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RE: Active crossover with 48dB slope capability?

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In Reply to: RE: Active crossover with 48dB slope capability? posted by T NUC on October 21, 2009 at 21:18:47

I don't know about the Marchand ss crossovers, but you can run your signal through his tube crossover first through the left channel and then through the right to get 48dB/octave slopes -- but then you will need two units for stereo. This is an excellent crossover, though. Phil might also make custom cards that can do 48 -- I know that the cards can be modded to give 6 to 18 dB/octave slopes and/or notch filters.

Have you tried DEQX or TACT?

Follow Ups:

RE: Active crossover with 48dB slope capability? - Jim_E 09:50:14 10/22/09 (5)
David,
The only advantage of the DEQX and TACT units is their room correction algorithms. Room correction algorithms are essential for very large rooms with multiple delayed speakers (such as churches, auditoriums, etc). With a pair of planer speakers in a home living room, I'm not sure that room correction EQ and delay processing is really all that beneficial.

The nature of the room correction will end-up balancing the combined direct and reflected sound with EQ. This will result in the direct sound having excessive EQ to make up for the absorption of the reflected sound by the room surfaces and furniture. This is not a bad approach with conventional box speakers, but some might find it unpleasant with maggies.

The room correction is also only as good a the measurement microphone which is used. Use of an non-calibrated microphone will introduce additional frequency and phase errors.

Finally room correction needs to be optimized for all the possible listening positions that you might use (only at the center of the couch, or each of the possible listening areas?). Many of these units will process multiple locations, but then your still just averaging the total direct and reflected sound.

Some EQ for the lowest bass frequencies (room responses) may be beneficial, but I personally find the higher frequencies room corrections to generally be unnecessary and objectionable, unless you have a very "live" room without carpet/curtains, etc.

There are a number of commercial (professional) DSP processors that provide this capability as well. In my opinion, the TACT and DEQX seem to be more about boutique hi-end marketing, than improved performance over the more widely available and better supported commercial products.

regards,
Jim
- RE: Active crossover with 48dB slope capability? - hemholtz 12:55:46 10/26/09 (2)
  when you make your crossovers on a deqx the correction is anechoic and is to correct the speakers. it aligns the drivers in time so you don't get the phase shift. the room correction is mostly for the lower frequencies, which is needed more in small rooms than large ones. the difference in clarity is night and day.
  - RE: Active crossover with 48dB slope capability? - Jim_E 16:16:19 10/26/09 (1)
    If you have a users manual I'd be interested in seeing it. They don't have them online.
    
    Driver phase delay adjustment for a planar speaker seems pretty pointless.
    
    There is commercial software (MLSSA) that allows a pseudo measurement of anechoic characteristics using gated response measurements and FFT algorithms. One could use this data to then apply digital filtering to correct the direct response for one point in space. The DEQX is likely using some variation of this approach. The ability to gate low frequencies signals is pretty limited (wave length vs. reflection), so this technique usually falls apart below 500 Hz or so depending on the room size, etc.
    
    There are no free lunches however, all the EQ that is used also modifies the phase relationships and the impulse responses.
    
    It sounds like your pleased with final result of this product, which is great.
    
    respectfully,
    Jim
    - RE: Active crossover with 48dB slope capability? - hemholtz 18:26:17 10/26/09 (0)
      if you look a little deeper into the deqx site you will find more info. the phase alignment on planars is definitely worthwhile. the point is to maintain flat phase through the crossover. the way they do it is to divide the frequency spectrum into many (thousands?) slices and then align the slices. they call it group delay as certain groups of frequencies need to be aligned (especially the ones in the mid/high crossover). the only way to do that is to very carefully measure the system output. i admit they try not to be super specific about their algorithms but it's pretty damned good and repeatable by my experience. i've gone so far as to use other measurement software just to check what they're doing. here's a phase measurement at the listening position after correction. this is absolutely amazing. i know for a fact that results like this are not only very audible, but not attainable by any other means with multidriver loudspeakers. the included parametric eq can fix just about any room issues you might have. they call it "minimum phase" parametric, but at those low frequencies it's just trial and error to get it all to line up. i didn't use their "room correction" software, i just did trial and error with cuts and adds to flatten things out and time the different bass drivers in my system for maximum impact and dynamics. i tried the room correction wizard once but thought it was a little too conservative to my ears. it found the same room modes, but didn't make the cuts and adds as steep or as much as i liked. etf5 measurements confirmed what i was hearing.
- RE: Active crossover with 48dB slope capability? - David Yost 04:41:08 10/23/09 (1)
  Thanks for the info, but I mentioned the DEQX and TACT only because of their aggressive (> 24dB/octave) crossover capabilities.
  - RE: Active crossover with 48dB slope capability? - Jim_E 08:58:06 10/23/09 (0)
    David,
    All the digital crossovers I've used will support at least 48 dB/octave filters in either Butterworth, Bessel or L&R configurations
    
    I'm aware the DEQX box will support even higher order filters. The Rane RPM series allows you to design your own filters, thus one could cascade several 48 dB filters as well.
    
    In theory, an infinitely steep crossover would prevent the two adjacent drivers from both radiating the same frequency. This approach eliminates any constructive/destructive interference (comb filtering).
    
    In practice, fourth-order (24 dB/octave) passive crossovers have provided excellent sound for years. These eighth-order digital crossovers are twice as steep as any traditional crossover, which seem more than adequate. I'm not sure going to any higher orders (96 dB/octave?) would really provide any real-world audio improvement. At some point a cliff is a cliff.
    
    regards,
    Jim

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