If you own a combo amp, means an amplifier with an in-built speaker, it mostly has a 1×12 or 1×10 speaker.
Looking for a sonic variation, most guitarists start with replacing the speaker of one manufacturer by a suitable model from another brand.
But the alteration of the speaker sizes can also effect decisive sonic changes.
Doubtlessly, the replacement of a speaker by another one with another size is more complex, for you will have to modify the baffle board or even install a new one.
But granted that we have perfect conditions and the desired amp would be available with every kind of speaker sizes and speaker combinations, which one should you choose?
A small speaker mostly provides a lower level. This has advantages as well as disadvantages.
If you are looking for a heavy overdriven amp with a certain interaction with the speaker, a small amp is more suitable to achieve this aim.
But the small amp offers a certain sonic image. It has less low end. Therefore, the attack is more directly and mostly, a 10” speaker cuts through the mix pretty well.
The attack of a bigger speaker is more sluggish and therefore less crunchy.
But it offers more volume and are able to upgrade a weak amp.
Most combos have one single speaker. Less weight and the small size make a transport more comfortable.
Regarding the huge Marshall stacks, the 4×12 cab was quite popular. 4 speakers with about the same size offered an extended speaker surface area. And for the output of the amplifier has been divided to the four speakers, these were able to produce a higher level.
Cabinets with two speakers are pretty common as well. But the usage of more than one speaker frequently causes unintended frequency interactions between the different speakers. In this case, it is decisive to take care about the phase and the capacity or the respective speakers.
Regarding the micing, you will be spoiled for choice and can choose the one you like best.
If your combo has an input for an external speaker, you can also use a big cab if you like.
The most common models use AlNiCo or ceramic speakers. The sound of the AlNiCo has a punchy mids, the treble comes around more directly and they provide less low end.
The sound of the ceramic speaker is quite modern and more balanced. Therefore, it does not offer the typical Tweed sound.
The diaphragm also effects the sound. Speaker with a thin diaphragm have less power and start to overdrive pretty soon. Some manufacturers offer the same speaker with different diaphragms. Depending on your own preferences, you can form the character of your amp by choosing a certain type of diaphragm.
Mix and match
Although most of the 4×12 cabinets have four identical speakers, you can replace at least several speakers.
Many manufacturers already offer the combination of different speakers in their 2×12 cabs. Thereby, you can form the character of the sound as you like. You can experiment with different types of speakers (AlNiCo/ ceramic), with varying capacities or different brands.
The less low end of a Celestion Greenback can be strengthened by a combination with a stron ceramic speaker.
Or you use an AlNiCo with a limited capacity to add some kind of dirt to the mids and the treble.
And a combination of a 1×10 with a 1×15 has a charm all of its own.
For most speakers can be replaced quite quick and easily, it is worth it, to start experimenting.