Impedance is one thing, efficiency and good low end response is another. IME the audio technica headphones are not very good, and I had several of the ATH-M30x headphones to use as recording monitors for band members to wear while tracking. Everyone hated them, they were harsh and midrangey with no balls whatsoever. And the ATH-m20x was the step down from those.They're Audio-Technica ATH-M20x rated at 47 ohms. They seem quieter than they should be with my Ampeg SCR-DI as well so that may be the problem. Thanks for the info, I never gave different headphone impedances a thought.
Sennheiser HD280 for the win. But at the time I bought the ATs, they were like $39 compared to $99 sennheiser. The 20s were like $29. What did they cost you nowadays? This was around 99-2000.
Another thing about the sennheiser, they actually isolate about 30db of sound, like putting on earplugs or pro IEMs, which really gives a great experience, the audio technicas don't really cover the ear the same. I used the hd280s on airplane rides too, finally could hear all the bass even in a pressurized cabin. I need a new pair, mine still work great but all the black pleather does flake off after years of use. But that happened even sooner with my ATH-M30x's