Well to me the app serves marketing.
I redid the test a couple of times. The lowest audible tone is not low enough.
The test was done through the ie600 and audiojack of a device using internal SD865 Dac.
The aforementioned app I referred previously (e-audiologia.pl) is way more accurate.
It allows you to manually calibrate the gear you use. And the tones go way lower (which is perfectly audible by my ears as I may add) than the lowest tone used by Sennheiser app.
I will confirm the difference in test results between both apps and have scheduled a hearing test with a certified audiologist.
I'll happily share the results.
-25db right and - 35db left is borderline hearing aid necessity and no previous certified tests I did gave me these numbers.
I dismiss the sennheiser app as marketing unfortunately, bold move Sonova