Pauln
Well-Known Member
Interesting thread; a lot of misunderstanding about headphones and how they work (and how amps work). Here are some insights from an unimpeachable authority:
"The matching of impedance between a source and a load becomes important when maximum power has to be transferred. This is not the case with headphones. They will require only a very small power in the order of a few thousandths of a watt." - Sennheiser
"Since power considerations are more or less insignificant (all amplifiers have ample power to drive a headphone), we have to focus on the available signal level, measured in volts. Each headphone has its characteristic efficiency and impedance, and the listening volume will therefore be directly related to the level of the audio signals." - Sennheiser
"A home-type hi-fi amplifier delivering 10 watts into an 8 ohm speaker develops 9 volts at its output terminals." - Sennheiser
To put these values in perspective, my phones are 2000 ohms and deliver 102dB at 0.001 watt (1.41 volt, 0.00071 amperes).
Think about the implications of this... until the output current exceeds twice the bias current, a class AB amp is operating in class A. This suggests to me that virtually all headphone listening is in class A.
"The matching of impedance between a source and a load becomes important when maximum power has to be transferred. This is not the case with headphones. They will require only a very small power in the order of a few thousandths of a watt." - Sennheiser
"Since power considerations are more or less insignificant (all amplifiers have ample power to drive a headphone), we have to focus on the available signal level, measured in volts. Each headphone has its characteristic efficiency and impedance, and the listening volume will therefore be directly related to the level of the audio signals." - Sennheiser
"A home-type hi-fi amplifier delivering 10 watts into an 8 ohm speaker develops 9 volts at its output terminals." - Sennheiser
To put these values in perspective, my phones are 2000 ohms and deliver 102dB at 0.001 watt (1.41 volt, 0.00071 amperes).
Think about the implications of this... until the output current exceeds twice the bias current, a class AB amp is operating in class A. This suggests to me that virtually all headphone listening is in class A.
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