This post suggests a general approach to applying FAC Tweaks.

The A Multiplier Default:
Recommendation:   A Multiplier Default @ 0.8

The A Multiplier Def tweak was originally a way to put an FAC Tuning’s A4 closer to A440.
Setting the A Multiplier Def to .8 will accomplish that task.

In addition, now that the AccuTuner IV has the Partial Change Correction (PCC) feature, this feature can be used to correct A4.

The A Multiplier Default @ .8 will contract the width of the A2-A4 double octave.

The A Multiplier Default can also be used to expand the width of the midrange A2/A4 double octave as well.

So, if you are continually wanting more or less stretch in the midrange of an FAC tuning, you can set the A Multiplier Default  to your preferred setting.

And once the desired amount of midrange stretch is found, the location of A4 can easily be made to be at exactly A440 using the PCC feature.

The first step is to tune A4 to A440 and measure the location of A4’s 4th Partial.
Do that before measuring any FAC numbers!  This will give you the exact setting you want for A4 on the FAC tuning.  Write that number down, or remember it.   You’ll need it later to correct the location of A4 after using the PCC feature in the upper half of the piano.

Now go ahead and measure the FAC numbers as usual and store the tuning to a page of memory.

The next step is to lower the tenor partial change from B2/C3 down to G#2/A2. 
Lowering the tenor partial change results in a two-octave A2-A4 range without any partial changes in it.   This removes even the possibility of an error at and partial change within the temperament area.  This makes for much more reliable aural checking within the temperament range.   On most of the shorter scales, lowering the partial change from B2/C3 to G#2/A2 puts it onto the bass bridge.

Here is a video on how to lower the tenor partial change:  Lowering the tenor partial change.   

Now that the tenor partial change has been lowered, use the Partial Change Correction feature to check and/or correct ALL the partial changes found in the FAC tuning.   

You can find complete instructions and videos here:  The Partial Change Correction Feature

As part of the PCC,the location of  A4 can be corrected after the two treble partial changes (B4/C5 and B5/C6) have been corrected.

Start at the top with the Treble (B5/C6) partial change, and then do the Midrange (B4/C5) partial change.

Once both of those are corrected, use the C8 tweak, which is part of the PCC feature to correct the location of A4.

After A4 has been corrected, correct the Tenor partial change which is now located between G#2/A2.

You can find complete instructions and videos here:  The Partial Change Correction Feature

The FAC tuning is now ready to use.

Now should hear no hiccups in the tuning related to an error at a partial change!

Going the extra mile ~ Taking your tunings up a notch!!

Now that there is are no partial change issues to worry about, if you want, you can tune some selective notes within that A2-A4 two octave range to see if you might want to contract or expand the A2-A4 midrange stretch.

Some suggestions might be to tune A2, D3, E3, A3, D4, E4 and A4.

Remember too that DOB is being used here as a ‘global’ effect, not for individual notes.   If you hear something you don’t like, first check to make sure the note is in tune.   Then re-listen.

You’ll want to have at least two checks telling you the midrange needs to be expanded or contracted (with DOB).   Sometimes what you’ll be hearing are scaling issues,  I’d advise against trying to overcorrect here.  Just find the best compromise with as little DOB as possible and go with it.   I think you’ll be pleased with the end result.

Tuning the A’s and Ds & Es in that 2-octave range will probably be enough.  With those notes you’ll be able to listen to 2 single and one double octave.  With the D’s and Es you’ll be able to listen to some 4ths, and 5ths and a pair of 12ths.

{Once you decide which notes you want to tune regularly to make these checks, you may want to create a tuning sequence of just those notes.  Using a tuning sequence can be a handy time saver.  You can see how to create a sequence here:  Using a Sequence

Here’s some guidance from Al Sanderson:
You can find this is Appendix E of the SAT instruction manual, where he says that if A2 starts to get much below -4.0, the double octave may be too wide:

“Step 2. Tune A2 from A3 as a 3-6 octave 1 cent wide. Check the A2-A4 double octave, and if it is more than 4 cents wide, divide the excess by three and narrow both octaves by this amount. (E.g., if double octave is 5.5 cents wide, 5.5-4 is 1.5, divide by 3, and narrow both octaves .5 cent.)”

