You can mix speakers to achieve just the tonal blend you want. The possibilities here are endless - here's a basic primer to get the ball rolling.
— Turtle 🐢
Three simple rules
1) Match impedances (ohms): All speakers in the same box should have the same impedance.
2) Power handling: As a rule of thumb, in a 2×12 cab, max power is 2x lowest rated speaker and in a 4×12, it's 4x lowest rated speaker.
3) Sensitivity matching: for best performance, speakers should have less than 3dB difference in sensitivity.
Some tried and tested standards
G12H Anniversary + Celestion Blue
G12H Anniversary + Celestion Gold
G12H Anniversary + G12M Greenback
G12H Anniversary + Vintage 30
Vintage 30 + Heritage Series G12H-65
Vintage 30 + Celestion Gold
Vintage 30 + G12M Greenback
Vintage 30 + G12H-75 Creamback (Periphery / Animals as Leaders)
G12M-65 Creamback + G12H-75 Creamback
G12M-65 Creamback + G12H Anniversary (Mastodon)