What makes strings go sharp?

[Brucebubs]

Warm day yesterday, no heating required last night, cold front came through early this morning all my guitars are slightly flat today.

[gibpicker]

We had a very dry day in San Diego a few days back that made my Mando go WAY flat as opposed to normally being sharp the next day.

[tinnitus]

I know humidity plays a role, especially as we change from dry AC in the summer to heat in the winter, and then reverse that. Leaving windows open can exaggerate moisture changes too, as can proximity to vents.

But in my experience, temperature changes are the quickest, most noticeable, culprit. Have you ever played guitar in a campfire setting? On a chilly evening?

Depending on how close you get to the fire (and even which way you turn - to face the flames or other people), various components in the guitar (and the strings themselves) will expand and contract.

This can produce significant pitch changes, especially when it's teeth-chattering cold just a few feet away. In very simplistic terms, it's temp-change tug-o-war between the strings and the guitar. (According to Fender, a set of light guitar strings can put 200lb of tension on a neck.) As temps go up and down from moment to moment, materials will expand and contract. Strings can go flat/sharp in a big hurry.

"Wait a second, I just tuned up half a song ago. What's going on here?

I have a "campfire guitar" just for outings like this, while my nicer guitars stay safe and snug at home.

[ljguitar]

Hi Wade…
Temperature produces more sudden changes in intonation.

We keep our house 63°F overnight, and 72°F in the daytime. That's at least a 9° F swing.

I tune my guitar in the daytime or early evening at 72°, and then wake up with the house at 63° and throw the tuner on it, it's always sharp just from the cold.

If I tune my guitar in the morning at 63° and play, and then pick it up again in the evening when it's warm, it's always flat.

Humidity doesn't cause short term sudden shifts, but temperature does. When we take delivery of a guitar which was shipped, we don't check the humidity, we monitor the temperature (to prevent cracking the finish from sudden shift of temperatures).

[KevinH]

Originally Posted by ljguitar

...I tune my guitar in the daytime or early evening at 72°, and then wake up with the house at 63° and throw the tuner on it, it's always sharp just from the cold...

Interesting. Do you keep your guitars cased, or out? Have you measured the humidity change between night and day? The reason I ask is that wood (guitars in particular) only takes several hours to respond to humidity changes. So if the humidity changes overnight, a guitar would keep up with that.

[rollypolly]

This happens to me very frequently, like pretty much every day. I pick up a guitar and all the strings are sharp. I can only assume the high humidity levels are expanding the wood and pulling them tight.

[TennesseeWalker]

here’s my critique - - -

Originally Posted by zmf

For me, living above 7000 ft in the dry Rockies, strings go sharp on my most lightly built guitar when I'm away for 5-7 days. My working hypothesis is that the guitar doesn't come out of its case, and humidification in the case is higher than ambient humidify it experiences when it regularly comes out of the case.

The guitar absorbs water, swells, scale length effectively increases, and it tunes sharp.

Please critique this hypothesis.

[ljguitar]

Originally Posted by KevinH

Interesting. Do you keep your guitars cased, or out? Have you measured the humidity change between night and day? The reason I ask is that wood (guitars in particular) only takes several hours to respond to humidity changes. So if the humidity changes overnight, a guitar would keep up with that.

Hi Kevin
Cased and humidified…

[DBW]

Were you in the Southern Hemisphere?

[Shadowfox]

For me, it's usually a sign that I should change strings. They start to go sharp for me as they start to deaden.

[turbotom1052]

My guess would be that the changing atmospheric conditions that affects all wood built stringed instruments, would have a great effect on a mandolin over a guitar, because the mandolin has a much shorter string length. If you figure the change in a guitars pitch as due to changing humidity as a "spit in the ocean", then figure a mandolin as a "spit in a pond"

[bizango1]

It's humidity at my house. I live close to the ocean and it is frequently foggy and drizzly mixed with bright sunshine while the temp may only vary 10-15 degrees from am to pm. RH regularly swings from a low of 45 up to 70+. When humidity rises all of my guitars go sharp and the action rises, and together go flat when it drops. I can almost predict the RH after I put a tuner on a guitar. The RH swings are so dramatic I bought a second gauge bec I didn't believe the first one. Now they sit side-by-side with the same reading.