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POC 3 TH upgrade - linearity tests

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  • POC 3 TH upgrade - linearity tests

    I had the opportunity yesterday to perform some linearity tests on my POC3 tapped-horn that I recently upgraded (swapping out the Dayton PA310 driver for an Eminence 3012LF-4 driver). I tested at various input voltage levels (3dB steps) all the way up to 40 V (the HornResp sim says that it would be beyond Xmax at this voltage level). I like the results, as they show one of the main advantages of a good TH alignment - no "port compression" effects at high output levels. The TH output remains linear at low frequencies all the way up and beyond its sim'd linear voltage maximum. The graph does suggest some non-linearity at 40V above 50~60 Hz, but I think that's because the mike was getting overloaded at that point (REW measured signal level was into the red). I may repeat the tests at some point to confirm whether or not this is the case. Note: the FR slopes down after ~100 Hz as the TH was driven by I used a car audio amp with undefeatable LP filter set at 200 Hz @24dB/octave, and the source was a car audio deck also with an undefeatable LP filter (200 Hz @ 6dB/octave).

    ​I'm going to put this upgrade generally in the PLUS column. The 3012LF is significantly more expensive than the PA310, and appears to suffer from more motor noise (the pole vent, the main source of the noise, is tiny, compared to the one on the PA310), but it is capable of more output in the same alignment, and the resulting box is lighter to boot. Hopefully it doesn't end up suffering from the cone-sag that my PA310 seems to have come down with after being mounted facing up in my POC3 TH for a few years.

    Brian Steele
    www.diysubwoofers.org
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