Hi all,
I service professional audio power amps. And I am always asked the question, how can this
amplifier which states a power output of 1200 watts/channel at 4 ohms (both channels
driven 20hz-20khz) can actually put out 2400 watts total when the power consumption is
only 1800 watts.
?!?!?
thanks.
It's called IHFM rating ;-) The trick wording is "instantaneous
bursts"... in other words it's a lie.
'IHFM Music Power Output Rating
"The IHFM Music Power Rating uses a technique that makes power
measurements at a frequency of 1,000 cycles per second to indicate the
capability of an amplifier to handle instantaneous bursts of music
power peaks. Since no distortion levels are defined in this method,
the Heath Company has performed its IHFM music power ratings at the
same level of distortion as is maintained in its own system of
standards for the Hi-Fi use category. That level is 0.7% total
harmonic distortion at 1 KC. We believe that this figure is the
maximum total harmonic distortion tolerable for high fidelity
applications.
"In determining the advertised power ratings of Heathkit amplifiers
using Heath and IHFM standards, we measure a group of amplifiers
selected by statistical techniques to represent normal variations that
can be expected in production. These measurements are averaged and the
advertised power rating is the nearest whole number of watts.
"You will also note that the Heath power Output Rating figure is
always lower than that obtained for the IHFM Music Power Rating. This
indicates Heath's policy of conservatism in advertised power ratings
for its power amplifiers. It is also another assurance to you, our
customer, that Heathkit products have quality that you can depend on
and trust--with guaranteed performance specifications."
Excerpted from 1962 Heathkit catalog '
...Jim Thompson
