"> sound striking the curved surfaces of the pipes is reflected over a wider angle than if it struck a flat surface <
Doesn't this depend on where they're placed? I see these things in photos in many different places - right in front of the speakers, off to the side (where no sound will reach them), near the front wall (again where little sound gets to), and so forth."
Does what depend on where they're placed? There are no soundwave free zones in a normal room. Wherever these things are placed in a room, some soundwaves will be falling on them, and those waves will be reflected over a wider angle. The only question is what soundwaves are falling on them. Yes, they are placement sensitive, both because distance from a reflective surface will have an impact on their effect and because where you place them determines what sound will fall on them. If you want them to reflect some of the early reflection path sound, you need to place them where that sound will strike them and you have to play with their angle in order to direct the reflections where you want them.
"Has anyone measured their room's response and ringing with and without these things in place? Has the original manufacturer ever done this? I've looked in the past for such information and never found any."
I said I hadn't measured them. I don't know of anyone who has. All I have to go on is my own experience and I said that up front. I'm not going to apologise for that fact.
"Again, I'm not saying they make no change in a room. I just can't see how any change they'd make could be for the better. But if I'm wrong, please educate me! However, I'd much rather see hard dĎk than read subjective opinions."
I can only say one more thing over what I've already said. You say "I just can't see how any change they'd make could be for the better…" I'm not certain what 'better' means here. We all know that people sometimes like things that measure worse—tube amps are a good example, and there's a hell of a lot of personal taste that flies in the face of measurement when it comes to speakers. I'm not saying that measurements are useless because they aren't. They do tell you what's going on. It's just that I don't think they're necessarily all that predictive of how we're going to feel about the sound. I've had DIY room lens units in one form or another for something like 5 to 6 years now. In fact, they were the first acoustic treatment I played with and they were chosen in part because of their relatively small size which was important in the smaller space I had back then. I wouldn't regard them as having as noticeable an effect as my bass traps or my 2 panels, and they wouldn't be the first thing I would recommend to someone wanting to treat their room, but their effect is noticeable. I've played with positioning and unit configurations and I've had them in my room and taken them out. They're in the room at the moment and I have no desire to remove them because I prefer the sound with them to without them. In fact, I probably won't remove them unless I need to stick some furniture into those corners or I decide to treat the 2 corners where they're currently located in some other way. I could use absorption and put bass traps there but there's already a fair bit of absorption in the room and I think a bit of diffusion is a positive.
David Aiken