Krohn-Hite filter...useful as subwoofer x-over?

[Freq Band]

Just checking....this will work, right?....

....from a preamp's extra mono output,
...into the KH filter (low pass)...
...into subwoffer amp..
...and adjusted to proper cutoff freq of main speakers..

??

KH makes many filters, so I assume a 4th order butterworth or ?

Adjustable slope too ?

I am using NYDave's style "mono summing" circuit to achieve a mono output tapped off the preamp's stereo output.

Yes, I could build a x-over, but I live in a curved universe. :?


=FB=

 

[emrr]

Should work fine. Not sure about the later ones, but the earliest are "24db/octave with peaking factor to reduce attenuation at cut-off frquencies." 5K ohm output in 'high', 500 ohm output in 'low'.

 

[bcarso]

Besides the slope and peaking of the lowpass, look closely at the main speaker characteristic. Phase effects, especially in the crossover region can lead to remarkably large effects in amplitude. Try inverting relative polarity as one of the variables.

The classic crossover with flat amplitude response is four-pole, made from two identical two-pole butterworth, for both LP and HP, same 3dB freq for each of the four two-poles. But this assumes that the drivers are raditating from the same physical position, and this will not likely be the case. And of course the room modes need to be considered in woofer placement. A few moderate Q parametric dips can be helpful for the sub, as well as multiple subs in strategic locations. It can be quite tricky to get good flat bass coverage for multiple listening positions, which if not addressed can lead to serious producer/engineer conflicts.

 

[JohnRoberts]

The 4 pole L-R crossover is popular for steep roll-off and being so far out of phase it rotates back in again at crossover point. This phase response is important for symmetrical crossovers between adjacent drivers in the same box but perhaps less so with a mono add on sub.

Ideally you would want to mimic the inverse of the main loudspeakers LF which will be pretty low order (depends on if ported and box tuning). This assumes that a low order crossover provides adequate driver protection at upper limits of sub's response.

For this application I like the behavior of a "staggered pole" approach where crossover region is low order to mimic speaker's response with additional poles maybe an octave higher if needed for driver protection.

Another angle, if the SUB is big dog compared to full range speakers, using a true symmetrical crossover (like 4 pole L-R) say an octave higher than the box's LF roll-off will also increase it's excursion limited power handling, but viability of this depends on sub's and box's relative bandpasses and power handling.

JR