Low Pass Filter...why?

[Ollie]

I read in another post (Ron K) that he sets a LPF at 14k & a 24db slope.
OK, I realise that our hearing is starting to fall away up in these sort of frequencies (some more than others) but what are the technical reasons for a LPF?
Is it to simply filter off frequencies that will not be missed in the mix, to prevent unnecessary load on the piezos / compression drivers, high end distortion or what?

[J_Dunavin]

I always thought that was the idea. Why spend the extra power where you won't miss it.
I also remember reading somewhere that some amps can experience some high freq. oscillations that could cause distortion, but I also thought that was in the MHz range.

[Radian]

With piezos, passive LPF's prevent ultrasonic resonance from toasting your amps. Active LPF's save power on tops by knocking out HF noise in the signal chain, maximizing efficiency.

[Ron K]

Why amplify what you cannot hear anyways? Also some instruments have hiss in their signal path. I like to try and filter that out pre fade but sometimes (Hammond's, Old Vox organs, Fender Rhodes,Old Cat9 Synths etc) have so much hiss that even a good HPF on the channel isnt enough without setting it so low you destroy the actual usable frequency range.

So to help control any nasties like High End Hiss,Radio interference from 2-way radios etc., overhead crane remotes etc,and simply not amplify what you cant and dont really need to hear.Some will argue they can hear even and odd order harmonics up that high which I wouldn't doubt if their hearing is impeccable and they were in a good studio but not in an inherently noisy environment like a concert or a bar etc.! I've found the noise floor alone kills any intelligible HF Response above 16K so I start the roll off at 14K.