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can´t help it playing around with filter slopes to see if that reversed mid-driver can be forced to behave otherwise.
I´m a strong proponent of the magnepan stock slopes, but I´ve now tried a few settings with the mid-driver in same phase as the bass and ribbon, but all other soundstage issues aside, the bass just gets mudded and un-precise.
...and then a little thought came to my mind :
I wonder if the mid-driver needs to be reversed to counter-control the amplitude of the bass driver ?
does that make any sense ?
after all we know that the mylar hardly has any damping on its own and the better / lower the amplifiers output impedance, the firmer "grip". could the mid-driver be a part of that equation ?
any thoughts on this ?
kind regards
The reason for inverting the mid driver is due to the phase shift caused by the filters. Consider a classic 2nd order Butterworth symmetric crossover. The LP and HP filters are 180 degrees out of phase so at the crossover point the signals subtract and cancel each other out leaving a hole. If one of the filters is wired in opposite polarity the phases are now the same and the signals add to each other resulting in a 3db bump at the crossover. If one uses a 12db L-R then the net output will be flat. With other filters, the decision to invert depends on the paramaters. The idea is to get a flat curve. As Davey has pointed out this is just the electrical response and the accoustic response must be figured in. It is the acoustic response of the drivers that determines the -3db points, slopes and orders of the filters. The whole thing is pretty much trial and error, as best as I can tell.![]()
I plan to procrastinate my demise for as long as possible. In the meantime, I practice by putting off all the little stuff.
Edits: 06/30/09
I've experimented with the 3.5 panels, eliminating the high pass crossover from the bass wiring to the midrange wiring. Things are more integrated this way but there is a loss of detail in the midrange (which is why we buy Maggies, innit?)....
I think this is (at best) a compromise design.
The 1.6 and MG12 seem a better midbass transducer to my ear.
I keep coming back to the SMG design as the "decathlete" in the family.
You can make the experiment by using a jumper to elimate the bass panel crossover, although you will lose any equalization in the design.
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