Fun with an RTA

Discussion in 'Subwoofers' started by theJman, May 3, 2012.

  1. theJman Audioholic Chief

    Oct 15, 2011
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    In an attempt to have my subwoofer reviews be more objective I decided to make time -- you know how that goes -- to learn how my XTZ Room Analyzer II Pro functions. I've read the manual twice now, so I have at least a passing familiarity with all the features (which turned out to be more then I had anticipated).

    My first set of measurements have been taken, so I wanted to get some feedback from those who know about measured testing to see if these numbers appear legit. I already have an opinion formulated, now I need to see if the neophytes measurements -- that would be me -- are corroborated by people who know what they're doing.

    I tested two different subwoofers, the Simply Sound Audio Rumba 12 I just recently reviewed, and another sub I'm currently reviewing. The former is acoustic suspension with a front-firing 12" driver, while the latter is an 8" driver with an 8" passive radiator. That one has the driver and PR on opposite sides of the cabinet. For both subs I pointed the mic directly at the center of the driver, exactly 1 meter away. They were at least 1.5 feet from the nearest wall. The room is carpeted.

    I disabled the PEQ on the Rumba, so no boost or cut was used. The PR was not mic'ed for this test. The XTZ software has a meter which denotes clipping so all tests were run up to clipping, then the gain was turned down to just below that point. You only have preconfigured tones you can send out, so the possibilities aren't endless, which is why you'll see gaps between the frequencies. I started at the lowest -- 10Hz -- and stopped at 125Hz, even though I could have gone to 250Hz. 125Hz seemed like a reasonable ceiling to me though, so I'll probably stick to that in the future as well. I haven't figured out how (if?) to save the graphs in JPG or PNG format yet, so unfortunately there are no pictures to show.

    That should cover all the background info, so without further ado...

    Simply Sound Audio Rumba 12
    10Hz - 86dB
    12.5Hz - 91dB
    16Hz - 97dB
    20Hz - 98dB
    25Hz - 106dB
    31.5Hz - 109dB
    40Hz - 110dB
    50Hz - 107dB
    63Hz - 114dB
    80Hz - 116dB
    100Hz - 109dB
    125Hz - 105dB

    The sub I won't identify just yet :D
    10Hz - 57dB
    12.5Hz - 60dB
    16Hz - 67dB
    20Hz - 77dB
    25Hz - 89dB
    31.5Hz - 98dB
    40Hz - 101dB
    50Hz - 94dB
    63Hz - 103dB
    80Hz - 107dB
    100Hz - 107dB
    125Hz - 103dB

    The Rumba 12's numbers look like what it sounded like to my ears, so I'm pretty content with that one. The unidentified sub looks about right too, except for that bizarre dip around 50Hz (which I tested 3 times, just to make sure I wasn't losing it), so I image it's probably pretty accurate as well.

    But that's a novice talking, now I'd appreciate hearing from those who know what they're doing. Do these numbers look as though they could be legit to you? I realize without having actually heard the subs yourself you can't make a definite assessment, but in general how do they fair? I want to see if I'm doing this properly, or if I need to go back to the drawing board.
  2. Gordonj Full Audioholic

    Apr 28, 2012
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    Fun stuff for sure. While it is fun to look at dB info it does not tell you the full story. Try using the FFT function. This function will compare the source signal with the information that the mic "hears". That will tell you exactly what the subs are doing verses your source signal. And therefore how the subs are "translating" the source to acoustic energy. Don't forget to delay align you mic to compensate for the acoustic delay verses the electronic noise source.

    That plot you get will tell much about your two subs.


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