Extending window for outdoor

[Matthew J Poes]

Hi Jon,

You mention the need to extend the window for very large spaces and outdoor measurements. Is there any kind of window for CEA-2010 measurements and if so any lengthening that is needed?

For sweeps, what is the benefit of extending the window?

James and I had been ignoring this issue to date, considering it minor. However on our last measurement session we were forced to measure at about 200 feet from a bunch of homes. We could clearly hear a delayed echo during tests and wondered if they could possibly be corrupting the measurements. Just curious if we need be thinking about this.

 

[John Mulcahy]

There is no impulse response from a CEA-2010 burst measurement and so no IR window, the burst itself has a Hann shaping window applied to it but that is really using the word in a different context. The response to the CEA-2010 signal is captured and put directly through an FFT to generate the spectrum view on the RTA.

In the case of sweep measurements in large spaces a longer sweep might be needed if the RT60 times are approaching or exceeding the sweep length, want the response to decay within the sweep duration. The choice of window length for the resulting IR depends on what you want to capture, and is a trade-off between showing the full reverberent behaviour and excluding any unwanted reflections. In the case you mentioned I'd shorten the right side window to 170 ms or so to exclude the reflection from the nearby homes and the comb filtering it would cause.

 

[Matthew J Poes]

There is no impulse response from a CEA-2010 burst measurement and so no IR window, the burst itself has a Hann shaping window applied to it but that is really using the word in a different context. The response to the CEA-2010 signal is captured and put directly through an FFT to generate the spectrum view on the RTA.

In the case of sweep measurements in large spaces a longer sweep might be needed if the RT60 times are approaching or exceeding the sweep length, want the response to decay within the sweep duration. The choice of window length for the resulting IR depends on what you want to capture, and is a trade-off between showing the full reverberent behaviour and excluding any unwanted reflections. In the case you mentioned I'd shorten the right side window to 170 ms or so to exclude the reflection from the nearby homes and the comb filtering it would cause.

Ok this is really helpful. Thanks.