OK, you're right, those aren't very useful. I'm more used to looking at the response after the crossover / EQ is in place, at which point the frequency range of interest doesn't include as much of a dB range, so you can see more detail in the un-normalized sonograms.
I'm not saying the PDR doesn't bloom. All I'm trying to say is that the big difference between the two sonograms at 7kHz is more of an artifact from the null. At that frequency, the on-axis response is lower than the next 3 curves, which results in the off-axis being a darker red than the on-axis.
Thanks for running these tests, keyser.
I would disagreeYou could have two drivers with identical off-axis curves, and one of them has a deeper notch on-axis. The normalized curves would show this same difference. Would you describe that as one driver blooming more than the other? I wouldn't. I guess technically you would be correct, but that's not what I think about when I think 'bloom'.
Yes, that is correct. The dipole bloom doesn't seem to be well understood. The PDR, having better horizontal dispersion, acts as a dipole to higher frequency, thus the on axis notch around 7k Hz is more pronounced. As the position moves off axis the effective dipole moment becomes shorter and the peak/notch move higher in frequency. The polar response broaden while the on axis response starts to dip. The result is that the normalized sonograms look more distorted than the actual polar response indicates. This is why I prefer to look at polar plots because the are much clearer as to what is going on. But the bottom line is that this behavior is why I use a wave guide on the NaO Note. It eliminates the on axis dipole dip seen in the naked PDRW response and gives better control of the off axis response.
Since all the links are dead 11 years later: what was the baffle width and shaped used for these measurements?
Nice to see this thread restarted, right around the time I've found new inspiration to see if I can take Rudolf's concept of back-to-back domes to the next level: https://www.diyaudio.com/community/threads/on-the-directivity-of-dipole-tweeters.161299/
I've still got one Neo3W, which I'll use as a reference.
To answer your question: the tweeters were measured without baffle. The images in the opening post have disappeared, but the pdf file can still be downloaded.