BillFitzmaurice.info

It has been a while ago, but I've build my T39's and Optop12J's! Still playing with EQ settings, but so far they sound great and can go very loud.
The only thing I'm missing is high tones off axis. The CD's in the Otops have narrow dispersion. Great for long distances, not for small spaces or near stage.

I know that there is the piezo option... they might sound okay, but my biggest concern is reliability.

Is there a way to use CD's or other great sounding reliable units and have a wide dispersion?
There are wide dispersion horns on the market, but they are not high enough to fill the whole cab. But, if it's for only the bottom Otop, would it be okay if I but that horn next to the top of the cabin? Then it still couples to the top above.

The CD's in the custom designed horn should have around 100 degrees of horizontal dispersion, provided you built them as per plans with the diffraction rod.
That's 10 degrees better than most commercial variants, and off axis response should be pretty good at 45 degrees as long as the cab stacks aren't overly separated.

If you do have wide mains stacks, it might be worth thinking of an extra Otop12 as a centre fill.

The melded array has 120 degrees of horizontal dispersion and is only a couple of dB down from on axis response, at 45 degrees.
The main reason piezo's get a bad rep is they are often used alone as single units.
As single units they are often considered harsh and unreliable.
The melded array combines large numbers of them, series/parallel wired to increase power handling.

I have DR250's, and my melded arrays have been solid to date.

The usual recommendation would be to build melded arrays in the lowermost used cab each side, and use flat arrays or CD horn in cabs above that, so that's a thought.
Or use the increased power handling of the NSD equivalent and change the crossover, which may or may not work to your satisfaction.

But a melded array Otop12 as a centre fill will absolutely fill in the middle, it may even be to much, requiring it to be turned way down.
A little toe out on the mains + centre fill will present a wall of highs...

This is the only thread I could find claiming a blown piezo (turns out it wasn't)
piezio sounding blown

Here's a review from someone who switched from CD to piezo array.
DR280's....from 2" comp drivers to cheap piezo's......

The other google search results for "blown piezo" on this site were about being "blown away".

A note on Dave Perry's post. Back in 2007 the DR280 was the piezo version and the DR290 the compression horn version with the same low frequency horn. With the last revision both versions were put in the same plans.

Well, I will probably go for a melded array then... Thank you all!

Seth, thanks for posting that old review from Dave Perry - very insightful. Never had run across it when perusing the archives.