ECM8000 gurus - need your expertise!

[smellygas]

I've looked all over, and I couldn't find the answer!

If I want to measure a DIFFUSE FIELD (i.e. automobile cabin), and I aim the ECM8000 towards the ceiling (long-axis pointed up), will my measurement be flat or does it need to be corrected? I have calibrations for 0 deg and 90 degs. I guess part of my question implies whether or not the ECM8000 response is free-field or diffuse-field corrected (I know it's omnidirectional). Thanks!!

SG

[Pan]

The ECM8000 is more or less flat which means it is accurate in the free field, not diffuse field.

A car cabin can not be said to have diffuse field properties for most of the audiorange.


/Peter

[smellygas]

Originally posted by Pan
The ECM8000 is more or less flat which means it is accurate in the free field, not diffuse field.

So how would it respond if its measuring sound in a diffuse field?

A car cabin can not be said to have diffuse field properties for most of the audiorange.
/Peter

This isn't the case, according to an AES article "Aspects of the Vehicle Listening Environment" (87th AES 1989).
"The multiple early reflections in a vehicle interior yield a type of diffuse sound field where 90% of the energy occcurs within the first 10ms of the direct wave arrival."
I have also seen at least two empirical studies published by JAES that support the notion of the very-early high-amplitude reflections (especially off the windows), which seems most consistent with a diffuse field environment. It certainly isn't a frontally-incident free-field.

SG

[Pan]

Originally posted by smellygas
[B]

So how would it respond if its measuring sound in a diffuse field?

It will show gradual roll off where it starts being directional which would be above 4k or so.


/Peter

[smellygas]

Originally posted by Pan


It will show gradual roll off where it starts being directional which would be above 4k or so.


/Peter

Great, thanks.

SG