There are lot of tricks used by piano tuners. The tricks are called ‘checks’. Stated simply, if note x and note y are properly tuned, they can each be checked for accuracy by comparing each to note z.
In the photo above I am comparing note F2 to note A4. I set A4 to 440 using a tuning fork (and my brain).
Once A4 is set, then the rate of the tuning fork equals the rate of A4.
For a fine tuning adjustment, I compare the fork frequency to F2. It beats wildly. Since A4 = tuning fork A, it should beat wildly with F2 at the same rate as A4 <=> F2.
If the beat rate of A4 <=> F2 is faster than the rate of the tuning fork, then the interval is wide A4 is a little bit on the sharp side. If the beat rate is slower, then the reverse is true. By adjusting the F2 <=> A4 interval, you can fine tune A4 to the rate of the fork more precisely.
Checks like these are used throughout the piano. There are countless relationships between the notes. Thirds will beat faster as you go up the scale. A tenth (an octave plus a third) will beat a hair faster than a third in the octave below. So, F4 <=> A4 is a hair slower than F4 <=> A5.
The third (F4 <=> A4) finds a complement in the sixth (F4 <=> D4) and beats one beat per second (BPS) faster.
A tuner will often set three intervals of thirds in the temperament in order to establish a rough estimate of a proper tuning. F4-A4; A4 – C#4; and C# – F5, are most often used. The beat rate/second will be approximately 7, 11, 15, or “fast, faster, and fastest.” If any one of those intervals creates a slow beat rate, then you know the interval of the third is not correct.
It is through using comparison checks that the piano can be tuned by ear. Some tuners rely on machines to help them tune. The note is adjusted until the machine indicator says the note is tuned. This might look impressive, but the use of a machine detracts from using your brain to hear the variations. Since the variations are excruciatingly tiny, a tuner may fudge a bit on the mathematically correct frequency in order to allow for a more pleasing, albeit subjective sound. Machines help less experienced tuners, but they do litle to aid ear development. Ear training and use of checks is the best way to tune a piano.
Your brain gets exhausted from listening to intervals. You aren’t aware of the exhaustion of course, but after a lengthy period of time you will notice that you are fatigued from listening. The brain is tired. You can rest for a period and recover quickly, but customers do not want to allocate hours to a piano tuning. It is not necessary to be a fast tuner, but it is best to be an efficient one. When I tune a piano I start at A4 and do not stop until the whole piano is tuned. The whole process seems to be one fluid movement. Here’s how I do it.
Set your temperament in the F4-F5 octave. Move upwards one octave and continue checks and adjustments in the temperament octave. Only tune the middle wire until you reach the treble break, then tune every treble note all the way to C8.
Now return to the middle octave and tune downward starting with E4-E3. Only tune one wire in the unison all the way down to A1. Now move back up to the lowest bass note that has two strings and tune the second wire to the first. Keep doing that until you reach the trichord unisons. Tune two wires to each tuned middle wire all the way to the treble break, and the tuning is finished.
How do you learn to tune a piano? I have received the same answer from countless tuners: tune 100 pianos and then ask me again.
And then the next answer is, tune 100 more and come back to see me.
and 100 more…
After tuning hundreds of pianos, you become a piano tuner. I don’t know how it happens. It is a mystery.