Robert Conrad, Registered Piano Tuner/Technician, Tucson, AZ

FAC Tweak: Trying a Different “F” Number for the FAC Tuning

This post is part of a series on working with an FAC tuning so it most accurately fits the piano.   There are a number of tweaks that probably should be done before changing the F number.

So, before messing around with the F number, make sure to set the “A” Multiplier Default to .8 , and move the tenor partial change down to A2, so that there is a full A2-A4 Two-Octave Temperament range with all notes in that range using their 4th partials.

Al instructions in his Two Octave temperament reveal a guideline for the location of A2.   In those instructions he indicates if the A2/A4 double octave is more than about 4 c. wide, it is probably too wide.

But the setting for A2 is not absolute by any stretch.    Even though the average location for A2 in most of my work tunings is around -2.5,  I do have tunings where I had to put A2 all the way down to -5.8 o so.

But for most pianos, if after lowering the tenor partial change, A2 ends up being lower than -4,  A2 probably needs to be raised somehow.   Let your ears and the piano be your guide.   Before making any changes, tune the As, Ds, and Es in the A2-A4 range and give it a listen.

Raising A2 is probably most easily done with DOB but A2 can also be raised or lowered using a different F number in the FAC tuning calculation.

A good approach may be to use DOB to easily help find the direction and the amount for the desired location of A2.   And then, after doing some testing with DOB, recalculate a new FAC tuning using a slightly higher or lower F number.

Generally speaking, a higher F number means more stretch in this area, and a lower F number means less stretch.

So, for a higher A2, use a lower F number, and vice versa.

Of course if you change the F number in the FAC tuning,  you will be starting over to some extent, only with a little more information about the piano.

Put the 2nd new FAC tuning on a separate page in the SAT and then lower the tenor partial change again on this new tuning.

Now check out the new numbers around A2 to see if they are close to what you expected and wanted.  Re-tune the notes in the sequence (A4, A3, D4, E4, D3, E3 and A2) paying extra attention to the A2/E3 5th and the E4/A4 4th.   If tuned accurately to the FAC tuning and both are beating too fast, the low 5th (A2/E3) is saying A2 should be lower (the double octave needs more stretch), but that upper 4th E4/A4 beating too fast is saying the opposite.

In a generic way, the fast lowest 5th is saying ‘more stretch’, while that upper most 4th is saying ‘less stretch’.

This piano’s scaling may need some very individual treatment within each of those octaves.   The scaling within the A3/A4 may need a different amount of ‘stretch’ and a different ‘curve’ within that octave all it’s own compared to the shape of the curve and the amount of stretch needed in the A2/A3 octave.

There is really no ‘global’ way to tweak the mid points of the curves within the octaves there.  I feel trying to have different DOB amounts for each of those octaves, is generally a bit beyond FAC and beyond the scope of these tweaks.    One of my goals for this type of FAC tweaking is to create a few tweaks that can be remembered or written down and applied to the tuning that can be easily repeated for a second pass or a unison pass.   Something that can be easily repeated.   Trying to roll on DOB in the course of an octave, and then rolling on more or rolling it off while tuning down into the next octave is possible, and it can be repeatable, but with each rolling on or off of DOB, each change from one DOB to the other, does insert a ‘hiccup’ in the tuning numbers.   Those hiccups in this area can be .2 c. or .3 c.  and sometimes maybe more.

You can decide for yourself if you think it’s worth it, but I’d suggest after lowering the partial change on a 2nd ‘F’ FAC tuning,  to find the best sounding compromise using a single DOB for the midrange and let it go at that.

All we can really do to an FAC tuning is make the double octave wider or more narrow.  We can use DOB or we can use different F A C numbers, but that’s about it.

DOB can be really nice to further adjust the highest or the lowest octaves if desired, but trying to roll off or on DOB in the midrange is something to try after all these other tweaks are common place to the tuner.

None of the computerized tunings have the ability to tweak the shape of the tuning curve between the ‘A’s and none of them are any better on these pianos than FAC.

Spending a little time making these tweaks and finding the best sounding compromise will be doing better than most – and much better than a straight FAC tuning – or a tuning straight out of the ‘can’.

With each new recalculation of FAC numbers, you will need to redo what you have done before when it comes to lowering the partial change, basically starting over, since the different F number will effect the middle of the piano.

Use a different page for each new FAC tuning.   Lower the partial change and see where A2 ends up.   Use whatever DOB is necessary to get A2 to be less than -.4 c.    Then use the sequence and tune A4, E3, D4, E4, D3, E3 and A2 and give it a listen.   You should hear fairly soon which one will give you the best – the least bad – compromise for that particular piano.

You can always go back to the previous page and re-tune those 7 notes and listen to it again, and see how it sounds there.   And you can always just do a straight FAC tuning and be done with it.   That’s always an option, as a fall back position.

Some pianos are just very challenging, and hard to make sound really good.  There is only so much customizing that can be done with an FAC tuning short of aural tuning.   Knowing when you’re there takes some experienced listening.   You will eventually have to make a decision as to which compromised solution is the least bad one.    All tuning systems have trouble with these pianos.

At least, you won’t have any partial change in that A2-A4 range muddying up the situation.  Every other tuning system has a partial change in that area, and on these pianos, unless it is fixed – which it never is and they don’t even talk about it –  it can cause a hiccup in the tuning – depending on the size of the error.

Using tuning sequence speeds things up for all of this.

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