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Old 17th October 2012, 01:56 AM   #41
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Originally Posted by Pano View Post
Really, once you get a really great crossover you shouldn't be hearing it anyway, so what does it matter?
There's a factor that maybe is sometimes overlooked in measurements, and perhaps it doesn't show up clearly in typical audiophile music, but I think that I sometimes perceive a system 'pulling its punches' i.e where there should be a devastating transient, the system doesn't quite deliver. If this was the case (and not my imagination) I would point to a passive crossover as being a very likely culprit. The world class passive crossover may give a flat frequency response but it's still a high impedance in series with the drivers (that gets hot when driven hard), doing weird things with the phase, and it's absorbing a large amount of the amp's power.

With the expectation bias caveat, my active system just seems fabulously 'transparent' at all volume levels, and perfect with particularly meaty transients. I don't get this with my (on-paper far superior, and now hardly ever used) passive system.
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Old 17th October 2012, 02:08 AM   #42
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The world class passive crossover may give a flat frequency response but it's still a high impedance in series with the drivers (that gets hot when driven hard), doing weird things with the phase, and it's absorbing a large amount of the amp's power.
The only elements in passive xovers that should get hot when driven hard are resistors and this is deliberate. Capacitors and inductors do have their own internal losses, but if correctly chosen should remain cool under normal operating conditions.

Passive xovers also don't do weird things with the phase, both passive and active alter it in the same way.
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Old 17th October 2012, 02:36 AM   #43
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If anything in a passive XO gets hot, it is under built.

Well, I guess the lightbulbs in a PA speaker XO are an exception.
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Old 17th October 2012, 02:38 AM   #44
Remlab is offline Remlab  United States
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Raising the volume on a 4 ohm bass driver by 3db to bring it in line with the mids and tweets is a lot easier on an amp than using two of those bass drivers at two ohms to get the same audible result. The same that is, if the amp is stable into two ohms(expensive).
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Last edited by Remlab; 17th October 2012 at 02:42 AM.
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Old 17th October 2012, 02:38 AM   #45
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Originally Posted by 5th element View Post
The only elements in passive xovers that should get hot when driven hard are resistors and this is deliberate. Capacitors and inductors do have their own internal losses, but if correctly chosen should remain cool under normal operating conditions.

Passive xovers also don't do weird things with the phase, both passive and active alter it in the same way.
What proportion of the amp's power does a crossover absorb? 30% typically? So if the amp's delivering 50W or something like that, the crossover surrounded by stuffing is presumably going to get quite hot. I see a lot of speakers for sale on eBay with burned out crossovers, at any rate.

And I'm pretty sure that my linear phase filters and direct drive off the amp are doing something quite different with the phase, compared to the passive version..?

Edit: I have to admit that I have little knowledge of passive filters because I've only just started fiddling about with adapting my own speakers, and I've gone straight for the Rolls Royce solution. But reading someone else's stuff about passive crossovers:

Quote:
...To evaluate the coherence of a given pair of filters, we measure the electrical sum of their outputs, then mathematically add them; examining the result for amplitude and phase distortion. On some filters we find that inverting the output of the high or low pass filter results in more accurate total amplitude or phase response...

Figure 2 shows the results of such a test with some reasonably common crossover network types.... Of all these filters only one, the lowly 6dB/octave crossover has both accurate amplitude and phase response when the outputs are reassembled.

Last edited by CopperTop; 17th October 2012 at 02:54 AM.
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Old 17th October 2012, 03:10 AM   #46
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Active or passive or no crossover at all, people have gotten together to do blind tests with two fullrange drivers crossed over to each other, and could not tell them apart. The key is to get the same frequency response in each crossover. Make sure that the same DAC and amps are being used with active, if you want to compare.
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Old 17th October 2012, 03:44 AM   #47
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Originally Posted by CopperTop View Post
What proportion of the amp's power does a crossover absorb? 30% typically? So if the amp's delivering 50W or something like that, the crossover surrounded by stuffing is presumably going to get quite hot. I see a lot of speakers for sale on eBay with burned out crossovers, at any rate.
Well the passive components increase the impedance of the total network to reduce the current flowing through the circuit and reduce the overall power dissipated by the circuit. How much any of the components will dissipate is determined by the slopes and xover points chosen. 30% seems quite high, but it really depends on the xover specifics.

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Originally Posted by CopperTop View Post
And I'm pretty sure that my linear phase filters and direct drive off the amp are doing something quite different with the phase, compared to the passive version..?
Ah see, but here, we're not really comparing like with like and we're doing things that a passive xover cannot do, it's also something that is quite difficult to do with an analogue active crossover too if I understand it correctly. DSPs on the other hand are different again and add in yet another set of things to the mix that an analogue active xover cannot really do well. So in terms of potential usefulness you've got passive, then analogue active, then DSP driven active crossovers.

But if you compare a standard second order electrical passive filter designed with a specific driver to arrive at a 4th order acoustic LW slope, then it will have exactly the same amplitude and phase response as the system doing the same thing but actively using standard sallen key type filters.
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Old 17th October 2012, 03:45 AM   #48
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Passive crossover versus active crossover? Hehehe.... active crossover is "crossoverless" so it should be better from speaker point of view. But don't forget that this is NOT about speaker (crossover) but about AMPLIFIER :P

Yes, the active crossover is part of the amplifier chain. So the question is can you design a good amplifier. If you use discrete opamps and are an amp designer already, you may be able to create a good active. The question is: can your complex multi-stage amp outperform the best simple full class-A amp?

It is just similar like CFB versus VFB debate. Or who can make a better amp, NP or JC. Useless.

What many may forget is that people preference or hearing capability is different. Active will easily impress everyone, and it will (yes, sonic is what will be heard first by everyone). But only a few who can hear a hint of fatigue (or minor flaw in the amp design) and take that kind of performance seriously.

And then many forget that in crossover design you don't take any two drivers arbitrarily and make a crossover for them. Some combo will never work well. From this point of view it is clear that passive has real limitation, regardless of design skill.
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Old 17th October 2012, 04:23 AM   #49
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I can see that they can be good enough in many cases, but better than active?
For example an active XO (as opposed to a PLLXO which have different issues & advantages) will introduce higher order harmonic distortion products (which the ear/brain readily detects at very low levels) that a passive XO will not have.

Some active XOs have very complex circuits. A pre-amp is very hard to make transparent, an XO will often have many times the circuitry.

As with everything it is all about execution.

I'm a fan of active systems but not unless they are well done.'

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Old 17th October 2012, 04:25 AM   #50
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Show me a passive xover that can compare with a DEQX.
By default, one that is in a system where the budget it less than the cost of the DEQX.

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