Question

The frequency of a drum not is 20 Hz. What does this tell you about the drumskin movement when it is struck?

Answer 1

• A drum is beaten in this case. The oscillation of the drum skin transfers sound waves to the air particles which move at the same frequency before reaching our ears. If the frequency of the sound wave is 20 Hz this means that the wave is oscillating 20 times in one second.

Answer 2

Explanation:

Actually, drumskins have extremely complex movements. Consider for example a round one. To imagine the drumskin moving as a whole, in piston like fashion, would be nonsense. After all, the rim holds the drumskin fast, so it flexes with its center displacement being the greatest. But that movement “spreads” outwards, and upon reaching the rim, it reflects inwards towards the center, crossing with itself in a concentric fashion. Eventually such reflections cause the center of the drum to stop vibrating while all the energy will appear as concentric rings, which immediately spread inwards and outwards. These are the “radial modes”. But irregularities in the drumskin will cause some vibrations to spread circularly around the rim, circulating clockwise and anticlockwise, crossing itself, and creating “spokes” just like a bicycle wheel, which spokes will also rotate both ways. These spokes cross the concentric rings, creating a sort of chessboard of increasing and decreasing sizes of squares, which interfere with each other and reflect from the rim………..Actually, even today, nobody has understood fully the movements of a drumskin, or of any other diaphragm. If the most notable frequency is 20 hz, very good…..but the drum produces a rather wide spectrum of wavelengths. It is easy to build a rather small drum with such a low main vibration, using a very loose drumskin made of hide WITH THE HAIR left on it. In South America there is a fine example, named Bombo Leguero.