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Author Topic: Creating high pass with PEQ  (Read 5080 times)

Helge A Bentsen

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Creating high pass with PEQ
« on: December 07, 2017, 09:30:44 AM »

On a speaker system with a fixed mains HP on 60hz and selectable 60 or 100hz low pass on the subs.

If you wish to use 100hz on the subs and minimize overlap with the flown mains, is there a way to make a 100hz HP with PEQ filter(s)?

Or do I need to look in the direction of external processing?


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Chris Grimshaw

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Re: Creating high pass with PEQ
« Reply #1 on: December 07, 2017, 09:45:25 AM »

On a speaker system with a fixed mains HP on 60hz and selectable 60 or 100hz low pass on the subs.

If you wish to use 100hz on the subs and minimize overlap with the flown mains, is there a way to make a 100hz HP with PEQ filter(s)?

Or do I need to look in the direction of external processing?

Definitely possible. Try 75Hz, Q=2.4, -15dB. That gets you a -6dB point of 100Hz, which should work nicely with a Linkwitz-Riley crossover on the lowpass of the subs once delay/polarity is sorted.

Probably worth getting out the measurement system to make sure you've got it nailed down, but in theory this'll work fine.

Chris
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John Roberts {JR}

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Re: Creating high pass with PEQ
« Reply #2 on: December 07, 2017, 09:53:27 AM »

active crossovers are the right tool for the job... a PEQ will only offer a bandpass cut, or bandpass boost. Tricking one of the bandpass skirts as a HPF or LPF ignores the other skirt...

JR
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David Morison

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Re: Creating high pass with PEQ
« Reply #3 on: December 07, 2017, 10:09:13 AM »

On a speaker system with a fixed mains HP on 60hz and selectable 60 or 100hz low pass on the subs.

If you wish to use 100hz on the subs and minimize overlap with the flown mains, is there a way to make a 100hz HP with PEQ filter(s)?

Or do I need to look in the direction of external processing?

Depends how much PEQ you have available and just how close to an ideal HPF alignment you need.
Obviously, the fixed HPF in your example above takes care of the low frequency skirt JR alluded to, for the high side it's just a case of finding what works for you.
Below are two options - white trace is the target curve of LR24, Purple is 65Hz, Q 3.5 -15dB which gives a reasonably good match to about the 60Hz point, and green is more complicated - that's two stacked filters each of 40Hz, Q 2 -15dB plus one 130Hz Q 1 +3dB. That gives a closer match to the target curve over a wider bandwidth, but obviously uses 3x the number of filters.

Also - bear in mind different platforms calculate filters differently - I modelled these in WinISD, in this program Chris G's suggestion gave a different -6dB point of 136Hz.
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Mark Wilkinson

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Re: Creating high pass with PEQ
« Reply #4 on: December 07, 2017, 11:43:18 AM »

Ditto to above ....totally works,
since the only side of the bandpass you care about, is for using the PEQ as a high pass filter.

FWIW, so far all the regular channel/main lowcut filters I've measured have all been LR12's,
which you could put 2 together to effectively get a LR24 HP .....if desk allows.


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Helge A Bentsen

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Re: Creating high pass with PEQ
« Reply #5 on: December 07, 2017, 04:16:53 PM »

Thanks guys.

I have something like 6 PEQ filters available but for some reason this manufacturer has decided to not give us the option of an adjustable HPF.

I'll try a couple of your suggestions and see if it measures right.

BTW: Because it's an install, I'm trying to do this using the manufacturers DSP/amps.  If it was a touring setup, I'd just bring a Lake.
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Chris Grimshaw

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Re: Creating high pass with PEQ
« Reply #6 on: December 07, 2017, 05:30:07 PM »


Also - bear in mind different platforms calculate filters differently - I modelled these in WinISD, in this program Chris G's suggestion gave a different -6dB point of 136Hz.

I was using Hornresp. The horizontal scale is course, but I didn't think it was that course.
Suppose it's best to measure the end result - IIRC, Ivan has mentioned that different processors give different curves with the same settings.

Chris
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David Morison

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Re: Creating high pass with PEQ
« Reply #7 on: December 07, 2017, 05:54:05 PM »

I was using Hornresp. The horizontal scale is course, but I didn't think it was that course.
Suppose it's best to measure the end result - IIRC, Ivan has mentioned that different processors give different curves with the same settings.

Chris

You're not wrong - Hornresp does indeed give -6dB @ 100 for the settings you suggested - it's just an example of how far off the calculations can be when they're done differently.

WinISD's reckons the Q needs to be as tight as 5.2 to get that same -6dB point.

I would however still recommend starting with a centre freq lower than 75Hz if LR24 is the desired target - it has it's -15db point at 68Hz anyway, so I wouldn't want the -15dB point of the PEQ any higher than that.

FWIW,
David.
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Mark Wilkinson

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Re: Creating high pass with PEQ
« Reply #8 on: December 07, 2017, 06:14:22 PM »

OK my measuring skills far surpass my modeling skills,
so I just quickly put together what I'd do to make a LR24 HP with PEQ, knowing a 60Hz HP is already in place.

Board is a x-32..sorry Helge, I've none of your exemplary gear !

Oh, another FWIW, I've measured a bunch of filters, x-32 vs qsc vs linea research, and they all measure the same...I'm not so sure simple widely used filters are much different anymore....maybe they start to differ when they get complexly combined???  I plain dunno....

But using three PEQs, 60.4Hz, -14.5dB, 5.0Q, 79.6 Hz, -15dB, 2.4Q, and 82.4Hz, +4.75, 5.0Q, (frequencies are as available on x-32)
I get the following transfer,
 
x-32 24LR HPF @100Hz as reference, PEQs as measured.....

edit: sorry, too much wine ...redo



« Last Edit: December 07, 2017, 06:26:41 PM by Mark Wilkinson »
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Chris Grimshaw

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Re: Creating high pass with PEQ
« Reply #9 on: December 07, 2017, 06:30:19 PM »

You're not wrong - Hornresp does indeed give -6dB @ 100 for the settings you suggested - it's just an example of how far off the calculations can be when they're done differently.


Amazes me every time. Thanks for the sanity check.

Chris
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Re: Creating high pass with PEQ
« Reply #9 on: December 07, 2017, 06:30:19 PM »


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