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Passive high pass filter - Marchand XM446XLR-A

So, I am about to set up a new pair of monitor speakers and fill in the lower frequencies with two subs.  The monitors are Aerial LR5s and the subs will be two Aerial SW12s with internal 400 wpc amps.  The LR5s weigh 105 pounds each and play flat to just a bit above 40Hz (-6dB at 35Hz).  The Aerial subs are fast, powerful and musical and should integrate well with the LR5s.  My pre and power amps are solid state, fully balanced and the power amps provide 300/600 wpc into 8/4 ohms.  I will be running separate ICs from the preamp to my power amps and a second set from the preamp to the input on the subs.

My first question is whether I would benefit from using a high pass filter between the preamp and amplifiers to limit the low frequencies going to the LR5s so the amps are not trying to drive them full range.  

I didn't find a DIY design that I was comfortable with but I did run across several posts by people using a Marchand passive high pass filter.  The Marchand XM446XLR-A is fully balanced and has a high pass corner frequency of 80Hz (i.e., the frequency that is down by 3dB).  The Marchand has a standard slope of 24dB/octave but can be made for other slopes.

My second question is whether anyone out there has experience with the Marchand passive high pass filter and is it sufficiently transparent or should I expect to hear unwanted artifacts with the filter in my system?  

Finally, is there a higher quality alternative or should I simply play with the low pass on the sub and forget about filtering the signal to the main speakers?
http://www.marchandelec.com/xm46.html
mitch2
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bdp24
9,487 posts
 
Dang, my momma was right when she told me I shoulda finished high school.
mitch2 OP
3,697 posts
 
Thanks again Al.  It seems the 0.047uf caps will be a good start.  If the cut-off is at 68Hz then that will actually be perfect and if it is at 34Hz then it still relieves the amplifier from trying to drive the lowest frequencies.  Another thing I could do is to try some less expensive caps first to determine the correct value, and then later move up to the caps I want to use.

I also appreciate the analysis and technical information because one of my favorite things about this site is learning about stuff I don't fully understand.

In summary, there doesn't seem to be anything close to a universal answer to this situation.  I have decided not to pursue a Marchand filter at this time because I don't want something in the path that may negatively affect the signal going to my main speakers.  The subs do have a (reportedly) high quality on-board high pass filter so I can give that a try.  The single cap in-line interests me and I may give that a try.  If it works well, I could actually wire them inside of my preamp, or make a pair of balanced cables with the capacitors in-line.  From what I have read, it doesn't seem to matter where the caps are placed as long as they are between the preamp output and the amplifier input.  Some put them inside the input of the amplifiers.

Thanks for everyone for the comments and help.
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almarg
9,670 posts
 
Sounds like a plan, Tim!  Best of luck.

-- Al
 
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bdp24
9,487 posts
 
For owners of Music Reference RM-200 power amps, a bit of clarification: Al's input impedance figure for the amp is correct for only the original incarnation of the amp---30kHz balanced, 15k per leg. In the Mk.2 (current) version of the amp, RM-200 designer Roger Modjeski increased the figure to 60kHz, 30k per leg. That's better for use with some tube pre-amps, which often have somewhat higher output impedances than most solid state pre's.
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