Hi
Could you pleae recommend any interesting diy project?
Start from scratch and do it yourself.
First, don't go 2.5 Way, go for a true 3-way design with an active Sub. Or fully active.
Second, use low distortion drivers.
I like Wavecor or purifi 6.5" as midrange, obviously the Wavecor WF182BD04 costs a lot less. Tweeter, again Wavecor TW030WA12 is a good balance of high quality design and lowish cost. It should be possible to find a 2-way project with these drivers. Use a relatively low crossover frequency, for a number of reasons ` 1.2kHz is a good choice. Woofer in a sealed enclosure for Qt=0.7 filled with rockwool or basotect. For the Wavecor that looks like ~ 6 liters sealed, giving ~0.7 Qt and 80Hz -3dB point, so crossover should be at least 160Hz or higher.
Using a minidsp DSP crossover is an option. In this case Aliexpress offers both replica's of John Linsley Hood's Class A designs with up to 25W per channel (not exactly "low distortion" by ASR standards, but good enough in my books) or LM3886 based units (these will likely cost less and have a bit more power). Use these for MF & HF. Class D has come a long way but I still think classic linear Amplifiers are preferable for low to medium power in Mid's & Highs.
Third, use big woofers.
Add a pair of the biggest bass drivers you can fit in the sides of the speaker, I'd probably go for 12" to 15" arranged in "force cancelling" arrangement. Remember 10" and smaller is for girly men. Use a sealed enclosure and a big amplifier and suitable EQ to get the correct flat response. I'd shoot for 0.7 Qt again.
If we stick to Wavecor a pair of SW312WA03 look the part, give them at least 1kW/2Ohm Amplifier, Class D is fine. It should be crossed over below 250Hz, so around 200Hz or so crossover, matches perfect with our Midrange. A box for two of these needs around 120 Liters and will give 42Hz -3dB Point.
For extra points use 3pcs in 180 liter total with the third driver in the back of the woofer section and inverted in polarity. This will create a cardioid Woofer system with theoretically no rear output.
Perhaps a nice setup would be a stereo Linsley Hood Class A 25W X 2 per side for MF/HF, backed up by a TPA3255 based Stereo Class D Amp for the bass. Amplifiers stacked behind the speakers,short speaker cables and long interconnect cables.
Personally I would use likely use passive LCR line level crossovers for MF & HF and active "Op-Amp Grave" as LF EQ (Linkwitz Transform), Crossover (derived subtractive crossover with passive 1st order HPF for the MF section) and LF semi-parametric EQ (at least 4 Bands, 8 bands preferred). One can of course go all DSP, but I'm oldfashioned.
A lot of the electronics DIY can be based on designs found at RoD Elliott's site:
https://sound-au.com/p-list.htm
I'd say building an active or semi-active (amplified woofer) setup like this will kill most commercial or similar kit speakers out there, especially if build as Cardioid Woofer setup.
Thor