Speakers drastically affect your overall sound, as much as any other component in your signal path — including your guitar! Think about it; the speaker is the last link in the chain and it is responsible for physically re-creating your sound. Speakers literally move the air to create the sound wave that your ear perceives and actually create some of the sonic goodness known as “tone.”
Speakers of different sizes and wattage ratings have obvious differences but comparing 12″ speakers in the 50-75 watt range, for example, can be a daunting task. Different materials can be used in the components of a speaker, as well as different designs, all influencing the resulting sound. Natural fibers such as paper and hemp are the preferred cone materials for guitar speakers, but subtle differences in composition and thickness contribute to differences in the sound. A thinner, lighter weight cone tends to add break-up to the sound at lower volumes. Dust caps can vary in material and size, significantly affecting the top end. Even an element as small as the voice-coil former material can affect the tone of a speaker.
The speaker component that receives the most press however, is the magnet. Ceramic, alnico, and neodymium are used for their different magnetic properties and cost but don’t have that much affect on the overall sonic makeup of a speaker. Alnico is a composite and is the most rare and expensive of the three. Neodymium is also rare but is a single element and becoming more extensively mined, reducing the cost. Ceramic is the most common but also the least efficient, requiring a heavier magnet to do the same job as alnico or neodymium. The positioning of the magnet and the differences in magnetic flux that it creates affect speaker tonality more so than the actual material.
With all of the variations in the speaker-making process, tonal options are plentiful. The best option is to read, listen, and experiment to find the speaker or speakers that fit your need. Cabinet design, number of speakers in an enclosure, and pairing different types of speakers are other ways to dramatically affect speaker sound. Remember to always match the speaker ohm load to your amplifier’s ohm load to prevent damage to either. Speakers are the easiest mod or upgrade you can do to your amp, so dig in and have fun!