Why a 128 Hz Tuning Fork Shows 3 Frequencies Vibration Mode Analysis Using High-Speed Camera & DIC

We marked a tuning fork engraved 128 Hz, yet three frequencies were measured: 103 Hz, 128 Hz and 205 Hz. Why does this happen?

In this video, we adopt a Revealer high-speed camera combined with Digital Image Correlation (DIC) technology to conduct vibration modal analysis on a standard 128 Hz tuning fork. The full workflow is documented, including speckle marking, system calibration, data acquisition and post-processing calculation.

Frequency domain curves are reconstructed via RVM software, revealing three distinct vibration modes:

✅ 1st-order in-phase swinging (103 Hz): barely radiates audible sound

✅ 2nd-order opposite breathing motion (128 Hz): the source of audible tone

✅ 3rd-order S-shaped torsional distortion (205 Hz): sound waves largely self-cancel out

This demonstration showcases the strengths of DIC: full-field measurement and non-contact detection. We also clarify the critical difference between **frequency** and **vibration mode**.

128 Hz is not the only resonant frequency; it is merely the mode easiest to excite and most efficient at radiating sound.

Ideal audience: enthusiasts of physics experiments, high-speed videography, DIC technology and vibration modal analysis.

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Leave a comment: How many resonant frequencies do you think a 440 Hz tuning fork will produce?