Fig. 6

An example of Helmholtz resonance (small bubble, case 5). \(V = 0.6\) \(\text{ cm}^3\) bubble bursts while it is rising in a suspension of \(\phi = 0.4\). a Time-lapse images (see Additional file 2: Movie 2). \(\times\) and \(\bigcirc\) indicate before and after aperture opening, respectively. b Waveform (detrended, highpass filtered at \(> 800\) Hz). c Spectrogram of (b) using a 1.024 ms sliding window and a 1 ms overlap. \(\bigcirc\) indicates \(f_{\mathrm{H}}\) calculated from Eq. (11) using measured \(R_{\mathrm{a}}\). d High- (\(> 10000\) Hz, left axis) and bandpass (800 - 10000 Hz, right axis) filtered result of (b) shown for a shorter time span. e Waveform shown for a longer time span (running-averaged raw data) indicating Helmholtz resonance followed by a low-frequency air flow. A red \(\times\) indicates the time of film disappearance