absorption coefficient

[AoifeMcSweeney]

while studying vibrations I constantly came across 2terms: transmissionloss factor and absorption coefficient.
Where excatly is the difference? Can one generaly say, that the transmissionlossfactor is for menachnical vibrations, whereas the other one is for acoustical purpose?
Thanks,
Aoife

 

[GregLocock]

Sort of. You can have an acoustic TL, in an exhaust for example, or when measuring the sound transmitted through (as opposed to reflected off) a panel.



Cheers

Greg Locock

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

 

[testbench78]

for a sound wave, when it encoutered a plate or some object, the energy (E) will be seperated into three parts. some of them (Er) will be reflect, the other part will enter into the structure. then some energy (Ea) will be absorbed by the struction because of damp and visuoelastic. finnally, the energy left (El) will be through the structure. So,
E=Er+Ea+El
for transmission loss, is E-El.
for aborption coefficient, is Ea/E.

 

[SomptingGuy]

Note also that TL requires an anechoic termination. It is the ratio of incident sound power to that transmitted downstream to an anechoic termination.

- Steve

 

[Rob45]

One (TL) is a measure of barrier material performance; the other (absorption coefficient) is a measure of absorber performance. TL in acoustic usage describes an acoustic property, not a mechanical one.
Just as the two types of materials are fundamentally different, so are these tests.

 

[Tmoose]

"transmission loss factor and absorption coefficient"

When I lived in a 1960s side-by-side duplex apartment our neighbor had a teenaged daughter, and my outspoken wife is from the Bronx, New York . I bet we all were glad the "common" wall had a relatively high transmission loss, and it was sealed at the edges, so there were no flanking paths for sound to sabotage its performance.