Finger Piano Tuning

  1. Provide a step by step approach to tuning your instrument.
    1. Set up an electric amplifier and attached microphone in a quiet workspace.
    2. Hold the microphone against the edge of the finger piano’s resonator box opposite from the keys.
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    3. Strike a key and adjust the audio quality of the amplifier to produce the clearest possible sound.
    4. Loosen the wingnuts on the right hand side and the center of the bridges by turning them counter clockwise. This should allow the bridge to be lifted slightly.
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    5. The right side of the bridge will hold the keys that produce the higher frequencies – E3, D3#, D3, C3#, C3, and B2. Place the shortest keys underneath the right hand section of the bridge.
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    6. Adjust the length of the free section (not constrained by the bridge) of each key to match the length calculated using the general equation.
    7. Tighten the wingnuts to exert the greatest force possible on the ends of the keys (in order to restrict the motion of the ends of the keys).
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    8. Open the ClearTune app on an IPhone and place the IPhone on the resonating box between the microphone and the keys.
    9. Pluck each key (from highest to lowest) and record the frequency and note measured by the tuning app.
    10. Compare the measured frequency to the desired frequency.
      1. If the desired frequency is higher than the measured frequency, loosen the wingnuts and shorten the free section of the key. Tighten the wingnuts, strike the key, measure the frequency, and continue to adjust as necessary to reach the desired frequency.
      2. If the desired frequency is lower than the measured frequency, loosen the wingnuts and lengthen the free section of the key. Tighten the wingnuts, strike the key, measure the frequency, and continue to adjust as necessary to reach the desired frequency.
    11. Repeat steps E-J on the left hand side of the bridge using the longer keys.

How did you measure the frequencies produced by your instrument?

I amplified the sounds produced by the vibrations of the keys using a microphone and an amplifier, then used the ClearTune app for IPhone to measure the frequency produced by each key at various lengths.

Provide details on the frequency you measured versus what you calculated.

  • The frequencies on which I based my length calculations corresponded directly with the desire notes. The frequencies to which I tuned the finger piano are 10 or fewer Hertz away from the desired absolute frequencies of the notes, depending on the key.
      • How did you go about fixing the discrepancy?
        1. The discrepancies in frequency between the absolute frequency of the desired note and the frequency of the key at its calculated length were reduced by adjusting the length of the keys until the frequencies produced by striking the keys was as close as possible to those of the desired notes.
        2. The following are the calculated lengths of keys vs. the lengths of keys after adjustments to produce the correct pitch.
        3. Note f (Hz) L (m) Actual Length (adjusted) (m)
          F2 87.31 0.061345708 0.0681
          F2# 92.5 0.05959987 0.0652
          G2 98 0.057903277 0.0627
          G2# 103.83 0.056254174 0.0612
          A2 110 0.054653734 0.0599
          A2# 116.54 0.053098062 0.0589
          B2 123.47 0.051586428 0.0567
          C3 130.81 0.050118228 0.0547
          C3# 138.59 0.048691172 0.0525
          D3 146.83 0.047305189 0.0496
          D3# 155.56 0.045958644 0.0488
          E3 164.81 0.044650302 0.0476
      1. The ClearTune app was accurate enough to allow me to adjust my keys to produce the desired notes. I tested the ClearTune app against a Pitch Pipe app called Pitch Perfect (for Windows phone). A Pitch Pipe produces single, sustained notes, and I assessed the accuracy of ClearTune by playing individual notes and testing whether the note detected by ClearTune matched the note played by the pitch pipe.Did you feel that the frequency measuring device/software was accurate?  How did you validate its accuracy?

Summarize your learning:

Any future builders should be very cautious when adjusting the length of a key to ensure that they do not slightly shorten or extend any other key — even the slightest adjustment to the length of a key can drastically change its pitch.

It is essential that the wood used for the bridge is stiff (but not brittle). If the bridge is pliable, the keys in the middle of each subsection will not be held in place, allowing the portion of the key underneath the bridge to vibrate against the wood, producing an unpleasant sound. If the keys cannot vibrate underneath the bridge but are not held firmly in place, the lightest bump can jar the key and change its length, thus changing the note. To fix this, simply tape the end of the key (on the opposite side of the bridge from the free section of the key) to the box to hold the key in place.

Be sure that no keys overlap each other. Overlapping keys will restrict the vibration of said keys.

What should the next builder be cautious about when they build and when they tune? What do you wish you had known/thought of during the construction process?  In other words,  what issues cropped up during tuning that you might have avoided if you had taken care of it during building?

The resonant frequency of the resonator box is closer to that of the higher-frequency notes produced by the finger piano. When these notes are played, the latch that closes the box vibrates, producing a rattling sound that is both nearly as loud as the note itself and very unpleasant. During construction, I should have either removed or better secured the latch to avoid this sound.

For explanation of the harmonics:

Harmonics of Finger Piano

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