Distorsion vs Power graph explanation

[Zamiel]

hello, i have a question: i don't think i understand the graph that is shown in every headphone amp review.

look for instance at the review of the topping l30 ii

Topping L30 II Review (Headphone Amp)

This is a review, detailed measurements and listening test of Topping L30 II. It was sent to me by the company and costs US $149. It comes in a number of colors. Usability could not be better with positive clicking switches for power/pre and gains. Three gains are provided with the low gain...

www.audiosciencereview.com

sinad at mid gain is 121db but the graph at 300 ohms shows 106db at low gain and 113db at high gain. at 32 ohms 106db and 112db respectively.

can you please explain to me the correct way to read that graph?

 

[amirm]

There are some differences in the measurements. The dashboard runs with a load of 600 ohm which is not represented in the power curves. And due to historical reasons, the power curve doesn't use the high performance sine analyzer in audio precision. Both of these contribute to lowering the SINAD in the power graphs. I probably should fix these inconsistencies but then it breaks backward compatibility with current database of measurements.