Celestion 70/80 and Greenback are two different types of guitar speaker models made by Celestion.
The Celestion 70/80 is a speaker with a neutral tone, balanced frequency response, and tight bass, designed for modern high-gain amplifiers.
The Greenback, on the other hand, is a classic vintage speaker known for its warm, punchy, and musical tone with emphasized mid-range frequencies and somewhat loose bass response. It is favored for its classic rock, blues, and country tone.
So, the main difference between the two speakers is their tonal character and frequency response, with the 70/80 having a more neutral, modern sound and the Greenback had a more classic, vintage sound.