In article , Arfa Daily
wrote:
Ok, so who knows a bit about measuring audio power ? Setting aside any
furious arguments about peak power, rms power, average power,
backpeddling average peak music power on any given friday in March etc,
does an audio power meter sum the power in both half cycles to arrive
at a reading, or just one.

I suspect this depends on the actual 'power meter' in question. :-) May
have a precision rectifier and take an average from that , or may use
something else. e.g. the old avos tend to give a decent result if
calibrated, you know the load, and are using a sinewave.

I guess what I'm asking is half wave reccy ahead of the meter, or full
wave bridge ?

If it uses a rectifier then takes a time-average I'd expect a good one
to use a full wave precision rectifier - i.e. one that suppresses the
forward voltage drops in the diodes. Cheap enough to do at audio
frequencies.

These days a meter might simply sample rapidly and work out the rms
voltage and report that. Years ago, it might have used an analog
multiplier to obtain the square-law for audio. I guess people like
Burr-Brown still make these. (?) As Don has pointed out, a thermal
meter might be used in some applications. These (and single diodes)
still get used for RF power measurements.

However unless you are using a sinewave, the reported value may be
misleading. Ditto if the load isn't resistive.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

"Jim Lesurf"
Arfa Daily

I guess what I'm asking is half wave reccy ahead of the meter, or full
wave bridge ?

If it uses a rectifier then takes a time-average I'd expect a good one
to use a full wave precision rectifier - i.e. one that suppresses the
forward voltage drops in the diodes. Cheap enough to do at audio
frequencies.


** OPs needs real info - Jim.

Not dumb guesses from someone with no idea how a DMM actually works.



These days a meter might simply sample rapidly and work out the rms
voltage and report that.


** Pigs might fly as well.


Years ago, it might have used an analog
multiplier to obtain the square-law for audio.


** Got no idea at all how a " true rms" DMM actually operates - Jim ?

Never come across any " rms to DC " converters made by Analog Devices?

Only been around for over 20 years.



I guess people like
Burr-Brown still make these. (?) As Don has pointed out, a thermal
meter might be used in some applications.


** The ASS said no such thing.

Why cover up for the demented fool ?



These (and single diodes)
still get used for RF power measurements.


** Damn shame then how OP is asking about **audio** !!



However unless you are using a sinewave, the reported value may be
misleading. Ditto if the load isn't resistive.


** Better have a look at the AD636.

http://www.farnell.com/datasheets/57885.pdf

Covers audio band measurements very comfortably.





........ Phil