The subject of ‘the width of the A2/A4 double octave’ is too big a subject for this particular post on which of these FAC tweaks to do first.

So let me condense some of my observations and experiences to give you some basic guidelines for you to used regarding the location of A2.

As Al says, when A2 starts to get down to a setting of -4.0, it’s time to do some checking.   The A2/A4 double octave may be too wide (beating too fast).   You might want or need to contract the double octave to reduce some of the beating.

***But on some pianos, an A2 @ -4.0 may not be low enough.   On some pianos to get the best compromise, A2 may end up being lower than -4.0.  Listen to the A2/E3 5th, and the A2/A3 octave as well as the A2/E4 12th, and the double octave to help you decide.  Simply set the DOB to the new amount and retune those 4 or 5 notes.   The best compromise will present itself with a little bit of listening and experience.   Use whatever DOB used here for all the notes below A2 (A0 – A4).***

DOB is a very useful feature of the AccuTuner, and can be used in a number of different ways to either contract or expand the stretch of the memory tuning – FAC or otherwise.   DOB can be used on any tuning in the SAT’s memory

You can read up on in in your instruction manual, but for purposes here, I will say that in the bass .1 DOB will lower A2 by .4 c.  and lower A3 by .2 c.   A4 is not affected.   -.1 DOB will raise A2 by .4 c, and raise A3 by .2 c.   A positive amount of DOB expands the stretch, and a negative amount of DOB contracts the stretch.

*** .1 DOB means that the beating in the double octave has been increased or decreased by .1 beat per sec.  A .2 DOB setting means the beating in the double octave has been increased by .2 of a beat per second.   When adjusting DOB we are adding beating or removing beating by a very specific amount.   To change the beating in the A2/A4 double octave by .1 beat per second, the A2/A4 octave needs to be expanded by .4 c.   That’s why when we add .1 DOB to the tuning, the setting for A2 will be lowered by .4 c. ***  

So, if after lowering the tenor partial change,  using the PCC to correct partial changes, and  using the C8 tweak to  make sure A4 is @ A440, if you are now looking at an A2 setting of -4.0 or lower, you might want to use a little DOB to contract the midrange.   Any DOB adjustments will not affect the PCC corrections!  They will still be fine and correct.


More guidelines regarding the location of A2: 

Here’s something you can do on your own:

Tune the A2/A4 double octave a number of different widths and decide for yourself when you think it’s getting too wide.
Tune A4 to A440, and then tune A2 as a double octave 1 c. wide.
then tune the A2/A4 double 1.5 c. wide
then tune it 2.0 c. wide
then 2.5 c. wide
then 3.0 c. wide
then 3.5 c. wide
then 4.0 c. wide
then 4.5, c. wide
then 5.0 c. wide
and then 6 c. wide.

Somewhere along the line, you will hear a width you will think sounds too wide.

Now you’ve got a number for A2 you can use for your tunings.  Your own ‘guideline’ or ‘tolerance’ of your own.

If your reference is 3, or 3.5, or 4 you can use that along with Al’s 4.0 width.

A bit of my own empirical data:

I just averaged the A2 settings for 261 tunings in my database.  The average A2 setting was -2.6 c.  (a 2.6 c. wide, A2/A4, 4:1, double octave.

However, within that group of 300 tunings I had a -6.5, a -6.1 a -5.9, a -5.8 a -5.1 a pair of -4.7’s and so on.

Yes, a -6.5, and yes, a -5.8.  But those were rare.  But there were times when the piano needed an exceptionally low A2.  On those pianos it was part of the best compromise I could make.

There are always exceptions in piano tuning land.  Thank goodness the exceptions are rare.   But they’re out there.  I just hope when you come across one, you will have some idea as to how to deal with them.   The AccuTuner has some built in tools that can be a great help,  but you will need to be able to recognize them first so you can find a decent sounding compromise for those challenging scales.

On the other end of the spectrum, my database contains a few -1.5’s and a number of pianos with A2’s less than -2.0.

This is all piano dependent, of course.   But it’s up to us to try to find the sweet spot for each piano.

If you do these routines, in this order, you will hear a difference in your work on a consistent basis and I expect your results will be worth the little bit of time and effort.