Why do some metals ring when struck while others don’t?
In: Physics
Sound is a mechanical wave, so it needs a medium (the air, water, a drum, etc.) to travel through, it does so by agitating the molecules of its medium along the way, which expands in the direction of the wave, by second hand agitation and so on.
Different materials have different characteristics on how well it transfer the sound across it depending on composition, shape, etc., some grant less “room for movement” between its molecules (think of how well sounds navigates in a room full of water vapor compared to screaming to the same amount but in the shape of a block of ice). Even wood has different propagation properties if you consider across the grain vs against the grain (which is the reason a lot of speakers use [MDF](https://en.wikipedia.org/wiki/Medium-density_fibreboard) like materials as medium, as it can be more uniform).
tl;dr Sound uses things to travel, some things are better for sound traveling due to their physical and chemical properties.
Tons of wrong answers or partially correct answers in here. I’ll chime in, as I am a specialist in vibration of metallic structures.
Natural frequency depends not only on material properties, but physical arrangement and constraint as well. Consider a bar made of 6061-T6511 aluminum. If you clamp it at one end and strike the middle with a mallet, you’ll get a totally different response than if you clamp it at both ends and strike the middle with a mallet. The natural frequencies will depend on the choice of material, the dimensions of the bar, and the method of constraint. The response will depend on both the natural frequencies and how the bar is excited (where, how it is struck).
Real structures have multiple (infinite in fact) natural frequencies. If you want to design something to be useful in producing musical tones, you want to come up with something that has a fundamental (lowest) natural frequency that corresponds to some particular note, such as 440 Hz for concert A4, and upper natural frequencies that are well spaced or if possible integer multiples of the fundamental frequency. When you excite it, the response is going to contain a combination of the natural frequencies, so you want to design it such that the fundamental is a strong contributor, and other frequencies that aren’t multiples of the fundamental are weak contributors. Simple structures are good for this, and you can choose the clamping points carefully to try and get more harmonics to be multiples of the fundamental. Taught strings and xylophone keys work well. Structures like circular membranes don’t work well for producing tones, since you’ll get a jumble of diasonant frequencies in the response and this is why drum heads don’t tend to produce as distinct tones as other instruments.
Beefy structures or structures made of stiff materials will, in general, will have really high and diasonant frequencies, so you’ll hear a clang or thud when you whack it. Sometimes you get lucky and find a structure that makes a nice sound when you excite it, but it’s not entirely material dependent.
Material damping will play a role in how sustained the tone is, if you get one. For this reason, some materials will sound inherently better even if you nail the configuration for producing a tone. This is why you see different woods, for example, being prefer in crafting quality instruments.
Designing structures to have certain frequencies requires knowledge of structural dynamics. This is one of my areas of expertise, as I design aircraft components for a living. We design for frequencies not to produce certain tones, but rather to not coincide with frequencies from rotor blades or rotating engine components.
An objects density (how tightly packed its molecules are) had a direct impact on the frequency an object will vibrate at. Denser materials will vibrate at lower frequencies than less dense materials because there’s not as much room for the molecules to move around. For sound to be created, an object has to vibrate at a frequency that causes the surrounding medium (air, water, etc.) to vibrate as well. Lower frequency waves create lower pitched (thud) sounds while higher frequency waves produced high pitched (ring) sounds. So dense objects will vibrate less and create more of a thud than a ring.
Other factors that impact the sound produced by an object slightly outside of an ELI5 scope are:
* Energy
* Resonant Frequencies
* Shape and design of object
* Acoustics
* Medium Density Changes (Warm air is less dense than cold air)
* Atmospheric/Barometric Air Pressure
Pretty sure this is a result of density, as well as shape. Take a cymbal on a drum kit, you strike it and it makes a loud crash fallowed by a low hum. Taking the same material if you constructed a large brick and struck that, you’d get a tapping sound.
This is the result of vibration running through the object, with a brick, it’s so dense the vibrations arnt as pronounced, hence the lack of ringing. Similarly if you took, say lead (rather then brass) and made a cymbal and struck that, you wouldn’t get the same ring, as the stick would strike the lead and instead of the lead vibrating, it’s density would cause the vibrations at the end of your stick, and depending on how hard you hit it even your wrist might vibrate more then the lead.
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it’s not so much the composition of the metal (although that has a lot to do with elasticity/stiffness and the length of the ring) but the shape of the resonator.
bells are shaped so because they specifically make a big ass noise
organ pipes are cut and measured in a certain way to naturally want to resonate at their designated frequencies.
if you made a cube of brass it won’t ring because the shape doesn’t vibrate and wobble long enough or create soundwaves in a certain shape, but if you made a bell out of the same brass it would work.
They all do, but at different frequencies (pitch) at different volumes (amplitude). You hear the ones our ears are better at perceiving.
It depends on the shape of the metal item as well. If it is shaped such that it can not vibrate freely it won’t ring
Crystal thingies ring – not crystal (plastic) doesn’t.
Think stack of attached lego (organized, crystalline) vs. poured out (random, viscous) mound of lego.
Depending on the molecular structure and conditions of cooling to a solid state, crystalline structures may or may not have been formed.
Typically, quick cooling / super saturation leads to large, ringy crystalline structures, your mileage may vary, but I’ll use that as my jumping off point…
Crystalline things that have broken bits also don’t ring as well.
So when you look at a material and zoom way in on it, you’ll see each molecule or atom of the material. When struck, the force will make each molecule or atom move a tiny bit, passing the force along to the next one minus a small amount of energy. Depending on how much each atom wants to stick to the others the material will vibrate as a shock wave runs through it.
Some metals are soft, the molecules or atoms are loose and don’t want to stick very much. These have lower tones and ring less.
Some metals are hard, the molecules are close and tight together, these have a high pitched ring.
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