Cello week 6 – Plate tuning

Plate tuning

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:

  1. Free Plate tuning, Part Two: Violins by Alan Carruth with an excellent cello example
  2. On Graduating the thickness of violin Plates to achieve tonal repeatability

Here is the mode #5 (bell-mode) on the back.

Back mode 5 @127.5Hz
Back mode 5 @121H

 

 

 

 

 

 

Here is the mode #5 (bell-mode) on the front

Mode 5 on the front @121Hz
Mode 5 on the front @121Hz

and mode #2 (x-mode) on the front

Top mode 2 @ 56.8Hz
Top mode 2 @ 56.8Hz

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.

Fitting the bass bar with chalk
Fitting the bass bar with chalk

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:

Mode #5
Mode #5

I must admit I wasn’t sure at first that this was actually #5 as it looked pretty weird!

Mode #5
Mode #5
Mode #5
Mode #5
Mode #5
Mode #5
Mode #5
Mode #5
Mode #5
Mode #5

 

 

 

 

 

 

And the mode #2 looked like this:

Mode #2
Mode #2

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
Back 669g 30Hz 57.6Hz 122Hz

Back mode #2 - final
Back mode #2 – final

Back mode #5 - final
Back mode #5 – final
Belly  490g (without bass bar) 28.4Hz 58.4Hz 120Hz

Belly Mode #2 - final
Belly Mode #2 – final

Belly mode #5 - final
Belly mode #5 – final

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