Impedance of only 80 ohms, but the sensitivity rating is relatively low, meaning they need more power to drive them to produce the same volume.
I tested several headphones in conjunction with my Yamaha P-525 piano... Yamaha HPH-150B, AKG K-702, beyerdynamic DT-990 Pro 80 Ohm, and Sennheiser HD 560S... only the Sennheisers had both excellent/neutral sound AND all the volume.