Trying to better understand sound & vibration on textured surfaces

[Kwag]

Hi,

First thank you in advance for reading and answering my question. I am very much a newbie when it comes to physics, so while I feel my question in pretty straight forward I'm sure it's more complex than my thinking.

OK so here it is... Does the texture of two surfaces change the decibel level of sound emitted when colliding the two together?

Example: You have two pieces of rubber or plywood, one has a completely flat surface and the other has grooves in the surface that extend out to its edges. If you were to collide one flat surface onto the grooved surface of the other with equal distribution, would this combination produce less, more, or an equal amount of noise than if the two surfaces were flat? ... and why?

Thank you very much!

 

[anorlunda]

Welcome to PF. That is an unusual and interesting question.

Do you mean the slap sound, or perhaps the crunch sound? A clapper makes a bell ring, but if the clapper was covered in cotton, it might thud. There are many types of sounds that could be produced by collisions. The collisions themselves can be spread in time as the objects deform, or crumble, or come into full contact.

I think you have to be more specific about the kinds of sounds, collisions, and textures you are asking about.

 

[sophiecentaur]

@Kwag
I think the answer to your question is that (usually) the textured surface would have high spots and low spots all over it. That would mean the contact time until the motion ceases would be longer (the surfaces would distort and 'cushion' the impact. The longer time involved would reduce the frequency of the sound spectrum and it could well sound different (less 'toppy'). Probably the distance over which the impact is spread could mean that more energy is absorbed within the material, rather than being emitted as sound energy so it could involve less sound energy, too.
If you took this to an extreme and had significant peaks on the surfaces, the impact could be more or less silent. The strength of the material would also have an influence; small peaks / ridges on a wood surface would distort and absorb mechanical energy.
Otoh, with two extremely flat surfaces, the air would be expelled out of the edges very fast as they get closer and you could imagine a 'slap' (irrespective of how strong the materials were).
To sum up, it's a complicated business and the actual details and textures would need to be specified. But very flat surfaces would mostly make more noise, I think.

 

[Kwag]

Welcome to PF. That is an unusual and interesting question.

Do you mean the slap sound, or perhaps the crunch sound? A clapper makes a bell ring, but if the clapper was covered in cotton, it might thud. There are many types of sounds that could be produced by collisions. The collisions themselves can be spread in time as the objects deform, or crumble, or come into full contact.

I think you have to be more specific about the kinds of sounds, collisions, and textures you are asking about.

@Kwag
I think the answer to your question is that (usually) the textured surface would have high spots and low spots all over it. That would mean the contact time until the motion ceases would be longer (the surfaces would distort and 'cushion' the impact. The longer time involved would reduce the frequency of the sound spectrum and it could well sound different (less 'toppy'). Probably the distance over which the impact is spread could mean that more energy is absorbed within the material, rather than being emitted as sound energy so it could involve less sound energy, too.
If you took this to an extreme and had significant peaks on the surfaces, the impact could be more or less silent. The strength of the material would also have an influence; small peaks / ridges on a wood surface would distort and absorb mechanical energy.
Otoh, with two extremely flat surfaces, the air would be expelled out of the edges very fast as they get closer and you could imagine a 'slap' (irrespective of how strong the materials were).
To sum up, it's a complicated business and the actual details and textures would need to be specified. But very flat surfaces would mostly make more noise, I think.

Thank you very much for your responses. That actually makes perfect sense is there a principal that deals with this or would that mostly be based on the texture and material used?

Thank you again this has sent me off to read some more.