Line Source Compression Driver Horn

[AcousticScience]

I've heard the vertical dispersion of the diffraction array is 60 x 90 degrees which means when you stack boxes there might be a bit of overlap.
I've also heard Bill Fitzmaurice advises against stacking co-axial horn designs because the tweeter spacing is too far apart.
What's the difference between this then and a standard 60 x 90 co-axial horn especially on designs that use two of them vertically?

To get line arrayable treble you need a horn with built in path length equalisation to control the vertical dispersion like this https://www.ebay.com/itm/Line-Array-Spe ... 2850588990 which would be a pain to DIY. Danley's goal is similar with his paraline "lens".
I understand that the piezo tweeter versions approximate this better by having lots of tweeters close together to roughly approximate a line source and I could tell from listening to a someone else's tops that this did control the vertical dispersion well.

How does the diffraction horn control interference any better than just a coaxial 60 x 90 cd horn in the middle of the tops?
I had two of my omnitop 12s stacked and one rotated slightly and you could hear a bit of a seam between tweeters but it wasn't that much of a deal breaker. You could probably hear more combing if they were in a J-Array and you moved backwards. Stage stacked line arrays are probably the least interference problem as you are almost always the same distance between boxes.

[Bill Fitzmaurice]

It's not so much the distance between the elements that's a problem with coaxes, it's the distance between the radiating planes, ie, the horn mouths.

You could probably hear more combing if they were in a J-Array and you moved backwards.

The further back you go the less audible it would be. If you're close enough you can hear the separate drivers as separate sources, but their separate wave fronts combine into a single wave front at a distance.

[AcousticScience]

It's not so much the distance between the elements that's a problem with coaxes, it's the distance between the radiating planes, ie, the horn mouths

With the standard diffraction horn though, even though the physical horn is column shaped and spans the entire height of the cab, am I right in thinking that sound will exit the centre of the horn first, creating a curved wavefront in the vertical? Whereas the line source horn will have sound exit from all point of the horn at the same time, for much tighter vertical directivity (this is approximated better with the piezo array and its 2" spacing of hf elements). This is what you want for a J-Array so most of the highs are heard from one box at a time in the nearfield, reducing comb filtering. Now obviously it is hard to DIY such a horn.

You could probably hear more combing if they were in a J-Array and you moved backwards.

The further back you go the less audible it would be. If you're close enough you can hear the separate drivers as separate sources, but their separate wave fronts combine into a single wave front at a distance.

True, but I'm talking about the changes you hear as you walk from the coverage pattern of the bottom box of a J-Array flown way above head height (close to the stack) and backwards. As speakers higher and higher up the stack become pointed at your ears, you might hear a bit of interference between box "seams". When you are really far away (the back of Glastonbury festival) you hear most of the top boxes at the same time and there is little interference pattern.
A stage stack line array at ear level and with no J, you hear all boxes at the same time unless you are practically within kissing distance, thus especially at far field the destructive interference is negligible and you hear less interference total unless you moved up to a raised balcony at the back of the venue.

[Bill Fitzmaurice]

If that's what you heard I chalk it up to operator error. I've never experienced it with the systems I've heard, and I've heard quite a few, when I worked as the sound monitor at an 8,000 seat outdoor amphitheater. One of my duties was to check levels throughout the venue, so I wandered the entire grounds. The only time I heard, and measured, level and response anomalies was circa 2004, when there was still an occasional cluster array in use by acts that had not yet upgraded.

[AcousticScience]

What speakers were used at the 8000 seater? Was it DR200, 250, 280 or 300 or OTop J? Piezos or diffraction horn?

Or was it a commercial brand? If so I guarantee they were using horns like the link above so as to obtain laser beam directivity in the vertical and yet wide horizontal dispersion, which is why you heard the fantastic results you did. Piezo arrays should also do quite well or anything that limits vertical dispersion to 10 degrees. Usually the line array horns have multiple tunnels to try and simulate a column of closely spaced compression drivers rather than one in the centre, thus getting better hf coupling. Narrow vertical dispersion designs are the rule for line array tweeters.

As an aside, I've found my Omnitop 12 to be somewhat directive in the upper mids, which are the first things to attenuate if I move below or above the speaker. I've heard the piezo type and they were much more directive in the vertical just as I thought.