Why do people mic acoustic guitar at the 12th fret?

[Brian Brock]

I had some Ideas about recording the Acoustic Guitar today, and I realized, I really don't get miking the 12th fret. This is usually where the neck meets the body, or even a couple of frets away from the body. 90% of the sound you hear from an acoustic guitar is from the soundboard.

What happens is the strings moving back and forth pull on and release the bridge, causing it to twist the soundboard at the same frequency. This moves the air near the guitar, the sound waves inside the guitar bounce off the back and invigorate the top even more, and so on.

At the twelfth fret you've just got a bunch of finger squeaks and structural components to keep the guitar from collapsing. The strings themselves impart very little motion to the air.

So what gives? If it sounds good to you, can you explain what's going on that makes it sound good?

b

p.s. I also realized that the twisting of the soundboard means that the sound an acoustic guitar produces is out of phase with itself, because the part of the soundboard towards the neck moves in while the part towards the heel moves out. Not so on an archtop guitar or violin, though - there the soundboard doesn't twist, it moves up and down.

[Landon]

Just my 2 cents... Has anyone ever tried putting two mics each on the parts of the sound board that are out of phase with each other and reversing the phase on one of the preamps? I'm gonna try it. I imagine you'd have to have pretty exact placement for it to work right and a matching pair of mics. Yeah, I second Brian?s question, why do people put mics there? I like it much better mic'd near the head pointing towards the soundboard or mic'd from a distance.

Landon

[Glory_Morris]

I've never actually heard of micing an acoustic at the 12th fret. I usually just put on the headphones and move the mic to taste. Where did you hear of this technique?

[ryanlikestorock]

I find the mic placement has a lot to do with the purpose of the guitar in the song. If the guitar is the primary instrument, I'd mic it with a bit more body than if it's one of 10 instruments in the mix.

[mwingerski]

When I was 12 years old, I saw an episode of Mr. Wizard on Nickelodeon where they asked "why does a guitar sound like a guitar?" (I got my geek on way early)

In it, they examined the timbre of a variety of instruments and they had a guitar in an anechoic chamber with an array of like 100 measurement mics and so forth. They then had a 3D model of where the sound emanates from the instrument. (In classic TRS80 style graphics)

It turns out that most of the volume emanates from the soundhole (as expected) but then they found that a surprising amount of sound comes from where the neck meets the body. (ie, the 12th fret).

I've found a lot of the time that somewhere around the 15th fret (a bit closer to the body) is a good balance between too much bottom end and too much string noise.

There is a huge variable though with this. What kind of guitar, how the player is playing, what kind of mic you're using, how the room is affecting the sound and most importantly, how the track is going to be used in the mix.

I often use 2 mics, one pointing at the sound board about 4 inches below the bridge (using a large diaphragm condensor) and another one around the 12th to the 15th fret (usually a small diaphragm condensor). This gets a pretty good blend of low end and definition and as long as they are in phase, can give you lots of options at mix time so you can decide how you want it to sit in the mix later.

But I've never noticed any discernible phase issues from micing at the 12th-ish fret as long as the mic is far enough back from the gutiar.

The phase flipping idea sounds interesting. Might have to try that... probably be a bit "woofy sounding" is my guess. Not many people listen to a guitar from the back side. Would at least be good for novelty...

[Mark Alan Miller]

At the 12th fret, with the diaphragm pointing at where the neck meets the body, the microphone is 'seeing' a wide range of sound coming off the guitar, from the soundhole, too. And being a little off-axis from the soundhole on many instruents yeilds a slightly more defined, less 'boomy' sound.

I move my head around the instrument to listen to where I think I hear a good balance of tone, and put the mic there (or mics, if I'm stereo micing.) 95% of the time I don't have to fuss with it, at least not much. (The second mic is almost always out beyond the end of the guitar looking at the area between the end and the bridge... so both mic are kinda looking at it at a 45 degree angle...

[jamoo]

non-technical, punk answer: it sounds good.

the soundhole is just too plain boomy in proximity, and there's nowhere else to maintain the volume, particularly using a dynamic. you could aim at the body, off the soundhole, but that's pretty similar.

if you have a better technique, go for it.

[JASIII]

12-15 fret, about a foot away has always sounded best to me. set up mic, put in headphones, move mic until it sounds best.

[sdelsolray]

I think the reason this placement is used is simple - it sounds good for a whole variety of applications, from strummed chords destined to be buried in a full mix to solo fingerstyle.

I look at it this way. It is true that most of the sound comes from the soundboard. By placing at the 12th fret (or thereabouts), you are getting the sondboard information off axis and the 12th fret area (which adds air and direct string sound), in essence mixing the two together for a composite. If the room is cooperative, the most accurate representation will come from 3 to 4 feet out in front.

As far as two mic placements go, one popular placement is a variation of spaced pair - one mic at the 12th fret and the other down (closer to the floor) pointing at the soundboard behind the bridge (further away from the soundhole). A pretty good rendition of the instrument can be had if you collapse these two sources to mono, or if you pan then a bit for a pseudo-stereo image.

[drumsound]

I really don't get miking the 12th fret.

Micking at the 13th fret would be bad luck!

[vvv]

I really don't get miking the 12th fret.

Micking at the 13th fret would be bad luck!

Damn, an' I went and waited forever for this thred to open (what's up with that, anyway?) and here you went and beat me to posting my first thought on seeing the title.

[Roboburger]

I discovered one benefit to micing around where the neck meets body- It gives the player something to "Aim" for. It might just be wishful thinking, but I would swear the image stays tighter and more consistent if I get the guy to aim for something.

[drumsound]

I really don't get miking the 12th fret.

Micking at the 13th fret would be bad luck!

Damn, an' I went and waited forever for this thred to open (what's up with that, anyway?) and here you went and beat me to posting my first thought on seeing the title.

Sorry to steal your fire. I usually skip my gut instinct smart ass remark based on thread title, but I couldn't resist!

[vsr600]

p.s. I also realized that the twisting of the soundboard means that the sound an acoustic guitar produces is out of phase with itself, because the part of the soundboard towards the neck moves in while the part towards the heel moves out. Not so on an archtop guitar or violin, though - there the soundboard doesn't twist, it moves up and down.

There are many many many different modes in an acoustic and the one you described is probably the second most dominant. the first is the basic body moving up and down which you described for archtop and violin. Ironically being as those instruments are made a bit sturdier, probably their most dominant mode is the so called "rocking" one. Where the bridge rocks back and fourth causing the top half of the instrument to be out of phase with the bottom half. I have a friend who did some modal analasys of a chello and that's the most dominant mode she found.

[vsr600]

In it, they examined the timbre of a variety of instruments and they had a guitar in an anechoic chamber with an array of like 100 measurement mics and so forth. They then had a 3D model of where the sound emanates from the instrument. (In classic TRS80 style graphics)

heh 100 mic measurements... we got it easy now just use a scanning laser doppler vibrometer from Polytec. 1000 measurements in under a minute and the software it uses runs on windows.