There are plenty of nominally 4 ohm 'speakers around, which means that under
IEC rating, the impedance can go down to 3.2 ohms. You may recall the KEF
104.2 which was 4 ohms almost exactly at all frequencies, the Linn Isobarics
were 4 ohms, and several European 'speakers are 4 ohm rated.

The specification of 90w into 8 ohms, 125W into 6 ohms actually seems
inconsistent in that into 8 ohms, the amp will generate a voltage of 26.8v
rms, whilst into 6 ohms it will generate a voltage of 27.4v. Normally, the
voltage generated into lower impedance loads is equal to or lower than into
a higher load. If the specs are true, then that implies a negative output
impedance, not normally found on modern amplifiers, although was once used
by Pye amongst others in the valve era.

S.









"Chris Morriss" wrote in message
...
In message , Martin
Hardy writes
How can you tell that the power will be low into 4 ohms? I don't know much
about this subject, but I would have thought that if you get 90W into 8
ohms, 125W into 6 ohms, then reducing the impedence further to 4 ohms
would
have meant the power would go up again- not fall. How does this work?



Usually because the PSU or the output transistors have run out of current
capacity when feeding low impedances.

I'm not sure there's that many speaker (except car ones) that are really 4
Ohm over the whole frequency range though. Certainly there's a lot of
speakers that don't have impedance compensation on the drive units and so
they have some very reactive regions in the input impedance to the
crossover where the Z does fall to this level (or even below) for certain
frequency ranges.
--
Chris Morriss