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mashaffer 25th September 2008 10:37 AM

Measuring current distortion
The recent resurrection of the current drive thread on the loudspeaker forum got me to thinking about measuring distortion current rather than voltage.

I don't have the equipment but it would be interesting if one of you who did could measure the distortion current of an amplifier driving a single full range driver. What I have in mind is say a single ended topology with triode output v.s. pentode output with no feedback driving a full range speaker. Place a low value (1 ohm or less) non-inductive power resistor in series and put your scope or distortion analyzer across that resistor. This way we can measure the harmonic distortion series in terms of current. One could also measure frequency response in terms of current as well.

Not sure what we would find but it might be interesting and enlightening. This is based on the theory that driver output is more closely related to voice coil current than voltage.

After getting basic numbers we could then check the effects of local and global NFB and even various enclosure options. It might also be instructive to measure a lowish Qm speaker like the Pioneer 4" fullrange (Qm=1.4) v.s. one with a more normal Qm of 4 to 6. I have often wondered if the highish Zout of a naked pentode might be advantageous for fullrange drivers or even bass drivers with more mechanical damping capability.

Whacha think?

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