Metal grills on guitar cabs...

Im guessing that they don't do that much if they are put on properly(So they don't flex or rattle.).
Not sure though, so it goes under the category of "thoughts". ;)
 
I don't know to be honest. Having something metal right in front of the speakers absolutely has to affect high/high mid frequency output, even if the grill is fastened properly so its self-resonance isn't so much of an issue.

I tend to make it a point to remove the grill of whichever cab I record, if at all possible.
 
i have tried that on my own made cab,

and the only thing you get is more gain on the signal (as the mic is more close to the grill/speakers) and affect like if you where putting the mic in any other place of the cab ..
 
I would think a metal grill would let more highs trough, as a piece of cloth is more likely to dampen high frequencies.

All I can say is my metal grill half-back Mesa cab is leaps and bounds better in A/B tests against my old V30 loaded cab and my bandmate's Soldano cab for both of our amps. That's mostly due to the EVM12Ls, though.
 
I think it's been discussed here before and the consensus was that it doesn't affect the sound as much as you'd think, if I remember correctly.

~006