[Arny Krueger]

"Chris Hornbeck" wrote in
message
On Thu, 27 Nov 2008 09:56:58 -0500, Kalman Rubinson
wrote:

On Wed, 26 Nov 2008 20:43:03 -0800 (PST), vlad
wrote:

From now on I will be looking AV receiver that
exp[lisitely made for 4ohm speakers.

None are. All are made for 8ohms but many will
accommodate 4ohm speakers as well.

And really, this just isn't something to get excited
about. Speakers aren't really "4 Ohms" or "8 Ohms" or
whatever, but are a very, very complicated load,

The usual convention is that a speaker's rated impedance is actually its
minimum at any frequency.

Often the frequencies associated with the minimum impedance are in a few or
as little as 1 narrow band.

Music is composed of multiple concurrent tones, often at harmonic intervals.
The thermal load on the amplifier will be more like a weighted average of
the speakers impedance curve. The weighting constants are based on the
music. Therefore, the odds that the entire output of the amplifier will fall
into just these few narrow band(s) is very small.

and an
amplifier must to designed to deal with the real world of
real loudspeakers with complex impedances and some motor
characteristics.

The power supply and heatsinks are designed based on a single frequency that
drives a the minimum rated impedance. They are therefore likely to be
overbuilt for use with real-world music and real-world speakers. In a modern
duel between amplifiers and speakers, the speakers usually lose out first.

But folks have had many decades to get a
handle on this, and competence doesn't cost much these days.

Not only that, but the cost of capacious power transformers, heat sinks and
transistors has fallen quite a bit.