Headunit preout voltage and electronic crossover?

[momofx 10+ year member]

I am kinda debating preout voltage when adding an electronic crossover (input sensitivity 100mV and has 5V outputs) between the HU and the amps.

My assumption was that even if your HU had a pre-out of 1V or 2V it does not really matter as long as you set it to its max unclipped volume going INTO the electronic crossover and then set the crossover's max. unclipped output and then the amp gains.

Than I keep finding posts that 4V or more would make a different in ANY setup with or without a crossover. The theory just does not make sense to me if the crossover can accept a signal all the way down to 100mV...

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[pickup1 5,000+ posts]

The higher voltage the better.You have to take in account you get a voltage drop thru the rcas,especially if the are 17-20 foot long.

 

[keep_hope_alive Premium Member]

I am kinda debating preout voltage when adding an electronic crossover (input sensitivity 100mV and has 5V outputs) between the HU and the amps.
My assumption was that even if your HU had a pre-out of 1V or 2V it does not really matter as long as you set it to its max unclipped volume going INTO the electronic crossover and then set the crossover's max. unclipped output and then the amp gains.

Than I keep finding posts that 4V or more would make a different in ANY setup with or without a crossover. The theory just does not make sense to me if the crossover can accept a signal all the way down to 100mV...

small voltages have poor signal-to-noise ratios. figure with a 100mV signal you have to max out the gain in order to get the same signal that a 4V signal would with gain at minimum. lower amplifier gain = less noise.

you want gain as soon as you can get it - i.e. at the head unit. then try to keep reducing gain at each piece (crossover/eq/amp). the result will be minimal noise (assuming the head unit is of good quality).

otherwise, you can get additional gain out of a crossover/eq to treat it as a line driver - but you still want it to get the highest signal possible as soon as possible. I consider 2V as a minimum head unit output.