HOW CAN THIS BE?
We live in a world of rapid change and nominal progress, sometimes even real progress. So one has to ask one’s self from the start how can it be that a speaker that is in effect a modernized version of a design from more than forty years ago is still among the best speakers available. How can the LS3/6 compete in today’s world?
For one thing, while audio has changed, acoustics is a mature science and has been for some time. Great acoustic ideas of the 1960s are great ideas now. Second, the main change in speaker design, with all due respect to developments since, has been in improvements in driver behavior, and the LS3/6 uses modern drivers. The drivers are proprietary and custom-manufactured to specifications for Stirling for the LS3/6. Stirling is reluctant to reveal what company actually manufactures the drivers and I respected its privacy to the point of not pressing the point. But the bass/mid driver in particular, the heart of the speaker, is a superb one, to the degree that it seems to me really competitive with the Harbeth bass/mid driver, which is to say, with the top of the class. (Indeed, if I had not known that Harbeth’s RADIAL material is proprietary to Harbeth, I would have suspected that this material was used, so similar are the drivers in sonic character to my ears.)
It is worth pausing for a moment to appreciate what the seemingly eternal acoustic ideas are that, combined with the superb drivers, contribute to making the LS3/6 a design still among the best of today.
First of all, the speaker covers the whole range up to 3kHz with a single driver. This means that it has a kind of coherence that escapes multi-way speakers with crossovers somewhere around 500–600Hz, say. In the LS3/6, the whole range of musical fundamentals and a good portion of the harmonics of most musical notes emanate from a single driver. Of course many two-ways follow this pattern, but the LS3/6 has a large enough (7") driver and box that it is much more convincing in the bass and the lower mids than small two-ways. While for large music to be played really loudly in very large spaces, one might want to add a subwoofer or two, the LS3/6 is convincing on its own with orchestral and rock music. It will play quite surprisingly loudly without difficulty, and it has in-room bass extension sufficient to cover the normal orchestral range as well as most rock.
Moreover, the box shape—the classic two cubic foot box, a foot square and two feet high—is tried and true. I always like to hazard a scientific explanation for these things, but I am not really sure of the reason that this particular shape and size work so well, but the fact that they do has come rather emphatically to my attention over many years (the BC-1 itself, the Spendor SP1, the Spendor SP1/2).
In addition, the use of two tweeters offers benefits. The LS3/6, like the other related models, has three drivers but two are tweeters, one crossed over to at 3kHz and one much higher, at 13kHz. This idea, which is all but unique to this series of speakers, makes it possible to have a large lower tweeter which is operating with ease down to the crossover point and a smaller higher tweeter which has a wider pattern than if one ran the main tweeter all the way up. Originally, as I understand it, the two-tweeter arrangement arose out of the need to simply cover the whole range cleanly and completely, but in fact there are advantages even in these days when very wide-range tweeters are available.