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TOPIC: Re: 4th order bessel crossover

4th order bessel crossover 9 years 5 months ago #3156

  • john.reekie
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Hi, a fourth-order Bessel filter crossover would be handy. See:

www.rane.com/note147.html
I am not miniDSP support.

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Re: 4th order bessel crossover 9 years 5 months ago #3169

  • devteam
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Hi John,

How about simply plug-in it into the biquad spreadsheet (i.e. update the custom spreadsheet) and you can build it in very little time?

There are many filters out there, and put it simply, we're never going to be able to have all of them implemented. There will always be a new one required.. :-)

DevTeam
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Re: 4th order bessel crossover 9 years 5 months ago #3175

  • john.reekie
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The spreadsheet only does second-order filters.
I am not miniDSP support.

"You must ask the right questions." - Dr. Alfred Lanning's hologram.
-> Have you read the User Manual??
-> Have you drawn and posted a diagram?
-> Have you posted a screenshot?
-> Have you posted your config file?
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Re: 4th order bessel crossover 9 years 5 months ago #3179

  • dreite
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John,

Do you know how to do this, or are you aware and just asking miniDSP to incorporate the functionality?

If the former, then it's a little cutting and pasting from the spreadsheet and you can get there in a few minutes.

For example: For a 4th-order, 400Hz Bessel LPF, you'd input 400Hz and Q=0.759 into the spreadsheet which will generate a set of 2nd-order coefficients. Paste those into the biquad1 and biquad2 locations and fill in the rest as usual to paste into the advanced plug-in.

This will yield a 400hz Bessel LPF with Q=0.577.

Your result should look like this:

biquad1,
b0=0.000662395277357,
b1=0.001324790554713,
b2=0.000662395277357,
a1=1.930694674258500,
a2=-0.933344255367930,
biquad2,
b0=0.000662395277357,
b1=0.001324790554713,
b2=0.000662395277357,
a1=1.930694674258500,
a2=-0.933344255367930,
biquad3,
b0=1,
b1=0,
b2=0,
a1=0,
a2=0,
biquad4,
b0=1,
b1=0,
b2=0,
a1=0,
a2=0,
biquad5,
b0=1,
b1=0,
b2=0,
a1=0,
a2=0,
biquad6,
b0=1,
b1=0,
b2=0,
a1=0,
a2=0,
biquad7,
b0=1,
b1=0,
b2=0,
a1=0,
a2=0,
biquad8,
b0=1,
b1=0,
b2=0,
a1=0,
a2=0,

Hope that helps.

Dave.
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Re: 4th order bessel crossover 9 years 5 months ago #3188

  • knuisje
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The biquad spreadsheet calculates 2nd order filter coefficients. Higher order filters for dsp's are constructed by cascading 2nd order filters. So a 4th order filter is constructed by using two 2nd order filters, a 6th order by using three 2nd order filter and so on.

The trick is to use the correct Q values for calculating higher order filters. At section 16.9 in this document you can find these Q values (for Linkwitz-Riley filters look here).

In table 16-4 you'll find that a 4th order Bessel filter is constructed by cascading two 2nd order filters, the first one having a Q of 0.52, the second one with a Q of 0.81.
In the spreadsheet you calculate these two filters (400Hz LPF) giving the following result:

biquad1,
b0=0.000652401784953,
b1=0.001304803569907,
b2=0.000652401784953,
a1=1.901566473590970,
a2=-0.904176080730782,
biquad2,
b0=0.000663788184815,
b1=0.001327576369630,
b2=0.000663788184815,
a1=1.934754605093700,
a2=-0.937409757832964,
biquad3,
b0=1,
b1=0,
b2=0,
a1=0,
a2=0,
biquad4,
b0=1,
b1=0,
b2=0,
a1=0,
a2=0,
biquad5,
b0=1,
b1=0,
b2=0,
a1=0,
a2=0,
biquad6,
b0=1,
b1=0,
b2=0,
a1=0,
a2=0,
biquad7,
b0=1,
b1=0,
b2=0,
a1=0,
a2=0,
biquad8,
b0=1,
b1=0,
b2=0,
a1=0,
a2=0
Last Edit: 9 years 5 months ago by knuisje.
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Re: 4th order bessel crossover 9 years 5 months ago #3192

  • dreite
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Yes indeed. Thank you for correcting my mistake.

Cheers,

Dave.
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Re: 4th order bessel crossover 9 years 5 months ago #3208

  • john.reekie
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Thanks guys! I'll give that a try.

With regard to the specific suggestion I was suggesting that miniDSP might be interested in implementing the "phase match" normalization described in the Rane paper: "Rane's Bessel crossover is set for phase match between low-pass and high-pass. This minimizes lobing due to driver separation, and also results in a pretty flat combined response."
I am not miniDSP support.

"You must ask the right questions." - Dr. Alfred Lanning's hologram.
-> Have you read the User Manual??
-> Have you drawn and posted a diagram?
-> Have you posted a screenshot?
-> Have you posted your config file?
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