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Helium - a true micromonitor

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  • Originally posted by scottsehlin View Post
    There are a couple of key things that using the Dayton data doesn't take into account.

    1. Effects of the baffle. My understanding is that the Dayton FRD files use an infinite baffle measurement. In that case, the driver is mounted on a large (typically 4' by 8') baffle to eliminate baffle effects. The actual baffle causes a reduction in output at low frequencies and some further variation due to diffraction effects at higher frequencies. My driver measurements were taken in the actual enclosure.

    2. Time of flight. The sound coming from the woofer is coming from farther behind the baffle than the tweeter. This effects the way the responses of the drivers sum together (frequency response includes a magnitude and a phase). When I measure, I use a fixed microphone position, then measure both drivers from that position so I capture time of flight differences in the phase information.

    I know there have been a few articles published about how to use manufacturer's data to do a reasonably accurate sim. Paul Carmody did a good writeup at some point that is still on his website the last time I checked. 15 years ago, when I was getting started with designing crossovers, there weren't very many DIY'ers with accurate measurement capabilities, so we used to do a lot of simulations from manufacturer's data. Now, it is quite a bit easier to pull together an affordable and easy to use measurement setup.
    Scott,

    Thanks for posting these comments. I'm in the midst of building your Lithium speakers. I'll build the crossover and, as you did when you were designing, take measurements before gluing everything up since one only gets one chance at the crossover before its permanently locked up inside the cabinet.

    I recently built Jeff Bagby's Quarks. Unfortunately, my measurements didn't quite match up with Jeff's :-(.

    With the Lithium, I plan on following the procedures you indicated above.

    Thanks,
    D

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