You probably are aware of the Raal Solaja Audio Constellation, see Rocky Mountain Audio Fest Show Report 4 ?
Aha! so that's how the Raal Solaja works. I saw pictures of it at the RMAF but couldn't decipher what was going on. Thanks.
The ribbon tweeter in the RAAL is housed in one of the tubes and is firing into the side of the adjacent tube. It therefore creates sort of a hybrid omnipole/bipole waveguided tweeter that radiates exactly the same to the front and rear.
I believe Raal has some sort of alumimun piece, kind of like a phase plug, in between the tubes that acts to guide the sound to the front and to the rear. This is probably done to reduce reflections and improve the smoothness of the top octave response.
I did something similar using a wegded shaped piece of plastic running vertically between the tubes, with some felt added to the sides of the wedge in my dome based design to smooth the top octave. I believe this is the reason that the Vifa OT19 measured flatter between the tubes in comparison to the OX20. The OT19 has its own phase plug.
I believe Raal has some sort of alumimun piece, kind of like a phase plug, in between the tubes that acts to guide the sound to the front and to the rear. This is probably done to reduce reflections and improve the smoothness of the top octave response.
I did something similar using a wegded shaped piece of plastic running vertically between the tubes, with some felt added to the sides of the wedge in my dome based design to smooth the top octave. I believe this is the reason that the Vifa OT19 measured flatter between the tubes in comparison to the OX20. The OT19 has its own phase plug.
The distance between the tubes is probably the most critical item, in my expereincem, but horizontal position of the tweeter is also important.
For my version, I experimented with distances between the tubes by stacking thin rubber spacers between the tubes. Also, the tweeter was mounted inside a tube, mounted 90 degrees to the center of the two tubes This allows the tweeter to be slid in and out, closer or further from the opposing tube.
So, for each tube to tube distance, I could also slide the tweeter in an out to find the optimum horizontal position of the tweeter. Each incremental change had to be measured. Eventually, I found what I felt was the best combination of distance between the tubes and horizontal tweeter position for the OX20 that I had decided to use.
For my version, I experimented with distances between the tubes by stacking thin rubber spacers between the tubes. Also, the tweeter was mounted inside a tube, mounted 90 degrees to the center of the two tubes This allows the tweeter to be slid in and out, closer or further from the opposing tube.
So, for each tube to tube distance, I could also slide the tweeter in an out to find the optimum horizontal position of the tweeter. Each incremental change had to be measured. Eventually, I found what I felt was the best combination of distance between the tubes and horizontal tweeter position for the OX20 that I had decided to use.
Very interesting link and use of a ribbon. At 1st glance it looks like it is conventionally loaded between the cylinders, until i looked again. I once considered trying one of those inverted cone type reflectors with a ribbon, and concluded that the shape could be made more wedge-like. I wonder if that would work?
If the dome tweeter was deep enough in the cavity, you are probably right there would be some resonance. That is also a good reason to have it addjustable to find the perfect position that gives the best overall result.
The challenge with a ribbon in this type of design, especially for DIY, is finding one that is small enough to fit inside the tube and not make the volume of one tube significantly different than the opposing tube. You want the paired mids in each tube to see a similar volume. If you can find a ribbon or planar small enough in its rear volume, it has to then be narrow enough to mate with a pretty tightly curved surface. If you're Raal, you engineer your own. We have to choose from what is available, and there is not much.
I do know one guy who mounted a BG neo3prd between the tubes,keeping the back cup on, and not aletering the front face and reported very good results from a listening standpoint, however, I did not see any measurments. One drawback of that is that the tubes would probably need to be furher apart and the further the mid tubes get apart, the more cancellations you get off axis horizintally betweent the mids.
This is why I believe the design is sort of a bipole/omnipole hybrid. As you move off axis, there is cancellation between the side by side mid pairs, reducing output to the sides. Also as you move off axis, there is a reduction in tweeter output due to the controlled directivity of the waveguide.
The challenge with a ribbon in this type of design, especially for DIY, is finding one that is small enough to fit inside the tube and not make the volume of one tube significantly different than the opposing tube. You want the paired mids in each tube to see a similar volume. If you can find a ribbon or planar small enough in its rear volume, it has to then be narrow enough to mate with a pretty tightly curved surface. If you're Raal, you engineer your own. We have to choose from what is available, and there is not much.
I do know one guy who mounted a BG neo3prd between the tubes,keeping the back cup on, and not aletering the front face and reported very good results from a listening standpoint, however, I did not see any measurments. One drawback of that is that the tubes would probably need to be furher apart and the further the mid tubes get apart, the more cancellations you get off axis horizintally betweent the mids.
This is why I believe the design is sort of a bipole/omnipole hybrid. As you move off axis, there is cancellation between the side by side mid pairs, reducing output to the sides. Also as you move off axis, there is a reduction in tweeter output due to the controlled directivity of the waveguide.
My point is if the amp is not good enough, reducing diffraction cannot make much difference. Diffraction does help improve image focus of sound, but the amp has to be VERY good to make the results really shine. Sometimes it's possible that long development time is due to unsatisfactory listening perception, yet the fault may not be in the speakers. High quality speakers are more revealing of faults upstream of the signal path.
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