It will depend on what people consider a resolving speaker. You can have resolution related to detail, dynamics, localization and nuance. Sometimes a loudspeaker which excels in one of these aspects is not the best in the others.
Micro, could you expand on your interpretation of resolution? What I had in mind was the ability to resolve fine micro detail across the spectrum.
Sorry for the delay in coming back to this sentence. The main question was resolution - the minimum change that the system must experience to generate perceivable output difference. The thread quickly degenerated in a detail oriented debate, especially after the (IMHO!) misleading image analogy was introduced.
Again IMHO speaker resolution is very strongly dominated by psychoacoustics - our brain recognition capabilities play an important part in this task. A high resolution speaker should have characteristics that make us focus with less effort in small changes that make us perceive something different.
Decades ago, most box speakers were so colored that electrostatics and panel speakers easily created the myth that they had intrinsically better resolution because of the lower mass of the membrane and lower stored energy in it. Although most panels have high resolution, we find that their resolution is very variable with the level they are playing. Although I have owned (and still own ) several specimens of Quad ELS57 and ESL63, and agree they would easily deserve the epithet of high resolution, they were not the more detailed speaker I have owned – this epithet is by far deserved by the Swiss mini monitor Ensemble Reference loudspeakers with the matching stand. But their resolution in micro and macro dynamics gradation was not on par with the Quads or the Wilsons. Surely the electrostatics had limited dynamic range – but if you accepted the risk of pushing them, they had great macro dynamics before dying. The capability of the speaker to separate the natural occurring layers in the music can also be considered resolution. Some speakers make an amalgam of sound – everything seems mixed together, although detailed and with good image. Other excel in depicting that separate entities have intrinsic properties – either by directionality, decay or power they emit. Excellent imaging can also help a lot in speaker resolution – my short experiences with MBLs have shown that when everything is perfect with these speakers have unique properties in this zone of defining the zone of influence of each performer.
My suggested tests for resolution:
1. Detail resolution – the horse flies and water flow noise in track 10 - 4’26’ of Gregorio Paniagua La Folia.
2. Dynamics resolution - Iannis Xenakis Pleiades - Les Percussions de Starsbourg – each of the six percussion instruments has different dynamics
3. Localization – Claudio Monterverdi Vespro della Beata Vergine, La Petite Bande, Sigiswald Kuijken – you must feel the stage and everyone on it. When the singer sings to the tuned back to you, you should feel it – it is not only muted.
4. Nuance – Shostakovich Piano trio nº2 Glinka Quartet. The connection between the performers is established by the subtle nuances of the players of this mono close milked performance. Most speakers can deliver a boring performance.
Just one concluding remark – the resolution is a system property, some times created by the synergy of the system. Changing source, electronics or cables can strongly affect our perception of the resolution of the speaker.