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REW gate settings, help please.

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  • REW gate settings, help please.

    HI All,

    Well, I'm now using REW and merrily getting FR response plots for a lot of speakers I have. I'm learning a lot and can use a number of features of REW adequately, however I would like to be able to get FR data that is less affected by room issues than I am now. With the automatic gating it appears that my FR plots are dominated by room effects from about 900HZ down. There are differences between different speakers, but the general contours are so similar that it looks like the room influence is much more than the differences between the speakers.
    So, I've searched the web and now know how to access the gate or "window" page, and know that I should uncheck the automatic option and enter new millisecond values in the left and right windows instead of the default 125 and 500 values. If possible I would like to use values that let me do a single full sweep to get a FR plot. I've read a number of posts that have said their FR plots end at 200Hz because of in room issues and would be pleased if I could get my sweeps to have good speaker data down to that point. I will want to get data for response below 200 at some point, but for now it is still "baby steps for baby feet" for me.
    Input on the various values to enter and what results will ensue would be greatly appreciated.


  • #2
    I do gating w/ARTA. A gate of 3.33 milliseconds gives you accurate measurements down to 300Hz, BUT . . . your tweeter and mic need to be 4ft away from any reflective surfaces. So in a room w/an 8' high ceiling, you'd raise the speaker/mic up to be 4' off the floor (and 4' from the ceiling as well), and positioned out in a room 4' from any wall.

    To get measurement down to 200Hz requires a gate of 5.0ms, but you need to be 6' away from all surfaces.
    If REW REALLY sets your gate at 125ms (that's 1/8th second, which is long for a camera shutter speed, but way too short for meaningful measurements), it would show you response down to 8Hz, but reflections will be included from anything within 150ft of the mic. Yeow!


    • #3
      Sounds like you're coming along just fine with this stuff.

      How to find your gate. I've attached a snip from a recent Overnight Sensation TMM build. One measurement was taken outside on the patio, with the speaker sitting on top of a 16" tall motorcycle stand. The only wall was 15' away, and the ceiling is fairly tall with that being lightweight plastic stuff. Mic was @1meter.

      On the first pic you can see the reflection lies around 5ms, that's my gate.

      Click image for larger version

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      Second pic is with the speaker about 6' from the rear wall, mic @1meter, but otherwise sitting right between where the pair of speakers normally set when listening to them. I have a very 'live' living room. See the difference in time of the first reflection, that's my gate time. Look to the left of the pic, see the IR window. On the top menu bar select Tools>IR Windows>right window>enter gate time>apply windows. Your measurement is now gated.

      Click image for larger version

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      Anyhow, that's the way I do it.


      • #4

        Can't tell from the impulse if the gate is set to the 1st reflection. Opinions?

        Click image for larger version

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        • #5
          Originally posted by Chris Roemer View Post

          Can't tell from the impulse if the gate is set to the 1st reflection. Opinions?
          Buy high, sell low. Oh wait, that's what I've been doing wrong.
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