I had to buy a cheap 25W amp and a hefty 8″ driver unit to excite the resonant frequencies in the back and top.
I then used a free app on my Android as a variable frequency sine wave signal source and tea leaves to see the patterns!
There is a lot about plate tuning on the Internet with several systems used. I found two particularly useful articles:
- Free Plate tuning, Part Two: Violins by Alan Carruth with an excellent cello example
- On Graduating the thickness of violin Plates to achieve tonal repeatability
Here is the mode #5 (bell-mode) on the back.
Here is the mode #5 (bell-mode) on the front
and mode #2 (x-mode) on the front
The back is still a little high compared to the top but I will come back to that once I have cut the f-holes and fitted and tuned the bass bar.
Having cut the f-holes and glued the bass bar I then re tuned the top to bring the bass bar into balance.
Both Modes #2 and #5 had gone up with the bass bar fitted.
This is how the mode #5 shapes developed as I cut down the bass bar:
I must admit I wasn’t sure at first that this was actually #5 as it looked pretty weird!
And the mode #2 looked like this:
At this stage I had got the mode 5’s on back and front equal at 130Hz and the mode #2s to 60Hz on the front and 64Hz on the back so a little more to do still.
Final adjustments made.
|Mass||Mode #1||Mode #2||Mode #5|
|Belly||490g (without bass bar)||28.4Hz||58.4Hz||120Hz|