The A4 Numbers

The term “A4 Numbers” refers to the specific locations of the 2nd, 4th, and 8th partials of the A4 note when A4 is tuned to A440.

Significance of the A4 Numbers

When an FAC tuning is used for piano tuning a piano, when tuning A4, the FAC tuning is ‘listening’ to A4’s 4th Partial.    Other systems may use a different partial for A4, but this system uses the same 4th partial for tuning A4.  So, the first thing we need to know is the location of A4’s 4th Partial when A4 is tuned to A440.

Measuring A4’s Partials

Accurate measurement of the A4 partials is essential for accurate mapping.
The following procedures utilize an Electronic Tuning Device (ETD), such as an AccuTuner:

  • 2nd Partial: After tuning A4 to A440, set the ETD to listen to A5, play A4, and use the cents buttons to stop the lights.
    The resulting cents setting indicates the location of A4’s 2nd partial.
  • 4th Partial: After tuning A4 to A440, set the ETD to listen to A6, play A4, and stop the lights with the cents buttons.
    This gives the location of A4’s 4th partial.
  • 8th Partial: After tuning A4 to A440, set the ETD to listen to A7, play A4, and adjust the cents buttons until the lights stop.
    This reveals the location of A4’s 8th partial.

Except for the 4th Partial of A4, the other A4 Numbers should be used as reference points and not as tuning targets for the higher octaves.   It’s goo to know where those partials are, but they are not absolute locations for notes A5, A6, or A7.

Mapping for Optimal Tuning

Mapping involves gathering information about the piano to make informed decisions that best match its unique inharmonicity. This approach reduces guesswork and minimizes trial and error, enabling the technician to develop an effective tuning strategy from the outset. Measuring the A4 Numbers is an excellent starting point for this mapping process.

With experience, technicians will quickly learn to recognize both typical and atypical A4 Numbers, enhancing their ability to tailor tuning to each piano. As with traditional aural tuning that begins at A4 and expands outward, this system does the same thing but uses technology to analyze the inharmonicity of the A4 string by examining the locations of its 2nd, 4th, and 8th partials.