Corvus:  Thanks for the additional input.  The variety of picking and strumming styles is one of the things that make dulcimers fascinating.  I've played the banjo for about 12 years and the dulcimer requires a whole different skill set.  I'm looking forward to the challenge!

I find that playing over a dulcimer strum hollow is the perfect place for me to play. I use a thumb pick and finger picks, and the extra space between the strings and wood top allow me to use my playing technique without any compromises whatsoever.

Also, I much prefer the dulcimer tone I get from playing over the strum hollow. I play the dulcimer because of the bright dulcimer tone, and the strum hollow area produces that bright, cutting tone perfectly for me. If I wanted a mellow tone, I'd just play a guitar. To my ears, playing over the fretted areas sounds like a second rate guitar. But a guitar can NEVER get that beautiful, bright dulcimer sound you get from playing over the strum hollow.

Remember, it's all about personal preference, we all hear differently, people have different musical needs, there's no right or wrong and diversity rules.

Wow, even more interesting dulcimer information to store in my memory banks!  Thanks again for the great instruction!

Which is why some older dulcimer ancestors had their frets right along the edge of the instrument- because either they had no raised fretboard, or one that was less than 1/2" tall off the top of the instrument. Having the frets run along the edge of the body enabled using a noter when the frets were on or immediately above the soundboard itself. Imagine trying to use a noter on frets that are installed down the middle of the soundboard, directly into the instrument top rather than on a raised fretboard.
One of the very definitions of the mountain dulcimer specifies it having a "raised fretboard running down the center of the instrument". Many instruments that are earlier dulcimer ancestors have frets along one edge of the instrument- epinettes, hummels, langspils...

As to strum hollows and 'sweet spots', it's true that the mellowest sound of all will come from plucking/strumming a string near the halfway suspension point. Yet violinists, guitarists, banjoists, etc don't generally bow/strum/pick in the middle between nut and bridge. Some oldtime banjo players play "up the neck" to get a particular soft mellow effect, but bluegrass, tenor, classic, and Irish banjo players play near the bridge purposely because they like the crisp snappier sound. The strings are more rigid to play on right next to the bridge, with almost no flex. So most folks feel more comfortable plucking/strumming several inches away from the bridge, where the strings begin to have more give. On the other hand, bowing at the halfway point creates just too much string bouncing and flexing, thus a bow is usually kept pretty close to the bridge where the string tension is stiffer. Another physical issue is that the halfway point is where the seventh fret octave is, and people do a LOT of fretting in that area- you can't be both fretting and strumming or picking in the same area at once. (I'm assuming folks define the 'sweet spot' not as exactly the halfway point, but rather as somewhere between halfway and the bridge.)

Thanks Ken, I was never sure why the fretboard was raised so high.  Clearing the soundboard with your knuckles makes sense.

I agree Matt.  Physics tells us the most appropriate place to pluck a string is have way between the two ends, at the maxium amplitude.  Since one end of a dulcimers' fretted string is always changing, the "average center" of a vibrating string is somewhere around fret 12-14. Olde tyme traditional dulcimers that were both fretted and bowed invariably had the traditional taller fretboards --  on the order of 1" -- which is useful both for noter-knuckle clearance and easier bowing.  

Yes, I realized when I posted my comment it would be controversial, but I stand by what I said.  The sweet spot on the dulcimer is not the strum hollow, but on the strings between the 12 and 14 fret and that is where most people play.  Similarly, if you watch how fingerpicking is taught (and I do watch how teachers play, not what they say), again, the sweet spot is over the 12-14 fret.  (Try building a dulcimer with the strum hollow between the 12 and 14 fret and see what people say!)  As far as using a bow,  look at the curve saddle/bridge on a violin and you will understand why the bow is not popular for the flat dulcimer.  A bowed dulcimer has a much bigger space between the finger board and the saddle and the saddle is curved.

Anyway, you know my opinion is worth what you paid for it.

Thanks everyone for your kind and valued input.  You're responses have all increased my knowledge of "dulcimology"!

