Need to make a simple mechanical system quiet
Need to make a simple mechanical system quiet
(OP)
I am trying to make a very simple system quiet - in essence, a simple thin-cross section beam banging the thin edge into piece of soft rubber. Can't change the rubber.
Looking at natural frequencies, etc. of the beam. Looking at the peaks in the acoustic measurements. Any resources online, recommmendations, etc? Not looking for complex solutions -- looking at simple things first.
Thanks!
Looking at natural frequencies, etc. of the beam. Looking at the peaks in the acoustic measurements. Any resources online, recommmendations, etc? Not looking for complex solutions -- looking at simple things first.
Thanks!





RE: Need to make a simple mechanical system quiet
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Need to make a simple mechanical system quiet
Not exactly sure -- looking into that now via FEA (it's really not a beam, but conceptually, for this discussion, it is.)
what is its radiation efficiency?
Don't know -- what is this, or where can I read up?
why not put damping pad
It's needs to be precision located (start and stop). Might be possible to put something along the width dimension
or constrained layer damping on the beam?
Not sure what this is.
Clearly, I'm a rookie at this noise stuff -- thanks for the help.
RE: Need to make a simple mechanical system quiet
Make the beam flexible, e.g. like a piece of music wire, so it bends elastically at impact? It will eventually stop ringing; the rubber will help a little with that.
The presence of rubber as a stop seems inconsistent with (continued) precision.
Immerse the whole mechanism in a liquid?
Mike Halloran
Pembroke Pines, FL, USA
RE: Need to make a simple mechanical system quiet
RE: Need to make a simple mechanical system quiet
We don't expect you to give away the store. Maybe you can find a way to reveal the core of the problem you are trying to solve, without revealings its 'gozinta'. Then you will get suggestions that are more directly useful.
Mike Halloran
Pembroke Pines, FL, USA
RE: Need to make a simple mechanical system quiet
-The future's so bright I gotta wear shades!
RE: Need to make a simple mechanical system quiet
RE: Need to make a simple mechanical system quiet
That tiny cross section in some ways makes things difficult, and in others makes it easier. Are you sure the sound is coming from the beam and not the rubber it is contacting? Can you put some duct tape on the beam to see if it helps (by providing damping to the beam mode if there is one).
Can you drill holes in the beam?
Can you change the edge profile or the beam dimensions?
-The future's so bright I gotta wear shades!
RE: Need to make a simple mechanical system quiet
No. It could also be coming from the mechanism moving the beam.
Can you put some duct tape on the beam to see if it helps (by providing damping to the beam mode if there is one).
Been done -- not sure of the results yet.
Can you drill holes in the beam?
yes.
Can you change the edge profile or the beam dimensions?
Somewhat, yes.
Just trying to understand the underlying physics a bit. :) I didn't see a lot of straight forward references out there.
Thanks for the interest and questions.
RE: Need to make a simple mechanical system quiet
"Is it bigger than a breadbox?" is a parlor game.
RE: Need to make a simple mechanical system quiet
We don't even know the problem frequency or how much noise reduction is needed. It may be that the beam is not an efficient sound radiator, and the dominant sound is from another part of the structure. Sure the beam impacts may be the excitation force, but what is actually radiating most of the sound? Consider reducing impact energy or sound radiation or a combination of both.
Walt
RE: Need to make a simple mechanical system quiet
As a side note, good call -- testing seems to suggest the noise source may not be a resonating beam, but something in the mechanism, as there is a peak at a certain frequency when using multiple beam materials....just different in magnitude. If it were a resonating beam, I'd expect the peak frequency to shift with materials having drastically different E/Density.
Sorry guys/gals -- I'd love to give you more but can't.
RE: Need to make a simple mechanical system quiet
Brüel & Kjær (188-81)
RE: Need to make a simple mechanical system quiet
Where is the observer located in relation to the mechanism? Perhaps you can do a better job on enclosing this mechanism and reduce any noise perceived by the observer. While this is obviously not the ideal solution, given then fact that you are apparently severly constrained in the actual mechanism design maybe this is more practical.
RE: Need to make a simple mechanical system quiet
Here is another book that may help your knowledge base:
"Machinery Noise and Diagnostics" by Richard Lyon 1987 Butterworth Publications ISBN 0-409-90101-6
Walt