OK, those bass drivers are ARO 9408 made by Tesla in Czechoslovakia around the mid to late 50s.

So there is a full compliment of vintage drivers with the common traits of paper cones, alnico magnets and high sensitivity. This will make for a well voiced, coherent sonic output over the entire frequency range. There in no problem with foam support rot which bedevils later old drivers, as in the 50's the drivers were made to last almost forever.

The sound will be 'relaxed' detailed and beautiful, particularly when married up to valves.

These speakers are very much a DIY project and from a wonderful start, can be considered a work in progress, with the ability to improve on every element. All parts are available still, and if you are like me, much of the fun is in being able to understand and improve them if you wish whilst being captivated at every point.

They work fantastically well with most genres of music except heavy rock head bashing. In particular Jazz, Irish, Country, 60s pop, Club Dance, Reggae and Dub music - this for me incudes Dire Straits, Leonard Cohen, the Shadows and Bob Marley.

Heavy Rock is compromised in OBs due to an indigenous lack of very low frequencies, but what there is in the bass is real and full of impact.

In summary a wonderful pair of speakers.