[Audio Empire]

On Mon, 25 Oct 2010 07:09:55 -0700, Arny Krueger wrote
(in article ):

"Audio Empire" wrote in message

On Sat, 23 Oct 2010 10:36:51 -0700, Arny Krueger wrote
(in article ):

"Dave Cook" wrote in message


I also tried measure the Vrms output from the amp with
a voltmeter, But mine does not seem to be accurate over
1kHz or so.

Most general use voltmeters are that way. Their major
purpose in life is measuring 50 or 60 Hz power.

Just use a 400 Hz test tone!

It's better than acoustic.

Far better. There really is no such thing as 0.1 dB accuracy or resolution
with acoustic measurements. Have someone else walk round the room, or simply
wait for the air currents and temperatures to redistribute themselves, and
you will measure a different number.

Acoustic measurements with pure continuous tones haven't been used by
professionals for decades. The first refinement was to start using swept
tones, and the second refinement was using spectrum analyzers to measure
artificially generated noise.


Besides, absolute accuracy is
not important here, anyway. What's important is RELATIVE
accuracy. I.E. that the meter read EXACTLY the same for
all of the units under test with the same 400 Hz TONE,
and that the scale can be sufficiently expanded to get
the outputs as close one another as possible.

Agreed. Matching is of the essence, not absolute frequency response.

Most cheap digital voltmeters are already a dB or more down at 1 KHz. But
they can generally be used for comparisons up to about 10 KHz or more. The
frequency response of DVMs is not always specified. I have two DVMs - a
Fluke and a Protek, that are flat within a few tenths of a dB up to 20 KHz.
The rest are not really audio instruments, but I could and have used them
for level matching.

Good frequency response is actually a distraction when you are metering the
power line and batteries, which is what most people use DVMs for.



Yep. But like you say, good frequency response or accuracy are not important
here, but repeatability is. Still, in all, I consider my E-Bay purchase of an
HP-400E to be about the best $15 I ever spent on audio (and my Behringer
cable-tester box with the built-in 400 Hz and 1KHz oscillator was the best
$30 I ever spent on an audio device - BTW, If you don't have one, American
Musical Supply is selling these puppies fro $21! )