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In Reply to: Is a 12db slope good enough for an active x-o? posted by RickeyM on March 30, 2007 at 09:43:48:
Can it do asymetric slopes, like the 12db/6db slopes on the original mmgs?
Follow Ups:
Nope, it only does symetrical slopes, 12db per octave.
I would give it a try, you have nothing to lose but some time. As mentioned by DR you will have to do some surgery on your speakers to by-pass the passive components. Here are some points to consider:
1)The crossover is frequency is approximately at 750 Hz.
2)Remember with a 2nd order xo you should wire the tweeter in opposite phase to the bass because the low pass and high pass filters are 180 degrees out of phase relative to each other.
3) 2nd order filters can have different slopes depending on the Q of the filter (L-R has a Q=0.50 and a Butterworth has a Q=0.707. The L-R will be flat across the xo point while a Butterworth will have a +3db hump). It would be nice if you knew whether your active crossover uses a Butterworth or L-R configuration.
4) Magnepan typically uses low Q values (0.43 for the MGM 2nd order low pass) which mimic 1st order slopes with 2nd order phase. If your unit uses a Butterworth filter, you may not like the change.
I may be an egoist but at least I don't talk about other people.
neo, thanks for the input ;^) .The stock x-over parts are long gone, thanks to a gen-2 to gen-1 upgrade with big ol' Erse coils & aftermarket caps externally box mounted.
The active x-o uses L-R slopes. You say the crossover is frequency is approximately at 750 Hz. Is that for the MMG x-over or the MG12?
I'd like to emulate the MG12 x-over because I likes the results when I installed a MG12 spec passive x-o on the MMG's.
I think I'll try both x-over points and see ( hear :-] ) what I like best.
Hey Neo,Fogive my ignorance here.
Is it necessary to wire them out of phase if both the low and high passes are 12db. Or is it always required when a 12db slope is used regardless of what other slopes are used?
I can see if one is 6db and the other 12db, but why the need if both ar 12db slopes?
It is most important to "phase align" or "phase correct" 2nd order crossovers because of the phase change.
The phase relation is independent of the slope or Q of the filter. Note also that while we use 2nd order and 12db interchangeably, only a Butterworth (Q=sqrt of 2) is down 12db at one octave. The L-R as shown here is down ~13.7 db at the octave reflecting its softer slope.
I may be an egoist but at least I don't talk about other people.
I guess I am really clueless on this.How do a second order high pass and low pass end up with different phases?
I will email you with a more detailed explanation but you may want to check out Mart's excellent article on basic circuits in the Articles section of this forum.
I may be an egoist but at least I don't talk about other people.
k
You could certainly try it, but I am not certain of the results. Also, you have to bypass the passives completely.FWIW, I did do the mmgs at 1000hz with symetric 24db slopes, and it worked fine, so maybe the 12db slopes could work, but it may not be optimal.
I could try a 12 12 slope and see, but right now, the thing is not even hooked up, so it may be a long long while.
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