choose speaker cabs with 10-inch speakers rather than 12-inch speakers?
Guitarists certainly use 12s. While bass players sometimes use 15s instead of or along with 10s, it’s common to use just a 4 x 10 cabinet.
Everything in audio has tradeoffs.
Large cones, 12, 15, 18", move a lot of air at once due to having a large surface area, and can create a big boom, but due to size and weight, take longer to accelerate and decelerate, in the process sacrifice quick transient response (snap, or crack)
Small cones can accelerate and decelerate faster, improving the transient response, but sacrifice the large air movement that lets you ‘feel’ the bottom end, ‘boom’.
So you take 4 -8 of quick moving 10" speakers, mount them in a properly sized box that accounts for the response parameters of the drivers, and when done right you end up with quick transients AND a lot of surface area to push air.
There is math (of course) behind all this, but I’m not the one to delve into that.
The things about larger cones being “slower” is a myth. Any size cone can be “fast” or “slow” (meaning overdamped or underdamped), depending on the individual speaker and the tuning of the cabinet. The cone size does affect the higher frequencies to a certain extent. A 15 may not have as much in the way of useful upper midrange, so that might tend to make it sound more muddy or “slow”.
The speakers bassists use are different than guitar speakers. A bass 10 will move more air than a guitar 12. Part of the reason bassists use tens is simply because the Ampeg SVT used them and that was a classic rig. Also, bass speakers and cabs are heavier so a bass 4x10 might weigh as much as a guitar 4x12 and a bass 4x12 might be impractically heavy. (There are lighter speakers available these days that use neodymium magnets, though.)
A 15 has something like 2.5 times the cone area of a 10, so if the excursion (the distance the cone can move back and forth) is the same, then a 15 will be about equivalent to a 2x10 cabinet in the amount of bass it can produce, and a 4x10 would be closer to 2 15’s.
Guitarists use 10s as well, sometimes. My old Fender Blues DeVille was a 4x10 combo.
To get rid of the fundamental. Taste aside, they provide a cleaner sound with less power required.
Bottom E on a bass is around 41Hz, roughly only one octave above the lowest note that a human can hear. It’s been years since I had an interest in sound reinforcement, but I recall that notes that low are difficult for the even best ears to discern while listening in an ideal listening environment. For the average person in an arena or small club, all of those low notes will echo back and forth and come off as a muddy mess at best. The lower notes also require more amplification to produce.
So (as the theory behind small speakers for bass amplification goes), instead of wasting a lot of power to produce sound which people can’t hear or can’t hear clearly, why not just remove that part of the spectrum altogether? The low notes are still heard, only they’re pieced together from all of the harmonics produced when a string is played.
I’m not an expert here, but I don’t see 18s or 15s really being able to reproduce much sound between 1 KHz and 2500 Hz efficiently, due to the difficulties of moving a 3" voice coil and the connected cone at the speed necessary. There is a reason those size drivers are not used for the midrange frequencies. Technically, any driver can do DC to Light, but you don’t consider it useable, or honest when those frequencies roll off more than 10 db or so. Once again, someone with more math/physics experience can bring the proof.
Modern bass guitar sound has been considered a ‘full range’ reproduction job since the 70’s, with most mid and high level gear including cone and/or horn type high frequency drivers in the cabinets. Good 10" speakers will get you up to 2500-5000 Hz, where the signal is then crossed over to a horn. The bottom end will start rolling off at 60 hz-70 Hz, but the surface area of multiples, and the cabinet design will move that roll off lower, sometimes into the 30 Hz range.
Regular guitars don’t sound good as a full frequency instrument. Using 10s or 12s for reproduction inherently roll off the top and bottom frequencies and keep the guitar from sounding too harsh in the top, and too muddy in the bottom. This is why guitar amps usually use 10s and 12s, or multiples thereof.
Thanks to all for the technical explanations and aesthetic considerations.
Of course, YMMV depending on what sound you like to hear. My cab is a 2x15.
To simplify this explanation even further, the operative words are “note definition”. If you want each individual note played by the bass to be distinct (such as when the bass player is the type who plays fast, complex lines), you’ll want smaller speakers. With larger speakers the notes are likely to run together and turn to mush.
The general rule of thumb that I’ve heard as a bassist is that to obtain the same volume as my guitarist, my amp needs 4x the wattage of my guitarist’s amp. So if my guitarist is playing through a 100-watt Marshall, I should be using a 400-watt bass amp.
As for speaker sizes, my big cab features one 15" speaker, two 8" speakers, and a compression horn tweeter.