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Cross-over slopes...

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dj jammin View Drop Down
Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dj jammin Quote  Post ReplyReply Direct Link To This Post Topic: Cross-over slopes...
    Posted: 20 August 2014 at 8:32pm
When manufacturers state recommended cross-over frequencies, for example: 

Eminence PSD2002, Usable Frequency Range - 1.2kHz-20kHz, Recommended Crossover - 1.2kHz-20kHz/18dB or 1.8kHz/12dB... etc

Does this mean a 24dB filter would be not suitable or possibly could it be better than a 12 or 18dB slope?

I've got all the crossover points in my home-made crossover using link-witz 24dB slopes and it seems to work well but maybe different slopes are better for certain jobs? 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote sn95 Quote  Post ReplyReply Direct Link To This Post Posted: 20 August 2014 at 9:57pm
you can use 24db slopes
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TONY.A.S.S. Quote  Post ReplyReply Direct Link To This Post Posted: 20 August 2014 at 11:54pm
Sometimes complete separation is the answer using steep slopes. Other times lesser slopes are preferred because the overlap that can be heard may suit better. Sometimes steep slopes are required to adjust the response of a speaker that may have some kind of response shape that needs to be got rid of. There is no right or wrong way. A lot of Hi Fi cabs, when used passively, sometimes only have 6 to 12 db slopes. This also keeps the crossover simple and with less components to muddy the water.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 21 August 2014 at 12:18am
ideally you want to get the phase difference at the crossover frequency to be a multiple of 180 degrees so you can get them in phase by reversing polarity if necessary (although an active LMS allows you to add any amount of phase shift). and you want to get the slopes of the phase graphs parallel to each other so they stay in phase either side of the crossover point. remember that the driver and enclosure have mechanical, inductance, and acoustic phase shifts of their own before you apply any crossover. if you don't have measurement equipment you can get it right by looking at simulations and experimenting - a HPF adds phase and a LPF subtracts phase. but i agree with tony, if you use very high order filters the crossover region becomes so narrow that any theoretical problem becomes inaudible.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 21 August 2014 at 1:53am
Originally posted by dj jammin dj jammin wrote:

When manufacturers state recommended cross-over frequencies, for example: 

Eminence PSD2002, Usable Frequency Range - 1.2kHz-20kHz, Recommended Crossover - 1.2kHz-20kHz/18dB or 1.8kHz/12dB... etc

Does this mean a 24dB filter would be not suitable or possibly could it be better than a 12 or 18dB slope?


The manufacturers reccomendations are to be considered the minimum slope used at those frequencies, so 24dB at 1.2khz is fine but 12dB at 1.2khz is not.


Edited by Conanski - 21 August 2014 at 1:54am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RobinMatrix Quote  Post ReplyReply Direct Link To This Post Posted: 21 August 2014 at 8:51am
Personally, for a PSD2002, I find a good crossover frequency to be about 32KHz. Providing you keep them out of the audible range, they are just fine :)

As Tony said, there is no "correct" slope, because you have to remember that the actual delivered response (and therefore the phase) are the combined result of the crossover AND the driver combined. Phase and magnitude response are inexorably linked, so it is a balancing act to get them to match the point on the bass crossover etc. A bass and HF crossover that electrically combine perfectly to give a nice flat response with no overlap and perfect phase alignment when tested on the bench into a dummy load, might work terribly when connected to the drivers with a big dip or peak, and a huge phase error.  Conversley, you could have a crossover that looks like it is terribly overlapped and phasy on the test bench, but produces a perfectly flat response on the actual drivers.

The only way I know that actually produces good results is software that takes the impedance sweep and phase/magnitude sweeps of the actual drivers, in the actual cab and then simulates the crossover circuit and lets you see what you will actually get. We've been able to get them bang on every time this way.  Of course, you still have to trial a few to settle on where you actually want to cross it over, but the design process does allow you to get accurate crossovers that do what you expect.
Matrix Pro Audio ::http://matrixproaudio.com/"
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TONY.A.S.S. Quote  Post ReplyReply Direct Link To This Post Posted: 21 August 2014 at 9:11am
When we were doing the Crossovers for our Auracoustic cabs, we just worked with the box all the time, no sims. The x\o would always be outside of the cab for ease. We would have spent days on them. Even when they seemed right, I was never 100% sure. In the end you have to make a decision. Although I always advocate neutral boxes, The balance of the x/o will always voice the cab. Quality of components will aways play a part in the sound. It's definitely a Black Art.



Edited by TONY.A.S.S. - 21 August 2014 at 5:44pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djeddie Quote  Post ReplyReply Direct Link To This Post Posted: 21 August 2014 at 9:26pm
Originally posted by RobinMatrix RobinMatrix wrote:

Personally, for a PSD2002, I find a good crossover frequency to be about 32KHz. Providing you keep them out of the audible range, they are just fine :)

Why, oh why, did it take me so long to get the humour! But totally correct!
Chas n Dave : it's like Drum and Bass but with beards.             E=mc² ±3dB
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dj jammin View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dj jammin Quote  Post ReplyReply Direct Link To This Post Posted: 21 August 2014 at 11:23pm
Did have to read that twice myself! This is not a driver I own just an example but I have heard they're not the best LOL

Thanks for all the answers, I think I have a better understanding of the subject now...
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