A bass speaker cabinet is a lot like a guitar speaker cabinet but is usually much more squat and is designed to direct and concentrate sound. I have never used them for low frequency work, but after the brainstorming sessions, PP 6V6 was the winner by people that know basses and bass amps a lot better then me. As I recall, 20-30 watts was considered the lower limit of a real practice amp (as opposed to a beginners amp) and fixed bias is clearly the way to go. That gives us from EL84 to 5881.
The power amp idea is a good way to go for just shear volume, but I’m sure the Marshall 4×10 was designed for guitar and probably doesn’t have much bass to it. A better amp and cabinet designed for bass would be the optimal setup, of course, but if you can find a bigger speaker cab and use it with the power amp, that will probably work for practice.
Most headunits have buit-in amplifiers , but these amps aren’t neither powerful nor adjustable as external amps.Additionally, a subwoofer requires more power to operate than what a regular headunit can put could also consider a separate amp to drive your subwoofer(s),and use the amps built into your headunit to power your speakers.Using separate amps requires crossovers between the amps and speakers to distribute the amp’s signal to the correct speakers.
Back in the ‘80s, most guitarists were taking signal processing gear from recording studios and putting it in their guitar rigs with varying degrees of success (and complexity) as they sought effects with better audio quality than most pedals offered, but these days, almost everything you’d like to put in your rack has been designed expressly with guitar players in mind.
A good approach, and the one I used for the 6S100-based amp, is to make an amp that sounds great, is loud enough for practice and can drive a cabinet on stage for a monitor, and incorporate a transformer driven balanced line out (XLR) for sending the bass signal to the PA. I also do sound, and the most common problem (besides the drummer showing up late) is TOO MUCH BASS FROM THE BASS AMP.
The absence of a 3-band EQ might seem like a bad thing, but I don’t think so. The Enhance and Tone knobs are voiced in such a way that there are just as many outstanding tones available as with an expanded EQ. An important feature in any bass amp for beginners is the ability to experiment with sound, and even though the controls seem limited here the EC8 may provide the best opportunity to do so.
They recommend smaller boxes because it sells more speakers and because THEY already decided and THEY dont think you need bass below 40 hertz!(talk about mood killers) All those technical woofer parameters like Vas and Qts is a pathetic way to measure the force generation potential of a woofer, furthermore they totally ignore the acoustic AIR FORCE LOAD.