I'm not looking to start a flame war; I'm looking for actual technical details. It's a serious question; I'm planning on replacing my aging keyboard combo amp.
Looking at the prices and specs of keyboard combos vs. powered speakers, it seems that powered speakers would be the preferred choice for keyboardists to use for monitoring or backline: better response, higher wattage, better price, lower weight.
Yet vendors still sell plenty of keyboard amps. Why is this? Is there some technical reason?
The reason I use keyboard amps rather than powered speakers is that I have the choice of which passive speakers (and which amp) I use on a gig. I'm talking here, of course, about separate amp and speakers - I stopped using keyboard combos some years ago.
Using powered speakers meant extra power cables to each speaker (something I prefer not) and if the amp in a powered speaker went down, that just wouldn't work. I now tend to use a stereo amp (150w) with two small (8") cabs - mainly for my benefit as monitors. Which can be added to for medium gigs. Bigger gigs then go through that and then the p.a. I get the benefit of stereo strings, Leslie wafting, chorus Rhodes, etc. The audience doesn't, particularly, but the band does!
As far as sound production is concerned, I don't hear much difference between the two, both will be full range, powerful enough for the job, so I guess personal choice is what it comes down to. Dedicated k'bd amps will have extra ports for fx send/return, and often a graphic eq., which are essential for some players, which won't be available on all powered speakers.
Differences are subtle. You probably have different inputs, an effect loop and/or reverb. The main difference may be that a powered speaker is more likely to have a ported speaker while a keyboard amp tends to have an open or closed box design that makes for a more direct bass response. The setup of speakers and crossovers for a keyboard amp also tends to favor rather direct response while powered speakers tend to have more linear frequency response, less colored and less direct.
For an instrument amp, the idea is that they produce sound while a powered speaker reproduces sound. If you want to reproduce a stereo recording, powered speakers are supposed to give you a soundscape where you can locate individual instruments well while two instrument amps would be allowed to sound like, well, two separate sound sources sitting in the corners of the room because their more direct response makes for a highly specific transient response.
That's all very handwavy. In my personal experience, a good (analog!) instrument amp wired up to an acoustic instrument can give you the impression that your instrument is merely sounding louder. Very organic. A powered speaker will give more of an impression that your sound is getting replayed separately.
Again: in principle the two are sort-of exchangeable; this here is more an impression of what the focus is on for things marketed as one or the other.
A lot of keyboard amps do not merely amplify, they also change the sound in keyboard specific ways:
Powered speakers might not have 1/4” inputs, so you might need an adapter. And keyboard amps might have other features such as auxiliary inputs and mixer for a microphone and/or other instruments or a DI output. I used to have a keyboard amp that had a tube channel and a solid state channel.
A better question might be why are there both keyboard amps and bass amps. One can usually do for the other in a pinch.
There are tiny 'combo amps' with a single, very basic input channel and quite large 'powered speakers' with effectively a small mixer built in. Don't worry too much what the maker calls it, look at the facilities and see if they're what you need.
