Benchmark HPA4 Calculator Results update on input change. Select DAC Calibration: +24 dBu at 0 dBFS, XLR Input (Benchmark DAC) 4 Vrms at 0 dBFS, XLR Input (Typical HiFi Balanced) 2 Vrms at 0 dBFS, RCA Input (Typical HiFi Unbalanced) Enter HPA4 Volume Setting: dB Enter Headphone Sensitivity: Value: dB SPL at 1 mW dB SPL at 1 Vrms Enter Headphone Impedance: Ohms Results Amplifier Output Power: mW (at peak SPL) SPL from single loudspeaker: dBm (dB relative to 1 mW) Relative Output Level: dBV (dB relative to 1 Vrms) Headphone Peak SPL: dB SPL Amplifier Headroom: dB (at peak SPL)