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  • Changes to ZRT2.5

    Somehow the tweet in my ZRT 2.5 got smoked the other day. I took this as an opportunity to tinker. I've never really fell in love with these speakers as much as I've wanted to. They weren't cheap to build. I've always thought the highs had an air of sibilance, and the mid range seemed bloated. They just didn't seem to blend well at all. The mid-range in my Solstice was far more revealing and natural in presentation. Being to lazy to swap out the speakers, I thought I would see what the CAT308s as replacements would sound like while I figured out what I would do with the 6600s, either get replacement diaphragms or change them all together.

    What happened next was totally unexpected and I didn't think possible. Swapping out the 6600s for the CAT308s DRAMATICALLY improved these things. Voices were more natural, every instrument was more life like and all those little details from the artist like their breathing, the smacking of lips, subtle sound differences in different types of guitars all became apparent. The mid-range and high end now seemed like a cohesive unit and not fighting one another like they seemed to prior. Imaging improved, sound stage was way further back and higher. I couldn't believe my ears. I was thinking, so THIS is why people use these 18W Scans. What a wonderful sound. Their bass was never questioned, but now somehow it was all integrated and you could just listen and not critique as I constantly did.

    Anyway, I was intrigued enough to break out Jeff's Crossover calculator and see what was going on from a theoretical standpoint. I've attached three pics, the first is the original layout, the second is the layout with the morel and the third is with a few tweaks to the crossover. I changed the MH value on the tweet from .25 to 50 and the series RC circuit in the woofer changed the UF from 80 to 100.

    I'm not saying that what I did was better or that the 308s are better than the 6600s. All i am saying is that I really enjoy them now and more expensive isn't always better. I'd enjoy hearing some thoughts on what I've done, possible pitfalls.


  • #2
    I am glad that you have found some positive improvement so a system that has troubled you, however I must say that something seems a bit "not right" about your story and the simulation. Are you sure your ZRT had the crossover correctly wired, and tweeters in the correct phase?

    With your simulation, are you using measured response, with correct driver offsets? The response you have modeled is quite a bit different from the modeled and measured response from Zaph. Additionally, the Aircirc 6600 is one of the best tweeters Scan-Speak makes, perhaps one of the best domes available period. I'm not saying the CAT308 is bad by any means, but properly executed I wouldn't expect anyone to say "dramatic improvement" when changing to a CAT308 if there wasn't something wrong with the previous installation to begin with. Click image for larger version

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    "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
    exactly a Fc 3K for both drivers, anybody can do it." -Xmax

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    • #3
      Dcibel,

      Thanks for the response. I purchased it as a kiit and the crossovers were prebuilt. Ah, you're right. In my model the 6600 was out of phase, changing that removes the sag. That said, I always felt something was off with the crossovers, but everything checked out. Even after troubleshooting here. The image your posted, is that for the 2 way or the 2.5 way?

      I agree with you about the 6600 in all respects, but something here works for the CAT that doesn't for the 6600s. The crossovers for the 18ws are on separate boards than 6600s so I may just rebuild the tweet crossovers myself. Question, do you know why on the 2.5s he uses a 16uf cap on the tweet and on the 2ways he uses a 30? Just curious.

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      • #4
        I am a big fan of morel drivers, but the 308 is not in the same league as the 6600. I would take a good look at the xover.
        craigk

        " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

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        • #5
          Thanks Craig. I am definitely going to back through it. I will probably take some cues from Troels Gravesen in the huge impedance peak at 500 Hz and incorporate some of his methods. Also, will probably use a little less BSC. We'll see. This can be the fun part of DIY. Besides I have some Silver Z caps that I'm dying to use and they fit the specs..

          Question, if I'm getting some sibilance from the 6600s, even slight, with the existing crossover would the "best/easiest" remedy be to increase the the inductor pad from 2.2?

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