The Boostaroo is an audio amplifier that separates the signal into individual stereo channels to drive 3 separate headsets or speakers. Depending on the ohm rating of your headphones, the Boostaroo will double the output of your player with no more than a 1% harmonic distortion.No difference in output or frequency response was observed when one headphone was plugged in or when 3 headphones were plugged in at the same time. Signal to noise ratio was measured -95dBa from clipping level into a 33 ohm resistance. Distortion was measured just below the clipping level, at 0.3%, which is the residual distortion of the generator used.The input impedance was found to be approximately 500 ohms. The output impedance was approximately 1 ohm. Maximum power transfers occur with an 8 ohm load.The Boostaroo employs similar output amplifiers to those found in CD players. Frequency response is equal to or exceeds specifications. Typical specifications are 20 to 20, 000Hz +/- 2 dB (EIAJ CP-307 Method).Output (@ 3VDC), under 1% harmonic distortion:Into 8 ohm headphones - approximately 40 mW per channel, 12 dB gain in sound per channel. Or 100% boost in loudness;Into 16 ohm headphones (stereo mini jack), approximately 40 mW per channel, 12 dB gain in sound per channel;Into 25 ohm headphones: approximately 40 mW per channel, 11.1 dB gain in sound per channel;Into 32 ohm headphones: approximately 30 mW per channel, 10.9 dB gain in sound per channel;Into 64 ohm headphones: approximately 13.8 mW per channel, 10 dB gain in sound per channel.Power Requirements:3.0 VDC: Two size AA batteries are required. Use of alkaline batteries is suggested for longer playing time. Also works with rechargeable batteries, nickel-metal hydride type preferred.