Hi all,
I have had the fortune to test a large number of drivers and horns over the years. There are of course many very good combinations with new being added all the time, but its just about time and money "find" to the perfect combination. Some experience and knowledge also comes into play...
Disregarding the fact that you need access to the actual units it is very time consuming to measure FR response on and off axis, distortion and horn load on large number of driver/horn combinations.
Regarding JBL large format drivers on the newer JBL wave guides (VTX, M2 & 4367) , all designed for the JBL D2, I think it is just cheer luck that they are such a perfect match. There are so many parameter that comes into play but the phasing plug seem to be the perfect design and distance to the wave guide throat turns out to be more or less optimal. Some other drivers do need a spacer to work reasonable.
If we disregard potential sonic views the large format JBL drivers on these new wave guides, they objectively measure better than most other driver/horn combos that I have had the chance to sample. Later drivers (incl 243X), even large format as 2453, does not show equally good coupling between driver and these horns. 2447, 2450SL, 2351, 476XX are just great on these waveguides.
Using coated SL diaphragms also contributes to the very pleasant combination. The coating (Aquaplas) reduces the ringing common in metallic diaphragms over 2-3k. Ti and sometimes Alu can be perceived a little harsh and give some "listening fatigue" even if EQ'd correct.
I also have JBL large format Be drivers here (now on M2 wave guides) and albeit one can potentially hear a very slight difference on a good day the fact that they "fall off" quicker requires more intervention in the filter to push them up 20k. JBL solved this in the K2S's by adding a small tweeter driver/horn, 045, and so did I. I do prefer that combo compared to push the Be's, even if its a fully active DSP setup. Just sounds more at ease.
With that comes the drawback that a 3-way system is much more difficult to get right. Given that this sport is all about compromises, I almost always prefer 2-way systems over higher order . The plain SL diaphragms in combo with a good DSP gets the large format drivers to 20k without any problems. Nice.
Having shelved out the money for BE drivers myself, I would say that IMHO it is not worth the potential improvement over SL's. And a 2-way is significantly easier to bring to success.
When you get to this level of sonic performance these speakers are not just drivers in a cabinet with some electrical stuff attached, they are integrated system where every piece contributes. Having built many full DIY systems over the years I have, as many others, come to the conclusion that it is to complicated to build from scratch. Now we typically find very successful speaker systems and tweak them with proven alterations that could have come from the factory but mat have been omitted for cost or marketing reasons. Hence building clones on 4367 but adding the large format drivers drivers from the K2S series, which would have brought factory 4367 out of their intended price bracket. Adding active setup inspired from the M2's also adds proven technology that could not fit in the price/customer bracket targeted for 4367. If these indeed are improvement or just alterations is in the eye (ear) of the beholder.
Regarding the wave guides in M2 vs 4367, the the M2 is more difficult to integrate in a residential settings due to its (almost) 90x100 dispersion. That gives lots of floor and ceiling bounces in a normal home. This is less critical in a controlled studio environment. I had a difficult time to get my M2's to work in my room. The 4367 fair much better in my room. My 4367's are the same setup as member Beatelund, with large format driver and full active DSP setup ala M2.
The 4367 wave guide is wider and hence load the driver deeper. I would say that the 4367 provides an additional usable low end of about 100-150Hz, compared to the M2. That extra range may be easier to exploit with the large diaphragm 4" drivers that can be used down to about 500Hz (in 1,5" exit drivers) on a sufficiently large horn.
I think the reason that we like the active DSP 4367/large format horn/driver combo is probably due to that we could lower the XO +100Hz (as member Beatelund pointed out) in the very sensitive mid range where there is a lot of voice and instrument energy is. Moving that that range from the woofer to the driver changes the sonic composition quite dramatic. At least we like it.
Much about little
If someone would be interested in measuring data, for private use only, just give me a shout
Rock-on
//Rob (aka "sebackman")