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.

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.

There were 2 versions of the Dunlavy 4 speakers.
The SC-4 and SC-IVA speakers.
One of the differences between the 2 speakers is the 1VA speakers use two 10 inch Scanspeak woofers and the SC-4 speakers use two 10 inch Vifa woofers.
I can remember when the SC-IVA came out, John Dunlavy talked how hard it was to integrate the 10 inch Scanspeak woofers in the crossovers. He mentioned at one point, he thought about going back to using the Vifa woofers again in the SC-IVA speakers.
But eventually Dunlavy got the Scanspeak woofers to blend in perfectly to the mids of the SC-IVA .
Here's a good review of the Dunlavy SC-1VA speakers, where Dunlavy talks about the difference between the SC-4 and SC-IVA speakers.
http://www.stereophile.com/content/dunlavy-audio-labs-sc-iva-loudspeaker