Celestion T1221 Classic Series G12M Greenback Guitar Speaker 12 Inch 25W Speaker 16OHM: Celestion's first guitar loudspeaker featuring a ceramic magnet structure, the G12M Greenback presented almost as much magnetic flux to the voice coil as an Alnico formulation, but in a much more compact space. As a result the Greenback became the guitar loudspeaker that paved the way for use with higher power amplifiers. And, of course, the ceramic magnet presented its own unique tonal characteristics.