I'm not sure if the super-tweeter is sourced from SEAS as they don't have a 20mm titanium dome listed in their webpage. All their Excel series are in 25mm whilst the Prestige series are in aluminium. The titanium is only available in 25mm sizes.
SEAS PRESTIGE Tweeter
http://www.seas.no/index.php?option=com_content&task=view&id=43&Itemid=48SEAS EXCEL Tweeter
http://www.seas.no/index.php?option=com_content&view=article&id=38&Itemid=44In the SHL5 brochure(from Harbeth's webpage), the drive units are described as follows:-
"HF: Custom 25mm ferrocooled aluminium dome ; Supertweeter: 20mm titanium dome neodymium magnet, waveguide face"
"SEAS 25mm HF unit and 20mm titanium super tweeter"
http://www.harbeth.co.uk/uk/uploadfolder/shl5bro1a.pdfNote that they did not mention SEAS 25mm HF unit and "SEAS" 20mm titanium super tweeter. Having said that, they do have inaccuracies in their description from time to time so best to take all that's written in their general papers with a grain of salt.