Making speakers sound tonally similar with an equalizer

As others have said, the only parameter that you can get to match, is frequency response.

But there are so many other parameters to take into consideration.

Just one example: different drivers have differences in: resonances, transient responses, dispersion, breakup, etc.

So, even if one were able to match frequency responses very closely, one speaker would probably still be better than the other with respect to: transient response, imaging, cone breakup within audible ranges, etc, etc.

Also, cabinet construction will not change. So, a resonant, poorly damped cabinet, adding it’s own set of distortions and inaccuracies, will still be there. Matching frequency response will not improve waterfall plots.

I created a mechanical equalizer using Helmhotz method that bent the room to the speakers large bandwifth response of timbre voices not using any thin test frequency...

Use ears not microphone..

Your two speakers sound will blend together their particular response more easily if the room is adapted to them by your ears guiding tuning..

It is a simple psycho acoustic fact that the ears/brain adapt itself rapidly to new acoustic conditions and translate sound wave into whatever the few second response to the room will make it meaningful for them ...

Acoustic is key way more than the choice of the speakers , especially if the speakers are already good...

Electronic equalization is a tool with very specific limits..

Mechanical equalization is done with Helmholtz resonators and diffusers that become integrated parts of a room..

It takes a dedicated room for sure...

Let’s take the same drivers, in the same box, and change only the passive XO.

Those two speakers will sound different. But the on axis FR can likely be made to be similar with a DSP.

However they cans still sound different due to the XO freqs and slopes affecting both the radiation pattern and the phase - particularly in XO band.