Woohoo....my very own thread!
Veff = Vrms = Equivalent DC voltage. The spec indicates that each of 4 channels puts out a maximum of 3V (rms) when driving a high impedance (10K ohm) load. I assume this means the peak voltage swing (Vpp) is 1.414 * 3V = 4.24V max.
So to translate, this means either 3V max or 4.24V max depending on if the device you plug into has a spec in terms of Vpp or Veff. Sorry, I'm not a car audio guru so I cannot say if Vpp or Veff is the 'standard' way these things are quoted -- or if there is a standard. The safe thing to do is probably assume you're working with the higher number and set your amplifier gain appropriately. If the volume level is insufficient then you can crank the gain up to support the lower voltage.
