Polk 7A measurements

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gatemplin
gatemplin Posts: 1,595
edited March 2005 in Vintage Speakers
I built a Speaker Workshop rig for designing my own speakers and thought I would test drive the Polks. I have been comparing my measurements to those done on the same drivers using Liberty, SpectraPlus and LspCAD. The results are all pretty close. Thanks to Jcaut for helping me out with the setup.

Graham
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  • gatemplin
    gatemplin Posts: 1,595
    edited March 2005
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    Here is the frequency response pretty accurate from up to 10kHz. Response rolls off on the top due the the mic response. This is ungated in middle of the room, so there are room interactions but it is also smoothed.

    This is pretty damn flat. It doesn't look like there is much if any baffle step compensation but that was probably typical of 70's speakers. Maybe these were designed to be placed near walls.
    Graham
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  • gatemplin
    gatemplin Posts: 1,595
    edited March 2005
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    Here is the total impedance. You can see that nominal is around 10 ohms, and the tuning frequency is near 46 Hz.
    Graham
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  • gatemplin
    gatemplin Posts: 1,595
    edited March 2005
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    Here is a pic of the Monitor 7A. I'm really not surprised at all that they measure so flat. They sound great.
    Graham
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  • gatemplin
    gatemplin Posts: 1,595
    edited March 2005
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    Here is a comparison of my results to results in LspCAD.

    These are some results from testing the Extremis on a 10x17" baffle. The white graphs are Jon's, the grey ones are mine.

    Near field

    attachment.php4?attachmentid=1818&stc=1

    attachment.php4?attachmentid=2461

    Far field

    attachment.php4?attachmentid=1817&stc=1

    attachment.php4?attachmentid=2460

    Impedance

    attachment.php4?attachmentid=1819&stc=1

    attachment.php4?attachmentid=2444
    Graham
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  • jcaut
    jcaut Posts: 1,849
    edited March 2005
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    Very interesting. Thanks for posting it!

    Looks like you've got SW working pretty well. Don't give me too much credit for helping out: I doubt that I mentioned more than, perhaps one thing that proved helpful. I am glad to hear that your measurements from several different sources are in pretty close agreement. What mic and preamp did you end up using?

    Was the room where you took the FR on the 7A's pretty large? I've got small spaces to work with and my in-room, ungated response plots are usually pretty ugly. Almost unusable, ugly. I know you said it was smoothed, but yours looks nice overall, like you didn't have much room-reflection interaction going on. How much smoothing did you apply?

    Jason
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  • jcaut
    jcaut Posts: 1,849
    edited March 2005
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    Those 7A's are great-sounding speakers.

    I got to listen to RuSsMaN's last year, and I thought they held their own against anything else there, except maybe the SDA's. Just a very easy-to-listen-to speaker. Easy to drive, too, looking at that impedance graph.
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  • gatemplin
    gatemplin Posts: 1,595
    edited March 2005
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    Thanks Jason. It was encouraging to know that I had someone that was willing to help. That motivated me to keep trying things to solve the problems.

    I ended up using my lowly $50 RS spl meter as the mic and pre amp. Now its not the best in the world, and I plan on replacing it eventually, but see the comparisons above. Pretty close where it counts compared to a $5000 B&K microphone.

    My room is about 15 by 12. I haven't tried gated response because these turned out well. I use 1/8 to 1/3 octave smoothing. I dont recall exactly what I used above. Probably 1/6th.
    Graham
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