The greenback has certain physical characteristics, as shown on its website, familiar to its users, from its 12-inch diameter to its Celestion label surrounded by distinctive green. The signature label has "CELESTION" stamped in white letters on a black background, with the model number G12M, power rating of 25 watts, impedance of 8 ohms and bass resonance of 75 Hz. It includes the following statement: "This loudspeaker is the original G12M specification. Care should be taken not to exceed the 25 watt power rating." The label described is a loudspeaker with an increased power rating.
The original Greenback, the G12M, had a power rating of 20 watts, which was subsequently increased to 25, the same rating as the G12H. There is a significant difference in the effects of the power rating on the sound coming from the Greenback, as the higher rating produces a louder, more powerful -- but not necessarily better -- sound. The reissued Greenback returned to the original 20 watts.
According to Retro-King, the Greenback, which could be coupled with high-powered amplifiers, was the first guitar loudspeaker made by Celestion to possess the ceramic magnet structure, which gave the Greenback its special sound, described by Musician's Friend as "the raw sound of '60s rock." Prior to the use of ceramic, alnico was the substance used in loudspeaker magnets, producing a classic sound. Ceramic, on the other hand, being heavier, could handle more power and produced a better sound at higher volumes.