Calling all Dunlavy Gurus

According to Dunlavy, the ScanSpeak woofer has a much more powerful magnetic structure than the Vifa, and costs about four times as much. To get the best in bass performance, there's no substitute for magnetic flux, and big magnets are expensive.

The ScanSpeak woofer apparently has great low-end extension, but it also has some nasty peaks at the top of its passband. John Dunlavy says that he almost abandoned using the woofer for this reason, but kept coming back to it as the best driver for providing the bass extension and power handling he wanted. His solution to the problem consisted of several resonant circuits in the crossover, providing electrical compensation for the peaks.

Thanks Doug99, I'll check out that article. Again, my feeling is that the VIA is definitely superior to the IV. The delivery guys took the IVs (traded) when they delivered the IVAs.
I heard the difference as soon as I fired the IVAs up.

I'v heard the Dunlavy SC-IVA and the Dunlavy Aletha and no doubt Dunlavy made the best crossover.
The way the bass blended in perfectly to the mids and highs were perfect on the 2 Dunlavy speakers i heard.

Americanflag: Once inside the speaker, you will be able to
see where each clip is connected and how to remove and cut
them. After which, you will twist together strands of the
internal speaker wire and proceed with soldering to the
connectors on the drivers. Since I had never done anything
like this before, I had a friend who is an electronics
serviceman perform the entire job. Incidentally, I have the
improved, Signature version of the IVs.

The entire line of speakers, from the SC-I through the SC-VI were "Signature". That's what the "SC" stood for in the entire line.... "Signature Collection"
The only variant from this was the SC-IV versus the IVa, where the IVa was considered a different model and was actually sold side by side for a short period of time.

A couple of the other models also went through minor driver changes during their manufacturing life span but no distinctions were made.
The IVa was specifically different because it was so much more expensive than the IV and because it met Stereophile's demand of 20Hz in room response for class A "full range".