A Challenge to Linkwitz-Riley ?

[jackinnj]

Rene Christensen has published "Active All-Pass Crossover Networks with Equal Resistors and Equal Capacitors" in the Journal of the Audio Engineering Society (Jan/Feb 2006) -- better group delay characteristic compared to LR.

[ShinOBIWAN]

Sounds interesting.

Could you post a schematic or any other details if possible.

Thanks

[Bose(o)]

WHOA?!?!? Really? I definitely must have overlooked that issue. If I find it I can scan her in.

[454Casull]

Originally posted by Bose(o)
WHOA?!?!? Really? I definitely must have overlooked that issue. If I find it I can scan her in.

That'd be awesome.

[AndrewT]

Hi,
maybe my question is a bit early, but are we talking about a crossover or a phase/time delay circuit?

[phase_accurate]

maybe my question is a bit early, but are we talking about a crossover or a phase/time delay circuit?

What's the difference ????

Fun aside:
It is an active crossover that trades slightly improved phase-characteristics against less steep amplitude response.
The initial rolloff rates of the high- and lowpass are quite shallow.

Regards

Charles

[AndrewT]

Hi,
an ALL-pass does not operate as a crossover.

It passes all frequencies upto it design roll off which is usually chosen to be beyond your chosen range of use. Further the ALL-pass is a low pass stage.

There's where my question comes from.

[ShinOBIWAN]

Originally posted by AndrewT
Hi,
maybe my question is a bit early, but are we talking about a crossover or a phase/time delay circuit?

There's no such thing as a Linkwitz-Riley all-pass. So you've got me wondering now. The Linkwitz-Riley is a high or low pass filter network.

I guess the clue is the wording of the article "Active All-Pass Crossover Networks"

It is rather confusing to convention wisdom on the subject. All pass says to me; delays and shelves. Whilst crossover networks suggests high, low and bandpass.

Perhaps this is an all pass network that simply is part of a 'crossover' network?

[ShinOBIWAN]

Found a little bit:

Active crossover networks can be constructed with all-pass functions and with the additional constraint that resistors and capacitors have the same value. Two such networks are examined: a fourth-order three-way filter and a sixth-order four-way filter. While the transient responses are not perfect, compared to the familiar Linkwitz-Riley configuration, the group delays are significantly smoother for filters of the same order.

From here:

http://www.aes.org/journal/toc/AES-JanFeb2006TOC.cfm

Looks to be a crossover filter from the description.

[heater]

All capacitors and resistors the same hey. That's easy, just use the state variable Linkwitz-Riley design as described by the Rane Corporation here http://www.rane.com/pdf/linriley.pdf

Features:

Fewer resistors and caps if you want to make an adjustable crossover.
Less opamps than say the Rod Elliot Linkwitz-Riley.
High and low outputs from a single "stage" that have identical crossover frequencies. Again nice for an adjustable.

I have only just started to think about active crossovers but I don't see what the problem with phase might be with this. High and low outputs are in phase to withing few milli degrees at all frequencies.

So far I have simulated and built the low and mid section as in the attched schematic.