Replacing active monitors' guts (class D -> AB)

A remarkable step up in studio monitors would cost me over 1kiloshekels. A remarkable step up in my current ones’ performance would fall under 300 shekels, I guess.
They have cheap D-class amps, cheap here being also in relative terms to the rest of the speakers, the design emphasis has went to their waveguides/shaping and the woofers. Great monitors, I’m just getting tired of what’s clearly that cheap Class D brashness.

So I was thinking to replace the 40W/driver internals with some affordable class AB plates, maybe a bit more juice for dynamic transients. Luckily there’s no DSP in these making that transition impossible, I just have to get the crossovers acting the same. How do I go on about replicating an electronic crossover exactly? I admit, electronic crossovers are alien to me in function.
Here’s a pic of the speakers’ internals. Could I basically just identify the crossover circuit here and literally cut it off and connect it to the ABs? Or is a Class D module’s integrated crossover not simply agreeable to a Class AB?

Should I just make the simplest passive crossover that parrots the response of the original? For this, what parameters do I need measured? I should have some way to quantify the horn loading aspect of the waveguides to not have to blindly fit the mid-high range.

Should I just give up on this idea?

What speakers are we talking about?

Why to you attribute the hash you are hearing to Class D per se? In my experience Class D, like many other topologies, is all in the implementation. There are great-sounding and bad-sounding implementations of Class A, AB, G, D, et al. Have you played with different sources and cables? There may be various causes for the hash you’re hearing.

Also, within an active speaker there are many variables, taken into consideration by the designer, which are more complex than the passive world where amps are designed to drive a wide range of speakers.

Short version, given that you are definitely voiding the warranty by replacing amps, I would save my shekels and apply them to the front end driving these speakers (many active monitors are quite transparent but I don’t know what yours are), or upgrade the speakers. Otherwise you are getting into quite an engineering project.

Would just love that, absolutely.
I’m quintessentially and throroughly BORED.
Won’t ever become an engineer of any caliper through endless idealism either. Dreaming (while twiddling my thumbs) of better performing equipment won’t get me any such equipment either.
I’d best be investing in something to improve performance where it’s most limited, here: the speakers. Buy new ones? No, that’s over a grand - what can I do for ~500$?
-Change plate amp modules to premium quality ones with power to spare
-Change tweeter to warmer more dynamic one - a well-rounded-corners-type-of-treble compression tweeter with a generally laid-back character would be NICE here. Know to name such drivers?

Well, coming out of the DIY/hobbyist world growing up, if you have some time on your hands (and don’t put music of a price on your own labor costs), the cabinetry aspects of loudspeakers are certainly one place to add this “sweat equity” (either kit speakers or re-implementing a design.

I probably wouldn’t gut an existing design but start with well regarded drivers that are a known quantity and built a kit speaker. A further step would be building a speaker from scratch (assuming that you can spare a couple hundred dollars for acoustic measurement equipment setup) and want to invest the time in understanding design.

Most inexpensive compression drivers aren’t particularly laid back sounding (and tend to be somewhat more complex to design a proper crossover passive crossover for), so I wouldn’t necessarily start there.

If you want to attempt to duplicate an active filter design passively, you need to measure the transfer function of the active filter (input to output).

You can also do the same with the passive filter like this:

Some of the free/inexpensive modeling software with an optimizer like Vituixcad is a good tool for a project like this.

However, there may be impedance considerations or other factors (like active LF boost) that you cannot duplicate, but this is a rough guideline.


Thanks for absolute advice again, Chris. No point going against your word.
So then, I would best be taking just the exquisitely shaped Navier-Stokes optimized (well maybe not but they look that way) waveguides from these speakers and using them with well-matched new drivers from say, Scan-Speak, with constrained-layer damped cabinets and passive crossovers from scratch.
Building completely new monitors from scratch essentially around a plastic waveguide might or might not be asinine. I want to believe in this geometry - it’s optimized and beautiful.

In addition to @Chris_Brunhaver’s link, I suggest Madisound Portal and Both are well worth a look for anyone looking into diy speakers / modifications. The audioexpress link Chris gave is the offspring of the old Speaker Builder magazine. Damn, I wish that mag was still around.

1 Like

OMG, I see that Madisound still has Vance Dickason’s Loudspeaker Design Cookbook, albeit now in the 7th edition. I had and loved the first edition back in the 70s and had it virtually memorized. Great book for beginners, as, although technical, it’s written so a novice can understand.