Ian Iveson wrote:

"John Stewart" wrote

...
In your example the DF for the group is 50. However, for each
speaker the source
impedance would be the amp Ro of 0.5 ohms plus the entire series
complex impedance's of
the other nine speakers in the group. That is a condition I would
prefer to avoid.
...

Seems to me this is the crucial point, John. Could be seen as
another example of current sources in series.

cheers, Ian

Nature (And Physics) abhor certain conditions. One of them is current
sources in series. By way of 'The Principle of Duality' another would
be voltage sources in parallel. The definition of each should tell us
something. A perfect current source would deliver the same current to
the load no matter what the load was from a short circuit & on up.
Similarly, a voltage source would deliver a constant voltage to the
load from open circuit & on up to ever increasing currents.

Fortunately for us, most of the circuits we have to deal with include
some positive resistance in parallel with a current source & a positive
resistance in series with a voltage source. That helps us quite a lot
to establish an operating point. Without those resistors the circuit Q
point becomes indeterminate. So a simple current source while not
perfect would be able to source a reasonably constant current over a
wide range of loads. The max load is simply limited by the max voltage
available.

If a negative resistance were to be introduced into the circuit than we
have the potential for an oscillator.

So, I would sure agree with your point Ian, in particular at the
resonance F of the speakers.
Z tends to get quite high at that (those if a bass reflex) point. Even
at mid-frequencies far from the speaker resonance, nine speakers would
add up to 45 ohms. The source for each speaker if all were simply
series connected as Patrick T remarked in the first paragraph of his
original post of April 27th would than be 45.2 ohms. For each
individual speaker, particularly at resonance the remaining speakers
form a rather good current source. If Patrick didn't mean them to be
all wired in series he should have made that clear in his post. The
second paragraph of his original post has the speakers all in parallel.
What next?

I see in Patrick's later response to my critic of his post that he has
suddenly got the clue to series/parallel the speaker array. I wonder
where he got that idea!

As always with anything, including technical advice, Caveat Emptor.

More to go on this yet. And,
Cheers John Stewart

PS- I guess I will have to post the graph showing individual (2,3,4..)
harmonics for pentodes. It is not it in RDH4, but it does show up
elsewhere. That way one can see why a steeper load line is a better
condition for pentodes, again opposite Patrick's opinion. Best example
without having to look it up would be the steeper loadline applied to
PP amps. That helps to reduce the 3rd harmonic & one of the reasons we
do it. Depending on speaker resonance & program material, the tube is
always well loaded, both above & below the knee. Below the knee at
speaker resonance & above the knee at
mid-frequencies. JLS