Why do Harbeth speakers have such a cult following

Interesting discussion. I have a couple of comments:

1) I don’t think Harbeth speakers are popular due to effective marketing or just because Stereophile highly rated them. Anyone who has ever relied on someone else’s ear to guide them most likely had been disappointed.
2) they can’t rock. That is false. I listen to a lot of good rock, Yes, Steely Dan, Gregg Allman, Mott the Hoople and many others. They sound realistic and great. They may not add artifacts like ear bleeding treble or artificial bass, but they are extremely realistic and faithful to the recording.
3) There is no “best” speaker in and of itself. You have to take so many their things (room, personal tastes, equipment, budget..) into account

so I think we are trying to answer an unanswerable question...like how many feet is yellow.

i can say that in my room, with my tastes, a Rega vinyl front end, with Exposure electronics make my Harbeth 30.1s sing 

two last things. I have heard it said that Harbeth speakers are what people choose when they are tied to listening to speakers. That is me. And secondly, with the Rega/Exposure/Harbeth set up. I spend a whole lot more time listening to music, and not my system

Good luck on the search. That is half if the fun.

I listen to rock primarily.  Some of the other speakers I've owned did some things better than my Harbeth Super SHL5 Plus.  My Legacy Audio Focus 20/20s and Klipsch KLF-30s conveyed more sense of scale and dynamics because they were larger speakers with more drivers and greater sensitivity.  They just move more air.  If you want to fill a room with sound and really rock out, those are great speakers.  Where they lose out to the Harbeths is on clarity and neutrality.  Instruments and voices tend to get pushed together more and at those higher volumes they can start to lose cohesion and start to hurt my ears.

Now that I'm approaching 60, the kind of rock I listen to is more stuff like Steely Dan, Pink Floyd, Jimi Hendrix, Santana, Steve Miller, etc.  I am not usually listening at high volumes, and I enjoy the nuances of hearing every instrument clearly defined and listening to the words and musicianship more than ever.  Which isn't to say that I haven't played some Iron Maiden, Tool, AC/DC, and the like through the Harbeths.  They can rock and can go loud without the harshness of many other speakers.  Having 4 subwoofers assisting them also helps make up for the smaller size of the Harbeths and gives things more of a "live" feel.  

I get that what sounds harsh to me can be appealing to many. I belong to a local music club.  On a number of occasions we've listened to a system consisting of either a Primaluna integrated or Anthem Integrated and a pair of Klipsch La Scalas.  I love Klipsch speakers, but the La Scalas hurt my ears at higher volumes.  When we cranked them up I couldn't wait for it to be over.  The other guys all loved them.  When I first heard a pair of Harbeths I fell in love with the sound and agree that there are some trade offs, but overall they do so many things right.

Certainly my favorite speakers in this line are the speaker model(s) without ports. I also favor the 2 ways due to the simpler crossovers. 

I agree that the Harbeths do as well on rock as they do other material. No speaker worthwhile does any type of music better than another. Aside from SPLs of course in which case horns are your best choice.

harbeths are more popular today than it was 3years ago.It was easier to sell them this year than 3 years ago:) 
Shl5 might lack body if they are in big free space .
If harbeths speakers are new ,they can sound bright and lean.Some people in this forum confirmed it.
Highs on shl5  sounded strained compared to dynaudio esotec and esotar or planar horns tweeters
Vocals ,dynamics were good on them,but horns speakers beat hartbeth in this area

I am constantly comparing live sound to reproduced sound - lifelong habit.  I often close my eyes and listen to voices around me just to take stock of the character of real voices, and note how they differ from reproduced voices.   I usually close my eyes in the presence of live instruments to do the same (e.g. just yesterday upon encountering a group on the street corner: drums, stand up bass, sax).  Same when I play my acoustic guitar, or piano, when my sons practice sax, trombone... 


When I do I perceive certain tonal qualities often more like tonal color.   When I close my eyes in the presence of most sound systems, they just sound wrong.  Voices, instruments may be dynamic, detailed, whatever, but the tonal "color" timbral match just isn't there.  Tends to sound artificial, steely or plastic, or just like someone has dialed the color dial a bit off on a TV.  (I also do this at audio shows - when a nicely recorded vocal is playing it can sound impressive in of itself, but if I close my eyes to directly compare it to the real voices inevitably talking nearby, the artificial nature of the reproduced voice sticks out compared to the fleshy, organic nature of real voices).

Harbeth were one of the very few speakers that survived the "closed eyes" test.  That is: eyes closed, they seemed to produce the right tonal/timbral qualities I get in the presence of real voices and instruments.   And they survive much better than many others the direct comparison to real voices.  They get something fundamentally right about voices that most speakers don't get.  IMO.  (Some Spendor speakers also do this).
I think this is how a lot of Harbeth owners feel.  That to their ears there is a particular "rightness" - where acoustic guitars, trumpets, sax, all sorts of instruments seem not just vivid, but timbrally accurate, right and natural.