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Author Topic: Crossover filters @ the processor outputs summed  (Read 3281 times)

Mark McFarlane

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Re: Crossover filters @ the processor outputs summed
« Reply #1 on: January 31, 2015, 06:12:08 am »

Thanks Timo.  FWIW, clearly captioned snapshots would be more useful for my learning rather than trying to scroll through a video with annoying noise :).
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Mark McFarlane
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Turn down what's too loud.

Timo Beckman

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Re: Crossover filters @ the processor outputs summed
« Reply #2 on: January 31, 2015, 07:33:08 am »

Thanks Timo.  FWIW, clearly captioned snapshots would be more useful for my learning rather than trying to scroll through a video with annoying noise :).

like......

Sorry ;-) but if i use music i'll probably end up paying for the use of that music.
For the rest of it You see things happening in real time which was what i intended. Maybe if i have time to explain everything happening with screenshots i'll do so but my time is limited for now sorry.
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Timo Beckman

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Re: Crossover filters @ the processor outputs summed
« Reply #3 on: January 10, 2016, 10:33:24 am »

I did another screen recording with a new "toy". 2 outputs summed out of a Linea Research processor.
First with linkwitz-riley 4rt order high&low-pass filters and after that LIR high&low-pass filters (phase linear filters) @1kHz.
2nd part the same as the first but this time the x-over frequency is at 125Hz. enjoy

https://timobeckmangeluid.wordpress.com/2016/01/08/playing-around-with-a-new-toy-linea-research-asc48/

Sorry for the pinkish stuff....... ;-)
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John Roberts {JR}

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Re: Crossover filters @ the processor outputs summed
« Reply #4 on: January 10, 2016, 11:35:17 am »

Summing outputs of active crossovers together is only part of the story.

The only crossover topology that looks good that way is a "derived" crossover. Effectively the HP is derived by subtracting the LP from unity, or vice versa. By definition they will sum to unity. Derived crossovers have other issues like asymmetrical slopes etc.

In addition to the perfect summed response you need to factor in driver response, and off axis energy. Lots of moving parts to consider and most crossovers involve compromises. i.e. a perfect summed response is not always the best solution or they would be more widely used.


JR
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Frank Koenig

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Re: Crossover filters @ the processor outputs summed
« Reply #5 on: January 10, 2016, 12:44:52 pm »

Hooking an analyzer to a processor is a good exercise in learning to use those tools and good for a visual demonstration of some of the properties of the available filters. Also, a knowledge of certain classic filter pairs, such as those that sum to unity or an all-pass is conceptually valuable.

For any real crossover development the electro-acoustic transfer functions of the loudspeakers need to be incorporated into the chain, so this all becomes more cumbersome. My preferred approach, and I assume that of most developers, is to gather electro-acoustic data over a range of angles using a measurement program, process these data statistically employing some judgement and heuristics to create a target electrical response, and then synthesize this response using some combination of mathematical analysis and simulation. Everything except the actual measurement can be done in the comfort of your office without having to listen to pink noise, and even if it's windy or raining.

I write my own simulations in R, many folks these days would use Python, and I'm sure general purpose electrical circuit simulation programs are used, too. Then I go back and measure and listen to see (hear) what I got.

As for classic pairs: There's LR (all of even-order). All odd-order Butterworths (of the same cutoff frequency) sum to an all-pass, the order of which depends on whether the polarity of one of the pass-bands is inverted. And, of course, the 2nd order Butterwoth with one polarity inverted as found in pretty much every old two-way Altec, JBL, etc. speaker. Add to this list.

Best,

--Frank

PS:This works for passive crossovers, too. In this case I measure the electrical impedance to incorporate into the model. I've been playing with using optimization to generate element values for passive filters given a topology and a target response. I'm not really an optimization guy so I've just been using the built-in optimization functions in R, and with a little fooling around, they seem to work.
« Last Edit: January 10, 2016, 12:54:06 pm by Frank Koenig »
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Timo Beckman

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Re: Crossover filters @ the processor outputs summed
« Reply #6 on: January 10, 2016, 04:47:43 pm »

I'm just starting with this unit so no speakers yet. This will be the next step when i have time. The video is just me learning about this unit and what it does just summing 2 outputs.
When i know what it is doing without speakers i'll start using it with speakers and see what happens.
It's also to show that going phase flat has a down side which is latency.
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Mark Wilkinson

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Re: Crossover filters @ the processor outputs summed
« Reply #7 on: January 14, 2016, 01:35:06 pm »

Hooking an analyzer to a processor is a good exercise in learning to use those tools and good for a visual demonstration of some of the properties of the available filters. Also, a knowledge of certain classic filter pairs, such as those that sum to unity or an all-pass is conceptually valuable.

Yes, this relatively simple exercise is helping me learn a few filter properties.....not to mention helping to learn how to set up tests.

For curiosity, and in case anyone cares,......I just ran transfers on various X-over filters, X-32 matrix outs vs QSC PLD amp outs.   
Everything I tried straight-lined, which I was really glad to see ......for consistencies sake between one manufacturer to another.
Going to check out parametric and shelving next...

edit:  thought I should add further evidence that the x-over filter implementations are the same between the two products.
The PLD has 0.77ms latency with no filters, vs a no-filter matrix feed from the x-32. 
Using another X-32 matrix channel with filters as reference,  when the PLD has the same filter settings as the X-32, latency remains the same 0.77ms....no matter what filters i've tried.

« Last Edit: January 14, 2016, 09:04:50 pm by Mark Wilkinson »
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Timo Beckman

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Timo Beckman

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Re: Crossover filters @ the processor outputs summed
« Reply #9 on: October 24, 2016, 12:39:35 pm »

And a brief explanation on the AP2 stuff while changing the drivers phase respons

https://timobeckmangeluid.wordpress.com/2016/10/24/once-upon-a-time/
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