John Williamson wrote:
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Paul Dorman wrote:
My meter is NOT a True-RMS meter, so I know if the signal is too far off
from an ideal sinusoid, the RMS reading will be off, but I am hoping it
will be close enough.
At the speaker, meter impedance is not critical, though using a VTVM is
still specified as most moving coil meters of the period did not have
either true RMS capability or a level frequency response, as well as
having a variable impedance at the test leads, depending on the range
that was set.
** VTVMs are not "true RMS" - none of them.
Multi-meters with that feature became possible with the advent of special linear ICs called "RMS to DC Converters" - in the early 1980s.
Modern DMMs often have such ICs in them but is still no guarantee of a wide frequency response.
OTOH The vast majority of old fashioned analogue meters DO have wide response - at least the whole audio band within a dB or so.
All the above will accurately read the RMS value of a *sine wave*, allowing for response limits as published in the handbook.
FYI:
I recently bought a Keysight U1232A meter with true RMS and speced to a few kHz.
On test however, it is flat to *over 100kHz* on all ranges.
https://au.mouser.com/ProductDetail/...2BgT2eJg%3D%3D
...... Phil