You barely give them a second thought, but speakers are where your sound comes from! And boy do they sound different. The variables are myriad, but the key spec points to understand are:

• Magnet weight and type – heavy magnets usually mean higher power handling. Ceramic and Alnico are the most common magnet materials; the latter usually associated with more vintage, 1960s tones. Most guitar speakers have ceramic magnets, with only a handful – headed up by the Celestion Blue – using Alnico.
• Power rating in watts – the higher rated your speakers are, the less they will distort under heavy volume. Too powerful and they can sound very squeaky clean; not powerful enough, and they can become a flabby mess, or fail entirely.
• Efficiency – also called sensitivity this is measured in dB at a distance of one metre. This has more to do with how loud a speaker sounds than its power rating. A Jensen P10R, for example, is rated at 95dB; a Celestion G12 65 at 97dB and an EVM12L at 100dB. The numbers don’t look that different, but the difference in terms of perceived volume is truly staggering.