The DT 660 is based on a closed headphone design and therefore attenuates ambient noise more effectively. In addition it also prevents the sound from inside the headphone to be heard outside
The DT 990's open diffuse-field system allows the user to be aware of ambient sounds creating an open spatial feel- important for professionals who require clinically accurate high and mid-range reproduction.
The SR80i will produce a sound that is pure Grado, warm harmonic color,rich full bodied vocals, excellent dynamics and an ultra smooth topend. Listen and Enjoy!