Attenuation vs frequency

[par1]

I have Attenuation(dB) vs frequency plot for the Assembly includes Intake Manifold, Air Cleaner, Resonator I & II & would like to know how to find out any specific spike is due to which component?

 

[GregLocock]

Detective work. Random guesses. Substitution. Hand calculations.

Cheers

Greg Locock

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

 

[fwcatr]

Par1,

In addition to what Greg Locock mentioned, I would start by testing each device by itself, if you can. Check the spectrums after you are done and see if you see anything that compares to the spectrums you have for testing with all devices present. If you cant find something there, test with one device, test with two devices, test with three, and so on. By changing one device at a time, you might be able to pinpoint what is causing a spike.

Are any natural frequencies being excited by the whole system being coupled? Do you have a soft tipped hammer to excite the structures yourself (without damaging anything) and get some natural frequencies?

Regards,
Fred

 

[Rob45]

Or you can do some measuring of the individual components, calculate which one should be attenuating which frequency.

But I much prefer Greg's approach.

 

[Warpspeed]

A spike implies a resonance of some sort. It may be part of one component, or due to the unfavorable interaction of several parts.

All you can do is start making some changes and see what happens to the results.

The Greg Locock, Sherlock Holmes approach should eventually guide you to the right conclusions.

 

[Rob45]

Warp:
Read again the original post.
He said:
"I have Attenuation(dB) vs frequency plot for the Assembly..."

A spike in atten vs freq would be an attenuation peak due to one of the elements; I interpret his post as wanting to know how to identify which element produces which "spike."

Having some rudimentary knowledge of theory, plus some test data should do it.

 

[Warpspeed]

Point taken,

But a spike can go in either direction, hehehe.

 

[Rob45]

Warp:
Well, there's that of course...

But I've never got hung up on a downward spike!