Why 2nd Order Is best or not

[Pallas]

Originally Posted by a.wayne

Wait , you are comparing adjustments made in a Passive xover to active EQing , let me have a seat ..

They're the exact same thing, just at a different section of the circuit. So his comparison is totally warranted.

Originally Posted by tvrgeek

I totally disagree. There in NOTHING magic, just several reasonable approaches.

FWIW, I've only found one approach to crossovers that has been consistently satisfactory: control the directivity of the treble unit (waveguide, coincident/Dual Concentric driver, etc.) and effect the handover where the directivity of the lower driver narrows to the pattern of the upper driver in the horizontal plane. The only interesting question left, I think, is how narrow or wide that pattern should be. But there's a whole long thread on that here already.

Other approaches can work ok, especially in heavily-treated rooms were one hears relatively more direct sound. But none of them seem to do as well as the above-outlined approach.

Originally Posted by tvrgeek

Unfortunately the kind of filtering I want to do with DSP relies on A2D and D2A of lower quality than I can get with analog. Catch-22.

Given the results of the Meyer and Moran paper, I wouldn't be concerned about a DA/DA loop.

IMO, the most pressing shortcoming of DSP crossovers today is that too much boost will lead to digital clipping. Not an issue for most uses, but for extreme Linkwitz Transforms for small subs, or dipole bass compensation, it can be an issue.

Originally Posted by AllenB

You know, it's just that I hear this dragged out all too often. I could just as well say that active gives good results to those who don't know what the worthwhile goals are.

Here I've taken a plain 2nd order passive electrical with tweeter L-pad and woofer rise compensation and added a single RLC conjugate (yellow), vs the woofer as the amp sees it on its own.

There's a teeny tiny bit of truth the argument, but it's mostly irrelevant. In addition to David Smith's points, on more: take a speaker with wide impedance variations in the midrange, and put it on two amps. One has high source (aka output) impedance, one has low source impedance. They will sound different, with the response of the former adversely affected by the interaction.

[tvrgeek]

Originally Posted by speaker dave

Yeah, I'm not buying the "passive networks are hard to drive" bit either.

I've read a lot of research on the speaker as a load and there are only a few things that matter:
1) The average impedance. The lower the average impedance level the higher the current requirement and the higher the general heating effect. Remember that most of the long term average power of music is in the midrange so that is where the impedance matters most of heating effects.

2) High phase angle combined with low impedance. If the real part drops low at the same time that the phase angle is high then this leads to high peak current and may trigger current protection circuits (in solid state amps). Ham-fisted passive networks with crossover points near woofer resonance (3 and 4 way) may lead to this but it is easy to design around if you know what to look for.

3) Low impedance at high frequencies. This tends to push amplifier instability issues. This was always an electrostatic speaker potential problem. Ironically, adding Zobel networks to tweeters is going in the wrong direction since amplifiers to to be very happy driving the rising impedance of an inductive load. Dropping it down to resistive doesn't do the amp any favors (although most amps are okay with it).

A passive network (compared to an individual driver) will have a more complex impedance curve (more "bumps"), but if you stay away from the above conditions the amplifier will be just as happy driving it.

David S.

Dave,
Only one that was designed not to be an easy load. A raw driver can be far worse than a well designed system with proper impedance compensation. High capacitance is the tough part. Rising inductance as you say, less so.

[a.wayne]

Originally Posted by Pallas

They're the exact same thing, just at a different section of the circuit. So his comparison is totally warranted.

Errr... No ...!!! not even in the same park ....

[PLB]

Hi OnAudio,

Excuse me for being a little late joining the party, but here is my two cents worth -
One issue that I am aware of that effects the quality of audio reproduction is that due to group delay, which has been documented and confirmed as being an undesirable byproduct of Xover filters. Group delay varies in a Xover as function of its crossover frequency, its Q and order. And from recent work by people like Geddes, it seems that our sensitivity to group delay is a function of frequency and also SPL.
So from this, my choice of filter order would include group delay as well as all the other many parameters that affect the overall quality of reproduction.
To show the variation in group delay between the various Xover filter orders, I’ve attached two sets of curves, one for even order and the other for odd order Xovers.
All of the responses are from LR type filters. Of interest in the odd order Xovers is that minimum group delay is significantly affected by the polarity of the tweeter.
The polarity of the tweeter in the even order Xovers is set to give a flat frequency response. One thing that stands out for me is that the 3rd order group delay with the tweeter polarity reversed is the same as that for the 2nd order Xover!
So Why not use 3rd order instead of 2nd order?
Another issue that comes to mind is that the LP and HP responses of a 2nd order LR Xover is –6.02dB down at the crossover, which gives perfectly flat on-axis acoustic summation at the crossover frequency, but only half the power. On the other hand, the summation using a 3rd order Xover gives a flat acoustic response on-axis, with only -3.01dB loss at the Xover frequency, thus providing no power loss. In my opinion, this is an issue that needs further thought.

Regards

Peter

[OnAudio]

Thanks PLB, lets assume one picks such a crossover point such that cabinet resonance fixes the power issue. Or picking such a point to cater for 200Hz room boom

[a.wayne]

lots of phase rotation there PLB, makes for tiny sound and poor coherency between drive units ...

[PLB]

Hi OnAudio,

"Thanks PLB, lets assume one picks such a crossover point such that cabinet resonance fixes the power issue"

Do you have any suggestions for simulation software for that? Or that can accurately model the polar response?

"Or picking such a point to cater for 200Hz room boom "

A tweeter that can handle 200Hz?

Regards

Peter

[PLB]

Originally Posted by a.wayne

lots of phase rotation there PLB, makes for tiny sound and poor coherency between drive units ...

I cannot accept that argument without documentary evidence from a respected authority.

Regards

Peter

[a.wayne]

Agree PLB on both accounts ....

[Pano]

That 450uS GD is equals about 6", right?