Active crossover questions

I plan to build 3way active front speakers, and although using a dcx2496 would be the easy option I would like to build the following if its not too much trouble/cost and can still be flexible.

I've got 3 stereo chipamp kits which will go into a box each and I was thinking I could put a band pass filter into each amp, with adjustable frequencies and gain. It doesn't matter if this costs more than using a dcx2496, but I'm thinking it should cost about the same as building a separate 6way Xover?

What I'd like advice on is what filters to use (and why). I must admit that I don't understand what the phase considerations are at crossover.

What if I just copy this design? http://www.siliconchip.com.au/cms/A_30278/article.html
Feeding the signal from one amp to the next.

Can I add a trim pot into the output opamp to adjust the gain for each of the drivers?

I'd like confirmation that this is feasible! The fact that I haven't found a previous example makes me worry that for some reason it's a dumb idea.

Also, my plan for setting all this up is to play pink noise and use RTA software to view the output!

And finally, how do I protect my tweeter from the amp switch on/off? Is it as simple as a capacitor in series?

Lot's of questions I know, but this way I may get some bites:)
 
jimbo1968 said:


What if I just copy this design? http://www.siliconchip.com.au/cms/A_30278/article.html

Can I add a trim pot into the output opamp to adjust the gain for each of the drivers?

It looks like a good design to me. Id just copy it. The ariticle says there are no output adjustments but VR1-3 look just like that. I didn't read the whole thing. Are they offering boards?
 
Re: Re: Active crossover questions

soongsc said:
If you design a high pass, a low pass, and a differential for the mid, it would be a much cleaner design. For 6 way, well take the low pass and do it again. Lot less OPAMPS.

I will look up differential.

Bill Fitzpatrick said:
It looks like a good design to me. Id just copy it. The ariticle says there are no output adjustments but VR1-3 look just like that. I didn't read the whole thing. Are they offering boards?
I was planning to split the filters between separate amp cases.


Now however I'm thinking of a bi-amp design with passive crossover of High and Mid. My thinking is that if I need a series capacitor to protect the tweeter in a tri-amp set-up, and if the the passive crossover for a tweeter is a series capacitor then where's the advantage? This is easy to implement as a neat 1 box design

Tri-amp vs bi-amp anyone? On the ESP site the bi-amp article is written as though tri-amp is not much advantage, then the tri-amp article seems to suggest that it is.

I guess I can do bi-amp and then upgrade to tri-amp. (which would be easy with the DCX!!!Damn... wish I could make a decision and get on with it)
 

soongsc

Member
2005-03-26 2:31 pm
Taiwan
Re: Re: Re: Active crossover questions

jimbo1968 said:


I will look up differential.


I was planning to split the filters between separate amp cases.


Now however I'm thinking of a bi-amp design with passive crossover of High and Mid. My thinking is that if I need a series capacitor to protect the tweeter in a tri-amp set-up, and if the the passive crossover for a tweeter is a series capacitor then where's the advantage? This is easy to implement as a neat 1 box design

Tri-amp vs bi-amp anyone? On the ESP site the bi-amp article is written as though tri-amp is not much advantage, then the tri-amp article seems to suggest that it is.

I guess I can do bi-amp and then upgrade to tri-amp. (which would be easy with the DCX!!!Damn... wish I could make a decision and get on with it)


I sort of simplified the expression when I said differential. I was thinking subtracting the high pass and the low pass from the full pass portion.

Ribbons commonly use a cap to prevent low frequencies from flapping them around. It also creates some phase shift you probably would want to consider.

I think you're asking for a really diversed response when you ask biamp or triamp, someone might just tell you to do an array. I really depends on what kind of drivers you want to use and the size of the room, your music preference, and look preference.

You could also do a triamp and mod the frequencies to biamp as well.:D
 

soongsc

Member
2005-03-26 2:31 pm
Taiwan
jimbo1968 said:
I plan to build 3way active front speakers, and although using a dcx2496 would be the easy option I would like to build the following if its not too much trouble/cost and can still be flexible.

I've got 3 stereo chipamp kits which will go into a box each and I was thinking I could put a band pass filter into each amp, with adjustable frequencies and gain. It doesn't matter if this costs more than using a dcx2496, but I'm thinking it should cost about the same as building a separate 6way Xover?

What I'd like advice on is what filters to use (and why). I must admit that I don't understand what the phase considerations are at crossover.

What if I just copy this design? http://www.siliconchip.com.au/cms/A_30278/article.html
Feeding the signal from one amp to the next.

Can I add a trim pot into the output opamp to adjust the gain for each of the drivers?

I'd like confirmation that this is feasible! The fact that I haven't found a previous example makes me worry that for some reason it's a dumb idea.

Also, my plan for setting all this up is to play pink noise and use RTA software to view the output!

And finally, how do I protect my tweeter from the amp switch on/off? Is it as simple as a capacitor in series?

Lot's of questions I know, but this way I may get some bites:)


If you want to put them in separate boxes, you need to add a buffer to each of the inputs to the box.
 
Re: Re: Active crossover questions

soongsc said:
If you want to put them in separate boxes, you need to add a buffer to each of the inputs to the box.

In the example: "Four op amps, IC1a, IC1b, IC5a & IC5b, act as input or output buffers while the remaining eight op amps......."

So, I don't mind having an input buffer before every bandpass filter, it does not look like it is necessary.

But there may be an advantage??

Also a buffer in each amplifier fits with my 'modular' approach. Bypassing the filters leaves me with 3 buffered chipamps (stereo if I wire another input, or mono if I parallel or bridge the amps)
 
crossover frequencies

What is the ideal target for music (ie don't worry about Movie effects).

Based on reading the ESP Bi-amp article, how about something like:

Low: 40 - 300 (8" in 40l sealed)
Mid: 300 - 3000
High: 3000 - 20K

If music doesn't need to go very low, I will use a separate subwoofer for effects below 40Hz !