I have built many speakers over the last 5 years and for nearly all of them have chosen to use the APT80. They are simple, small but amazingly powerful super tweeters. They are perfect for both indoor and outdoor applications and throw a great distance. Have used in a homemade line array system for large outdoor events and the clarity is fantastic, especially when you consider the price. I have found some drawbacks. The diaphragm can be replaced if it ever goes but in my opinion the results are hit and miss and i'd recommend buying another. Even with the most accurate hand and soldering techniques, the tweeter is still likely to blow again the next time used as if it is not perfectly aligned, the design means that it will blow. That said, the price is extremely reasonable so this should not be a problem. I have tried using this more recently in conjunction with a Eminence PXB-3k5 crossover and with the addition of the fuse lamp, have never had a tweeter blow on me, even when cranking it up to silly volumes with a heavy metal band. On the whole, a great product but do seriously consider putting an eminence crossover with fuse lamp on as it will save you loads of hassle.
