The current presentation of waterfalls is not opitmal. Scale could be 60dB instead of 30 dB and the z-axis cycles instead of fixed time. The interesting is with a cycle-normalized waterfal is, that for any given frequency, the tweeters response time should be the same in CYCLES. It shows more details.

At 20kHz it can be seen that It takes several cycles before maximum sound pressure is reached. An interesting part of the waterfall diagram cannot be seen. The attack is behind the main ridge. Please look at 20 kHz. The first graph is a set with the Scan Speak 18W8546/revelator 2905/9900. The second system is with the Focal TC 120Tdx/Scan Speak 18W8545 placed on a baffle with Fron Tex.  The revelator has faster decay and behaves better than the focal. The distortion figures for the revelator show 0.1% flat.    The bulge around 5kHz can also be seen with an other design with the TC120Tdx and the focal 5C011 (no picture). Thiel uses this measuring method to specify their drivers  www.thiel-partner.de.
(Source of the figures: Elektuur special, Hi-Fi Loudspeakers 11, measured with ATB)