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Old 6th August 2008, 02:43 AM   #1
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Default Changing a passive crossover to active

Hi,

Just wondering if I currently have a pair of 2 way bookshelf speaker using a passive crossover and if I find out the crossover point, could I then buy a Behringer SUPER-X PRO CX2310 (http://www.behringer.com/CX2310/index.cfm?lang=ENG) and set it to that crossover and it would work?

Along with 4 channels of amplification.

Is it that simple?
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Old 6th August 2008, 02:59 AM   #2
DougL is offline DougL  United States
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Quote:
and it would work?
I want to give you a qualified yes.

If the passive speaker is exceptionally well done, you may have more issues than the passive crossover. Also, you are removing the notch filters, BCS, etc.

Will it play, absolutely. Will it sound different, almost certainly.
Will it be better, it depends on your goals, the Speakers and other variables.

Good Luck.

Doug
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Old 6th August 2008, 02:59 AM   #3
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Thanks Doug!
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Old 6th August 2008, 03:02 AM   #4
pjpoes is offline pjpoes  United States
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yes and no. First, you need to remove the original crossover so that its no longer in the signal path. Then directly wire the speakers to the terminals, and set everything up as you had mentioned.

However that makes some assumptions that are likely not right, which is that the speaker is using a text book crossover transfer function. Because of something known as Baffle diffraction, the crossover more than likely uses some form of baffle step compensation. The biggest problem with using an active crossover like you intend is that the large majority of crossovers for less than 2-3 grand do not have the ability to modify the transfer functions beyond slope and frequency. You need the ability to change the q, poles, and also parallel multiple filters.
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Old 6th August 2008, 08:24 AM   #5
Fosti is offline Fosti  Germany
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pjpoes is right! You have to measure what is happening! If you put the "text book crossover transfer function"-activated bookshelf speakers into a bookshelf, the chances that it works are quite good if the transfer functions of both drivers are quite smooth in the crossover region. Placing the speakers in a (filled!) bookshelf is like in-wall-mounting the speakers. There will be no baffle diffraction effects. But without measuring equipment it is quite difficult.
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Old 6th August 2008, 03:20 PM   #6
pjpoes is offline pjpoes  United States
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I'm hoping some of what Fosti was trying to say was lost in translation, but if he is saying that adding stuffing, as in polyfill to the inside of an enclosure gets rid of baffle diffraction, that is completely wrong. On a book shelf the response begins to slop off around 500-700hz, no amount of stuffing will fix that. To further illustrate my point I have made up some pictures of transfer functions and the subsequent responses on a real driver response.

Click the image to open in full size.
this is a standard 3rd order transfer function. This is what can be done with any number of analogue or digital active crossovers. This is all that can be done, the other transfer functions I will show you can not be easily replicated with these standard active crossovers (There is a way in theory, but I've never tried it, and I highly doubt people do it).

Click the image to open in full size.
here is the response you get with that transfer function. The dark blue is the actual driver response, and the lighter blue is the response with filter. Notice there is both some rising in the response around 500hz, and then a further much worse rising caused by a mixture of cone breakup and the natural tendency for drivers to do that.

Click the image to open in full size.
This is the transfer function I achieved using just 4 parts, and it takes into account all of the mentioned issues. This type of transfer function can not be achieved with a normal active crossover such as the mentioned one.

Click the image to open in full size.
Notice here that the response is much smoother and would integrate far better with a tweeter. This is why I believe that for the average consumer, the use of active filters above 500hz is problematic.
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Old 6th August 2008, 03:32 PM   #7
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I read it as he meant the bookshelf was filled with books thus the speaker mounted in said bookshelf was like in-wall, thus no diffraction. Nothing wrong at all with his English
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Old 6th August 2008, 03:35 PM   #8
Fosti is offline Fosti  Germany
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I didn't say filled (stuffed) speaker boxes with polyfill, but a filled bookshelf (filled with books!!!) and inbetween the books place the speaker boxes as if they were in-wall-mounted!


EDIT: Thank you richie00boy
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Old 6th August 2008, 03:45 PM   #9
sreten is offline sreten  United Kingdom
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Hi,

The short answer to the original post is :
No. It will not work. Do not go there.

/sreten.
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Old 6th August 2008, 06:53 PM   #10
pjpoes is offline pjpoes  United States
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Ah sorry, Fosti, I misread that. Yeah that would be true. Though why you would want to do that is beyond me.

This still doesn't change my point though, the issues are far greater than just bs, but response issues with the speaker. While you could use eq as well, that doesn't make sense, your better off using correct filter slopes in the first place. Something tells me the original poster has lost interest though as he hasn't posted again, maybe realized that its not such a good idea.
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