ok, so I've been examining my acoustic guitar, seeing the damage its taken in the 4 years ive had it and noticed fret buzz. lots of it. on pretty much all the low strings when tuned down, sometimes in Estandard. and it gets even worse when i put a
Capo on it, its the worst on frets 1-4, after that it lessens to a reasonable amount.

thinking about it, the neck must be bowed slightly, is there anything else it could be besides that?
could be quite a few things, like neck relief, a raised fret or frets, fret wear, improperly cut nut which can wear over years as well, saddle is worn down some. If your tuning down too low, your acoustic may need a full set up to compensate for the tuning, or try using thicker gauge strings if your acoustic is built to handle them, some acoustics I would personally stay away from heavier strings.
if it didn't have buzz before and now it does I'd think it's probably not the neck bending forward as that would raise the action. Although you did say when tuned down so it could be the neck bending backwards due to years of less stress than usual, do you leave it tuned down all the time? On the simple side I'd guess the nut needs some tending too, on the not-so simple side could be the fretboard is coming loose and needs a re-glue. What brand/model is it?

Either way I'd think a proper set-up is in order and even if you need a new nut/saddle/fretboard re-glue it probably won't be much more than about $100 to fix it up.
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usually its in standard but on fridays i occasionally do acoustic gigs/practices so it gets all the tuning changes then, but most of the time it is in standard when i use it at school. over the summer its ocassionally in Eb for a week or 2 at a time.

i seriously doubt the neck has been bending away. maybe the nut has worn out because everything past the first 5 or so frets its fine. im going to talk to my local tech soon and see
I typed out an incredibly long message about how to adjust your relief and action correctly, but Internet Explorer ate it. Boy, I love using library computers.

The long and short of it is that relief is not action. They may produce the same effects, but they are not the same (sorry, functionalists). Relief is checked by fretting the sixth string (low E in standard tuning) at the first and fourteenth frets, then checking the distance from the string to the fret at the fifth, sixth, and seventh frets. There should be a hairline of space between them no bigger than a business card (but no less, either).

Action is adjusted by checking the nut, first. The nut is checked by fretting each string at the third fret and checking for snugness under the string at the first fret with a piece of paper. Each string should be adjusted this way. After that, all that remains is the saddle, which is extremely subjective and has no easy rule. Personally, I find that using the saddle to keep the string at a slightly higher angle than the neck works well and keeps the string nearly the same distance from each fret across the board, while eliminating possible buzz.

Good luck. I'm not typing this out again.
Sincerely, Chad.
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