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Near field measurements with phase plugs?

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  • Near field measurements with phase plugs?

    Happy to recently find the Bagby white paper on how to measure in-room responses with OmniMic. When measuring near field response, how far away should the microphone be when you have a driver with a phase plug? For example, I have some TB W4-1337SDF full range, 4" speakers. Per Jeff's recommendation the mic would need to be 1/10th the distance of the radius of the radiating area. In the case of these W4's, there's a phase plug protruding from the center much farther than the recommended distance from the actual cone. Also wondering what impact a phase plug may have on near-field measurements in general... Thanks guys!

  • #2
    Near field response is generally for obtaining accurate low frequency response of the speaker. Essentially, the phase plug has no effect here, just move the mic over to the side a bit and measure away. Since you have the mic, you really should be able to answer the question for yourself. Put the mic in front of the cone 1/4" away in a few different locations and measure, how does the response from <500Hz compare?
    Don't waste your money on a new set of speakers, You get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!


    • #3
      I asked the same question of him at one of his seminars. His response was basically, just get it as close as possible without touching it. I assumed he meant to still center it but he didn't state it. dcibel has a good point... that you could experiment with both and see if there are any differences. I bet it's minimal, but not sure.

      *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
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      • #4
        Thanks guys, I appreciate your insight on this. I'll do some experiments on my own to get a feel for what's actually happening. Come to think of it, I have some 4, 5 and 7" drivers with phase plugs, so as I was reading the instructions about placing the mic in the center of the dust cap, this was one of the first questions that came to mind...