I have a 1967 Martin D-35 purchased in 1969 new. We lived in Idaho Falls, ID for 10 months, through a super cold winter with temperatures as low as -22°F and summer temperatures well above 100°F. The humidity out in Idaho Falls was extremely low, around 20% RH much of the time, and my D-35 never got a crack anywhere.
In those days I had no idea about the need for humidification. I was just extremely lucky.
A D-35 has light, quarter-inch bracing. This model has Brazilian rosewood back and sides and a sitka spruce top. But the grain on this wood is fairly close grained and fairly straight, which may have saved me. Also, the guitar was not new when we lived there in 1975, so it had probably had a chance to make a lot of internal adjustments that kept the residual stresses from causing a crack.
As dreadnoughts go, this guitar is pretty flexible, not stiff, and makes a great fingerstyle guitar, which is how I have always played it. This is not a heavily braced guitar.
I think sometimes dumb luck plays a part, sometimes the quality of the wood has a big impact. To this day, there are no cracks in this guitar anywhere. I feel incredibly lucky!
- Glenn