I'm often asked to determine proper preamp gain based on vague phono cartridge level specifications.
Often an output level is quoted without any reverence to velocity.
"3.5 mV" doesn't tell me anything.
3.5 mV compared to what?
One manufacturer of some very expensive cartridges when asked by my client said "I've never heard of an output level being referenced to a speed. The level is an absolute measurement."
This was supposedly from the guy who actually assembled them.
Really?
So we're supposed to believe this cart outputs its "2.12" mV whether the platter is stopped or spinning.
Yeah right...
Some manufacturers may specify 5 mV at 5 cm/second 1 kHz.
But what is "5 cm/second?"
Is it RMS or peak?
We're left to guess.
A search of my library led me to Vogel, "The Sound of Silence."
"Phono Cartridge Transfer Factor," Vogel, The Sound of Silence.
Vogel says that the peak velocity provides the units for an RMS voltage measurement.
The mixed units seem odd.
Every test disc I have states velocity as an RMS unit, not peak.
Where does Vogel get his 8 cm/second peak value?
Converting 5 cm/second RMS to peak is 7 cm/second.
I'm sensing a lack of consensus here.
When a manufacturer specifies 5 mV at 5 cm/second we can be fairly certain that the voltage measurement is RMS. (Though we can't be too sure of that either).
But when they say 5 cm/second what do they mean? RMS or peak?
Do they themselves know?
I checked a Stanton 681 with a stated Transfer Factor of 1 mV/cm/second at 1 kHz.
Based on 5 mV I applied the amount of gain that would be required to bring it up to +4 dBu RMS.
Both channels were within 1/2dB based on 5 cm/second RMS lateral modulation and within the cart's channel balance spec by a wide margin.
(It was actually an STR-100 at 3.54 cm/sec RMS Left and Right only equivalent to 5cm/second RMS lateral/mono.)
Stanton used RMS measurements consistently...
For the manufacturer who stated "2.12 mV is an absolute" there's no real hope in decoding the specification. We can only guess.
But for a manufacturer that at least provides a velocity what is safe to assume?
RMS?
What do real standards tell us?