Swans M1B / HiVi RT1.3 Crossover

So I'm looking to build a set of DIY Swans M1Bs and wondered if someone would be able to help out with the crossover :)

I found a German build of a replica M1B, but even with Google Translate I cannot work out quite what they did Cotton Fields Compact (CFC), Lautsprecher - HIFI-FORUM

The original Swans M1 are identical in all but the tweeter used - the M1 uses the RT1C-A, and the M1B uses the RT1.3WE

From Swans:
"The M1B. This model is an M1 but with a larger, second-generation planar magnetic tweeter and a veneered cabinet. It is parametrically almost identical to the original M1 - its bass performance is the same. The crossover point between the drivers is lower and the tweeter is slightly more directional than the M1 above the M1's crossover frequency."

The only differences between the two are: the 1.3 is slightly less sensitive (92dB vs 94dB @ 2.83v/1m) and the 1.3 can be crossed at a lower frequency (2.5K vs 4.5K)
The impedence vs SPL seems different also - if this will affect the XOver I don't know

Now, I have been in contact with another member who is upgrading a set of M1s to M1Bs and he is trying this:

"I have this tweeter and it measures much flatter, the RT1C drops ~5db above 10k. As a starting point I am going to remove the contour filter (12ohm resistor and 1.8uf capacitor) and see how it sounds. The RT1CA needs the countour filter to lift the top octave but the newer tweeter doesn't. This looks like a great tweeter and it plays 1.5 octaves lower than it's predecessor also. It is used in a number of the Swans hi-end designs now."

Any help would be brilliant!



Original Swans M1 Crossover

Thanks, Nick