Boy is that reviewer a lousy writer. I assume the photos showing the differentiated woofer and passive radiator diaphragms are out of date, as his description of the woofer diaphragm seems to conform with the more recent Thiel website photos showing it looking just like the passive, that is to say not dished.
He seems not to have heard any current Thiel models for quite a while. As Unsound said, some of his caveats about past Thiel models' sound seem a little weird, to the extent that Thiels have typically offered an acceptably wide sweet spot due to their wide-dispersion design, and I've never heard the bass described as being slow on any Thiel. (Obviously it's not news to say many people have objected that Thiels can sound bright, which they can, for reasons we needn't go into again.)
Prior Thiels not using a coaxial M/T do have a narrow vertical sweet spot however (true of any multi-driver first-order array), and since larger Thiels have featured strong bass using low-impedance woofers, it's possible to result in an overdone bottom end response with the wrong room/speaker/amp combination. But it's true, as he found, that the 1.6 is a sweeter-sounding, less-demanding (and somewhat less critically revealing) Thiel.
