I've just bought a pair of vintage Quad IIs and love them. I'm thinking about a speaker upgrade and am considering bookshelf Harbeth or Spendors. I understand sensitivity is an issue with lower power valve amps and note that the smallest Harbeth has a sensitivity of 83. I just wondered if you had a view on this. Love your site by the way, it really does convey your love of this stuff when compared with unit shifting sites. All the very best. Ian
Hello Ian. I would really like to give an uncomplicated answer to this. But it's beyond my capability. I'll explain why.
First things first though, like you I am deeply impressed with the Quad IIs. A classic, in the proper sense of the word. I don't, for commercial reasons, stock Quad. On the other hand, that doesn't stop me acknowledging a major brand who have throughout their existence demonstrated industry-leading integrity. Superficially there might appear to be a sensible correlation between output power of an amplifier and input sensitivity of a speaker.
Ideally of course, and depending on your sonic preferences, you'd either have phenomenal speaker sensitivity, such as horn speakers coupled with a wonderful Class A limited power design such as a Sugden. Again, a brand I don't represent but who produce products I thoroughly respect. Or as an alternative, massive amp power (the Musical Fidelity KW series giving literally 5000 watts RMS into 2 ohms I seem to recall) with medium sensitivity speakers.
The real world, or at least audiophile world sits relatively comfortably between these two extremes.
Err, I'm not helping here am I? Okay, given the extraordinary electrostatic-like clarity of all of the Harbeths, this being a common denominator through the range) people usually find that to get the detail they crave, that they listen at lower SPLs (sound pressure levels) than they would ordinarily.
This is very good news for people like you with wonderful, yet low powered, amps.
So in that specific context I am convinced that the Quads, in a typical UK living room would drive any of the Harbeth range beautifully. But that's not quite the whole story. One of the wonderful and undocumented aspects of the bass performance of all Harbeth speakers is that they have deliberately engineered into them a variable (per model) Q. Q in this context refers to an aspect of acoustic engineering relating predominantly to bass performance.
There are well-intentioned but seemingly endless debates about the relative merits of a high Q and low Q. These arguments all have merit. Suffice to say that Alan Shaw, the designer of all the current Harbeth range has engineered in a Q that varies per model. This very neatly takes into account the potential acoustic environment of the model in which the Harbeth speakers might be used. A 'live' acoustic' would benefit from one level of Q while a comparatively 'dead' acoustic would benefit from a different Q.
I am resisting stating which is the preferred Q simply because these are only guidelines rather than strict rules.
That's why in demonstrations in customers' homes I take a couple of pairs of Harbeths with varying Q factors.
This means that (a) not always are the most expensive ones the most appropriate for the room and (b) explains why there appears to be a curious overlap in models that have fairly close prices in the range.
And yes, I still haven't given you a precise answer yet. Hopefully though, you can now see why me attempting to give you any definite answer would in turn make me either a fool or a charlatan. I hope I'm neither.
The sensible answer would of course be for you to visit here, with your wonderful Quad IIs and experiment during the course of an afternoon. After that, you'd buy your selected pair, on risk-free purchase, to determine if they were right for your room. I hope this has helped, if only a little bit.