HI NN,
On fritz website he shows that how smooth the impedance of his spkrs over the audio freq vs others.
Yep, that's a function of the series crossover design the man is fixated on. :)
Does it mean for the same db of music in a room the other spkrs demand a large watt/current amp for the db of music ?
No, what it means is, regardless of frequency, the impedance is relatively constant. It is a super easy load and particularly beneficial to tube amps. To compare it to a random, typical commercial speaker, like these monitor audio:
https://www.stereophile.com/content/monitor-audio-silver-300-loudspeaker-measurementsWith a high impedance amp (i.e. tubes) the frequency response changes to match the impedance curve. This is less troublesome to solid state amps.
Also he mention about series xo .Any comments on this would be valuable.
The other benefit he claims is that because of how the parts are arranged, they stay out of the path of the drivers. A $30 cap in his speaker is equivalent to a $300 cap in others. The schematic and series XO theory bear this out, but I've not done a listening comparison. However, given that I think he has very good ears (based on listening to his products and conversations) I have to believe he's onto something.