Answers sought for the following questions:

1. What causes the many large impedance peaks seen above Fs in compression
horn midrange drivers?

2. Are series notch filters used to "flatten" impedance peaks within the
bandpass (i.e. for frequencies higher than the crossover frequency)? If
yes, then what is the effect on the frequency response?

3. If I sweep the frequency from above the crossover to one octave below
the crossover, what would the corresponding impedance graph look like
(assume the driver is pure resistive load)?

Hi John,

1. What causes the many large impedance peaks seen above Fs in
compression
horn midrange drivers?
Horn resonances... These differ from horn to horn. Some horns can have
multiple serious resonances, other horns can have just one minor
"hump".

2. Are series notch filters used to "flatten" impedance peaks
within the
bandpass (i.e. for frequencies higher than the crossover frequency)?
If
yes, then what is the effect on the frequency response?
A series connection of a R, L and C can be connected parallel to the
driver to compensate one impedance peak. Use more of such RLC networks
to compensate other peaks. These networks themselves don't change the
SPL frequency reponse eminating from the driver, BUT, as the impedance
curve of the driver is "straightened" out, the designer of the passive
X-Over has a much easier job. So if in a given situation, where such a
RLC network is utilised in a passive X-Over and it is removed, then in
that situation, yes, the frequency repsonse WILL change. Usualy the
designer compensates the peaks at and near the X-Over frequency. Near
being something like within two octaves of the X-Over freq.

3. If I sweep the frequency from above the crossover to one octave
below
the crossover, what would the corresponding impedance graph look
like
(assume the driver is pure resistive load)?
The filter will be of a high pass type, so above the pass frequency,
one would more or less "see" the driver impedance, looking into the
filter. Below the pass frequency one would see an impedance rising
with decreasing frequency. How steep this rise is depends on the
filter order and its topology.

Hope this is of some help.

Regards Xavier.