Criterion ESL tweeter project??

Hi

I picked up a pair of older Criterion es85s and have just started to play with them. They originally came with wimpy extended range 8" woofers which I just replaced with some Infinity woofers(Vifa I believe)
The sound is really quite good and the tweeters have that air and crispness that I find very appealing.

Im wondering if placing the tweeter drivers in a line will work better than the current configuration (Im assuming that cabinet size constraints helped dictate the layout) OR if I could mount a nice 3" FR driver in the middle of the tweeter. Sort of a reverse coax design.

Any thoughts are welcome. BTW, Im going to go through the xo/transformer and replace caps etc. Not sure yet the crossover point but I think that the woofer is run FR and the ESL is just cut off.

amt
 

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Yikes! Those ESL drivers are spaced apart by a distance that corresponds to multiple wavelengths at the upper end of the band, both in the vertical axis and in the horizontal axis. There will be severe lobing in both axes (peaks and dips as you move around). It’s doubtful that there is any one axis that has a flat response. I’ve never seen this model before, but it is most unusual to see this kind of thing in well engineered modern products. Your instinct about putting the ESLs in a vertical line might be tried, although there doesn’t appear to be sufficient height on the front of this box. Your “reverse coax” idea goes in the wrong direction regarding wavelengths vs. spacings, so I wouldn’t pursue that. If the ESL drivers appear to be intrinsically decent, I might be tempted to redesign the whole speaker with a small midrange above the woofer (in the box), as you suggested, and then to put the ESLs in a separate frame in a vertical dipolar line on top of the cabinet for the highs only. This means what I just said, a new design, which isn’t easy. Can you tell if the ESL drivers are push-pull and are they open on the back side?
 
Brian,

They are monopole and only radiate one direction. The odd spacing does create strange effects and the sweet spot is not only in the vertical and horizontal, but also with regard to distance. But the high frequencies seem to be intact with a problem in the middle freqs. A hole exists and is probably due to the woofer Im using rolling off way too soon. I plan on building new enclosures and using different woofer(s) so the best utilization of the tweeter is my main concern.

If I mount them in a vertical array, how much will the 2" gap between each driver effect the sound? I can cut off the 2" plastic tab if needed, but then I will have to devise a mounting scheme. Then would a woofer next to the array be best or maybe a MTM affair?

amt
 
Oh, monopoles, huh? Interesting. There are bound to be some cavity resonances too then. But many dome tweeters have the same problem. They’re probably single-ended as well. But if you like them, they’re probably worth a little effort. Now, are you saying that those flat black areas in the corners of the square array are attached to the ESLs as flanges? The picture doesn’t make that clear. It would be preferable to stack them vertically with the skinny dimension in the side-to-side direction, if those flanges can be dealt with. And do avoid the 2” gaps as those discontinuities will make lobing/grating pretty bad. If the flanges prevent such mounting try a vertical stack with the long dimension sideways. This will limit dispersion in the horizontal direction, but no more so than some commercial ESL designs. You could set the vertical array (either orientation of the drivers) in a slightly bowed arc (convex) to broaden the vertical dispersion since this line array is not very tall. Make sure to cross these ESLs over at a high frequency, since, if they are single-ended, they won’t handle much voltage. They are probably already crossed-over at some high frequency as you said. It’s no surprise that there is a hole in the middle of the frequency range since an 8” driver and these rather fragile little ESLs will have a hard time meeting in the middle. A mid-range cone may be needed. If you have to build new cabinets and add new drivers and a crossover, you may be stretching beyond what these drivers are worth. In that case, you may want to consider making your own ESLs, perhaps ones that will work at lower frequencies with less distortion. There are plenty of references in this forum. Keep us posted.