Thanks.  It appears dulcimer construction has a lot in common with banjo building...  You never know exactly what tone you'll be getting out of your choice of woods, design, hardware, strings and any number of other variables.  It's the combination of all the variables that determines tone.  In other words, it's like a box of chocolates.  Thanks again! 

As Ken says, it depends on who you talk to.  The idea is, more or less, to free up more top to vibrate and also reduce the overall mass of the fretboard, thus enhancing the sound.  Some of us arch the fretboard, many more of us cut a channel down the length of the inside of the fretboard.  Both work, or or less, depending on the impact of the many other design variables.  "Ya pays yer money an ya takes yer chances".

Well, it depends on who responds. The theory is that with less contact with the fret board, the top is freer to vibrated thus enhancing the sound. There are so many variables to what effects the sound of the dulcimer and this is just one of many.

Ken

"The dulcimer sings a sweet song."

Is there an advantage to fret boards that are scalloped on the bottom so they only contact the instrument's top at a few points?