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Old 24th April 2006, 04:35 AM   #1
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Default Active CrossOver

Hi

Ive just been converted from making a passive crossover to an active

and would like to some help in designing it, I have no knowledge on them how ever and can not find any books explaining them

I now know they work off intergrated circit chips and fixed cap values...but how do you figure what chip I need?

all the crossovers are at 8 ohms

My specs I want for this are: these are the easier options

2nd order highpass @ 18hz
2nd order lowpass @ 80hz if it has to be fixed (varible if possible)

or the same as above but with varible highpass (if thats even poossible)

and the most wanted crossover if possible would be:

varible highpass from 10hz - 25hz
varible low pass from 40hz - <500
switchable highpass orders 1,2,4
switchable lowpass orders 1,2,4

I think this bottem design is extremely difficult from what i have learned so far

oh and tell me how difficult it is to make
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Old 24th April 2006, 05:05 AM   #2
dfdye is offline dfdye  United States
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Here is some reading: http://www.linkwitzlab.com/filters.htm

You should get a better idea of what will be involved in making them work after perusing that for a while. As for difficulty, the circuits themselves are pretty simple for fixed value passive components, but variable xovers are indeed complicated by the need for precise gang pots.

Also, the active filter group buy contains some good information, especially the excellent manual that Bob and Jens wrote. Here is a link to the post with the manual: http://www.diyaudio.com/forums/showt...946#post886946

Hope this gets you started.

David
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Old 25th April 2006, 05:25 PM   #3
AndrewT is online now AndrewT  Scotland
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Hi Toast,
I'm guessing you want all this adjustability to allow experimentation and thus find the best set up for you final crossover.

If you want to experiment then buy a cheap or secondhand Behringer dxc2496. You can download a manual from the web to see just how flexible it is at crossovers and equalisation.
DCX is so quick and easy to set up to various filter/eq options that comparing frequencies, Qs, slopes, Linkwitz, Bessel Butterworth, limiting, etc etc. just a flavour of what can be adjusted.

It has two downsides.
1. it is wired for balanced input and output (2 in, 6out), but can be adapted to unbalanced.
2. it has a fixed level of output (well nearly fixed but not a volume control) that needs a preset or adjustable attenuator to suit the sensitivity of your power amps.

Both these can be overcome on a more permanent basis if you decide you like the sound and quality of the dcx digital filters.

However I suggest you learn how to make your speaker sing using the DCX as a tool only and then copy your final settings when making your active analogue filters for highest quality. You can use opamps or probably better still discrete opamps, even using valves (tubes) as your active devices if your persuasion goes that way.

Then sell your DCX or spend lots of time and money converting it to best suit your sound aspirations.
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Old 25th April 2006, 09:05 PM   #4
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Don Lancaster's book, 'Active Filter cookbook' is a good one.

Try Rod Elliots site too for some reading.

http://sound.westhost.com/

Rob.


AndrewT - I'm keeping my DCX thankyou very much. (How would I add 9' of delay to my mains with analogue op-amp based active xo's ? )
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Old 26th April 2006, 08:39 AM   #5
AndrewT is online now AndrewT  Scotland
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Hi Robwells,
a good question.
Somehow I managed to forget to add delay to my earlier shortened list.
Have you written a review of how it sounds in another thread?

Presumably, you've already looked for other solutions and chose DCX as a delayline, for your bass horn? Once you have committed to using DCX then it might as well be used for other things it's good at.

Btw. I just bought a pair of 6way motorised pots in case I need to make integration more permanent. I too have a plan for a bass horn and may end up delaying all the other speakers to match.
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