How much do you focus on the signal to noise ratio of a HU? What kind of difference could I expect to hear between 81dB and 105dB?

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-Evan

IMO, S/N ratio isn't a big factor when looking for a HU. However there's a huge difference between 81dB abd 105dB. Which HU has a 81db S/N ratio? Some cassette players have higher S/N ratios than that!

Yeah, that is pretty low, but even still I think it's worthless... you'll have far more noise picked up in your RCA's then the amount of noise coming from the headunit.
In a home audio enviroment it might matter, but in a car, doesn't matter at all.

However other factors could be important... the fact that it has such a bad S/N rating could say something about the over all quality of the unit.

You won't hear ANY difference at all. Besides that, these specs were not at all standardized. So they may, or may not be, useful in comparing one manufacturer's unit to another's. As a side note, the recent movement to standardized testing parameters should generally result in specs that do not look as good as in the past. Not to worry though, an 80db noise floor is inaudible.