Quote Originally Posted by John Mallett View Post
The b139's bass units have quite a wide alloy surround which i notice some don't have.
These will be the earlier bass units as Spendorman mentioned The driver parameters are pretty similar, the only difference in a more major way is the power handling. They might be happy up to a maximum of 50W RMS amplifiers, the later thicker chassis unit which was smaller & had slightly pointed corners (rather than being a true oval) would be happy with up to 100W RMS fed to the system as a whole.