History on ohm A's and F's.

Dale,
I have enjoyed following your progress over the last couple of years with your walsh refinements. First, do you have any working versions of the "A" type? I only see finished F's on your site. Also, I have to disagree with you concerning doppler effect. You mentioned earlier that there are several modes in operation simultaneously with this kind of driver. I have noted that the pistonic action causes the entire driver to move at lower frequencies which may cause the other frequencies to be affected. When I had my F's and they were driven reasonably loud I noticed this, first with a playback of reggae music. (BMW live disc). When "family man" hit those low notes, the whole driver would shake and cause Bob Marley to sound like he was gargling. No, the amps (2 bridged Dyna ST-400's) were not anywhere near clipping (less than 100W peak transients) when I noted this effect. If this is not doppler effect, then I would like to understand what it is. Best Regards.

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?

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.

Mapman,
the F's were definitely being overdriven at times. I often played them as loud as I dared with bass-rich material and had considerably more power on tap than they could safely handle. I would watch the cones achieving very large excursions; probably exceeding the limits of the surrounds. I am sure that this also contributed to the distortions I heard. If you have listened to a pair of these being played then you are also familiar with the visual performance they can provide. The actual source material is largely irrelevant; the BMW recording is simply the one I remember most clearly. If there was music combining loud, low bass notes with midrange such as voice or saxophone, this issue could appear. I myself have 4 pairs of the later Ohm walsh speakers and have not noted this phenomenon with any of them, even at high volumes.