Re: Thoughts about amplifiers at 3/4 volume.
While *technically* correct, there is practically no reason to turn down the input attenuators of a modern day amplifier.
Why?
Because they have superior S/N that the rest of the audio electronics, especially once mics are open.
Most mixers can barely muster 80-90 dB of SNR with the channel gain trims all down. Fahghettabatit when more than a few are up. Basically, what boils down to is nearly every amplifier on the market has a 20-30dB S/N advantage on the rest of the system. Turning those trims down is just masking the noise.
If you have a DSP, turn down the crossover outputs, if not... bring down the master fader by the same amount. You'll see that the same result is gained, plus like another poster mentioned, you don't have to worry about someone fiddling with the knobs "on accident."
Another bad thing that can happen that Bob Lee of QSC used to mention is that when you turn those attenuators down, you make it easier to overload the input stage of the amplifier. I.e. if the amp clips at +8dBu and you turn it down 10 dB you have to drive the line that much harder with 18dBu to clip the amp. It' only gets progressively worse the more you turn it down.
If you really don't believe me, the next time you fire up a system, and you notice some "hiss" from the speakers, unplug the drive lines from the amplifiers. I guarantee you the hiss will go away. Amps are not hiss makers. Mic gain stages and electronics are.
I also agree with JR on the WOT for Rock and Roll too. At most live gigs, your going to be dealing with a 80 dB (A) SPL noise floor (maybe worse). What ever gain the system has is only going to amplify that further. Hiss from the speakers is your least worry here.
If there is a lot of hiss with the mics open, where it's litterly distracting, find the source and antennuate it. More than likely it's an FX return (from an old FX unit) or a wonky channel gain. I've also found this to be a reason to always start a show with all pads out. I once mixed a gig where all the pads were engaged (programming error on a digital console). There was so much hiss it was unbelievable because each gain knob had to be turned up more, relative to the input and it seems digitally controlled pre-amps seem to be exponentially more noisy at the top end of there gain. I've also found that systems that do have a lot of hiss are more unstable feedback wise.
