Acoustic of air cleaners with/without filter elements
Acoustic of air cleaners with/without filter elements
(OP)
Does anyone have any information (links, measurements, plots, anecodotes, or even uninformed hand-waving opinions) about the effects of air filter elements on the acoustics of automotive air cleaners?
Typical engineering practice is to assume the elements are acoustically transparent. My intuition says that they _probably_ give broadband attentuation and could possibly inhibit large-amplitude standing waves (in the way porous hose can). I don't see how they could shift resonant frequencies around though.
Can anyone shine any light on this?
Typical engineering practice is to assume the elements are acoustically transparent. My intuition says that they _probably_ give broadband attentuation and could possibly inhibit large-amplitude standing waves (in the way porous hose can). I don't see how they could shift resonant frequencies around though.
Can anyone shine any light on this?





RE: Acoustic of air cleaners with/without filter elements
If you've got folded paper in there then you might get some interesting effects around lambda/4=thickness of filter pack, but it seems unlikely to be significant.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Acoustic of air cleaners with/without filter elements
I've been given a couple of TL curves and asked to comment. There's a clear attenuation caused by the element, which increases with frequency. But what's odd is that with the element in place, the TL shape is similar, but the frequencies are all reduced (proportionately). It's almost like the speed of sound has dropped. As with all these situations, I didn't witness the testing and temperature variations from test to test are denied.
Assuming that the element doesn't have some heavy gas trapped in it, are there any other potential causes of frequency shifts?
RE: Acoustic of air cleaners with/without filter elements
(1) To optimize volumetric efficiency, if duct length need
to tune is any preference for dirty or clean side of
duct? (dirty side -before air cleanr & clean side
refer to after air cleaner connected to Th/body)
(2) Can we analyze clean/dirt side duct selection without
going for prototype/actual testing ? any software
suggestion
RE: Acoustic of air cleaners with/without filter elements
I haven't measured the TL of filters, only the noise.
johnab - you have to tune the clean air duct. the dirty side will be decoupled by the filter box's volume.
Ricardo Wave is the usual recommendation, I've never used it.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Acoustic of air cleaners with/without filter elements
RE: Acoustic of air cleaners with/without filter elements
I don't like this theory - after all, microphone diaphragms, however heavy they are, do not change the frequency of the measured noise.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Acoustic of air cleaners with/without filter elements
But in a microphone you measure the frequency of the diaphragm, this problem is transmitted noise. If we scale the diaphragm up to a wall, tranmitted noise is clearly restricted in frequency?
RE: Acoustic of air cleaners with/without filter elements
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Acoustic of air cleaners with/without filter elements
That is a fascinating theory and I must admit I do find it plausible and attractive. The paper would have nearly zero stiffness and could consitute extra distributed mass.
ivymike,
A diaphragm would be a spring-mass-damper system with all mass at one point. I think the filter element would act as a distributed mass.
CinciMace,
The diaphragm is a microphone is designed to have its first mode well above any frequency you might want to measure with it.
johnab,
Greg is right - tune the lengths in the clean side to optimse volef. The dirty side only really has an effect on radiated orifice noise.
RE: Acoustic of air cleaners with/without filter elements
https://w
The two phrases of interest are:
"Fibrous structure of the filter element is modeled as a micro-perforated panel using the flow resistivity and porosity"
and:
"enhancement of TL at troughs and shift of troughs to low frequencies"
So there is no distributed mass in the model, just extra damping. And I guess the extra damping could be what reduces the frequencies of the forced modes?
RE: Acoustic of air cleaners with/without filter elements
RE: Acoustic of air cleaners with/without filter elements
RE: Acoustic of air cleaners with/without filter elements
RE: Acoustic of air cleaners with/without filter elements
So, do the measured results show a change in damping as well as a shift in frequencies?
That paper sounds exactly what you are looking for, here's another one (can't find it on the web)
The insertion loss of air - filters in HVAC systems R. Dragonetti, C. Ianniello and R. Romano
Internoise 2004
Looks at the 1/3 octave IL of the rather heavier elements they use - typically 3 dB . It also includes a very useful equation which I am not going to attempt to reproduce here.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Acoustic of air cleaners with/without filter elements
RE: Acoustic of air cleaners with/without filter elements
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.