# Simulating Linkwitz Transform with bfd



## thxgoon (Feb 23, 2007)

I'm trying to cheat a little with my upcoming build so I thought I'd consult with you genius' :R. Is there a good way to simulate an LT circuit using the BFD? Adding a large boost at 20hz and a wide cut at 35hz gets pretty close but wasn't sure if there might be a better way :huh:


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## Wayne A. Pflughaupt (Apr 13, 2006)

Don't know of it's a "real" LT, but that is a good approach to get the BFD to affect response below 20 Hz.

Actually, boosting at 20 Hz will create "haystack" response at that frequency - i.e., response falls sharply on both sides of 20 Hz. For flatter response below 20 Hz, simply apply a cutting filter further upsteam, and boost the overall signal level to compensate. 30-35 Hz might be a good place to start.

Regards,
Wayne


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## texfrazer (Oct 25, 2006)

Yep, Wayne's thought about boosting your overall signal and then cutting higher up is the best way to go to avoid some possible problems with headroom when you start boosting from the BFD. BruceK has a very good write-up around here somewhere describing why it isn't a good idea to boost from the BFD, but to do what Wayne suggests.

Hope this helps.


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## thxgoon (Feb 23, 2007)

Thanks for the input guys! 

I like your idea Wayne, makes sense about the haystacking affect. What if I took a sweep with REW when the sub is in place and lowered the target level to the 20hz mark or so? I think this would accomplish the same thing..


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## myn (Sep 19, 2006)

Very cool 

Any success yet?

If so, do you mind posting your BFD filters?

Thanks!


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## thxgoon (Feb 23, 2007)

Ya, I got the sub built and eq'd and things are flat down to about 15 hz. I'll post some plots and filters a bit later.


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## myn (Sep 19, 2006)

Can't wait!


Thanks.


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## Andysu (May 8, 2008)

That’s a smashing idea as the curve is unique in way -12db -24db and -48db has type style to the curve I’d say its go call it if you want trial and error can’t do any harm.

Merry Christmas


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## myn (Sep 19, 2006)

Not that I am anxious or anything... Do you mind posting your BFD filters to simulate the LT?

Thanks


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## myn (Sep 19, 2006)

How's it going with the filters?


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## bcharlow (Dec 23, 2008)

I'm intrigued with this idea, but in the dark as to what you're doing here to simulate the Linkwitz Transform circuitry's results. Is this purely to get response below the normal level for your sub driver?

I've got a curious side question here because I'm considering DIYing some slave subs in very small boxes for 10" drivers. The Linkwitz website shows plans for doing this with some Peerless 10" subwoofer drivers in about a half cubic foot box (delightfully small), but they caution that you must have the LT circuit to run these. 

I wouldn't have a clue on how to do that on my own. Can the BFD simulate this effectively for the admittedly sub-optimal size sealed boxes????


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