History on ohm A's and F's.

Sure sounds like IM distortion to me!

Yes, However I believe that the IM distortion is the end result which is preceded by doppler frequency shifts of midrange audio frequencies produced by the cone that is also producing low audio frequencies. Wonder how this is mitigated in Mr. Harder's updated designs? I noted this issue with both older F's and in a brand spankin' new pair straight outta Taffe Place. I have wondered if insufficient wave termination might also add to this effect. The newer F style versions appear to have the same surface pattern and termination materials as the original (an assumption). I wonder if other patterns have been used or if there is a way to calculate them. Anyone applied Bud Purvines's enABL process? Does this work?

Spike,

Which Marley live recording?

Were the Fs possibly being over-driven? It was not hard to do this with Fs from what I have heard.

If the source was vinyl in particular, was it possible that low frequency noise (rumble, etc.) was present? That might contribute significantly to a problem as you describe if so.

Hi Mapman,
It is the Babylon by Bus album, specifically remembering "Punky Reggae Party" as the worst offender, which I had recorded to maxell XLII tape with an Akai glass head tape deck using DBX NR. Shouldn't have been any appreciable rumble since it went straight from Technics SL series TT, w/ Ortofon Concorde cartridge through an Apt-Holman preamp with subsonic filter on, into the deck. I had a pair of Dynaco ST-400 bridged amps driving the F's, so probably (definitely) no clipping. I am sure the soft spider contributed to the excessive cone movements, but when the bass notes hit, you could see those cones really dance, and that's when the distortion set in.

Spike,

My educated guess is that the Fs were starting to be overdriven at that point, which as I understand it was common and easy to do with the Fs, and their acknowledged achilles heel that Strohbeen tackled by switching to the CLS design with Walsh driver not as wide range as the F Walsh driver.

I may still have a similar cassette recording of Babylon sitting around. I'll have to give it a play on the latest and greatest Walshes from OHM and see if I hear anything. I have not noticed the sonic artifact you describe on any CLS OHMs I have owned, however.