Patterns in the Sand

Check out this demonstration of Chaldni plates!

The demonstrator changes the frequency by changing the position of the bow and his finger at the edge. For every frequency a different sand pattern arises according to the vibration pattern of the plate. Where there are few vibrations, called nodes, the sand settles, and where there are a lot of vibrations, called antinodes, the sand scatters. These resonance patterns arises for any instrument with a resonant body, including bells.

Furthermore, an instrument, such as the bell, will vibrate at several different patterns at the same time. These different vibration patterns are what create the multiple overtones present in any given pitch. Below you see an exaggerated scheme of just a few of the vibration patterns for a bell. (There are six half profiles presented.) The “K’s” stand for nodes and the “B’s” stand for antinodes. Try imagining a bell vibrating all of these different ways at once!

Bell vibration patterns. Diagram courtesy of André Lehr.
Bell vibration patterns. Diagram courtesy of André Lehr.

3 thoughts on “Patterns in the Sand

  1. This is very wack and lots of questions:

    1. Are nodes and antinodes different in kind or different ends of the same spectrum?
    2. Is this a magnetic of purely physical phenomenon?
    3. Are Chaldni plates actual instruments or just meant to demonstrate here?
    4. If they are instruments, how are they operationalized in a song context? What are the key variables, plate size/thickness, bow action, finger placement?

    I’ve been on this big Elton John kick lately and “Tiny Dancer” (“Ballerina, you must have seen her dancing in the sand”) along with perennial favorite “Cowgirl in the Sand” suggests the suggestiveness that sand possesses in a musical context, at least in the 70s, demonstrated here physically. Perfect objective correlative–simultaneously utterly physical and ephemeral.

    1. Hi BDF, thanks for your questions!

      Nodes and antinodes are different extreme ends of vibration patterns. Nodes are the points where the physical vibrations are the least, while the antinodes are the places within the vibrating body where its position fluctuates the most. Think of a long string fastened at both ends (like a guitar string). The simplest vibration pattern of the string when it is strummed would be to have nodes at both fastened ends (the string will move the least at either end) while there would also be an antinode at the very middle of the string, where the string will be moving back and forth the most. With any instrument, there are multiple vibration patterns occurring all at the same time, which is what creates the various overtones in any complex tone (as opposed to a pure sine wave).

      This means that these vibration patterns in musical instruments and shown here in the Chladni plates are physical phenomena, not magnetic.

      Chladni plates are not instruments, per say, but their flat surface allows us to see the interesting patterns of sand dispersal when they are activated by different frequencies.

      I do know that a Chladni plate can be electrically activated with a frequency to produce different sand patterns. I’m not clear on the details of how finger and bow placement along the edge of the Chladni plate can produce different tones on it. I’ll see what I can find and report back…

      1. I think I see what Daniel is doing in the video.

        Each plate does have a specific inherent tone (with overtones too). When he first plays the plate, you notice that he does not place his finger on it right away. He’s activating the fundamental frequency (the lowest, or main, tone in the plate). When the sand starts to move, you notice that he places the bow halfway between the lines of sand–he’s activating the plate at an antinode, which reinforces that specific frequency. At the same time, as the nodal lines are beginning to appear, he places his finger at one of the nodes. This reinforces the lack of motion at these points, and thus strengthens the tone and the sand pattern.

        From that initial sand pattern on the plate, he can spot where an antinode and node will be for the next overtone. So then he places his bow at the new antinode and his finger at the new node. He does this for the next couple of overtones present in the plate; he activates each subsequent overtone by bowing at an antinode and placing his finger at a node.

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