I have. OK, my opinion: Simpler is better, quality of sound goes down as the crossover order goes up. So 1st order is best, but you need drivers that can operate with first order crossovers(not all are good for this). 2nd order would also be a good choice. Whatever you do, don't get much more complex than this. Also, along the lines of simple, if you have a good design to start with, you need none of the other frills(impedence flattening, notch filters, trap circuits, etc.). If you see plans for stuff like that, look elsewhere, the design is flawed from the start. My reference speakers (bought, not made) are WATT/Puppy clones, and there are only TWO crossover components on the sats, a cap and a coil. If you have a good design, that's all you need. Also, making the crossover more complex makes the speaker a MUCH more difficult load for the amp. So, keep this in mind if you like tubes or SET. In order of importance: crossover, box, drivers. You can also argue that the box is number 1, and I won't argue much. Make the box as sturdy as possible. If you're not good at this, have a cabinet maker do it for you. They'll make you a great box for floorstanders for around $350. There are thousands of plans out there from the speaker manufacturers that give you crossover values for their drivers, and they WORK. Often, these values are far away from those you see in the "tables". Throw the tables out, and use the manufacturer's values. Check out $5000 speakers. More often than not, they use tweeters that YOU will pay $25 for(not ScanSpeak Revelators or Dynaudio Esotars, but Vifa or Seas) and coils that you would pass over. Use wirewound resistors, GOOD polypropylene caps, and 12ga OFC coils, and you have better components than the big boys. Most of all, KNOW the kind of sound you like. Do this by listening to manufactured speakers. Example: if you can't stand bright speakers, you probably want soft dome tweeters, and not metal or inverted domes. Don't build speakers that you think are great on paper, only to be disappointed because they don't sound the way YOU like. If you do it right, you can make a $5000 pair of speakers for 25% of that. Another idea, buy your speakers used.