Uncommon to begin with, ribbon tweeters are prized by true audiophiles,
and this vintage Decca London Ribbon is HIGH up on THEIR list!
Besides the high praise for these you can all over the 'net, you also find
people saying things like "scarce as hens' teeth."
For those (like myself) who are not intimately familiar with this speaker
you may enjoy this page about "A Particular Loudspeaker"
2 DECCA LONDON RIBBON Tweeter with Aluminum Horn
2 DECCA "551285/2" Crossover