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« on: 31 Aug 2014, 10:02 pm »
     Having finally become a member of the Music Reference amplifier owners fraternity, I have begun reading all of the MR AudioCircle postings, starting at the beginning, working my way forward. In doing so, I am having many misconceptions, half-truths, and outright mistaken ideas dispelled. A free (re)education! I am also having some of my long-held beliefs reconfirmed by Roger and ya'll, particularly regarding the benefits to be had by bi-amping speakers. Roger's idea to tear open boxed speakers to disable the enclosed passive cross-overs may be a bit too radical for many (and understandably unrealistic to expect the makers of such speakers to embrace), but bi-amping panel loudspeakers with simple 6dB/octave filters has been done for years and years. I first did it in '72 with the original Magneplanar I's, and then again in the late 80's when I got a couple of pairs of the original Quad ESL's, having Tom at Brooks Berdan's shop install the high-pass filter on the input jacks of my power amp. The trouble back then was finding subs up to the task of blending with the "faster" panels. That is no longer a problem, as subs have improved drastically in the past couple of decades.
     I am in the process of assembling my 'final" system (they all say that, right?!), with an RM200 powering the panels of a pair of Eminent technology LFT-8b's. The speaker comes with a fairly simple symmetrical 1st order x/o at 180hz (separating it's Magnetic Planar midrange-tweeter panels from it's cone-woofer), but can be ordered with the x/o modified/disabled for bi-amplifying the speaker. Ideal for one who wants to use glass on the panels and sand (I've seen that term used for solid state amps, and like it!) on the included woofers. Or, as in my case, with a separate woofer/sub in place of the LFT8's woofer. Here are my related questions for Roger and anyone else who wants to comment:

1- What value resistor/capacitor needs to be installed on the RM200Mk.II's input jacks to get a 6dB/octave 180hz high-pass filter, assuming a balanced input on the XLR's? Better yet, what is the formula for computing the filter values, regardless of the frequency desired? I think I remember it being posted here somewhere, but I haven't found it.

2- The same question, but for a 12dB filter?

3- Even better, and I think I've already seen it somewhere in the MR Circle, is the formula for figuring the resistor/capacitor values for different x/o frequencies and slopes.

4- The plate amp of the sub I will be pairing with the ET's has a built-in x/o with a choice of 12dB or 24dB/octave low-pass filter (all the way up to about 240hz) for it's driver. Are the phase/blending problems between the panel and the woofer resulting from using either of those slopes worth it, to get the benefits gained from such an arrangement, assuming there are any? I know there are trade-offs involved---what are they? Reducing the above-180hz output of the woofer is one, I know. Others? What would be gained/lost by going to a symmetrical 24dB/24dB x/o? Would that x/o need to be active?

Thanks everybody!
« Last Edit: 3 Sep 2014, 09:47 pm by bdp24 »