What causes this?

[B381]

It previously happened to my Kentucky KM150 and now it appears it's happening to my Eastman.

My Kentucky started playing two different notes on the E string at the 12th fret, the outer string was higher than the inner. Turns out the edge of the fret had come loose. Repair guy fixed it and it does as it should now.

Noticed tonight my Eastman seems to be doing the same dang thing. Also on E string, also on 12th fret.

What is happening??????

I live in NC, humidify when needed, although it rains a ton during the winter get here.

[George R. Lane]

Photos??? Can you show a photo of the 12th fret, both open and fretted.

[Phil Goodson]

How do you determine when humidification is needed? Are you monitoring constantly?

I ask because this has been an unusually dry winter in NC. My house has had many days of relative humidity in single digits.
I've hardly seen the humidity above 30 during Jan & Feb this year. I've had to keep instruments in cases with humidifiers whenever I'm not playing and actually had to raise the saddle at a jam one night because the strings were almost touching the fingerboard.

A bit of an unusual winter in my experience.

[B381]

Two stay in case with humidifier. One on stand. We have one of the mini humidifier scent things that runs all the time. I use the local weather, nothing in home.

I could take a picture but you can't see it. The way he found it on the Kentucky was a slip of paper slipped under the edge but to the naked eye it wasn't prominent.

[Phil Goodson]

Two stay in case with humidifier. One on stand. We have one of the mini humidifier scent things that runs all the time. I use the local weather, nothing in home. ...

I'd sure recommend that you get a few hygrometers and monitor the room where your instruments live. Weather reports won't tell you what's going on inside a house with heating/cooling and insulation.

You can pick up hygrometers that are accurate enough to be useful for $8 to $30.
Some are small enough to stay in a mandolin case. Some have magnets on the case and will stay on a metal instrument stand. Humidify if rel humid is under 35% for sure.
A change of a few degrees in a room can change the relative humidity more than you might expect.

[gtani7]

You can look at the strings' reflections off the frets, headstock pointed away from you, to see high frets, how much relief the neck has, if it has action increasing steadily from nut to bridge etc. It should be a nice smooth curve. That is if your frets are polished, which is easy enough.

[HoGo]

Typical cause for lifting fret ends is humidity swings and too much of fret tang removed prior to installation on bound fretboard. Sometimes careless installation. Less often worn fret slots (probably not your case if you bought mandolin new).
Makers often prefer bending frets slightly tighter radius than board so they spring down against board at edges and even on flat boards I like to bend the ends down a tiny bit. Many makers add drop of glue (usually CA) to the fret ends to keep them down during weather cycles.
Careless installation is when person hammers fret in the center first and actually bends the fret concave with hammer and then hammers the ends. The ends may hold fine for some time but sooner or later they will spring out of the slots... Good luthiers hammer the frets slowly and keep the ends seating hair before center of fret hits the board.