Transmission loss question
Transmission loss question
(OP)
Not a "mechanical" acoustics question I know, but acoustics anyway...
Measuring TL across a single-input, single-output component is well defined. But say I have multiple outputs. It strikes me that all I need to do is put anechoic terminations on all the outputs and then measure from input to each output in turn. Then add them up. For example, if I measure one at 40dB and one at 50dB, the combined TL is:
-10log10(10^(-50/10)+10^(-40/10)) = 39.6dB
(i.e. less TL than the lower one)
My concern is that maybe I shouldn't have an anechoic termination on the output I'm not currently measuring. Has anyone done this sort of thing before or got any good pointers?
TIA
Measuring TL across a single-input, single-output component is well defined. But say I have multiple outputs. It strikes me that all I need to do is put anechoic terminations on all the outputs and then measure from input to each output in turn. Then add them up. For example, if I measure one at 40dB and one at 50dB, the combined TL is:
-10log10(10^(-50/10)+10^(-40/10)) = 39.6dB
(i.e. less TL than the lower one)
My concern is that maybe I shouldn't have an anechoic termination on the output I'm not currently measuring. Has anyone done this sort of thing before or got any good pointers?
TIA





RE: Transmission loss question
For a start, if the output from the two outlets is coherent then all bets are off.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Transmission loss question
TL is defined in terms of acoustic power flow through a component. It doesn't matter what happens once it's left the component. If you do have coherent signals that cancel or reinforce in the free field, who cares? It doesn't alter the internal acoustic power flow. However, I think it's a pretty meaningless thing to try to measure.
RE: Transmission loss question
RE: Transmission loss question
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Transmission loss question
RE: Transmission loss question
"Personally I can't see the point of measuring it on a cold exhaust muffler with zero flow."
I see the point: it gives the clueless something to put on a print!
RE: Transmission loss question
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.