I made a slight error in my post above. The Velocity Dyads are like a heavier duty A23 (Dyad=525g and A23=450g). They are 1mm wider. Both are twin chamber designs.
When I mentioned the triple chamber design, I was thinking of the Atlas @620g and 25.4mm wide (1").
Interestingly Velocity does not show the Dyad in 700c in their Clyde/Athena section, but does have it in the tandem, touring, and cyclocross sections.
Their Twin Hollow @ 545g (27" only) is most similar to my old 27" Weinmann concaves.
Sorry for the mix-up.