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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

Showing 7 responses by bdp24

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bdp24
9,510 posts
 
Hmm Al, I'll have to get it straight from Roger. I got the impedance figure from my Mk.2 owners manual.
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bdp24
9,510 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.
bdp24's avatar
bdp24
9,510 posts
 
Dang, my momma was right when she told me I shoulda finished high school.
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bdp24
9,510 posts
 
Great, thanks Al---Eric.
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bdp24
9,510 posts
 
Great question Mitch, one I need the answer to as well! I've done it on a single-ended amp (my Bedini 25/25, for use with Quad 57's and subs), but not a balanced amp. Hopefully someone with more technical knowledge than I can help us out. I have a Music Reference RM-200 Mk.2 waiting for the answer! It has balanced/XLR inputs only. I'll be shooting Roger Modjeski an email, so I'll let you know what he says.
bdp24's avatar
bdp24
9,510 posts
 

Ah, okay, it's passive you want. The purist way to high-pass filter the signal going to your power amp and speakers, to relieve them of reproducing bass frequencies (a worthwhile objective imo), one that has been used since the DIY 1950's, is to install a single capacitor (the value of which is determined by 1- your power amp's input impedance, and 2- the desired x/o frequency) on the inside of your power amp, on it's input jacks. This will create only a 1st-order, 6dB/octave filter. That is the way to incur the least damage to the signal, both by the use of but a single part---a capacitor, and by removing the need for an extra inter-connect---no x/o box necessary. The formula for determining the capacitor value required for your application can be found all over the 'net.

What I have heard from other Magneplanar Tympani owners on the Planar Speaker Asylum, many of whom use Marchand active x/o's in their systems, is that the active Marchands are actually better sounding than the passive ones. How can that be, you ask? Aren't passive parts more transparent than an active circuit? Look at the parts inside those passive Marchands---the parts necessary to provide a higher-than-1st-order filter. Nasty, ugly sounding things, worse than the parts in an active circuit.

Speaking of ugly sounding parts---all Marchands contain Opamps (except the tube model, one presumes). The First Watt B4 is completely discrete---all resistors and capacitors, no Opamps, no IC's. The B4 provides 1st-2nd-3rd-4th order (6-12-18-24 dB/octave) filters from 25Hz to 3200 Hz, in 25 Hz increments. Incredible! Unfortunately, it is available unbalanced/RCA jacks only, so may be unsuitable for your system.

bdp24's avatar
bdp24
9,510 posts
 
The Marchand crossovers are very well regarded in the hardcore DIY community. The maker can supply the owner replaceable "cards" to insert in the x/o, providing just about any x/o frequency and slope one desires. And most are available with balanced XLR jacks, unlike the similarly-priced First Watt B4, another fine unit. The B4, unlike the Marchands, contains no Opamps, achieving filtering via all discrete parts. The B4 also needs no extra-cost filter cards, having internal dip-switches to set frequency and slope characteristics.
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