1 0.87 65.0
3 2.34 19.4
6 4.0 8.0
10 5.47 3.7

But the load isn't a pure 8 ohms resistive. It's a tweeter with
variable impedance magnitude and phase, even with a zobel. The
L-Pad isolates the input impedance of the tweeter from the amplifier.

This in turn causes the
attenuation of the filter to wander around.

Not if the L-pad starting attenuation is 15 dB.

I guess, but....

If we go back a number of posts, I provided a means that works with a lot
less fooling around.

That is because, it is an obscure form of distortion. :-)

It's actually very common and easy to understand if you call it by
its conventional name.

Than why didn't you call it by it's proper name?

I do.