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MultiWay Conventional loudspeakers with crossovers 

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4th September 2013, 01:38 AM  #481  
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Join Date: Apr 2005
Location: Sitting behind the 'puter screen, in Illinois, USA, planet earth

Quote:
If you can, try taking the measurement part of the process outdoors, at say 2 or more meters. There are several issues which complicate the “soup” here. The magnitude and phase one measures from the loudspeaker often change slightly with distance and more so with position left to right / up and down within the radiation pattern. Even a constant directivity horn has this effect to varying degrees. Your measurement mic only occupies one point in space and so what your electronic correction will be based on is that location. So far as fixing the loudspeaker, ideally you would measure at a distance more like how you listen. Even this outdoors could have a built in problem is the woofer is high enough to cause a ground bounce. No amount of eq can fill in a strong cancelation notch. Try an alignment this way with the system not including your room related issues, just loudspeaker correction. Best, Tom
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4th September 2013, 01:47 AM  #482 
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Thanks Tom. I have kindasorta done this, without taking the speakers outside. That is a major pain, as they are so big and heavy. They barely fit thru the door.
I've done the correction from measurements taken at 5 ft, at the listening position, and from simulated filters and box response. Trying to make sense of it all.
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4th September 2013, 05:43 PM  #483 
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Join Date: Jan 2006
Location: grenoble

Thanks pos !
also for the "dark side of the force" i 've just taken ŕ look to the brickwall implementation. as you said,complementary filter must be done manualy with the same parameters. after generating 2 complementaries brickwall filters with 2 differents types of windows, export to REW and process the sum it does not give an allpass. a lot of care and minimum training ... a deep look with rePhase next weeks. summer starts to get down PS:the raised cos EQ in a minimum phase option to apply shelving min.ph. 
4th September 2013, 09:34 PM  #484 
diyAudio Member

Hi Thierry,
Optimization and energy centering are automatically disabled when a brickwall filter is used, so you just need to use the same number of taps and windowing algorithm (and same sampling frequency of course) for the LP and HP and you will get a perfectly complementary crossover. Here is an illustration using a nuttall window: Now here is what you get if you mismatch either the windowing algorithm or the number of taps:
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No loudspeaker system even approaches real life so there is plenty of room for interpretation  Greg Timbers 
4th September 2013, 09:36 PM  #485 
diyAudio Member

Here is another set of pictures to illustrate the effect of the number of taps, frequency, or windowing algorithm
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No loudspeaker system even approaches real life so there is plenty of room for interpretation  Greg Timbers 
4th September 2013, 09:42 PM  #486 
diyAudio Member

I implemented brickwall filters them into rePhase because many people wanted them, and because they were easy enough to add, but using "real" complementary filter slopes (LR, HorbachKeele, or other available types) and making the result curves match the target ones as closely as possible (using optimization and the appropriate number of taps and windowing algorithm for the task) is probably the best way to go.
Brickwalls will give you the sharpest possible slope for a given number of taps and windowing algorithm (and even that is not true with optimization...), but not the lowest ripples, and no real control on the slope whatsoever. Plus, the fact that the exact same number of taps has to be used for the LP and HP is a waste of DSP power when most hardware solutions make it possible to arbitrarily distribute taps among channels...
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No loudspeaker system even approaches real life so there is plenty of room for interpretation  Greg Timbers Last edited by pos; 4th September 2013 at 10:05 PM. 
21st September 2013, 08:44 PM  #487 
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Join Date: Nov 2010

I sat and played around some and got some questions since I'm no FIR expert =)
Assume only phase correction: How big an evil is it to use few taps? Say you have a 24 dB roll off @ 20 hz and use 2048 taps with a FFT length of 8192. Apart from not having a perfect LR4 phase response what is the downside of doing this? Won't the speaker itself have much bigger phase response ripples or is there something I'm not seeing? My current plan is to phase correct a LR4 @ 100 hz, one at 200 hz and the question become if I should also correct the phase of the 20 hz LR2/LR4 low frequency roll off or should I let it be? Last edited by OllBoll; 21st September 2013 at 08:53 PM. 
21st September 2013, 10:25 PM  #488 
diyAudio Member
Join Date: Nov 2010

Or how small must the phase ripples be for it to be good enough? And lets say this phase compensation isn't broadband but rather up to 200 hz and above that another filter with less ripple is used, does that give us bigger room to play with?

22nd September 2013, 10:42 AM  #489 
diyAudio Member

Hi OllBoll,
When doing phaseonly corrections with few taps you will get alteration in the amplitude and phase curves, but the optimization steps will try to compensate any amplitude alteration. You can check this effect by choosing a very narrow amplitude scale like 1/+1dB, and you should see amplitude ripples around your corrected crossover frequency than should diminish with optimization iterations. But these optimization will cause phase to get worse, as you noted. The optimization focuses on amplitude as this was judged the most important thing to preserve, but there will eventually be a point of diminishing return. Having a phase curves that does not exactly follow target is probably not a problem (and it is still better than no correction at all), but rapid variations and ripples can be problematic. Best thing would be to check what group delay those will cause (adding a group delay visualization in rephase is on the todo list...). As to what should be corrected or not, it is up to you to try
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No loudspeaker system even approaches real life so there is plenty of room for interpretation  Greg Timbers 
22nd September 2013, 11:22 AM  #490 
diyAudio Member
Join Date: Nov 2010

Thanks for the answer =)
One thing I thought about when testing, would be nice to have the ripple denoted in dB instead of having to count zeroes =) 
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