It is about time that this simple, but amazing musical instrument gets some scientific attention.
"... Tanigawa and collaborators measured the 2-dimensional sound fields around triangles using acousto-optic imaging.
As sound waves move through the air, they cause vibrations which change air density and therefore the speed at which light travels through the air. Acousto-optic imaging can capture the differences in laser light travelling through this air to study sound vibration patterns. ...
“By observing the sound field of a triangle for the first time, we captured phenomena not previously explored through microphone observations.”
They found that acoustic resonance occurs in the semi-open triangular air created by the musical triangle. ...
“When the wave reached the bend, the direction of travel changed according to the triangular shape, and the first sound wave interfered with the subsequent sound wave.
The identical sound waves, moving in opposite directions through the instrument, become superimposed on top of each other to produce higher amplitude standing waves.
“These results suggest that the standing waves were formed by the combinations of radiations from the 3 sides of the triangle,” ..."
From the abstract:
"Musical triangles, known for their triangular shape with one open end, have fascinated people with their twinkling sound. However, the acoustic factors behind the triangular shape remain unexplained.
We discovered that their triangular shape induces a phenomenon conducive to sustained sound. We measured two-dimensional sound fields around musical triangles using an acousto-optic imaging method. Through our analysis, we found that acoustic resonance occurs in the area of semi-open triangular air created by the musical triangle. Consequently, the resonance produces a louder and longer sound. We believe that the resonances are the acoustical reason for the triangular shape."
Fig. 1 Experimental setup. (a) Schematic diagram of PPSI used in our experiment, (b) Experimental setup for triangle sound measurement. Data from the microphone and camera were recorded synchronously.
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