[Marvin7]

Since I consider upgrading the HD650 to the HE-500 I took a look at the measurements of the two and noticed the HD650 has higher THD in bass (which gives it a somewhat muddy sound) while it has a lower THD throughout the mids. So trying to compare the two, my question is which THD plot is considered better in theory and in practice?
 
HD650:
http://www.innerfidelity.com/images/SennheiserHD650.pdf
 
HE-500:
http://www.innerfidelity.com/images/HiFiMANHE500.pdf
 
(I was unable to upload the graphs)

 

[jerg]

Quote:

Since I consider upgrading the HD650 to the HE-500 I took a look at the measurements of the two and noticed the HD650 has higher THD in bass (which gives it a somewhat muddy sound) while it has a lower THD throughout the mids. So trying to compare the two, my question is which THD plot is considered better in theory and in practice?
 
HD650:
http://www.innerfidelity.com/images/SennheiserHD650.pdf
 
HE-500:
http://www.innerfidelity.com/images/HiFiMANHE500.pdf
 
(I was unable to upload the graphs)

Typically THD is a tool to diagnose if something has distortion issues, more than to distinguish performance between high-performance drivers. You might also notice that one of the HE500 drivers flairs up much more than the other driver, most likely because of some hair or dust. If you ignore the orange plot in the HE500 THD then it is close enough to HD650 THD that our hearing won't be able to distinguish any difference in blackness of background.
 
Of course with regards to the bass, it's a whole different story. HE500 and other planars are typically able to reproduce low (lower than 50 Hz) frequencies with much better clarity than dynamic drivers, and the THD differences as you can see are huge.
 
Remember, THD plots are logarithmic, not linear, and there is a pretty distinct threshold below which any differences are practically unnoticeable by human hearing.

 

[Marvin7]

Quote:

If you ignore the orange plot in the HE500 THD then it is close enough to HD650 THD that our hearing won't be able to distinguish any difference in blackness of background.
...
Remember, THD plots are logarithmic, not linear, and there is a pretty distinct threshold below which any differences are practically unnoticeable by human hearing.

If such THD levels are inaudible how is it amplifiers boast much smaller THD+noise rating. According to NwAvGuy it's well above the threshold of hearing.

 

[gurubhai]

The difference is certainly audible, purrin explained it nicely here :
http://www.head-fi.org/t/595683/fostex-th900-impressions-discussion-thread/1350#post_8550368
 

 

[jerg]

Quote:

If such THD levels are inaudible how is it amplifiers boast much smaller THD+noise rating. According to NwAvGuy it's well above the threshold of hearing.

AFAIK that's simulating static noise though, quite a bit different from actual harmonic distortion (which forms more to the music since it originates from the track itself). As opposed to hearing a background noise in music, with high THD it's not so much noise as opposed to a slight muddling, a bit less black of a background, so very low levels it can be much less obvious.
 
Heck even when I compare my HE400 midrange against my HE500, which is a HUGE THD difference relative to HE500 vs HD650 (check InnerFidelity if you don't believe me), I barely notice the slightest hint of difference in blackness of background, and even then it was masked a lot by the difference in sound signatures.
 
 
Quote:

The difference is certainly audible, purrin explained it nicely here :
http://www.head-fi.org/t/595683/fostex-th900-impressions-discussion-thread/1350#post_8550368
 

That's the bass region though, where THD difference supposedly modulates how tight the bass is. The only time I recall purrin mention actually perceiving harmonic distortion in the mids region  (in the form of a less black background) is with the horrendous THD of his HE400, compared to cleaner phones like HE500 or HD650. But that is a huge difference as opposed to the much lesser difference here.