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Old 27th October 2005, 11:39 AM   #1
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Question How to build DIY 8th order 48db active crossover??

Sorry about the long title...wanted to make it as search friendly as possible...especially since Yahoo! crawls this place.

Couldn't really find any information on it, but do you build an 8th order active crossover by cascading two 4th order Linkwitz crossovers?
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Old 27th October 2005, 11:56 AM   #2
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Linkwitz-Riley is just a filter slope characteristic. To make an 8th-order filter you just cascade 2 4th-order filters. The resulting Q will be filter_1 Q * filter_2 Q

If you want an 8th-order Linkwitz-Riley response, you need to cascade 2 4th-order Butterworth filters.
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Old 27th October 2005, 12:24 PM   #3
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I'd suggest doing a little research on Jon Marsh's Cauer Eliptical filters on the DIY portion of www.htguide.com. His filters typically exhibit 8th order LR slopes with less components.
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Old 27th October 2005, 12:36 PM   #4
Emiel is offline Emiel  Europe
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Elliott describes the construction of a 36dB/octave filter (only the high pass section) cascading two 18dB/octave Butterworth filters. See http://sound.westhost.com/project99.htm, maybe some interesting info there!

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Old 28th October 2005, 12:28 AM   #5
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I couldn't find the Project 99.

I found these active crossover filter circuit schematics. They cover;

Quote:
Butterworth 1st order Lowpass
Butterworth 1st order Highpass
Butterworth 2nd order Lowpass
Butterworth 2nd order Highpass
Butterworth 3rd order Lowpass
Butterworth 3rd order Highpass
Butterworth 4th order Lowpass
Butterworth 4th order Highpass
Bessel 2nd order Lowpass
Bessel 2nd order Highpass
Bessel 3rd order Lowpass
Bessel 3rd order Highpass
Bessel 4th order Lowpass
Bessel 4th order Highpass
Linkwitz 4th order Lowpass
Linkwitz 4th order Highpass
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Old 28th October 2005, 02:40 AM   #6
jdybnis is offline jdybnis  United States
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Look here: http://sound.westhost.com/articles/ntm-xover.htm

Also, if you want to go passive look at Jon Marsh's cauer elliptical crossover. Search for "cauer" on htguide.com. I like the transfer function better than the ESP crossover above. OTOH, implementing an active version is evidently challenging. You'll see something about that on htguide.
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Old 28th October 2005, 06:59 AM   #7
Emiel is offline Emiel  Europe
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Quote:
Originally posted by Hybrid fourdoor
I couldn't find the Project 99.
Sorry, here's the correct link:
http://sound.westhost.com/project99.htm


Kind regards, Emiel
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Old 24th April 2014, 03:54 PM   #8
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Quote:
Originally Posted by Hybrid fourdoor View Post
Sorry about the long title...wanted to make it as search friendly as possible...especially since Yahoo! crawls this place.

Couldn't really find any information on it, but do you build an 8th order active crossover by cascading two 4th order Linkwitz crossovers?
To make an 8th order Linkwitz Riley filter you have to cascade two 4th order butterworth filters to give you -6db at the cut off frequency. Cascading two 4th order Linkwitz riley filters would give you -12db at the cut off frequency which is obviously not wanted.
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Old 24th April 2014, 04:15 PM   #9
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I think the question of "what is an 8th order Linkwitz-Riley filter" has been put to rest. Every LR filter is two Butterworth filters of half the order in series. This is why the LR filter type is called "Butterworth squared" and only even orders exist.

Here is some advice on "How" to do it:
There is certainly more than one way to construct an active 8th order crossover (don't try this as a passive filter!). One way that I would suggest is using two 4th order state variable filters in series. Look up "state variable filter" for more info. For a crossover you will need THREE SV filters: the first provides 4th order LP+HP. You then connect another SVF to the HP output and use its HP output to get 8th order HP out. Likewise you connect the third SVF to the LP output of the first SVF and this produces the 8th order LP out.

By the time you purchase and build all of these circuits and the required power supply you could buy a MiniDSP 2x4 and easily implement an LR8 and many other filter types (all at the same time) and it will cost less.
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Old 25th April 2014, 01:07 AM   #10
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The question was never 'what is an 8th order Linkwitz Riley filter' it was asking how to build one.
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