"transient-perfect" crossover in 12/02 AudioXpress

[dorkus]

there's a follow-up article in this month's AudioXpress on a 2nd order, phase coherent, flat summed response active x-over design by John Kreskovsky. i don't have the original article (5/01) so some details elude me but it looks promising. it's phase coherent like a 1st order but with 2nd order slope and flat response (though you can vary an "overlap" parameter), and requires only one extra stage for equalization before the filters. anyone have any comments? i'm curious how it would sound, perhaps i'll try it sometime.

[Davey]

If you haven't seen it already Johns many projects and papers are on his website:

http://www.geocities.com/kreskovs/John1.html

I haven't built or listened to any of the transient perfect designs, but they are indeed intriguing.

Cheers,

Davey.

[planet10]

John does some pretty interesting and well thot out stuff, it might well be worth a shot... if you are just getting your aXp, mine should be in the mail in a week or so...

dave

[navin]

John claims the drivers must also be mounted on a sloped or stepped baffle for this XO any idea what modifications for a straight baffle?

[Pjotr]

Hi,

I’ve experimented with this and it sounds pretty good. I did the filtering and equalisation at low signal level and used two amps.

There are some drawbacks, you need to be aware of. First the radiation pattern is not symmetrical and it is irregular, as is the case with a normal 1st-order filter. Best results I got with a d’Apolito arrangement. Second the equalisation needed is somewhere between 4 dB and 6 dB, depending on the overlap. This means you need to put around 2 to 4 times the power into the speakers around the crossover frequency. This limits headroom and hence dynamics. Simply stated, If you can normally do with 50W amps, you will need 100W to 200W amps with this approach for the same dynamic range. So to be successful you need at least drivers with high efficiency. Also keep in mind that the speakers need to be capable of handling the extra power, it will put extra demands on especially the tweeters.

And yes navin, the acoustical centres of the drivers need to be in the same plane to get it working. Off-axis I’ve found it more sensitive for displacement errors than LW second order filters. For the experiment I used a stepped baffle. It has the disadvantage that the distance between the unit centres is more than needed. I did not experiment with an electronic delay.

In the past I was rather sceptic about “phase coherence” also because 1st-order filters have too many drawbacks. But after hearing many well designed ones, I must admit that phase coherent speaker systems add to the "naturalness” of the perceived sound.

[dorkus]

Originally posted by Pjotr
In the past I was rather sceptic about “phase coherence” also because 1st-order filters have too many drawbacks. But after hearing many well designed ones, I must admit that phase coherent speaker systems add to the "naturalness” of the perceived sound.

yes, we have to pick our poisons don't we?
1st order filters have drawbacks l as you mention, but when properly implemented they still simply sound better than steeper slopes. while i've heard a couple speakers with steeper slopes that sound pretty good the vast majority of my favorite speakers use the simplest 1st order x-overs. they preserve the essential energy and harmonic structure of the sound, i think because of both their phase coherence and lower energy storage/ringing. many high order filters seem to ring like crazy to my ears and screw up the imaging and harmonic integrity. 1st order systems don't "add to the naturalness," they simply don't destroy it the way higher order xovers do!

there was a recent review in Stereophile of an mbl speaker that uses high-order crossover. in the review John Atkinson says that the speaker is not phase-coherent due to the crossover, but phase coherence "doesn't matter" in loudspeakers anyway. what a crock! just another reason to hate that magazine so very much. (i still get it only because those bastards keep auto-renewing me, and i'm too lazy to call up their subscription department.)

[Fred Dieckmann]

NONSENSE!
The drivers out of band response pretty well assures that you will wind up with a higher order actual acoustic slope in real life. Go read a few books before you pass yourself off as a speaker designer.

http://www.amazon.com/exec/obidos/se...174812-1655011

I wonder why several decades of research into higher order cross
over slopes have occured if first order slopes are so slam dunk.....

LMAO,

Fred

PS Crossver design is very difficult to optimize even when you know what what you are doing and make good measurements.

[jam]

Marc,

I guess he just told you!

Jam

[dorkus]

whatever!


fred i guess i should clarify, i'm just stating my preference for the sound of 1st order designs, i'm not saying they're perfect. maybe you could refer me to a commercial speaker with a high order crossover that sounds really good, as i have not heard one.

btw the link you gave does not work for me.

cheers,
marc

p.s. wait i'm confused now... what exactly are you saying?

[planet10]

Originally posted by Fred Dieckmann
NONSENSE!
The drivers out of band response pretty well assures that you will wind up with a higher order actual acoustic slope in real life. Go read a few books before you pass yourself off as a speaker designer.

Such harsh words Fred Sounds like you've been reading too many books and not building enuff speakers.

He did say properly implemented. This means overlap on the order of two octaves. Even with this you usually make other compromises.

Some of the best commercial designs use 1st order XOs

I wonder why several decades of research into higher order cross
over slopes have occured if first order slopes are so slam dunk.....

Because speaker design in general got headed away from single full range speaker and headed down the multi-way route -- partly because of the more is better attitude. Now after some dissatisfaction with many-way speakers, there is a return to looking at full-range and simplier systems, just as the tube (particularily SE) has made a huge resurgence.

PS Crossver design is very difficult to optimize even when you know what what you are doing and make good measurements.

XO design is indeed very hard. One of the reasons i tend to avoid it, by choosing designs that can get away with minimal XOs, or easier to implement active designs. And you know what, some of this simplier designs let me at the music in a way much more expensive, more complex designs don't...

dave