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Author Topic: Crossover phase handling  (Read 6179 times)

Ivan Beaver

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Re: Crossover phase handling
« Reply #10 on: November 08, 2014, 08:48:15 pm »

and then again my main question is:
Do designers apply digital delay to the low frequency section of a multi way system or there´s an implicit convention or some other reason for not doing so and insert whatever it works on the other sections?
Thanks a lot guys!
Regards from Argentina!
So the ANSWER to that question is NO, because it is the HF driver that needs to be delayed-for the reasons Mac and I gave.

Impulse alignment is NOT the way to get a good transition between devices.  PHASE alignment is the proper way to get the best sounding alignment.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Peter Morris

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Re: Crossover phase handling
« Reply #11 on: November 08, 2014, 10:29:38 pm »

So the ANSWER to that question is NO, because it is the HF driver that needs to be delayed-for the reasons Mac and I gave.

Impulse alignment is NOT the way to get a good transition between devices.  PHASE alignment is the proper way to get the best sounding alignment.

Not always, here is an example http://eaw.com/docs/2_Legacy_Products/Processor%20Settings/KF750/KF700_Series_PROCS_rev1.pdf

Some times the LF needs to be delayed.
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Merlijn van Veen

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Re: Crossover phase handling
« Reply #12 on: November 09, 2014, 03:49:15 am »

Hi Everybody,

Maybe the slides from my seminar will help in illustrating the pitfalls from aligning a crossover with impulse response instead of phase.

As has been pointed out, the introduction of filters introduce phase shift on top of physical displacement. This also affects the appearance of the impulse response. Especially for low-pass filters. The impulse response gets stretched over time and amplitude "appears" to have been reduced.

When you align the impulse peaks of both drivers you basically align the high frequencies of the HF driver to the low frequencies of LF driver. As can be seen in the phase (group) delay slide. Chances are you'll achieve the opposite of your goal, summation at XO.

When you align with phase. The "low" frequencies of the HF driver will connect to the "high" frequencies of the LF driver, resulting in summation at XO.

disclaimer: In passive designs where delay is not available. Either driver might lead by physical displacement and/or design. Summation can still be achieved by a combination of 0.5, 1.5, etc... wavelengths out of polarity or 1, 2, etc... wavelengths in polarity phase shift. The payoff is response ripple throughout the XO region proportional to the difference in cycles.


Regards,


Merlijn
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Ivan Beaver

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Re: Crossover phase handling
« Reply #13 on: November 09, 2014, 09:18:03 am »

Yes you did.
But yours is an assumption and I´m providing facts.
The 1.4" compression driver is mounted in a 20cm long wave shaping device. The L.F. driver is a 10" cone.
Impulse measurements confirm, with HPF and crossover engaged, that the cone driver arrives first by far. I´m at home and don´t remember figures.
But forget for a moment this specific example and suppose that you do have a situation like this, would you be so kind to read my first post where I describe two alternatives to put them "in phase" and then again my main question is:
Do designers apply digital delay to the low frequency section of a multi way system or there´s an implicit convention or some other reason for not doing so and insert whatever it works on the other sections?
Thanks a lot guys!
Regards from Argentina!
Let's look at it from a little math approach.

Let's assume a 1Khz crossover and use assume 1Kz is 1' long (just to make it quick and easy). 

Each pole of a crossover is a 45° shift or 0.125' (at 1Khz)

Let's also use 24dB filters (4 poles).  The low freq filter will "move" the woofer back so it moves back 0.5'. 

The high freq filter will "move" the tweeter forward 0.5'.  So now (in most cases) the woofer is "physically behind the tweeter. 

And let's don't forget the possible additional 0.125' lag to the woofer because of the self inductance of the voice coil itself.

So the Tweeter is now "in front" (at least as far as phase is concerned) so it needs to be delayed-NOT the woofer.

Yes the actual physical layout of the cabinet will change things-but it is not a simple physical position that makes you delay one driver vs another.  It is the phase of the drivers at a particular position.

So the real answer is "It depends"
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Ivan Beaver

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Re: Crossover phase handling
« Reply #14 on: November 09, 2014, 09:20:21 am »

Not always, here is an example http://eaw.com/docs/2_Legacy_Products/Processor%20Settings/KF750/KF700_Series_PROCS_rev1.pdf

Some times the LF needs to be delayed.
Agreed-it depends on the particular layout of the particular cabinet.

But "in general" it is the HF that needs to be delayed.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Alberto Escrina

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Re: Crossover phase handling
« Reply #15 on: November 16, 2014, 03:47:22 pm »

Hi everyone,
Finally I have some time to thank you all for your contributions.
Unfortunately the request I presented in my first post took a different turn than intended.
I never actually asked if, in my example, it was the low frequency driver the one that must be delayed or not. I just presented an example when it is.
I never actually said that impulse align was better than phase align or viceversa.
Since English is not my native languague, as you might have noticed already, I might have not expresed myself properly. Sorry about that!
This is why I was asking you to reread my first post. Because the core of the issue was another one.
Anyway, Peter has provided one example that answers my question. EAW does.
Thank you very much for posting and sorry for those misunderstandings!
Best regards,
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Alberto Escriña
R&D for STS Sound Touring Systems
Buenos Aires,
Argentina

Doug Fowler

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Re: Crossover phase handling
« Reply #16 on: November 17, 2014, 04:52:45 pm »


The low pass filter causes an apparent time offset in the low frequency signal which puts it significantly behind all other drivers in the system

Mac

This is widely misunderstood.  I do a demonstration in my classes which easily demonstrates this.  Open the LPF to over 1 KHz, set your analyzer delay locator on "auto" and observe the latency.  Then, begin to lower the LPF down to say, 100 Hz and watch the latency increase.  It's also interesting to open an IR window and watch the IR begin to spread out and lose apparent amplitude due to the apparent "time stretching" of lower frequencies.
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Robert Lofgren

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Re: Crossover phase handling
« Reply #17 on: November 17, 2014, 05:34:43 pm »

Anyone who has any insight about the Le Cleach crossover theory and if it would be suitable for live sound?

http://www.audioheritage.org/vbulletin/showthread.php?4850-A-New-Crossover-Theory
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