Using crossover filters on X32

Mitch Miller

Sophomore
Oct 30, 2012
121
1
16
Trying to figure out how to use the crossover filters that were added in a recent (v1.10??) firmware update on the X32. I'm having trouble finding any documentation regarding this new feature, and what little playing I did, didn't seem real intuitive (at least for someone as inexperienced as me).

What I'm really trying to do is configure up an Aux-fed sub.

When we added the subs (and respective amp), I configured bus8 to send to output 13 and sent the audio source (I was playing mainstream music from an MP3 player via an AUX in) to the bus. I configured a low pass filter on the bus to cut everything above 150Hz (I realize the ideal location is something that should be measured and set respectively). But, considering I'm not using the new filters available on the EQ section to matrices, I'm bettin' there is a better way.

I briefly played with the new EQ options available on the MTX's, but I'm not quite 'getting' how say a BU12 is different from a low pass filter with a 12db slope, and why the BU12 uses a second EQ on the matrix.

I know this really belongs in the elementary-school category, but I didn't see one of those here. ;) Thanks in advance for your guidance.

-- Mitch
 

Silas Pradetto

Graduate Student
Re: Using crossover filters on X32

I have no idea to what extent the X32 implements crossover functionality. However, I can tell you a little about crossovers:

There are 3 common shapes, Butterworth, Linkwitz-Riley, and Bessel. They can all have different slopes, often in 6dB/octave increments.

I'm betting BU = Butterworth, and I'm guessing it uses up two EQ filters because it uses extra DSP power to process it.

Also, 150Hz is way too high for a subwoofer low-pass.
 

Mitch Miller

Sophomore
Oct 30, 2012
121
1
16
Re: Using crossover filters on X32

Thanks Silas. Yeah, I know the BU is the Butterworth, and they have BU's with multiple slopes (I think it's 12, 18 and 24db slopes, but would have to look again to be sure; I don't have it in front of me). There are two others, I believe BS was one (most likely Bessel), and I don't remember the 3rd.

-- Mitch
 

Silas Pradetto

Graduate Student
Re: Using crossover filters on X32

Thanks Silas. Yeah, I know the BU is the Butterworth, and they have BU's with multiple slopes (I think it's 12, 18 and 24db slopes, but would have to look again to be sure; I don't have it in front of me). There are two others, I believe BS was one (most likely Bessel), and I don't remember the 3rd.

-- Mitch

Crossover design is something a bit more complicated than I can describe in a single post. Each slope imparts a different amount of phase shift at the crossover point, and it can affect the overall polarity of the signal outside of the crossover region as well. By far the most common crossover design is using symmetrical LR24 crossovers on the low pass of the sub and high pass of whatever full range box is adjacent to it, but just because it is the most common does not mean it is the best. Crossover frequencies for real subs is often at 80Hz or maybe even lower, but as high as 100Hz is common also. Remember that the crossover frequency number has little to do with the acoustical crossover, which can be seen with measurement. Most often, the acoustical crossover is higher than the numeric crossover because subs are run much hotter than tops, relatively speaking. Running aux fed subs gives you an extra variable, since the relative level of subs to tops is now able to be varied easily.

You have to realize that crossover design is something highly measurement-dependent and could even change based on physical speaker locations.

Always remember, "If it sounds good, it is good."
 

John Roberts

Graduate Student
Jan 12, 2011
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MS
www.resotune.com
Re: Using crossover filters on X32

Another common standard filter alignment is Chebychev but using textbook filters to parse real world audio signals including driver transfer functions, and delays due to physical driver spacing is not trivial, or obvious. YMMV

JR
 

Mitch Miller

Sophomore
Oct 30, 2012
121
1
16
Re: Using crossover filters on X32

Thanks Douglas & John. I'll check out the video.

ETA: Ah yes, that is the video I found earlier. Thanks again.
 

Bennett Prescott

Just This Guy, You Know?
Staff member
Jan 10, 2011
10,858
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Wallingford, CT
www.bennettprescott.com
Re: Using crossover filters on X32

Another common standard filter alignment is Chebychev but using textbook filters to parse real world audio signals including driver transfer functions, and delays due to physical driver spacing is not trivial, or obvious. YMMV

Calling Chebychev common is a bit of a stretch, considering most DSPs don't even implement it. Even NTM is more prevalent.
 

John Roberts

Graduate Student
Jan 12, 2011
2,309
3
38
MS
www.resotune.com
Re: Using crossover filters on X32

Calling Chebychev common is a bit of a stretch, considering most DSPs don't even implement it. Even NTM is more prevalent.
You are correct, it isn't a common crossover alignment, just another type of filter. The last Chebyshev filter i designed was back in the '70s so not exactly done with DSP. The several crossovers i designed (also not DSPs) used Butterworth or Linkwitz-Riley alignments, which would be popular or common crossover filters.

Trying to KISS, I didn't mention staggered pole, subtractive (?), or asymmetrical crossovers. I even avoided my normal pedantry of observing that 4 pole L-R is actually two cascaded 2 pole Butterworths.

While not actually called Chebyshev, I've seen some very Chebyshev looking alignments used in some LF cabinets, where an under damped filter pole, tuned lower than the real pole in the box response extends the combined response flatter-lower, exactly like the namesake filter alignment.

This is clearly TMI for this thread, but I felt like a little "stretch" this morning.

JR