What would cause distortion if in/out impedance is flat?

[tifune]

Trying to understand this bit from the G5 review:

"I started with my hard to drive, low impedance Dan Clark Stealth headphone. I was pleased that I could get pretty high volumes out of it using high gain. For loud listening, I had to go to 3:00 pm on the volume control. There was a bit more volume to be had if you turned it to max. There, I only heard distortion when the sub-bass notes arrived. Otherwise, the sound was super clean, detailed and enjoyable."

If output impedance is "essentially zero" and Stealth's impedance is flat 22ohm, the G5 should be able to hit around 116dB when used with Stealth. Basing that on one of Stealth's more conservative sensitivity measurements of 86dB/mW.

Yet, I thought I detected the same thing on my (slightly more powerful) NX7. I don't think it was placebo related to reading the review because I "heard" the issue long before, which of course doesn't immediately obviate placebo in general, but what else could it be?

Just want to be sure I'm not missing something. I'm assuming no extra EQ was used on G5 review, maybe that's not the case but I don't see it mentioned

 

[staticV3]

Amir exceeded the G5's headphone Amp's current limit, resulting in a sharp increase in distortion is my guess

 

[DVDdoug]

The headphone amp might be clipping. How do we know it's not trying to put-out 130dB at subsonic frequencies, or something like that? It's really hard to know what's going-on in the deep bass or subsonically.

If it's the headphone itself, distortion would be caused by pushing the driver to the point physically-mechanically where it can no longer move linearly.

 

[solderdude]

Yet, I thought I detected the same thing on my (slightly more powerful) NX7. I don't think it was placebo related to reading the review because I "heard" the issue long before, which of course doesn't immediately obviate placebo in general, but what else could it be?

116dB in the subbass is not as loud as most think it is. One would be clipping the amp at that level.

Notice, just like with the Expanse the distortion starts to rise for lowest frequencies while most 'regular' planars do not at those levels.
It could also be that with large excursions (lowest frequencies, high power) the membrane can't 'push' the needed large amounts of air through the 'diffuser' in front of the driver.
You could test by not using a headphone amp but a speaker amp (connected to speaker out) and listen if the same effect happens then.
Note... you could potentially blow up the driver.

 

[sq225917]

Use a peq and clip 6db up to 40hz, see if thet sorts it then you'll know, it's either driver excursion or amp power.

 

[tifune]

116dB in the subbass is not as loud as most think it is. One would be clipping the amp at that level.

I think this is the part I'm confused on - assuming my numbers are correct, 116dB is just short of clipping. But, you're saying it might still be clipping anyway? Staticv3 had a good point re: V, but assuming (again) these digizoid etc power calculator are correct, I should be about .3V under max

 

[solderdude]

It's not only the bass.
The audiosignal is literally an addition of all frequencies so might well be 110dB low bass and 6dB added 'power peaks' reaching distortion levels.