Apogee Ribbon Loudspeakers vs. Quad Electrostatics (and vs. Cones) . . .
O.K guys, this is a subject right up my alley so be patient with me, this response is likely to be long...
As I have mentioned before on this forum, I am a long time user and an enthusiastic fan of electrostatic loudspeakers - while at the same time I try and keep an open mind and be objective.
I have owned Apogee Calipers and also have access to two pairs of very nicely driven Stages (I like the Stages a lot, to me they are much more lively and 'clearer' than Calipers). In addition, I currently own modified Proac Response 2.5's and a very nice locally built Avalon Eidolon style of speakers utilising state-of-the-art drivers (namely, it's a W.A.R Audio 'Reference Two' see www.warco.com.au ). This is a 95kg ten driver speaker array consisting of a Raven R-1 Ribbon Tweeter/Two 4" Accuton Ceramic mids/Two 8" Cabasse 21NDC Honeycomb Foam Bass units per speaker. The cabinet is 50mm thick and entirely lined with expensive Blackhole 5 & PAD sound deadening material - suffice to say it's about as inert and resonant-free as cabinets get. The parts cost alone of this behemoth is around $11,000AUD, so if it had a typical Wilson Audio or Proac price mark-up, it would probably retail for about $75,000USD!!
I also own three pairs of Quad ESL-57's (for stacking) and with enough spare
panels/rectifier blocks etc to build a fourth pair! I have access to and have listened to mint ESL-63's and Acoustats.
Oh, one more thing...I also own a pair of the thin-membraned "ER Audio ESL-3" Australian electrostatic loudspeakers that Danny/idb talks about above - THESE REALLY ARE 'THE JEWEL IN THE CROWN' OF MY SPEAKER COLLECTION!!
Comparatively speaking, the sound of all these speakers is very different and I like each of them for what they do. But a quick analysis of their sound is as follows...
QUAD ESL-57: A wonderful loudspeaker with which I had a love affair for 3-4 years. First time exposure to the Quad is an amazing mind-blowing experience. They have that superb mid and a boxless, seamless, open window character - the music just sounded natural through them! Ultimately though, it is lacking in extension both top and bottom. The treble is sweet and plentiful but nowhere near as ethereal and extended as the Raven Ribbon, and the bass although quite taut is one-noted (and annoying really)...ANYONE WANTING TO BUY FOUR PAIRS OF QUAD ESL-57's, PLEASE EMAIL ME??
Apogee Caliper & Stages: The Calipers have that great room-coupling effect of panel speakers in spades, with a nice mid and quite powerful bass response. This speaker didn't really grow on me though, I found it a bit soft in the treble and it lacked the requisite 'bite' to pull out micro-dynamic detail. The Stages on the other hand, I like a lot. It is a good performer, reasonably easy to drive, with heaps of detail and good bass. At times though, to me it's not quite as natural sounding as a good electrostat, having a steely character. Nonetheless, it is speaker I could see myself owning.
Proac Response 2.5: This is a classic high quality cone speaker, and deservedly popular! It's got that British BBC Monitor 'musical' character (like Spendor BC-1's which I've owned) but with tremendous bass, an incisive/interesting treble and an ability to fill a room with sound that belies it's dimensions. The secret of this speaker just HAS to be the modern Scan Speak 6.5" carbon mid-bass driver it uses, which is extremely fast and electrostatic-like. The designer Stuart Tyler has also done an outstanding job of the crossover and cabinet design to make this speaker sing! As likeable as it is though, it ultimately does not keep up with a good three way design or panels for detail retrieval.
Martin Logan Aerius: I haven't owned these speakers but have heard them on a couple of occasions. Quite nice, but to my ears the cone bass unit and ESL panel don't quite integrate seamlessly. I also think the membrane is a bit thick in the ML as it sounds more like a conventional cone speaker, and doesn't quite retrieve detail like an Apogee or other ESL’s.
Also, one of the used Aerius's I heard had dead panels. I've been advised to keep away from all secondhand Martin Logans as the metalised membrane they use slowly degrades over time. Apparently, the metal molecules 'float off' the membrane and attach themselves to the stators, a bit like electroplating, and the speaker eventually dies!!
W.A.R Audio Reference Two: This is a SUPERB 95kg/210lb ribbon-cone hybrid loudspeaker, easily beating the sound of the Sonus Faber Amati (@ $29,000AUD) and B&W Nautilus 802 (@ $18,000AUD) that I've auditioned! The combination of Raven Ribbon/Accuton Ceramic/Cabasse drive units in the big Reference Two work surprisingly well to give a coherent, detailed superlative result. The treble is VERY SPECIAL (extending to 45kHz on paper) and is the best I've heard, including that from panels. The speaker overall leans towards a neutral sound, with a superbly smooth mid and tight controlled bass ( some may want more bass out of this speaker, while others will love it for it's boxlessness and lack of colouration). This loudspeaker is probably a lot of people's idea of a 'desert island dream speaker'.

