What is a Partial Change?
When using any tuning software, different partials are used to tune different parts of the piano. The partials used are designed into the software. All tuning software systems therefore contain partial ‘changes’ as part of the tuning.
The higher partials are used for bass tuning and the lower partials are used in the treble.
A partial change is where the tuning software switches from one partial to another during the tuning.
The location of these partial changes varies depending on the tuning software. The fewer the partial changes the better, because every partial change is a potential tuning problem.
If the partial change calculated by the software doesn’t exactly match the piano, an audible ‘hiccup’ can be heard in the tuning at that partial change. And of course, the partial change error will effect all intervals ‘spanning’ the partial change.
FAC partial change arrangement:
As an example here, I’ll use an FAC tuning as an example:
The FAC tuning partial arrangement is as follows:
The 6th partials are used for notes A0-B2
The 4th partials are used for notes C3-B4
The 2nd partials are used for notes C5-B5
The 1st partials (fundamentals) are used for notes C6 – C8.
The FAC tuning partial arrangement contains three partial changes:
3. and B5/C6.
Here is a graph of an FAC tuning. The partial changes have been circled in red:
(Click graph image to enlarge).
Lets now look at some other tuning systems’ partial arrangements.
1. A two-partial change arrangement:
This first one has eliminated the use of the 2nd partials in the treble. There is one less potential partial change error in the treble for us to worry about with this partial arrangement.
You may also notice the partial changes locations are in different places. This partial arrangement, changes partials between G#2/A2 and A4/A#4 instead of B2/C3 and B4/C5 (as used in an FAC tuning).
This particular A to A partial arrangement provides a full two-octave range (A2 thru A4) with all notes using the same partials. This means there is no partial change within that two octave range that could cause a partial change problem in the temperament area.
Another advantage to this A-A type partial arrangement, is that note A2 is generally found on the bass bridge for all by the longer scaled pianos. Using the same partial across the bridge break and the plain wire to wound string break, eliminates any partial change from occurring in that often challenging tenor are of the piano.
Using the same partials going down to A2 is especially helpful for the 26-bass scales, whose bridge break is between notes A#2/B2.
The partials used in the below chart are the 6th (green line) for notes A0-G#2, the 4th (red line) for notes A2-A4, and the 1st (blue line) for notes A#4-C8. (Click to Enlarge)
2. A one-partial change arrangement:
This next chart uses the 4th partials from A0 – A4. The use of the 6th partials have been eliminated which eliminated all partial changes in the lower half of the piano.
(Click to enlarge)
Since the 4th partials are used from A0-A4 and the fundamentals are used from A#4 – C8, the only partial change in this arrangement is between A4 (4th) and A#4 (1st). This partial change location, between A4 and A#4, removes any possibility of an error at the partial change.
3. A 5-Partial change arrangement:
The above is just what you don’t want!
This partial arrangement has five partial changes with three of them in the lower half of the piano! No one is going to check and correct any of these partial changes. This partial arrangement might work on some large scale piano somewhere?
The larger pianos with their longer strings are quite forgiving since their scaling is generally better. But this 5-partial change arrangement used on anything but the longest pianos could be very problematical simply due to the number of partial changes contained in the tuning.
If you are using the CyberTuner system, I would suggest you investigate all the different tuning styles available in that system, and if possible, find one that has fewer partial changes.
Many tuners have mentioned they tune the bass by ear. Hopefully this post will help them understand why.