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Old 2nd October 2006, 08:08 PM   #1
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Default Linkwitz Transform Circuit for Dipole Bass

Greetings -

I wrote Siegfried himself about this a few day ago - I was just curious if the circuit could be applied to a dipole bass setup. This was his answer:

"The LT could be used to lower the low frequency roll-off of a driver before applying the 6 dB/oct dipole correction to it."

So now I'm wondering if any of you have considered this, or have actually built a system this way or are planning to?

Thanks!
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Old 2nd October 2006, 08:13 PM   #2
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It could be used, but the reason I suspect it hasn't is because it would quickly lead a system into silly power territory.
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Old 2nd October 2006, 08:24 PM   #3
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Ah - I see your point - best to just cross it to a sealed sub at a normal freq then?
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Old 3rd October 2006, 02:35 AM   #4
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Quote:
Originally posted by richie00boy
It could be used, but the reason I suspect it hasn't is because it would quickly lead a system into silly power territory.
Well, not really. The Xmax of the driver largely determines the SPL capability at low frequencies for a dipole config. And that is the frequency area you would most likely be correcting with a bi-quad setup like the LT. With or without correction, power requirements would still be considerably less than the same driver in a nominally-sized sealed box.
Equalization doesn't increase the ultimate SPL capability of the driver/amplifier combination, but it does make it use-able over a wider frequency range.

sdclc,

You can certainly use the LT topology to place two new poles even if the driver is not in a box. (The box is just really big.) Then, once you mount it in your dipole baffle of choice you should have just the 6db/octave cancellation and possible cavity resonance to address. Siegfried uses this same technique (with a somewhat simpler topology) on many of his designs.

http://www.linkwitzlab.com/filters.htm#9

Cheers,

Davey.
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Old 3rd October 2006, 03:49 AM   #5
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Thanks Davey -

Good info. I want to go dipole/OB/active as soon as I have the room, and I was just thinking I might want to try the LT on the bass module to get as much as possible out of it before crossing over to a sealed sub.
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Old 3rd October 2006, 10:00 AM   #6
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Yes, by silly power I did mean that excursion would get crazy as well.
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Old 3rd October 2006, 06:02 PM   #7
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Quote:
Originally posted by Davey


You can certainly use the LT topology to place two new poles even if the driver is not in a box. (The box is just really big.) Then, once you mount it in your dipole baffle of choice you should have just the 6db/octave cancellation and possible cavity resonance to address. Siegfried uses this same technique (with a somewhat simpler topology) on many of his designs.

More specifically SL seems to like shelving low-pass filters which each provide a single zero and pole.

If you look at SL's publically available Orion documentation you'll find a 20-110Hz shelving low-pass for driver eq, 20-305Hz for dipole eq, and final speaker high-pass response which retains the drivers' pole at 5Hz so the excursion increase doesn't continue to DC -

http://www.linkwitzlab.com/orion_asp.htm
http://www.linkwitzlab.com/orion_challenge.htm
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Old 3rd October 2006, 09:51 PM   #8
Davey is offline Davey  United States
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Drew,

Yes indeed, I'm well familiar. In the case of the Orion the driver-specific EQ required is almost completely accomplished via the simple shelving filter topology.

There is also another example of "cascaded" shelving filters to accomplish a specific goal in the EQ setup for the Thor, sealed-box subwoofer.

http://www.linkwitzlab.com/thor-eq.htm

The original reference from many years ago:

http://www.linkwitzlab.com/images/graphics/f0Q0fpQp.gif

The "realizability criterion" in the math result being the go/no-go decision as to whether the LT topology can be used.

Cheers,

Davey.
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