- #1
louisnach
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Homework Statement
A disturbance signal propagates in a ventilation duct with cross-sectional area A=0,04m2. The fundamental frequency of the disturbance signal is 250Hz and its spectrum consists of odd harmonics only.
Choose the appropriate filter options for rejecting this particular disturbance.
Justify your choice (advantages)
Choose the dimension of your filter in order to attenuate by 20 dB
Homework Equations
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The Attempt at a Solution
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I hesitate between two approachs: using a expansion chamber with transmitted power formula
= 4 / ( 4cos²(kl)+ (A1/A2 +A2/A1)²sin²(kl) ) where A area of the duct and A2 area of the chamber and l length of the chamber, and getting a transmitted value in order to attenuate 20dB, in the lectures the expansion chamber was not presented as a filter so maybe it is completely stupid thie approach
the other idea is using a helmotz band stop resonnator but then it become possible to attenuate completely 250Hz by designing a helmotz resonnator with resonnance frequency equal to 250Hz, so i don't understand why it is asked to attenuate 20dB
In both case i don't know what means "its spectrum consists of odd harmonics only" and how to use this.
Happy end of year for everybody (sorry for my english i am not a native english speacker)