At the same time as the Ceespeaker was in-house, I had Michael Børresen's compact 02 towers. Those add a second mid/woofer sized like Acelec's but in a series-filtered 2.5-way array. The relevant point here isn't their obscenely higher price. It's the transformer-less ribbon tweeter. Otherworldly finessed, with zero energy storage and 1/100th of a gram of mass behind which sits an N52 super neodymium motor of the most powerful magnets currently available, it's a state-of-the-art transducer. It's lightning fast and spans the size of about three dome tweeters. The far heavier folded 'ribbon' of the Acelec expands that surface area to 1'260mm², then exploits the breed's documented 5:1 acceleration advantage of squeezing not pushing the air. It's the reason for its air-motion transformer name.
Using the same amp of first Crayon Audio CFA-1.2 then Merrill Audio Element 14, I took the chance to compare treble performance between two such exotic tweeters. On "Schindler's List" from Nemanja Radulovic's Carnets de Voyage | Journey East album on Deutsche Grammophone, these drivers slightly disagreed on his most intense bow action starting at 2:23. With the AMT, the violin's tonality became more forward, glossy and wiry. As I've heard with other such tweeters, they can expose a dynamic imbalance against their chosen mid/woofer or dedicated midrange. It seems difficult to identify dynamic drivers that behave as dynamically vigorous as these zig-zagging tweeters.
Typical domes are dynamically far tamer than lower bigger cones. That's considered well and good because music rarely contains considerable dynamics that high. It's why amplifiers don't care so much about low impedance in the treble. It's when music there does get friskier that the dynamic AMT advantage can rear its head and lead to incidents of minor brightness from unusual dynamic contrast at the top end.
On Des pas sous la neige, Joël Grare plays a clavicloche of 3½ octaves worth of chromatically tuned Swiss cowbells recorded with high dynamic range. If you play back "Battements d'ailes dans le brouillard" over clean low-loss speakers then turn up the wick as though you sat very close, the vertical rises of the loudly struck bells with their first millisecond of upper-harmonic peaks, clear as refracted diamond light, are quite stunning. One feels transported into a Tolkien saga deep inside a mountain where artisanal dwarves fashion enchanted weapons with clanging hammers and gossamer sounds.
On speed as subjectively gauged by how steep and high the leading edges rose to discernably capture the 2nd and 4th harmonic an octave and two octaves above the fundamental, the Danish ribbon was faster. By contrast, the folded Mundorf was brighter and more incisive to have the dynamic advantage. Spinning up "Promenade" from the elegiac Vassilis Tsabropolous / Anja Lechner album Melos on the very protective ECM label [hence only a Spotify not YouTube link] with percussion by U.T. Gandhi, the triangle's very exposed silver strike at 0:17 and later again plus many deeply embedded far gentler recurrences exposed the same difference. With the ribbon, Vassilis' high piano tones had the more bell-like resonance decays. With the AMT, the initial hammer fall exciting the tautly tensioned short metal strings was more vigorous and brassy. The last tweeter of such butch dynamics I remember was Anthony Gallo's CDT III, a cylindrical foil affair with 360° dispersion.
By contrast, the AMT's radiation is far narrower. It concentrates its considerable displacement power in a tighter beam. Playing with toe-in can exploit this behavior and fine-tune its sonic consequence. Ditto the choice of amp. With the Crayon and even more the Merrill, I had two very fast lucid drivers to magnify this extra-dynamic treble potential of the Mundorf tweeter. Ditto these particular choices of music. Unless the speakers were toed-in face on, the electronics dialed for max speed and one went looking for 'trouble' by pulling out the odd score to trigger it, this is simply a very informative quick tweeter. Until last year and for a long time, it actually was my old boss at Meadowlark Pat McGinty's absolute favorite. Now he prefers the SB Acoustics Satori beryllium dome which Madisound sell for $385/ea.
Let's agree how that's being choosy at a most elite level. It's thus nice anecdotal evidence for what it might take to exceed the Mundorf. And, Gryphon's Mojo S [$29'500/pr in 2019] and Kaiser's Chiara [€16'200 in 2014 when I reviewed it] are a lot costlier than the Model One yet drive the same AMT. Acelec, we might say, are somewhat of the country bumpkin in this rather swish club. With us presently living in lost sheep land in the rural outback of Ireland's west coast, I'm allowed to say that. Which brings us to…