Im on it
I'm all over this issue 2camjohn. I have been selling tantalum capacitor passive filters for high end audiophile use (at a discount).
First, don't believe all that crap. Its mostly bad judgement propted up by big business that can't change. Jargon doesn't help. You can use tantalums where you use bipolar electrolytic. Actually a non-polar electrolytic can have higher reverse voltage than forward voltage which is why they started the jargon -nonpolar or bipolar. It is misleading. It only means this condition has been designed out by making the cathode larger instead of tiny so that if the liquid electrolyte does break over (normally it binds its ions tightly) there is no damage. First lets back up. All capacitors are polar. All have reverse currents called leakage. This reverse current must be present to reset the device to begin its next cycle of operation. To decouple the DC - a GREAT IDEA I may ad, you just use a large capacitor because it cannot pass the class A DC bias than is common on power amps and some op amps operate in class A mode. To couple with a capacitor in audio usually means just using a low value like 4.7uf because at somewhere between 3000 and 5000 hertz it will have an 8 ohm capacitive reactance and since that matches the speaker it will optimize power transfer. It also helps cover the high end of the spectrum. and NO YOU ARE NOT PICKING HIGH VALUES for your filter in the 30 to 90 uf range. The very small value use a very large inductor, (hi filter) and are trying to duplicate a Bessel filter. Really bessels are powered devices but the Butterworth have been called 'slow' due to the larger value capacitors.
Its easier to get a fast rise in the capacitive reactance and inductance combined called impedance when you use that method. But keep working on it and be VERY careful about talking to anyone who is not active full time in circuit design of filters and component selection. I have had no problems with tantalums at all. There may be a justified fear of DC, but you seem to already realize how to solve that problem. Block it. One side is enough. And to put to bed some other nonsense that is online all over the place - Tantalums store just as long as electrolytics. No, you can't put to tantalums back to back and make the bipolar. It is just jargon for the way the electrodes sizes are constructed. Yes they have much lower leakage currents. All capacitors act like rectifiers, it just means its a better capacitor, about 2-1/2 time more capacitance per surface area than electrolytic, thats why. Also the low ESR makes the coil Q higher, but that is not good if the Q causes reverberation past the time of the next cycle of the capacitor. Thats where the absurd idea that tantalum capacitors cause distortion when used in audio circuts came from originally I think, and now everybody with a theory is jumping on the bandwagon to claim a new piece of escoterica. Since my stereo splitter boxes get kinda ugly to use huge coils like a speaker crossover, I don't sweat this problem at all but sure, if you need to get more volume out because your pre-amp is a weener and your power amp cant budge out more than say 35 or 40 watts per channel, by all means, use 150 micro henries or more and pay some stupid price. I'll settle for turning up the amplifiers to max and not having it really loud, but just real solid backed sound. Some people should just listen to themselves. They'ld be emailing Kennedy Audio and asking more questions - like that ever happens..