This is a NOS speaker from early 2000's... It was installed into a cabinet at the Marshall factory and then removed due to production changes(which is not that uncommon in amplifier manufacturing). Look closely at the pictures and you can see a perfect speaker, just a little wear in the mounting holes from the bolts being inserted and removed. The speaker has not been played, nor soldered on. Since it is NOS, it will need to be broken in slowly.
The original G12M of the 1960s was Celestion's first guitar speaker to use a ceramic magnet and paved the way for high power guitar amplifiers. The G12M uses a medium weight magnet to produce a sound that is smooth and warm but bright enough to hold its own against any rock backline. Known simply these days as the 'Greenback', the G12M's fabled 'brown tone' is characterized by a warm, controlled low-end, a rich, vocal mid-range and a delicate, detailed top-end. Loaded into a 4x12 and driven hard, these speakers exude warm, crunchy chords and sweet searing single-notes