damping ratio

[14424]

Can anyone tell me how to run a simple (ball-park) test to determine the “Damping ratio” of an unknown material?

 

[GregLocock]

Hit it with a hammer. Measure the vibration with an accelerometer. Plot the time signal out . Eyeball the 'envelope'. compare it with an exponential decay curve.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[14424]

First – thanks for your response. I am a “starving consultant”, and would have to rent equipment to run any kind of test. The material I am looking at is similar to “ceiling tile”. Can you suggest a test for this type of material, using minimal equipment?

 

[GregLocock]

Well, as a starving consultant you need to not learn to waste people's time, if you want a full belly. I now gather you want the acoustic damping, not structural.

Clap your hands in a reverberant room damped by your material, use a microphone. Proceed as in previous post. Filter the time signal into frequency bands.

This is unlikely to be accurate.

otherwise use an impedance tube, intensity, a sound transmission loss suite, etc etc. Or hire someone who knows the basics. it is Acoustics 101 after all.







Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[SomptingGuy]

Hit it with a hammer

Isn't this the standard first approach to all problems?

 

[btrueblood]

Yup. Step two is find a bigger hammer.

 

[Twoballcane]

If you can hit with a hammer and figure out the damping ratio, would it not be between 2 to 5%?

Tobalcane
"If you avoid failure, you also avoid success."

 

[denis81]

hm... Is there any way to calculate it from stard characteristic of the material? I'm interested in the same question, but I need to choose a material. The structure is known, as well as conditions and damping ratio. So, how do I choose the material if I know the damping ratio I need as well as geometry of the part?

 

[GregLocock]

Are you after acoustic or structural damping?

Generally you ask the supplier for measurements or samples. Sorry, there is no satisfactory way of calculating the damping of teatments, so far as I know everybody tests them. You can build models of them which might work for tuning, once you have a concept in place with a measured response.

Specifically with regard to acoustic treatments you may get a fair bit of snake oil from the salesman, especially using multiple layers to give optimum damping at some frequencies. For some reason these work better in the lab than on the road.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[denis81]

thanks

 

[Rob45]

Just a little more specifically: to figure acoustic damping you might determine the "room constant" by performing Greg's hand-clapping test, and find the time to decay 60 dB.

Performing this test with the test material in the room and without the test material in the room should give an indication of the material properties.

As an acoustic consultant, I'm sure you know how to relate decay time to room constant, and room constant and material surface area to material unit properties.