I decided to have a go at another cello because I enjoy building them so much! Of course I also wanted to improve on the cellos built so far by making a few judicious design changes and tweaking the build process based on experience with the earlier builds.
The key design changes were:
- Sight changes to the archings (25mm belly and 23mm back)
- Reduce f/b side thickness to 7.5mm from 8mm
- Change break angles over the strings to improve playability (19.5 degrees ADG and 24 degrees DGC)
- Changed f/b profile to match change in bridge profile
- Increase over-stand by a few mm to 22mm
- Attempt to increase Mode2 and Mode 5 plate frequencies to around 65Hz and 130Hz
- Colouring the instrument a richer chestnut brown
The resultant design drawings done using solvespace are below.
I also decided to make use of my CNC router to build new 6mm MDF templates based on these drawings.
As usual, not everything went perfectly to plan but most of the desired changes seemed to work. The one area I had real difficulty with this time was tuning the plates especially as i was trying to hit higher resonant frequencies this time around. As I was trying to tune the top I was having real difficulty getting mode 2 and 5 and octave apart – the ring mode just didn’t want to drop. Then I happened to wash the outside of the top to get rid of some surface bruising (from when the top was drilled out) and the following morning it suddenly started to behave properly! My assumption is there must have been some latent stresses in the spruce and the wetting allowed them to settle out – a bit like annealing. Anyway I ended up with Mode 2 and 5 exactly an octave apart and matching on back and top at 60Hz and 120Hz respectively.
The finished instrument is a beautiful chestnut colour and has wonderful a rich singing tone using a set of Larsen Magnacores. I have christened her “Doris” and she weighs in at 3.01kg.
I am delighted with her – a definite keeper!
The following gallery illustrates the build process.