If you record acoustic guitar, you know how tricky it can be to position the microphone properly and keep the mic placement steady through a recording. The mic position needs to remain consistent between takes or else there will be a very noticeable change in tone when you punch in and out.
Wouldn't it be great to somehow clamp your microphone to the body of the guitar itself? That way, you could position the mic once and always keep the mic and guitar in the same relative position while you record. There are a few
clamps that do this on the market, but they are over $100. Not fun. Here's a quick and easy DIY alternative that's been working very well for me. Assuming you already have the microphone and guitar, this setup shouldn't cost you more than $30 (possibly much less if you already have some of the parts).

Here are the components of my setup:
- Acoustic guitar
- Irwin Quick Grip 12" Mini Bar Clamp (available at many hardware stores)
- Right angle chemistry clamp (check eBay or your local chemistry supply store)
- 6" goosneck microphone extension
- Microphone clip (you probably got one of these with the microphone)
- Microphone

The real trick of this setup is the Irwin Quick Grip 12" Mini Bar Clamp. This is what clamps to actual guitar body. These clamps are designed for small carpentry projects and are designed for clamping pieces of wood together. You have a lot of control over the pressure applied to the clamp, and it's probably possible to crack your guitar if you squeeze it too tight. I adjust mine until there's enough force to prevent the mic from moving around, but no more. I also try to position the clamp near the edge of the guitar body where it should be stronger.
Next, the right angle chemistry clamp connects right to the rail on the Irwin clamp. Not much to say about this piece; you just screw it in snugly and it stays in place.

Then, you screw a 6" gooseneck microphone extension into the other end of the chemistry clamp, and attach the mic clip to the goosneck extender, and you're done. Your clamp is ready to go. Look at the pic at the top of this article to see how it all fits together.
I use this clamp to position the mic somewhere between the 12th fret and the soundhole, depending on what I'm trying to accomplish. I personally use a stereo mic, but this setup works equally well with all of the mics in my collection (including large diaphram condensor mics that require a shockmount). I suppose you could probably find a mic that's too large for this setup, so just use your common sense as to how much weight to hang off this thing. I haven't had a problem with any of my mics, but to completely avoid damaging your guitar, smaller mics are best.
By the way, so far this clamp has not damaged the finish on my guitar. If you're worried about this, then you could use a soft cloth between the clamp and guitar just to be safe.
If you make a clamp like this, leave a comment below and let me know how it works for you!