I owe to Jorge, a gentleman from Mexico City, a BIG "Thank you!", as, asked for more details about his "secret";-), he sent to me the following text to be shared with everyone interested...
"Well, the idea about "the secret" is that Current Charged or Active Biased caps sound so good it will send high end cap companies to ruin;-), and they are making such a nice effort... we can use high end cap for coupling stages in amps, but for Xovers the best cap is a cheap electrolytic with batteries...
I am sending you a pic of the caps I have tried, all are the same value 4.7 mfd, first from the top is Vcap OIMP, wonderful cap, the best I heard with horns, next down is Mundorf Mcap silver in oil, very nice also very quiet and it has a spatial quality I really liked, the soundstage it makes is sort of hypnotic, but the Vcap is just plain more natural sounding. Jantzen Silver is a wonderful cap with attributes of both Vcap and Mundorf silver in oil, is like a mix of them but I will put it just under the Mundorf, but for the price, it is a winner. The Jantzen Superior red cap is a little bit more closed in than the Silver one but pretty good also. the Hovland can sound wonderful and open on some tweeters and horrible on other setups.
I tried Current charged capacitors with Jantzen Superior Zcaps, I bought a whole bunch of them since price wise they are the best buy, With the batteries they sounded better than any other cap, the Vcap or Mundorf Silver oil, I tried them first with just the tweeters and the difference was amazing, the highs were open extended transparent out if this world, they made the rest of the system pale in comparison, they also have less resistance so volume was higher with the current charged. I was so exited about this I couldn’t wait for shipping and etc of more Jantzen caps, so I hooked the Solen caps we all have in the drawer some where, It took me a couple of hours to make the whole Xover board for one side but when both were running it was excellent. I had to use all the plastic caps I had and some had different values and brands on some sides, you need 4 times more capas than original, so I decided to try exact values same caps even if they were cheaper electrolytics.
I run to the electronics shop and bought the first cheap electrolytics I could find (SC) with the correct values for the rest of the horns, to my surprise the electrolytics sounded way better than the plastic caps, the difference was almost as much as when I first put the batteries on the caps. This is the way to make them!
I started again with the tweeters since they are the easiest to make and the less problem if they burn ;-) I found Polarized electrolytics and non polar, so I started with the non polarized caps, they were wonderful, I was again amazed that they would sound even better than the plastic caps, the difference was a little like the difference between the Vcaps and the Mundorf, electrolytics sounded just more open and natural.
They didn’t have enough non polar caps at the store for the rest of the system, so I tested polarized: no problem they sounded just as good, now I have diagrams were they connect both positives to the batteries and others were the negatives go to the batteries, so I hooked the older tweeters and made the change from positive with batteries to negative with batteries, both worked the same and both sounded great.
When I finally finished the whole system the difference was jaw dropping...
You need to double the value of the caps and put two of them in series with the battery and resistor in the center. ie: If you have a 4.7 cap you can substitute it for two 10 mfd caps in series with the resistor and battery in the center, were both caps meet.... This is a more technical explanation I found some where on the net, I am sorry I don’t have the author.
"The networks employ DC bias to operate the capacitors effectively in a Class A mode. The batteries provide a voltage bias to each of the capacitor positions in the various networks. The biasing of the capacitors is done through a large value resistor (2.2 mega ohms) and thus draws no appreciable current. The expiration date printed on the battery generally coincides with the need to replace the batteries. Each capacitor position is actually made up of two capacitors connected in series. The battery voltage is applied to the center connection of the two capacitors. This produces a voltage potential between the two plates within the capacitor. When the two parts are taken as a whole, there is no DC voltage that appears across them, but individually they are each biased. The sonic result of the biasing yields an increase in detail, increased smoothness, and considerably more natural decay of sounds within the music."
So it is really simple to make and the cost of cheap caps and 9 volt batteries in nothing compared even to a good cable!
Another tip I can give you are the Jantzen WAX coils you see in the picture, just so much better than plastic covered foils. Duelund resistors are pretty good also.
I am using Series Xover..."
... I'll have to carefully re-read the above and to digest the drawings and instructions and squeeze them in my so un-tech head...
Anyone having similar Jorge's experiences? Must say - as I learned from Tim - JBL Everest is using such a layout in its filter, after the exposure I had months ago - in Akihabara, Tokyo - wasn't something I fell in love with, BUT possibly other details flawed my listening experience...
Worth adding also Y.B.Andrè and Vecteur from France (thanks Mirco...) experimented on this very path in the '80s... but not with high efficiency speakers;-)
Thanks again, Jorge!