ARX

There's a lot of useful information in this thread. To be honest, I've never really cared much for AMTs, but I've always had a weak spot for the big Heils, of which I own a pair. Unfortunately, the diaphragms didn't survive years of abuse in a cafe. IMO the horn loaded twin/stacked ESS AMTs beg to be used in combination with a Bert Doppenberg's Orelo-style horn loaded OB. The crossover point (560 - 600Hz) isn't ideal for multiple 15s, but should be low enough for 4, or 6x 10 or 12". Straight wings with a curved end flare could be used so that the stacked Heils can be integrated. Cheap 12" with Fs: 34 Hz and Qts: 0.59:

Not sure about this one:

Subtle difference:

Such (past) practices and habits also contributed to the bad reputation of horn-loaded speakers in general, not to mention the poisoning of visitors from the magical smoke released when yet another TAD Beryllium diaphragm gave up 😵

This is an Original Klipsch OEM DE75-8P. The "P" refers to Plastic phaseplug. Mine have metal phaseplugs. Newer, or upgraded doesn't always mean better, especially with companies driven by cost efficiency. B&C introduced TN diaphragms to comply with PA requirements. The (glue of the) original Mylar surrounds tended to melt due to the heat generated inside the gap at sustained high SPL. Depending on the horn used, the FaitalPro Titanium drivers can be crossed around 600Hz, possibly even lower with steep slopes. The B&C drivers with Mylar suspended diaphragms are best crossed >700Hz. Salient detail: Danley exchanged FaitalPro drivers for B&C DE880s in the SH96 (non-HO version), apparently because of a high failure rate.

A highly regarded Dutch PA company called Duran Audio - now part of Harman International - developed some loudspeaker systems using the DE75. 25 years after the introduction, quite a few of these systems are still in use today. Especially the mid-high section is praised for its high fidelity. The system shown below was removed from the Johan Cruijff ArenA in Amsterdam.

The original DE75 is still a very nice driver, even though it was first introduced in the 1990's. It's a legendary and game-changing B&C product as well, because its "hi-fi sound" was appreciated by big PA companies like EAW, NEXO and Martin Audio. This is a short and interesting interview with B&C's CEO Lorenzo Coppini in which the DE75 is explicitly mentioned. Personally, I prefer the sound of the DE75 to many later B&C drivers with pure Titanium diaphragm (drivers with the suffix -TN) . Here's a measurement of the DE75 with B&C's ME60 horn (I bought my DE75s for €100 with these horns attached). There's the usual breakup starting just below 10 kHz, but the resonances are pretty well dampened, as is visible in the waterfall plot. For comparison B&C's recent DE95TN attached to the same ME60 horn:

Yours look like this (mine)?

Tractrix or not, with a depth of only 127mm it's next to impossible to properly load the driver down to 500Hz. At best it manages 800Hz, but 1000Hz seems more plausible. The mumbs in the current K510 increase the pathlength (and resistance) and thus provide better loading. I expect the ZXPC 18 X 10 to beat this K510 clone wrt loading and polar response. Last but not least, the throat transition of the 18 X 10 looks a lot better (sometimes a little sanding is required to smooth out imperfections). I am looking forward to Chris' measurements though.

Yes, but the (4) buttocks of the M2 WG serve a slightly different purpose, namely wide dispersion. It's basically a reinterpretation of the old 2344. The mumps in the K510 improve pattern control as well as loading of the driver. The M2 waveguide doesn't load the driver well, because it's very shallow: If you want to manipulate the wavefront in a similar way, but at higher frequencies, you'll end up with something like this:

Sure, here's a link to the later version of this product line. Don't forget to check their loudspeaker processing technology, called NEWTON, which is undoubtedly the most advanced on the market. So far, it's only available for MacOS. This is an earlier version of the same horn top, which is loaded with B&C drivers:

Mumps... Klipsch isn't the only manufacturer to integrate those in horn designs. This is an Italian 2 way hornloaded cabinet from the mid 2000s:

I own the DE-75s as well, but you cannot use these with LTH142, because the throat is too small. You could use a JBL 1.5 exit driver with some sanding of the horn throat > use a drill press with a tapered plug wrapped in fine grid sandpaper. For those interested: This is a clone of the LTH142 for a fraction of the price. The LTH142 is not a constant directivity horn, but it's less 'beamy' compared to a round Tractrix.

In this thread some topics were touched on, that may not be clear and obvious to everybody. This easy to understand AES paper deals with some important issues related to horns, waveguides and drivers. Here's part 2.

I came to the same conclusion through different reasoning and sources, as I don't have first hand experience with K510 or K402. OS disciples are plentiful....that is: among the DIY crowd. To my knowledge OS waveguides were used in only a few professional products from the 1990's. It's rather old news by now. With the advent of advanced modeling and simulation techniques, only fundamental theories remain functional. This is not to dismiss OS waveguides completely, but to put things in perspective.