Note: This is not about Waterfall Charts, which is a completely different thing.
A good search term might be "cumulative spectral decay" ... or "energy decay relief" ...?
http://www.diyaudio.com/forums/multi-way/143821-css-lar1-ribbon-audax-pr170n0-usher-15hm-5.html
PolyCollection
demo: http://matplotlib.org/examples/mplot3d/polys3d_demo.html
Bunton, John D., and Richard H. Small. "Cumulative Spectra, Tone Bursts, and Apodization." Journal of the Audio Engineering Society vol. 30, no. 6 (1982): 386-395. http://www.aes.org/e-lib/browse.cfm?elib=3838
Berman, J. Michael, and Laurie R. Fincham. "The Application of Digital Techniques to the Measurement of Loudspeakers." Journal of the Audio Engineering Society vol. 25, no. 6 (1977): 370-384. http://www.aes.org/e-lib/browse.cfm?elib=3366
Jot, Jean-Marc. "An Analysis/Synthesis Approach to Real-Time Artificial Reverberation." In Acoustics, Speech, and Signal Processing (ICASSP), 1992. http://ieeexplore.ieee.org/document/226080/
Jot, Jean-Marc, L. Cerveau, and Olivier Warusfel. "Analysis and Synthesis of Room Reverberation Based on a Statistical Time-Frequency Model." 103rd AES Convention, 1997. http://www.aes.org/e-lib/browse.cfm?elib=7150
question (and answer) on stackoverflow
nice b/w example
an example with crazy colors
waterfall plot with Gnuplot
EDR @ CCRMA (using Matlab)