Playing with Danny Ritchie Style Wedgie Open Baffle Mid Range

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Along with S. Linkwitz, M. King, and John K., Dannie Ritchie has been experimenting with open baffle speakers for a long time. He was the designer behind the Mockingbird LS-X and the still born Serenity Acoustics Line Force speakers. More recently, he has been playing with “wedgies” that are based on the same, highly asymmetric, winged, open baffle concept. This is somewhat different from the small width, flat baffles used by SL, JK, and others.

Mockingbird Audio LSX Speaker System – Mockingbird Distribution LLC

Let's see your OB SW-12-16FR GR Research builds! (And plans for my own)

Scroll down for the Line Force renderings

Tweaking on the new Wedgie (learn about baffle shapes)

The thread above talks about tweaking on-axis response and it left me curious about off-axis response (especially off-axis horizontally) and open baffle cancelation. I decided to make some minor experiments. This point of this thread is to discuss my results, ask you about your experience with type of speaker, and discuss the merits/issues with this approach.

As you can see in the AC thread, the wedgie approach uses a narrow baffle, wings that go back to make the wedge (10 degrees per side outward from straight back), an open top, and highly asymmetric wings. In his latest experiments, DR is using an MMTMM configuration with his own 3” mids and a Neo-3 dipole tweeter. These are intended to sit on top of his open baffle subwoofers and cross over to the subs at about 200 Hz.

I have a couple of Aura NS3 mid range drivers available that would be a reasonable approximation of DR's mids. The Auras have much more travel than the DR mids, so I decided I would only use 2 of them if I were to actually build this speaker. As a quick test, I made up the cardboard baffle shown in the picture below. The sizing of the baffle is appropriate for an MTM configuration using a Neo-3 tweeter. The wings are either taken from information in the AC thread or are just an eye bell guess from the photos. They are not optimized and could be improved with experimentation. That said, the on-axis frequency response isn't too bad, especially considering I would probably cross over to the tweeter at about 3 kHz.

I did screw up in one way. The way I made the baffle meant that I couldn't measure off-axis horizontally beyond 60 degrees. Beyond that and the baffle was unstable. Still, I think we can learn a lot within +/- 60 degrees.

The first figure below shows on-axis response with 1 meter data spliced with near field bass response. Frequency response at a constant angle is shown over a broad frequency range in the next figure. In the next figure, this data is re-plotted as polar response with the on-axis response normalized to the 1000 Hz response. As you can see, the small drivers on a narrow baffle give a very consistent polar response up through 4 kHz. Even the roughly 3 dB fall off at 60 degrees for the 5 kHz curve is pretty good.

Here is where I wish I could have measured above 60 degrees, but I'm pretty comfortable with the polar response using a 3 kHz crossover.

I was able to measure this driver in a large room with first reflections above 9 ms. That allowed me to measure down to about 110 Hz and capture dipole baffle loss. From the graph (1/3 octave smooth), the corner frequency for dipole loss is about 275 Hz. That is a very nice result because it means that the proposed crossover frequency of 200 Hz is only ½ octave below the dipole corner frequency. One other observation is that the slope of response curve below 275 Hz is closer to 10 dB/oct than the expected 6 dB/oct. I can't really explain that one.

Overall, DR's approach seems very interesting. There is some asymmetry in the horizontal off-axis response, but nothing serious, and the overall performance of my eye balled, cardboard baffle shows promise for the concept.
 

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