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Old 14th September 2012
Originally Posted by Jimbo View Post
Sorry for hitting ye olde thread, but I'd like to know why adding resistance in series is not a recipe for high fidelity?

Thanks for 'splaining!
The impedance of a transducer like a headphone or a speaker driver typically varies with frequency*. Adding any series resistance means that the drive power will change with frequency because the series resistance will provide a different amount of attenuation as the frequency varies. That will significantly change the apparent tonal balance of the sound.

The second factor is that tranducers (like headphone drivers) really need to be driven from a source impedance that is much lower then their own intrinsic impedance in order to be properly damped. Adding a series resistor dramatically raises the source impedance and virtually eliminates the proper damping of the transducer usually resulting in "muddy" and "boomy" bass frequencies because of the internal resonance of the driver.

* A published impedance curve for the Beyerdynamic DT-800 headphones shows an impedance curve that varies from 55 ohms at 2kHz to 220 ohms at the LF resonance point of 95 Hz. Having an impedance curve that changes by a factor of 4 to 10 over the audio band is not uncommon.