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You may have seen this thread over on PR tech talk. ABS Waveguide Thread Dave Pellegrene has a thread about creating some elliptical waveguides using various plastic materials, a heat gun and a pressing method. He has sent me four samples to do some testing on. All were originally created for the Vifa OX20 ¾” neo dome tweeter. All are similar in profile. Two are opaque white and two are clear. Three were trimmed to about a 4.5”x6.5” rectangular face, one was trimmed to an elliptical face shape. Here is a photo of them:
The opaque/white ones are pretty much identical and measure that way. They are trimmed a little differently in the throat than the other two. These continue with the throat curve until flush with the tweeter faceplate. The other two have the throat bored out such that there is a lip at the interface with the tweeter face that is 90º for a distance of maybe 1/8”-1/4” before intersecting the throat curve. I point this out because I think this is the difference we see in the measurements, particularly with the dome tweeters.
Testing was done with waveguides 1-3 with the OX20 and its ring radiator brother, the OT19.
The fourth and clear waveguide was bored out in the throat with a 1-3/8” forstner bit, creating about a 1-7/16” opening and a very sharp edge at the 90º throat terminus. Since it has a larger opening, I was able to test it with the Transducer Labs N26C ceramic, the Airborne soft dome and the RS28F. It was actually too small for the RS28, but due to its sharp terminus, it fit inside of the metal ring around the dome and flush against the metal mesh grill.
Testing was done as described in this post:
Here are the results for the OX20 in waveguides 1-3. All are horizontal off axis at 0-15-30-45 and 60 degrees. Note the cancellations in the top octave of the WG1 and WG2, but not in WG3. Note that WG3 has the 90º bore to the throat terminus and it is different than 1 and 2 in that sense. These are posted in order 1-3.
The opaque/white ones are pretty much identical and measure that way. They are trimmed a little differently in the throat than the other two. These continue with the throat curve until flush with the tweeter faceplate. The other two have the throat bored out such that there is a lip at the interface with the tweeter face that is 90º for a distance of maybe 1/8”-1/4” before intersecting the throat curve. I point this out because I think this is the difference we see in the measurements, particularly with the dome tweeters.
Testing was done with waveguides 1-3 with the OX20 and its ring radiator brother, the OT19.
The fourth and clear waveguide was bored out in the throat with a 1-3/8” forstner bit, creating about a 1-7/16” opening and a very sharp edge at the 90º throat terminus. Since it has a larger opening, I was able to test it with the Transducer Labs N26C ceramic, the Airborne soft dome and the RS28F. It was actually too small for the RS28, but due to its sharp terminus, it fit inside of the metal ring around the dome and flush against the metal mesh grill.
Testing was done as described in this post:
Here are the results for the OX20 in waveguides 1-3. All are horizontal off axis at 0-15-30-45 and 60 degrees. Note the cancellations in the top octave of the WG1 and WG2, but not in WG3. Note that WG3 has the 90º bore to the throat terminus and it is different than 1 and 2 in that sense. These are posted in order 1-3.
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