Jim Lesurf wrote:

Eeyore wrote:
Jim Lesurf wrote:
Eeyore wrote:
Jim Lesurf wrote:

More to the point, the original IV limiting using on the 405 was
particularly severe for reactive loads - rather common for
loudspeakers!

I could write an article on the subject.

You mean something like the SCAMP (Society for Cruelty to AMPlifiers)
article in the Hi Fi News section of audiomisc.co.uk ? :-)

Very much so.

Keith Howard followed up 'SCAMP' with an article that established what the
worst choice of load phase angle would be for o/p device dissipation in
class A/AB operation. He tends to do the measurements for the HFN speaker
reviews. This was an issue we'd be discussing for a while.

Since then, he has tended to check each speaker to find at what frequency
it behaves 'worst' as a load, and then mention the results in the review.
This in terms of the resistive load that would place the same peak power
dissipation demands on the o/p devices. I don't think he always does this
as some speakers are 'gentle' loads, so their worst behaviour isn't a
concern. FWIW He also wrote about this for Stereophile IIRC.

Harder to assess the effect in secondary breakdown terms as that will vary
from design to design, so no single conclusion could be drawn about a given
speaker. Fortunately, the o/p devices these days should be less prone to
breakdown nowdays than back in ye days of yore...

It isn't a new problem. But speaker manufacturers simply tend to lob the
ball into the court of the amplifier designer and smile sweetly. I can't
complain too much as I've always favoured QUAD ESLs. :-)

How far do they swing ? Which model even ?

Years back I did the crossover design for a modest 'bookshelf' monitor style
speaker using Mathcad.. It's all 'impedance corrected'. I haven't actually run
a test myself as it happens (although my colleague did some 'empirical ones'
and found the impedance curve very flat using spot test tones but aside from
the usual LF peak, it should be as close to resistive as possible.

As a result it sounds sweet even on cheap amps.

Graham