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Get familiar with the reaction system: Introducing the Reaction System

Behind the 8 ball

That's what I'm calling the little speakers that I had at Indy, for the simple reason that the Nd140Pr on the front looks like a "Magic 8 Ball" and the active woofer is mounted behind it, so.....I had to name it something. It consists of a Dynavox LY302 in a seal enclosure and a passive radiator bandpass using the ND105-8 as the active driver. For all of you fullrange purists who believe there should be no passive components in the signal path, just stop reading right now and head over to a different post, because these guys took a boat load of parts.
I usually don't comment on how my designs sound, but in my opinion these sound bigger than they have any right to, and I was pleasantly surprised by their outcome, as I wasn't really expecting much. My intention being to have fun with a simple, unusual build, that used up some more parts on the shelf.
Here's some construction picks.

Bottom view

Front minus fullrange cut out



  • This is what they look like without the grill cloth.

  • I'm too old to have hearing that's capable of hearing the rise on the extreme top end, and as a matter of fact I think EQ was the only person in attendance that could hear it, thanks to his 19 year old ears. If you're Reading this EQ, it was nice meeting you and I enjoyed our conversations, hopefully you'll be able to make it here again from Singapore.

  • I've been wondering who would be the first to use that Dynavox. It got a great review a few years ago from Tim Feleppa when he tested it. Is the waveguide to control directivity or more to align the drivers?

  • It's to not have the grill interfere with the response too badly.

  • Ben is correct, I had to use a waveguide because that phase plug looking thing in the center of the cone is actually part of the cone, basically a dust cap that protrudes beyond the face of the driver. The waveguide accomplished spacing the cloth out away from the "dust cap" and it provided some gain, which I could burn off to most likely lower the distortion a bit.

  • Those sounded so good! Totally neato design, Nick👍🏼 Also, glad to hear the big ol monkey coffin units up on "stands" (thanks Craig!) Superb build right there.


  • Who doesn't like a nice bottom.

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