*ER Audio ESL-3: I've kept the best for last, this absolutely fabulous electrostatic loudspeaker is made by Rob Mackinlay, in Perth - Western Australia. Mackinlay is a mechanical engineer from England (working in the mining industry) who has for many years been fascinated by the electrostatic principle, and has subsequently built his own version to improve on past efforts by others.

The secret of Mackinlay's design is the very thin membrane (3.6 micron and the same one mentioned above by Danny/idb) coated with a carbon dielectric solution; close stator spacing for an increased field strength; and a 'curvilinear' frame construction among other innovations. Per speaker, there are two mid/bass panels about 8" wide and 4' long with a central 1.5" wide and 4' long treble strip (like PUR would have imagined, as mentioned above). The treble strip will do up to 25kHz, although the designer has rolled it off at around 20kHz as it gives a more neutral response. The entire radiating surface area of the ESL-3 looks to me to be about 40% greater than a Quad ESL-63. More radiating area in an electrostatic is a good thing with inherent benefits in loudness capability, giving more bass, suiting larger rooms etc.

The sound of the ESL-3 is in a nutshell - fabulous, it is all about...

And just like the designer drug - it is HIGHLY ADDICTIVE.
I can't get the sound of the ESL-3 out of my head...all my other speakers (as good as they are), now just sound slow and ponderous, and they don't hold my interest. Even my mint Quad ESL-57 (Serial No. 52,580, being very late production models as Quad only made 54,000 of them), which previously were a reference point for me (in what they do well), are sounding slow and muddled and don't hold a candle to the Mackinlay ESL-3.
Once you get ultimate transient response like that in the Mackinlay ESL-3, you can't look back! The way the speaker produces detail is incredible, small nuances and inflections in the performer's voice; or in the studio; or the way an acoustic guitar string is struck cleanly - with no overhang; all the individual details suddenly become very clear and delineated from the mix. The imaging is rock solid (better than any speaker I've heard), with the result that the individual players in a good recording are easily discernable and separated from each other... playing their own little song-in their own acoustic space - and at their own pace, rhythm & timing...uncanny realistic stuff!! not hi-fi, not speakers in the room...just music falling out of the air!!

I even prefer the bass note in the ESL-3 to a conventional cone driver. It is tight and accurate, extending quite low with texture and correctness. When I put my cone speakers on now, they initially impress me with their percussive whacks, but after a while it becomes boring and annoying...it's like the bass is slow and doesn't quite keep up with the rest of the sonic spectrum being presented by the mid and treble units.
After extensive listening and comparison between cone speakers and the ESL-3, I've come to the conclusion that the lack of integration and slowness of the bass is probably the main problem facing modern conventional cone speaker designers.

In case you are all thinking that I haven't had the ESL-3 for long and that these favourable comments are an initial euphoric rush on my part - I have to say that I've had them for about one year now and I am still enjoying them immensely.

The ESL-3 is not for everyone, and like all things in audio they are not perfect. They are quite difficult to drive and while valve amps are generally not up to scratch (I have tried 160w/ch monoblocs on them without success), a good solid state high current Class A 'doubling' amp of about 30watts/ch @ 8 ohms seems to be sufficient. They also have some of the usual ESL failings of being one-listener-position dependent (which IMO is a minor matter, after all, our audiophile systems are not meant to be used for background listening - are they!); they have a slight dryness with male vocals around the 200-300Hz region(which in my case is mostly ameliorated with a pair of large Sheldon Stokes style transmission line subs using quality Focal 8K5412 Kevlar drivers); and lastly they do not play real loud as they seem to have a ceiling of around 85-95dB.
(This was checked by ER Audio after this post and was found to be below normal due to a low polarising voltage setting. This was increased with a subsequent increase in max SPL capability – Rob Mackinlay)

To my ears anyway, the Mackinlay ESL-3 is the best loudspeaker I have heard to date if you want holographics, realism, nuance and microdynamic detail retrieval.
The REAL GOOD NEWS is that they can be bought from Rob Mackinlay as a Kit with a very clear and concise CD-ROM construction manual for about $900USD

ESL III “mini” review, posted on the Apogee User Group:

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