Tireguy: Metal coned drivers have been around since the 1970's. I think that Stuart Hegeman used them.
As to answer the original question, my contribution to this thread would be Audio General, Incorporated or as others may know them "AGI". They only produced one product over a 14 year span and it was their 511 / 511A preamp. Many of the folks that were into audio way back when will remember this preamp as it was written about in most every "underground" audio mag along with glossies like Audio during that time frame. If i remember correctly, J. Peter Moncrieff stated "this is the only product made that has ever challenged the residual noise floor of our test equipment".
I asked David Spiegel why he never came out with matching amplifiers. His response was that building / marketing amplifiers were FAR more costly, especially if done right. He did not have the capital to do that and didn't know how well they would sell if he did market such a product. Given David's very straight-forward designs, no-hype marketing and penchant for using the best parts available at the time, i'm sure that it would have been a great product. None the less, many "great products" were swallowed up by lesser products that had more financial and marketing support due to offering a bevy of "bells and whistles" during those years. After all, people were still using equalizers and tone controls back then. For the record, the 511 didn't come with tone controls, but did offer a specific loop for signal processing should one feel the need.
I can see why David was leery about going forward with an investment of that nature, but i really wish he would have. The little bit that i did read about the prototypes had them slewing at something like 1000 V/uS. Bare in mind that this was in 1978 -79 or so. Then again, the phono section of the 511 slewed at 370 V/uS and had a rise time of .01 uS and this was in 1974 !!! Not only were the circuits phenomenally fast and broad-band for that time period, David incorporated Zobel Networks to minimize transformer ringing / AC noise, star grounding to minimize ground loops, 24 Karat Gold plated Berryllium copper contacts for all signal connectons, Allen Bradley Mil-Spec pots, poly and tantalum caps, metal film resistors, coined silver contacts in the switching, etc... As one can tell, the quality of signal and components used were of utmost importance to David.
To top it off, David gave us all of this for an MSRP of $499. Other competing preamps that used far lower grade circuitry and parts were selling for $800 - $1200 back in the mid to late 1970's. In effect, the AGI and David Spiegel never gained the respect that they should have due to UNDER-pricing his product. As everyone knows, "real" high end audio products have to be phenomenally expensive to be good. If it isn't expensive, it can't be that good. After all, how could it be that a "commoner" could afford the best there is ??? Audio snobbery was alive and well LONG before many of today's "super manufacturers" ever thought about releasing a product. Sean
PS... David Spiegel was responsible for the first blind listening tests performed under controlled conditions. He "invented" the switchbox used for many of these tests. For the record, the only reviewer that i know of that passed this test in front of Spiegel was Edith Lumley. The reason that i know that Lumley was able to do so in front of Spiegel is because David himself told me so. Most other "golden eared" reviewers either didn't show up for the "challenge" that he issued to them or failed miserably once they did show up.
Moncrieff could supposedly identify whether this switchbox ( basically a high grade relay with the associated cabling and connecting jacks in a box ) was in the signal path or not with 100% accuracy. One would not even have to switch components but just placing the switchbox in series with the signal was audible to Moncrieff. Bare in mind that Moncrieff supposedly passed these tests with witnesses, but not in front of Spiegel. Trying to make the switchbox more transparent, Moncrieff and John Curl later came up with a design revision using a higher grade relay, but the initial design and concept was put forth by Spiegel.
As such, Spiegel may be the "Grandfather" of high speed, wide-bandwidth circuitry AND "controlled listening tests" aka "DBT" ( double blind testing ).