importance of output impedance for headphones?

[sgrossklass]

Not sure speaker performance would differ much between a DF of 4 and 1,000,000 (esp when you consider other resistances in the speaker circuit).

Nonlinearity, maybe not, depending on mechanical damping.

But frequency response, of course. If I plug the corresponding values for HD598s into my FR calculator (I looked them up - Zmin = 55 ohms, Zmax = 280 ohms), a DF of 4 gives me a FR deviation of 1.5 dB, which is not major but clearly audible in A/B. Using a nominal 4 ohm speaker with 3.2 ohms min and 10 ohms max yields about the same. This'll probably be swamped if you just move the speakers around a bit in an untreated real-life room (points for the headphones!), but still.

 

[AndrewT]

DF of 4 for a 4ohms speaker equates to a source impedance of 1ohm
DF of 4 for a 55ohms headphone equates to a source impedance of 14ohms

Is that what you are comparing?

 

[coluke]

Quite strange because high impedance drive on a loudspeaker may impair its frequency response but generally, it decreases non linear distortions (THD).

Probably you are referring to acoustical THD; as far as the electrical THD is concerned, this one clearly raises as the output impedance raises if the relationship between I and V in the load is non linear. The question is: how electrical THD relates to acoustical THD?

L.