I have heard multiple XBL^2 and other linear BL optimized subwoofers and I think they sound completely different from one another. Each subwoofer I've heard has been engineered differently from the other and have almost nothing in common other than the fact that they all maintain their individual "sound" and keep distortion to a minimum better over stroke compared to standard motor topologies. I suppose that is where a lot of people think they might sound similar - in that they don't distort like normal topologies do. It is odd, but it's pleasantly odd. I'm having a hard time enjoying the bottom end of my music with other subwoofers we have laying around since we tested the bejesus out of the Mag proto.
On the note of all XBL^2 drivers sounding similar here are T/S's from a few XBL^2 drivers:
Re: 3.6, Le:1.8, Fs: 19.2, Qms: 3.65, Qes: 0.44, Qts: 0.39, Vas: 218.44, Cms: 0.25, SD: 790, Xmax 30, BL: 16.5, Mms: 274.8, SPL: 87.3
Fs 34Hz, Qms 2.2, Vas 23.77 litres, Xmax 11.1 mm, SD 127.5 sq cm, Qes .41, Qts .35 Re 6.4 ohms, Le .75 mH, Z 8 ohms,
Fs: 17.1 Hz, Le: 0.87mH, Re: 3.1 Ohms, Qms: 6.88, Qes: .43, Qts: 0.40, Mms: 442g, Cms: 0.19 mm/N, Vas: 383L, Sd: 1182 cm^2, BL: 18.6, X-max: 33mm, 88.4dB/1W/1m
You're saying that all of those drivers will sound similar?