[wnmnkh]

http://benchmarkmedia.com/blogs/news/12838141-headphone-amplifiers-specifications-are-only-part-of-the-story
 
As far as I am concerned, this article and story had posted somewhere on head-fi several ago. It seems now Benchmark folks finished the paper with updated stuffs.

 

[KamijoIsMyHero]

So a new spec should be added, that involves impedance variance as a third dimension(I don't think this is the right term) to THD-N vs Frequency, for amplifiers.

 

[stv014]

It shows two already known issues: amplifiers usually distort more when driving low impedance loads (therefore, the specifications should include THD+N etc. with actual realistic load impedances), and dynamic headphones distort more when driven by high impedance sources because of the reduced electrical damping (for this reason, and also because it affects the frequency response as well, it is important to know the output impedance of an amplifier, yet it is often missing from the specifications).

 

[anthk]

The paper doesn't mention why in figure 6 there is a roll-off after ~11k with their dac1 though. Could anyone enlighten me on this?

 

[stv014]

Perhaps because the measurement is limited to 32 kHz bandwidth, and the DAC1 might have mainly 3rd order distortion and very low noise.