Looking for some advice: Avalanche 15 and Rythmik LT Amp

Discussion in 'Home Theater Projects' started by Rob Bird, Jan 27, 2005.

  1. Rob Bird

    Rob Bird Agent

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    I have been looking for a while, and am interested in building a sealed sub using the new Avalanche 15. To improve performance, I'm thinking of using an amp like the Rythmik 350 that has a built in LT circuit. My problem is this, when I model the LT circuit in WinISD Pro Alpha, I rapidly exceed the maximum excursion with all but the most minimal LT settings on the Rythmik amp. For example, if I choose an LT circuit with settings of 20hz and a Q of .7, a 300W signal is above 30mm excursion by about 22hz. If I choose an LT circuit with a setting of 20hz and a Q of .5 (F6 at 20hz, F3 at 30.5hz), a 300W signal is above 30mm excursion by 15hz. My results with the Tumult instead of the Avalanche are virtually identical.

    I'm confused? The amp doesn't seem particularly powerful, and the LT settings don't seem off the wall...the 14hz settings are completely useless, and the 28hz settings don't get me anywhere near what I'd hoped. I am starting with a box size to give a Q of .707. If I shrink the box size down to control the excursion (down to 40L or so), the transfer function, even with the LT circuit, goes right to poop. Am I doing something wrong?
     
  2. David_P

    David_P Stunt Coordinator

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    I've struggled with exactly the same problem/concept but using the FRD consortium spreadsheet.

    My take... (warning, this might be wrong)

    the spreadsheet gives two output curves:

    1) frequency vs power
    2) frequency vs. excursion

    IF (big IF) the frequency vs power curve says you reach max power at a HIGHER frequency than the frequency vs excursion reaches max excursion, your amp is most likely unable to overdrive the driver. The amp will give out first.

    I think... [​IMG]

    David
     
  3. Rob Bird

    Rob Bird Agent

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    In that case, will the Rhythmik amp be enough at 350W?

    I'm kind of surprised noone else has any feedback on setting up an LT subwoofer [​IMG]
     
  4. Jack Gilvey

    Jack Gilvey Producer

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    Depends on what's "enough". The LT is not magic, and you're still limited in the low bass by power and efficiency/Vb. The 350 watts won't get the Avalanche 15 to full output in a .7 (~55L)box, the amp would max out at approx half Xmax. Still, you'd get about 100dB @ 20Hz, with the rest of your FR curve determined by that. I'll bet it would sound amazingly clean doing it, too. Bigger boxes would give you more output down low with the same amp.
    One LT box I really like, and almost built before going IB, is an Atlas 15 (coils in series) in 125L with that same Rythmic amp. The power and Vb match quite well, with the driver reaching Xmax, but not exceeding it, from 30Hz on down.
    Of course, with either driver you can apply more power and go with a smaller box, but bigger boxes/less power are my preference.
     

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