There are no good references for designing reverbs because the info falls under 'Trade Secrets' in the audio industry. I develop commercial reverbs and other effects as part of my job and can give you a few tips:
- FDN is not used in any of the 'classic' reverb designs (Concert Hall, Plate, Chamber, etc). Eventide did start to use it in the late 80s, but their most famous reverb is not FDN based at all. A number of plugins and devices do use FDN now mostly for 'Room' type algorithms.
- The few patents for old reverb boxes are not very useful because they leave out all of the 'secret sauce'.
- Modulation is where the magic happens.
- Andy's on to something with investigating mathematical sequences and ratios
- Interpolation. When to do it and how to do it is also key.
- Filters. what type and where to use them
- Phase. Relates to filters and interpolation and creates some surprising results when used well.
- Move to Boston. Almost all of the major reverb developments where done here: Blesser(EMT/Lexicon), David G(Lexicon), Chris Moore(Ursa Major), Bill Gardner and so on. I think Miller even wrote the FDN paper at MIT.
Chris