I understand all that you have said, Opus88. But these changes were not something that John made a point of differentiating. It's not, as you implied, what made them "Signature". All of the models were always known as "Signature Collection". It would be more accurate to describe your units as being the most current version of the original. Semantics, maybe. But with all the information (and mis-information) on the web. I think It's important to make the distinction. Over time, and with endless random contribution, things can end up confusing to many.
All of the models, from the One through the Six, went through changes.
All of them had the tweeter change simply because the original, the D26, was replaced by the D27 by Vifa. The D27 had smoother response between 10k and 20k. As just one example. So it was easier to integrate. The handful of hardware changes were simply to give it a flatter response.
The SC-3 also went through a woofer change. Also from Morel to Vifa. And the SC-5 went through a upper midrange change, from a Vifa dome (D75MX) to a Vifa cone. The change in the SC-5 was purely for practical reasons as the D75MX did not stand up well to shipping conditions, let alone hard driving.
All of these changes were for practical reasons. If one were to look only at the measurement specs, the things John touted most highly, one could not likely tell which version of each speaker was being tested, so tight were his tolerances.
The IVa, on the other hand, WAS a significantly different speaker and as such received the "a" distinction. The rest of the changes, John himself argued, were not audible. Of course, most audiophiles trust their hearing far more that John did. After all he didn't believe in wire differences.
I, and a couple of my associates, have had in our possession at some point every single version of every model from the SC line with the exception of the SC-VI. I don't recall there being any internal bracing changed between the early and later versions of the SC-IV. But, it has been awhile since I looked. I'll have to check our records to confirm.
Never the less, the point here is not to call anyone out as being wrong or to argue. But the nature of the web is one of being timeless, so to speak. So for the sake of public record, I'm calling special attention to the above information.
True, ALL of the original Dunlavy models went through slight updates and changes as more preferable drivers models became available to Dunlavy. But, with the exception of the SC-IVa, these changes were not highlighted in any way by John or the company. Over the years salesmen have probably called attention to them. And I'm sure there are audiophiles who will insist that one version sounds better than another. But no special distinction was made by the designer.
Anyone interested in learning more about the Dunlavy designs should check out the link mentioned a few posts above. It has, by far, the most comprehensive information available on the web so far.
