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In Reply to: RE: Bought the 3.7i today posted by neolith on June 03, 2015 at 15:57:24
Speakers should be at home in 3 weeks. I have already made an educated guess about the crossover and just need to confirm the values when the speakers arrive. I already designed a PLLXO which should bring a smile to JBen. Here's my guess and emulation with a parallel xo (dotted lines).The first order filter on the woofer allows the driver to extend in to the upper reaches (totally different from the 4th order filter on the 3.6) and may explain some of the improvement in the integration of the drivers.
Edits: 06/05/15Follow Ups:
That seems to put a lot of stress on the ribbon tweeter. Quite different from the Tympani IV/20-series. What about the bass reaching into the territory of the midrange? Will the rather "massey" bass driver do that well? With the 3.6, it looks like Magnepan tried to restrict the midrange extension towards the tweeter in order to minimise the subjective transistion from each driver (wish english was a native language...). Will your arrangement create a small or large sweetspot? To my experience first order slopes combined with side by side drivers create a small sweetspot.
Having done exactly that I concur that the sweetspot can be rather narrow with 1st order and side by side drivers. But it depends on how much output the midrange (or bass) driver actually puts out at the higher freq.
I wanted to note that with 1st order slopes there is little benefit to triamping, though the normal benefits of biamping are retained since you don't use the same amp to produce high power signals for the bass and upper range. Speaker level 1st order XOs are innocuous to the amp and moving them behind the amp to line level has little benefit but for eliminating the mid LP inductor, which can be just done with a better quality foil inductor.
The parallel emulation is for biamping so the signal to the tweeter will go through the mid HP filter just like the OEM (note the 2nd knee in the tweeter curve). Making a triamp parallel XO would eliminate this knee extending the tweeter even lower. Remember this is all preliminary as I don't have the actual impedances of the drivers (other than the ribbon) or the values and DCRs of the inductors. OTOH the filters are suppose to be 1st order so the general shape of the Bode can't be that different.
As far as the sweet spot, I haven't seen much mention of that in the reviews and since I am the only one that listens to the system -- that maybe a sad statement on my social life or audiophilic heaven :) -- it is not of great concern to me.
Edits: 06/06/15 06/06/15 06/07/15
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