Audible Noise Calculator
Input your headphone's sensitivity (either dBSPL/mW or dBSPL/V), nominal impedance, and your amplifier's Signal-to-Noise Ratio (SNR) and the voltage used for the SNR measurement.
Maximum Output Calculator
Input your headphone's sensitivity (either dBSPL/mW or dBSPL/V), nominal impedance, your amplifier's output power at the closest specified impedance (e.g. 32 ohm for a 22 ohm headphone, 300 ohm for a 250 ohm headphone), and the crest factor (ratio of peak to average level) of your music.
Impact of Amplifier Output Impedance
Input your headphones' highest impedance from an impedance vs. frequency graph, the lowest impedance from the graph, and your amplifier's output impedance