True, there used to be quite a few coaxial speaker arrangements. If I remember correctly, what Tannoy did that was unique was to have the woofer cone flare act as an extension horn to the the coaxially mounted tweeter. If they did have a Patent on it, it's long expired. KEF, TAD and Thiel all have expoited this basic concept. The KEF Reference 20x/2 high frequency driver is a particularly good implementation. Look at the smoothness and uniformity of the 207/2 on and off axis frequency response plots over at Stereophile. About as good as it gets.