Braun L470 speakers modification

Hello,
Please feel free to express your opinions and advice here.
My audio system is mostly intended for monitoring soundtrack production for self-made films at home. I'm aware that active monitors are the best quick solution. I had before some Adam A3X monitors + subwoofer and they were fantastic. But then I sold them and built my own class-A (JLH 4ohm) amplifier, to learn and start from scratch. The amp is great and loud enough for monitoring, but I haven't found a good set of passive monitor speakers for it.
Currently I'm using a pair of second hand Braun L470 boxes that I really like for their flat form factor, since my studio room is small. Combined with an active subwoofer they do well, charm and soft, but I miss the sharp responsiveness and detail of my old Adams. Sweep tests show that these boxes are not very responsive over 10kHz, so I think changing the tweeters could a be solution. I never built speakers, I've only read about it, but I can imagine also that after 30 years the drivers have lost tightness and their soft signature is basically HD. I haven't opened the boxes yet, but I'm considering to change both tweeter and woofer for some modern ones, striving for a flat frequency response between ~80-15kHz (a subwoofer stands below).
I don't know if, since the boxes form factor, damping materials, protective net and construction in general, are exclusively designed for the original drivers, any change of drivers will end up in a complete mess, unless accurate measures and further modifications are made.

Also, if this project of modifying the Braun boxes makes sense at all, I'm also doubting about the type of tweeters to use in exchange, Dome or AMT. I loved the detail and HFR of my old AMT Adams, they really replaced my headphones for fine mixing. But I didn't like the limited vertical dispersion and never really tried good quality dome tweeters to compare with, some SB Acoustics domes that seem popular now.

Any words on this will be highly considered! Since I feel my inexperience on this.
Regards,
Domingo
 

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I tried removing the back lid to picture the crossover, but it is hardcore stuck behind the screws with some gummy glue all around. I'd have to find a way to open it without damaging the frame.
In any case the specs mention a 2nd order crossover at 1.5hKz, pretty low right.

The drivers work fine, sweeps go smooth without vibrations or cracks. But the boxes are far from linear and highs drop with drama around 10kHz.
Here is some pink noise measured at 1mt distance with an omni mic. Lows are not very representative because of environmental rumble (see picture 'nosound.jpg' for environmental noise-floor). Otherwise FR was roughly always the same for both speakers, in different moments and different room positions, showing up to 20dB drop around the crossover frequency and fall around 10kHz.


I wonder if raising the crossover from ie. 1.5 to 2.3kHz will shift the tweeter's high end from 10 to 15kHz. The woofer should suffer on the low end, but I guess I can cover that with the subwoofer. Maybe that's what you had in mind @Lojzek ?

How can I (in theory) improve flatness over the crossover region?
 

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Your measurement shows around 12dB drop from 10 to 20 kHz. Thats looks like natural rolloff of the tweeter. Raising the crossing point to 2,3 kHz wont extend the tweeters response. Also, its a question if woofer is good enough to play that high.
One solution is to add series coil to tweeter, to flatten the bump between 4-8 kHz. Plus some cheap supertweeter with series capacitor, kickin in at 8 kHz and above.
Other solution is better tweeter with better high end, or some small fullrange driver. Plus crossover redesign, which could also improve flatness around crossing region.
 
Thanks for the suggestions @Davor D. The second option sounds better to me, because I'd like to keep them 2-way if possible.

I've been looking for example to replace the tweeters for some SB Acoustics SB26ADC-C000-4. They extend up to 40kHz much like AMTs :) Their plot shows flat down to 900Hz, but that's with a 2.6kHz crossover on paper. No idea how that figure would change with my current 1.5kHz crossovers. I'm also blind to the sensitivity of my current woofers (undocumented).
In that case that the new tweeters are more sensitive than the current woofers, how is that usually compensated? Adding series coil to the tweeter–meaning an inductor before it?
 
Yes, series coil to tweeter means inductor before it.

That SB Acoustics tweeter looks like good choice. 2,6kHz crossover is for 120W power handling. L470 is only 28W, so lowering to 1,5kHz is not a problem.
If new tweeters are more sensitive than woofers, you simply add series resistor before it. Or L-pad, if higher attenuation is necessary. Since woofer sensitivity is unknown youll have to experiment with resistor value.
What I managed to find, woofer is 5in, in a 7,8 Liter closed box. To reach low frequencies, it will be low sensitivity.
My guess around 86dB/2,83V/1m. So start with 2-3 Ohm in series with tweeter.
 
Thanks for the suggestions I’ll check the tweeters when I remove them and see if there are any cracks or fluid.
I want to keep these chassis @as_audio and learn in the process of improving them. But you are right, considering also that my amp is only 10W I should care for efficiency and maybe later change the woofers as well.