First of all, let me start by saying that I do not intend to bash PSB in anyway, they are genuinely good speakers for the money. I just want to share my findings in a way that, hopefully, they can constitute some food for thought. I don't believe in a forum where there can't be different and sometimes, opposite, opinions. Otherwise, what's the point?!
So, after learning the fundamental findings from Dr. Toole's research, the next logic step for me was to try another loudspeaker company, other than Revel, with the exact same design philosophy in order to see if I could find something markedly common or clearly distinct to either sonic signatures, namely to Revel's Concerta2 M16.
And, PSB it was:
Acoustic Research Makes the Difference Through many years of research at the National Research Council Canada (NRC), home to one of the world's most advanced acoustical laboratories, our design team at PSB Speakers has learned not only what people love to hear, but also how they hear it in a room. Critical to the Imagine X design is this research into human perception of sound using double-blind listening tests. Double-blind testing removes any listener bias to give us the most accurate test result. It allows PSB to understand what is most important to listeners and allows us to create the ideal blend of performance and price for every application. In 1974, we were the first company to use the NRC for loudspeaker development and we remain the most active user of the facility today. Our experience with the NRC, how we interpret the data and implement it into the design of our Imagine X speakers, sets us apart from other speaker manufacturers. It has allowed us to focus on our primary goal—delivering real sound for real people.
"By conducting carefully controlled blind speaker tests, then measuring all the speakers to see what sonic characteristics appealed to the listeners in the tests, we were able to figure out what matters and what doesn't." - Paul Barton, Founder and Chief Designer
After listening to the PSB Imagine Mini and Imagine XB in my small room, I can confidently say that there is a common trait to them and to the Revel Concerta2 M16 (except for the Mini's clear lack of bass output) which is, for lack of a better word, sterile sound. They all have the toe-tapping factor, they are fun, but they also are sterile sounding and more clearly so when compared to the LS50s.
The culprit here can't be their spinoramas, I'm sure all these speakers measure quite well in that department, therefore I strongly suspect of their electrical high-order crossovers instead and the way they are voiced.
KEF with their combination of 1st and 2nd - order electrical crossovers managed to acheive something really special.
I guess that PSB like Revel are so obsessed with high SPLs that they always feel the need to shut-off the diaphragms as soon as possible in the crossover region to better control them and theirs dispersion characteristics when they become stressed from higher displacements at their lower operation range or when they become more directional at their higher one.
I've always had the impression with high-order slope crossovers that the so equipped loudspeakers sound unnatural and that 2nd-order (12dB/octave) electrical crossovers are, in general terms, a better compromise. Of course that, in order for this to be possible while keeping the speaker's high SPL ability, different and better materials should be used in the transducers. (It's very interesting to see that PSB already uses carbon fiber in the midrange transducer of their Imagine XT2 model but instead of relaxing the crossovers's slope to the tweeter they opted to extend the former's operation range, increasing the crossover point from 1.8kHz - which is incredible low - to a more sensible 2.2kHz).
I'm just pointing out spinoramas alone are definitely not the answer. Sure, they play a big part but there's a missing link. Maybe some contexts can expose it better than others. Just sayin'...
When I say sterile, I mean that some cues about the instruments and voices reverberant space are lost. Sterile is not equal to accurate in this context. I'm not talking about euphonic colorations that please the ear/brain, which is the opposite to accurate timbre, nor I'm talking about timbre alone. Timbre is correct in all of them (as the spinoramas will indicate), but with PSBs and Revels there is some unnaturalness in their presentation.
If there's a way of getting as good as spinoramas can possible be using less complex crossovers, with fewer electrical components, then that can only be a good thing. And, that's possible. KEF is just an example of a manufacturer doing it.
Do their loudspeakers go as loud as PSB's or Revel's? Probably not. But, how loud is it necessary for a loudspeaker to go in a room with traditional source materials?