Beware impedances!

I had held a small listening session comparative hd 25, sony both 7506 and 7509, the AKG K271 and Beyer DT770.
Without going into details, I went on the DT770 for comfort listening, and his response although somewhat exaggerated in low and medium BF. But I told myself as having too much than not enough bf (compared to the K271). Sony out of the race because of their high hump in the medium, 25 hd too bad ears (!), And the AKG K271 defined but not enough bf.

Then I realized that the DT770 80ohms version existed, so I ordered.

The result felt a filter on the hf (completely absent!), Far too low and medium bf (much more than the 250ohm version).

Hypothesis: different response of the headphone amplifier according to the impedance of the headphones.

So .... I will try to send it to beyer their version 80 ohms, which sounds not the same thing, and then make me return a 250 ohm version.

again, the difference in practice the impedance is not obvious. The knob was almost the same level racing
(For the same noise level) on a 80 and a 250! (How are they in beyer?!)

voilou sailing, so caution and a max of comparative test if you can

Tomtom2004