Originally Posted by Newbie01
Interesting... I didn't know the RAAL 70-20 was robust enough to work in a 2 way design due to cross over...that is why most people went with Fundtek because they are a little more "robust" and can be crossed lower? What are you crossing over the Sierra 1's with RAAL at?
, I am not sure where you are getting your info from ..... Weren't you at one time considering the SongTower with ribbon? That is a 2-way design using the 70-20. Most designs using the 70-20 are 2-ways as it is one of the few ribbon tweeters that can successfully cross as low as 1800Hz, which is actually the recommended crossover point for this tweeter. With a 2nd order electrical slope at 1800Hz, the RAAL 70-20 is capable of handling up to 200 watt peaks, making it one of the most robust ribbon tweeters available. Fountek ribbons are chosen because they are typically 1/4 to 1/5 the price of the RAAL's and they are not as robust as the 70-20. 70-20 = 70mm x 20mm ribbon = 1400 sq mm. That is approx. 3 times the radiating area of the Fountek NeoCD3, which is significant. A similar comparison in radiating area would be comparing a 12" woofer to a 7" woofer.
Aleksandar created the 70-20 for 3 main purposes, one of which was specifically geared to allowing easy integration in nearly any 2-way design thus designing it to be extremely robust while maintaining astounding transient accuracy. I know it can be confusing, but the RAAL 70-20 and RAAL 70-10 are different beasts...
True story -- in designing the RAAL 70-20 version of our Sierra-1, I accidently connected the low frequency output of my external crossover to the ribbon, and the highs to the woofer (something every engineer has done at least 1/2 dozen times). I was testing the low frequency response and I ran a 32Hz sine wave into the speaker at a voltage level that is equivalent to about 112 watts. I did this a few times as I couldn't understand why the woofer was not moving. Once I realized my error and overcame the horror that I might have just ruined a $500 tweeter, I tested the tweeter and it was perfect. This was shocking to me as I have destroyed a few very robust and very expensive dome tweeters in this same manner. One of the unique features of this particular tweeter is that it has a built in electrical high pass filter at 1800Hz, which also allows for less crossover parts. This undoubtedly helped the tweeter survive my rather crushing mistake