Grado's efficiency rating is 98dB @ 1mV (not mW)!
But actually it should be 98dB @ 100mV, which will translate into 103dB @ 1mW (Grados are 32-ohm headphones).
But actually it should be 98dB @ 100mV, which will translate into 103dB @ 1mW (Grados are 32-ohm headphones).















