Can I see sound?
Yes but not directly
A Chladni plate is a metal sheet that can be made to have visible moving patterns on its surface. The plate is a flat sheet of metal with a central stalk that attaches to the base. If sand or dust has been sprinkled on a Chladni plate patterns will appear when making it move using sound.
Chladni Plates are usually circular or square, with their central stalk mounted to a sturdy base. When the plate is oscillating in a particular mode of vibration, the nodes and antinodes that are set up, form complex but symmetrical patterns over its surface. The positions of these nodes and antinodes can be seen by sprinkling sand upon the plates; the sand will vibrate away from the antinodes and gather at the nodes.
The plates are made based on work found in Entdeckungen über die Theorie des Klanges, a late 18th-century work by German physicist and musician Ernst Florens Friedrich Chladni. Ernst Chladni's most important work was about sound vibrations. He calculated the speed of sound for different gases. For his amazing research on vibrations and the calculation of sound speed for different gases, he's sometimes called the "Father of Acoustics".
What are acoustics?
Acoustics are the science of sound. The study of acoustics is widespread – from the way that musical instruments produce sounds to understanding the effect of noise on the human ear. Sound is a form of energy that travels in waves through hot or elastic particles like air, water, metal or plastic. These vibrations create patterns called pressure waves – alternating high and low pressures
The discovery of Chladni plates
More than 100 years before Chladni, an English scientist named Robert Hooke looked at the nodal patterns on glass plates. He saw that they emerged when he ran a bow along the edge of a flour covered plate. Chladni then perfected these experiments with sand and included them in his book,"Discoveries in the Theory of Sound".
Mounting the plate to the stand
The plates are mounted to a metal stand that has been constructed using the same principles as Chladni's original device. When the plates are mounted on a base the assembly can be made to vibrate. When this happens, standing waves are established on the plate. Areas of maximum displacement are called anti-nodes. The areas of minimum displacement are nodes. If the plate oscillates in only one direction, say horizontally, then only odd harmonics will be present and vertical lines will form on the plate.
Using a tuning fork or transducer it is possible to produce a pattern of nodes and antinodes on the plate. If the plate is made to vibrate in two perpendicular directions simultaneously, then both odd and even harmonics will be present. In this case, diagonal lines form instead of just lines or spots. These lines and spots are called Chladni's Figures.
Another way to generate these patterns is by using a violin bow. The violin bow is strung with horsehair coated in rosin, and when bowed at the base of the plate in one direction only, waves will move along the plate from the base outwards towards the edges of the plate.
Are Chladni plates used today?
These days, people generally use digital equipment to analyze vibrations instead of using Chladni plates. However, some people still use them to understand the patterns that are created when sound makes an object vibrate.
Chladni plates can be used not just for looking at musical vibrations. They can be used in other science subjects, such as physics and maths, to make calculations of how much energy is being released by the vibration of a certain mass on a plate which is vibrating in a particular frequency.
How to make a Chladni plate
Chladni plates can be made in many different shapes and sizes. There are even versions of the Chladni plates that have been cut from stone and wood. To make a relatively small, circular plate you can use thin, rigid metal such as tin or aluminium pie pan. The more ridged the metal, the less flexible it will be but using too thin a metal will not allow for a large enough vibrating area to be generated.
- Drill a hole in the center of plate
- Fix a metal or wooden handle to the hole using a screw so that it is firmly attached and cannot be pulled out.
- To reduce the risk of cutting sand the outer edge of the plate with sandpaper
- attach the wooden handle to a weighted base so that it can stand upright. You may wish to glue the metal handle to the base first and then fix it upright with a screw.
- To see the nodal lines you will need to vibrate the plate using a single tone . This can be achieved by using a small speaker that is played at a volume too low to cause damage but still loud enough to vibrate the plate
- alternatively a tuning fork may be struck and touched to the plate or a violin bow may be
The original Chladni plates
It is possible to see the original Chladni plates in a museum in Germany. The plates were used in the late 1700s by Chladni to aid him in his research into the study of musical vibrations.
conclusion: can I see sound? Yes with a little help from Chladni plates
Chladni plates are an excellent tool for investigating the patterns of vibration that are formed when an object like a plate is vibrated at certain frequencies. Chladni plates are used in more modern times to show the pattern of sound waves that form when the air moves around an object. This "plate" has a handle attached and is able to vibrate freely because it is not fixed to anything. When regular vibrations from musical instruments, for example, strike these types of plates they will resonate. These patterns are Chladni's figures.
outer edge of the object and decrease toward the middle. When an oscillating sound wave hits this central area it will not be able to travel outwards as there is no room for expansion