Wow, Cdennyb!   The work you have put in has gotten an astounding amount of difference in the flatness of the curve as well as about a 10 db level increase!  Considering that was a nice instrument that had been professionally set up in the first place, that is amazing.  Beyond just good, that is crazy good!

I'll take a minute to break some of the tech talk down for people that maybe don't often relate musical sound to graphs.

10 decibels of difference in volume is about what it takes for the human ear to hear a sound as being twice as loud.  Now, you may think "louder isn't necessarily better, I don't usually play loud".  But more power to the sound gives a wider ranger for the musician to use for expression.  In a concert situation when playing with other instruments, it obviously makes it easier to hear you.  Beyond that, though, it also affects sound quality.  To have a 10 db difference in something like car stereos, if you wanted one that sounded twice as loud, you'd need to get one that has about 10 times the wattage.  That's the difference between a 10 watt "stock" stereo that came with the car and a 100 watt "custom upgrade".  Even when playing quietly, the more powerful one will usually sound more clear and just generally better.

 Now the flatness of the line in the graph is important too.  If the line has a lot of peaks on it, it means that the instrument is not as consistent in delivering sound at different pitches.  The flatter that line is, the better the instrument is at taking the sound from the string and putting it out into the room.  We usually think of only the pitch of the string or the note we are playing, one frequency.  But really, most instruments put out a lot of frequencies at once when you play a note.  The note that is actually being played (called the "fundamental" will be the loudest, but there will be a mix of higher pitches with it in octaves and other musically related pitches that are called harmonics.  The harmonic content is what gives a note played on an instrument the sound that lets us identify it and enjoy it as the distinct sound of an instrument. 

To give a simple example, think of the boops and beeps a cheap handheld electronic game might put out.  They are notes, sure.  But if you play the same notes on your violin/fiddle, the main pitch may be the same on an electronic tuner, but your instrument will sound much richer and more interesting than the beeps of something like an old Gameboy which will sound pretty dead in comparison.  We might say the notes played on the violin sound more "complex" or "rich" or "open".  The flatter the line in the chart is, the better the instrument is at doing that.  To a player is also shows how much the instrument can respond to changes in the tone or timbre of the sound, like the differences in sound one gets in choosing different contact points for the bow on the strings between the bridge and the fingerboard. 

I've oversimplified the matter a good bit here and the numbers I gave regarding decibels (db) are approximate, but hopefully it's enough to give an idea what sort of differences are being shown on the chart when comparing how the violin was when Denny got it as opposed to after he put some work into tweaking it. 

Considering that his new violin sounded quite good to begin with (to me, anyway), the degree of difference the chart shows is quite a lot.  It would be very easy to hear a difference, it is not all just numbers and graphs.

@ Daniel…

I couldn't have explained that better myself. Outstanding job of explaning the fundamentals of sound creation using a stringed instrument.

I actually knew what you were saying but it brought home the incredible amount of work it takes to achieve a tiny improvement in performance.

Sound is such a complex science…