Gate IR Window

Johan Rademakers

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Thread Starter
Joined
Dec 26, 2017
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My AV System  
Subwoofers
All
Hello,

I've added a picture of 3 graphs, each containing 3 measurements, all with 1/12th octave smoothing. In these graphs I've applied different gates (IR Windows --- right window --- time in milliseconds).
  • Left, 50 ms
  • Middle, 500 ms (standard)
  • Right, 20 ms
To me, these look like vastly different measurements, especially the one on the right. I've used 20 ms here, because for this particular set of measurements I'm mainly interested in 50 - 200 Hz.

Based on these 3 settings, I would make make very different choices on what my next step would be (I develop subwoofers). Which setting will deliver most realistic results (used by other people, in different environments, as well as by myself at home).

Also out of interest, what does the IR Windows --- left window do?

REW Gate 50 500 20.jpg
 

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John Mulcahy

REW Author
Joined
Apr 3, 2017
Messages
1,903
The left window controls how much of the IR onset is included in the response, it can be set quite short for full range measurements but typically needs to be longer for band limited measurements such as subs as the lower bandwidth means a longer rise time.

The right window is the main factor governing the frequency resolution of the response, roughly speaking the resolution will be 1/window width, so a 20 ms window would mean only 50 Hz resolution - similar to applying heavy smoothing. For low frequency measurements would usually need a much longer window to get good frequency resolution. The downside of a long window is more of the room's reflections are included, which can make it difficult to see the underlying performance of the sub or drive unit. Measuring outside can help with that, weather permitting, or finding a very large space.
 
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