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-   -   From passive to active filter (http://www.diyaudio.com/forums/multi-way/230296-passive-active-filter.html)

soren5 18th February 2013 03:00 PM

From passive to active filter
 
1 Attachment(s)
Hello DIY'ers.

I've built speakers before but always used active filters/crossover (miniDSP). So far I've primarily experimented with the FAST designs where I combine a 3-4" full range driver with a woofer and cross at around 250-300Hz.

Recently I've been interested in building more traditional 2-way speakers. I'd like to try a proven design, but instead of building the passive crossover, is there a way to "transform" the passive crossover design into a biquad filter that I can import into the miniDSP?

I'm looking at building a pair of simple and good-value 2-way bookshelf speakers, such as Paul Carmody's Overnight Sensations or the K&T Cheap Trick CT 248 with SEAS drivers.

I've attached the crossover design for the Overnight Sensations. Could any of you help me understand how to make the active filter based on these components?

Thanks a lot!

KyleinCowichan 18th February 2013 04:24 PM

Hey Soren,

Tuxedocivic (Ryan) did this very thing for me. You can see his measurements and settings here: LINK

The settings he recommended are:
Woofer
BW5 @ 2400
delay = 0.10ms
950hz, -4db, Q = 2
1700hz, -7db, Q = 1.5
4500hz, -5db, Q = 3

Tweeter
BW5 @ 3400hz
Level = -6db
5000hz, +2db, Q = 3
10,000, -2db, Q = 1
18,000, -5db, Q = 2

The settings sounded great. I had the whole thing powered with the miniAMP from miniDSP. I have since burned out one of the Dayton tweeters and Ryan is redoing the crossover for CSS ERT26s.

Kyle

soren5 18th February 2013 05:30 PM

Quote:

Originally Posted by KyleinCowichan (Post 3375111)
Tuxedocivic (Ryan) did this very thing for me.

Wow, thanks! Great to see this has been done for the overnight sensations. Was the active crossover made for the Dayton or HiVi tweeter?

I was hoping there was a general way of doing this without having to measure each driver. Is it possible to design a digital crossover simply by looking at passive design?

Davey 18th February 2013 05:41 PM

You can do this with any speaker system.

The best way is to use one of the measurement programs and take a differential measurement between crossover input and each of the drivers terminals. This yields an electrical response of each crossover section which you can then import into various design programs to generate an active alternative.

However, the first question that obviously comes up is........since I'm now using an active crossover why can't I improve upon the original passive design? :) Most likely you can.

Cheers,

Dave.

KyleinCowichan 18th February 2013 05:48 PM

Ryan would have more to say on going from the passive to the active. He aimed to improve it and decided to go off of measurements. That design used the Dayton tweeter.

I am quite excited to see what Ryan produces using the ERT26. The Hivi B4N starts having issues around 4k and that's right where the original xover point was centered. The ERT26 should be able to get much lower than the Dayton. I'll post the results when I get them.

Kyle

soren5 18th February 2013 06:19 PM

Quote:

Originally Posted by Davey (Post 3375230)
You can do this with any speaker system.
The best way is to use one of the measurement programs and take a differential measurement between crossover input and each of the drivers terminals. This yields an electrical response of each crossover section which you can then import into various design programs to generate an active alternative.

Thanks Dave. The problem with this approach is that I don't have any of the 2way speakers yet, so real measurements of the passive crossover is not a possibility. I could of course just buy the passive components and then build it, but since I already have a miniDSP, and I'm not really sure which 2way design to go after, I thought I could save some time and skip building the passive crossover, and then buy drivers for some different proven designs and see what I like.

Quote:

Originally Posted by Davey (Post 3375230)
However, the first question that obviously comes up is........since I'm now using an active crossover why can't I improve upon the original passive design? :) Most likely you can.

I've never made a passive crossover before, but I've read hundreds of times how you experts advice us noobs to begin with a proven design, that's why I'd like to "copy" instead of trying to "improve" as you suggest.

Another thing is that the Overnight Sensation is not available as a kit here in Europe (AFAIK). This means I have to buy each of the passive components, and this brings up a whole set of new questions such as "if a 6 ohms resistor is not available, should I then choose a 5.6 or a 6.8 ohm?" and "can I use a 1.0mH or a 1.2mH coil instead of a 1.1mH?"...

If I could go active I was hoping to avoid these dilemmas and also shorten the building process :)

tuxedocivic 18th February 2013 11:32 PM

Most designers should be able to offer active settings for their designs if you were to ask and they're accessible.

For Kyles pair of OS, I aimed to improve things by lowering and steepening the cross over. As well as flatten things. I thought it turned out pretty good until Kyle hooked things up backwards and forced bass out the tweeter :p

AllenB 18th February 2013 11:44 PM

Quote:

Originally Posted by soren5 (Post 3375278)
The problem with this approach is that I don't have any of the 2way speakers yet, so real measurements of the passive crossover is not a possibility.

If you can measure the driver impedance (or find a *.zma for it that someone else has done), you can simulate the passive crossover and there you have the transfer curve. You don't need any driver frequency response measurements.

KyleinCowichan 18th February 2013 11:47 PM

Quote:

Originally Posted by tuxedocivic (Post 3375737)
Most designers should be able to offer active settings for their designs if you were to ask and they're accessible.

For Kyles pair of OS, I aimed to improve things by lowering and steepening the cross over. As well as flatten things. I thought it turned out pretty good until Kyle hooked things up backwards and forced bass out the tweeter :p

There's nothing worse than crackle-pop-smoke. The miniAMP has some jumpers for configuring the 4 channels, I had left it set in 2x10w+1x20w. :o

KM

soren5 19th February 2013 09:34 AM

Quote:

Originally Posted by tuxedocivic (Post 3375737)
Most designers should be able to offer active settings for their designs if you were to ask and they're accessible.

Quote:

Originally Posted by AllenB
If you can measure the driver impedance (or find a *.zma for it that someone else has done), you can simulate the passive crossover and there you have the transfer curve. You don't need any driver frequency response measurements.

Thanks for the suggestions. I'll try to ask the designers for active filter settings, and also experiment with impedance measurements.


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