# Attempting to reduce the speed of sound on a plane/plank

I am trying to control the speed at which a sound vibration takes to travel the length of a plane/plank.

I have a plastic choppingboard, at one end is a contact microphone at the other end I tap the choppingboard to create a vibration.

Now, I want the sound to travel very slowly across the choppingboard, so I was thinking of covering the choppingboard in rubber because the elastic properties of rubber cause sound vibrations to travel very slowly.

However, I am worried that the sound will go thorough the thickness of the rubber into the plastic choppingboard, travel the width of the coppingboard quickly through the plastic and then go through the thickness of the rubber again and into the contact microhone.

So essentially, I imagine the rubber layer wouldent cause much difference at all?

Unless I some how muted vibrations before they hit the plastic, by having some kind of foam between the rubber and plastic layers??

Am I right? If so, what can I do !?!?!

Edit: also, wont the plastic choppingboard effect the intertia of the rubber causing the sound to not travel as fast as it would without the plastic choppingboard?

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The sound will travel through the chopping board at a constant speed, regardless of what you cover it with.

By adding the layer of rubber (I assume at each end of the chopping board), you will alter the speed of sound, as the average stiffness (poorly termed but serves it's point) is changed.

It is worth noting that unless you shorten the chopping board by the thickness of the rubber, you are increasing the overall distance it has to travel and so increase the time it will take anyway.

Over such a short distance, I'd say you'll be hard pressed to measure a difference in the speed.

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Okay well basically, I want to conver the entire copping board in a layer of rubber.

I want sound vibrations to travel from one end to the other of the rubber covered choppingboard at the same speed it would if there was just a rectangle of rubber with no plastic choppingboard in the middle.

With just the rubber I would get around 60 m/s with just the plastic I would probably get around 3000 m/s but my worry is that with plastic coated in a layer of rubber I would still get around 3000 m/s because the vibration would go through the rubber and use the plastic as a 'fast lane' to the other end where it would go though 4 - 6 mm thickness of rubber and into the contact microphone

get what im saying now?

So basically im looking for a way to prevent this happening - if this would happen, im not a in-the-know physics person atm. I imagine I would need a layer inbetween the rubber and plastic to mute the sound and prevent it jumping into the plastic and using the plastic as a 'fast lane', but what kind of material would be sufficient for this?

Okay well basically, I want to conver the entire copping board in a layer of rubber.

This won't slow the sound through the chopping board down.
I want sound vibrations to travel from one end to the other of the rubber covered choppingboard at the same speed it would if there was just a rectangle of rubber with no plastic choppingboard in the middle.

It won't. If you want it to take the same time as rubber, it needs to be a block of rubber. The only way around this is to have a material with a lower stiffness than the rubber surrounding the chopping board.

The stiffness would have to be low enough so that the combined transfer time through chopping board plus 'material x' is equivalent to the rubber alone.

With just the rubber I would get around 60 m/s with just the plastic I would probably get around 3000 m/s but my worry is that with plastic coated in a layer of rubber I would still get around 3000 m/s because the vibration would go through the rubber and use the plastic as a 'fast lane' to the other end where it would go though 4 - 6 mm thickness of rubber and into the contact microphone

get what im saying now?

Fast lane? Sound isn't electric. It won't "take the path of least resistance".

Think of it like this:

Let's say it takes sound 5 seconds to go through the chopping board and 20 seconds to go through a block of the rubber.

Now, this means you need a material on each end of the chopping board that will take the sound 15 seconds to go through in order to get an overall time of 20 seconds - equal to the transfer time through the block of rubber alone. That way the average speed of the sound through the two materials will be equal to the block of rubber.