How I find strum hollows essential in real life playing:

I used to play the mtn dulcimer in fingerpicking style long ago, with plastic fingerpicks because I have crappy fingernails. Playing on a dulcimer with a strum hollow was delightful and comfortable. Playing in that style with no strum hollow was an AWFUL experience for me because the tips of my fingerpicks were constantly bumping into the fingerboard accidentally, and made a racket with clicking sounds. Personally, I couldn't play in fingerpicking style without the strum hollow. Especially if doing 'pinches', which some traditional players did when playing with their thumb.
Strum hollows also facilitate playing with a bow- as you rock the bow a little to play either outermost string, as you have to do when there is not an arched bridge, you don't want to scrape the bow hair on the fretboard edge.. but that's less common than fingerpicking. Been there done that, and a strum hollow totally solves that issue.

I have similar issues with picks bumping into the fretboard on banjos with no strum hollow. That's why they are so common on banjos.

There are two traditions involved here: that of including a strum hollow, and that of NOT including a strum hollow.

Old Kentucky dulcimers have them (such as the J. E. Thomas design),  but old Virginia dulcimers do not.  There are many of these with significant scratching or even wood damage due to strumming over the end of the flat fretboard.

As Matt says, the strum hollow is another weight redution technique that was often not used by traditional (pre-1960) builders. 

The "strum hollow" idea was sold to modern players as a way to not scratch the fretboard in the area where the pick is doing all the strumming.  However, the best place to strum is about half way between the fretted string(s) and the bridge, which on average is somewhere around fret 12-14, not down below the 16h fret and the bridge.  Also, a good player doesn't dig the pick far enough below the plane of the strings to do much, if any scratching.

The purpose of the "strum hollow" or scooped area is really just to help make the entire instrument lighter.  You may hear a variety of other explanations.  The same is true with the scoops under the fret board.  The area they free up is much to small to add any vibration or sound, it is simply another way of making the instrument lighter,..., and it looks "cool".

My previous question dealt with the arched or scalloped bottom surface of the fret board.  My thanks to those who responded.  My current inquiry is regarding the "scooped" area of the fret board where fret board material is removed between the last fret and the bridge, resulting in additional space between the strings and the fret board.  Is it to reduce mass and therefore increase the transmission of vibrations?  Thanks for any insight you can provide.

Also, thanks for the additional technical information concerning scalloped/arched fret boards.  The many variations in construction in pursuit of tone and volume is fascinating to me and I really appreciate you sharing your skill, experience and knowledge!

The correct term is arch.  Not scoop or scallop.   That's why you didn't find anything.  You can have an "arched" fretboard.   The purpose of arches is two-fold. 

First, they remove a great deal of the overall mass (weight) of the fretboard -- makes the whole thing lighter and more responsive while still maintaining the rigidity of the fretboard for proper fret spacing.   

Second, arching frees up some small additional part of the dulcimer top to allow it to vibrate more freely.  Vibration is of course what causes the sound. Dulcimers do not produce sound in quite the same way as guitars, mandolins, banjos, etc. 

Because of the massive brace (called the fretboard) down the length of the top, very little top vibration is even possible.  The majority of the sound comes from the vibration of the back and sides -- even though we most often bury the bottom in our sound absorbing laps.  This is why a Galax-style double back instrument gives so much more sound than a single back instrument -- the entire back is free to vibrate.

Are arches necessary?  No.  The majority of dulcimers are built with solid or channeled fretboards. 
 
Are arches useful?  Certainly. Any time an oscilloscope can measure an increase in sound production, it's a net gain.

Are arches æsthetically pleasing?  Heck yes!  I even built one dulcemore with the size and spacing of the arches matching the size and spacing of the frets.

"Scoops" (scallops) are not necessary to get good sound or volume from a dulcimer.  Some people just like them and think they improve the sound of the dulcimer. Scallops free up the soundboard because the fretboard only contacts the soundboard in a few small areas. Some builders will also channel-out the center of the fretboard as well, to create even smaller contact areas.

Do I scallop my dulcimer fretboards?  Nope-- never have.  But I DO channel them, almost every time. Some Tennessee music boxes have "false scallops" on the sides of their fretboards, but they're just notches for decoration -- they don't go all the way through the fretboard.

I'm the new guy with the steep learning curve.  I did a forum search for "fret board scoops" and found nothing.  So, my question... What is the purpose of the "scoop" in fret boards?  Are they necessary?