Sennheiser HD-300 PROtect, Monitor Headphones, ActiveGard technology protects against loudspeaker peaks above 110 dB, Closed, Circumaural, Impedance: 64 Ohms, Nominal sound pressure level: 108 ± 3 dB SPL / 1 V rms / 1 kHz, Transmission range: 6 -25000 Hz, Harmonic factor