Re: distortion at 4 ohms vs. 8 ohms?

On Tue, 22 Sep 2009 15:23:54 -0700 (PDT), Michael
<mrdarrett@xxxxxxxxx> wrote:

I got a hi-fi amplifier (Harman Kardon AVR45) off Craigslist (what a
deal), and am running it on four 4-ohm speakers within the house.
(Two 10" subs, rated at 200+ W continous; two 6-1/2" speakers rated at
300W continuous). The manual specs say the following:

Five-Channel Surround Mode
Power Per Individual Channel

Front L&R channels:
55 Watts per channel,
@ < 0.07% THD, 20Hz=9620kHz into 8 ohms

Center channel:
55 Watts, @ < 0.07% THD, 20Hz=9620kHz into 8 ohms

Surround channels:
55 Watts per channel,
@ < 0.07% THD, 20Hz=9620kHz into 8 ohms


It sounds great on 4 ohm speakers.

I was wondering, what kind of increased distortion numbers am I
looking at, running at 4 ohms?

I know not to overdrive it too much, since it will get hot. Most of
the time I listen to George Winston piano solos, but during the
occasional party, ... well, it still works...

Just using 4 ohms instead of 8 should not cause
increased distortion at normal listening levels.
The problem with 4 ohm speakers is that you can
drive the amp beyond its rated power output. If
it doesn't have adequate limiting and shutdown
circuitry, you could smoke the output stages.

I'd guess this will not be a problem unless you
really work at getting loud. You'll probably get
clipping on peaks that will make it sound "gritty"
well before you get it loud enough to do damage,
and you'll naturally back off the volume when you
hear that (I hope!).

Possible exception: I seem to recall amps that
were unstable at 4 ohms, back in the "early days".
Doesn't seem likely here, though.

Best regards,



Bob Masta

DAQARTA v4.51
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