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RE: Neolith has posted Excel Spread Sheet for magnepan speakers

Posted by Satie (A) on April 25, 2017 at 20:26:55

In Reply to: RE: Neolith has posted Excel Spread Sheet for magnepan speakers posted by ghost4man on April 25, 2017 at 18:50:59:

The Lexicon is simply built to deliver the power and has appropriately sized power supplies and cooling capacity as do the older linear Theta amps (they are class D now). Theta amps employ no feedback so can't rely on that to iron out their distortion and departure from linearity so they are built to meet specs with raw power - power supplies with headroom, As many output devices as necessary and then some and ample cooling.

My idea was that using the 2 ohm tweeter with the 8.5 ohm bass is not going to work because both drivers are matched in sensitivity (at least OEM but probably pretty close) but due to differing impedances all the power in a passive would go to the tweeter through the crossover region, so the actual transition to tweeter dominance would be happening much lower, That might explain why your restorer chose to raise the size of the bass inductor while not using the original crossover freq with a bigger cap, but letting the high pass go up to 2.khz. So that left a spaced XO with the LP about 1khz and HP at 2khz.
So that is one sort of solution for the passive speaker level crossover. The other is to run the bass panels parallel and get a giant Crown Macrotech series amp built for the role (rated to 2 ohms stable to 1 ohm.). Or one of the classic heavy metal amps that were designed to drive the Apogee Scintilla.

The PEQ is not exactly the most transparent way to do a crossover. Costs allot in detail and tonal texture and imaging. Not surprised you liked the passive better.

Once your ribbon is repaired you should look at something around 5khz if it is a maggie tweeter. With 1st order slopes it can't handle a crossover below 4khz. The 3.x and 20.x had 2nd order high pass at 2.5khz till the .7 models came up but the latter use nested series crossovers so that the top drivers are both protected from overload with an additional pole besides the 1st order mid/tweeter XO. I do something like that and use a line level 6db high pass for the mid/tweet amp and then a 1st order for the ribbon at speaker level.

So if I understood what your restorer ended up doing, then just keep those values for passive operation and integrate a proper mid low pass and ribbon tweeter high pass to match. But for passive operation I would want the tweeter to have a 2nd order HP in this setup as everything over 1-2khz would be 2 ohms and that is going to restrict the amp options of the potential buyer so I would not want them to use a distressed amp on a tweeter operating at the extremes of its capacity.. .

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