Active vrs passive

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How important is this?

It certainly used to be an issue (still is) with tube gear and its inherent high IM distortion. Modern amps don’t have that much IM (and the better ones don’t have audible crossover distortion either), so it’s less an issue now. That said, any amp will have lower distortion overall if bandpass limited, and a single driver presents a much more predictable (and manageable) load than the typical “passive” crossover, even the better examples of which often compromise amplifier stability and ability to deliver power into their often substantial phase shifts.

Add to that the ability to “match” the amplifier to the driver, and to “normalize” frequency response well beyond the intended passband so that “textbook” crossovers behave in a textbook fashion, and it’s hard to see why not, except in the simplest price-point dominated designs. And with whole amplifiers (“chip” and “classD”) now coming in at prices less than some single passive crossover components even the price argument (in favor of passive) becomes less convincing. On purely technical grounds there can be no rational argument that active crossover is not superior . . .
 
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On technical grounds, perhaps. But to the ear?

Anyway, as 5th E and Bill point out, matching the amp to the drivers can really help. When running active I usually do put a resistive divider between the amp and the horns, if only for noise concerns.

Amps should be clean, and many measure thus, but measured how? Into a resistive load at 1Khz and a single voltage, or fuller measurements across the spectrum and at various powers and loads? Knowing what an amp is expected to do in an active crossover should be a guide how well that amp performs in that area. Just how many folks running active crossovers really do that? (I know, everyone here is above reproach, I mean those other folks) ;)

There are certainly a lot of issue to take into consideration with passive crossovers, but aren't there just as many with active? Is it really a panacea?
 
There are certainly a lot of issue to take into consideration with passive crossovers, but aren't there just as many with active? Is it really a panacea?
No, there are not. That doesn't mean active is "a panacea", it just means it's better in a number of ways and worse in none.

Oh, and if you need to "pad down" a tweeter because of amplifier noise it means you're using too big an amplifier (and a not-very-good one at that). It is still possible to poorly implement an active design . . .
 
Amps should be clean, and many measure thus, but measured how? Into a resistive load at 1Khz and a single voltage, or fuller measurements across the spectrum and at various powers and loads?

If someone is going to measure their amplifiers performance then they should do it into 8 and 4 ohm resistive loads and 2 if the amplifier is happy with it. This should be done from 20-20kHz as the spectrum from say 1-20kHz is far more interesting and indicative of an amplifiers performance then the region below it.

If your 2 ohm stable amplifier delivers suitably low distortion into a 2 ohm load, then you can be fairly safe knowing that your reactive 4 ohm loudspeaker wont trouble it.

The bottom line is that all amplifiers are happier driving the mildly inductive load that a naked driver presents, rather then what some passive crossovers can do to a loudspeakers impedance curve.
 
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Oh, and if you need to "pad down" a tweeter because of amplifier noise it means you're using too big an amplifier

Or sitting too close! Really, it's hard to find 1/4W power amps to drive horns in a domestic setting. Building them is a better option. Also, I've found that flattening the impedance curve of a compression driver/horn combo does not hurt, even for active drive.

106dB or better at 2.83 volts means you need very quiet amps. I tend to use 16 ohm drivers just for that little extra attenuation.
 
Well the IMD of the amplifier, or any of the non linear distortion products for that matter, should be significantly lower then any of those produced by the loudspeaker. It is obviously system dependent, but if you've got a well designed set of amplifiers, for the job they are asked to do, then any non linear issues, passive or active, should be off the audible radar.

'Should' doesn't relate to 'is' - I agree that electronics in theory should be transparent but the reality is it ain't. Amps do suffer from sibilance for example, none of my (extremely cheap) speakers do. Amps have varying amounts of tonal purity which can be detected through my speakers. Some just sound 'greyer' than others and I put this down to worse IMD performance. So there must be something different about amp IMD which allows it to shine through the considerable speaker IMD (which I'm by no means denying exists).
 
Well the IMD of the amplifier, or any of the non linear distortion products for that matter, should be significantly lower then any of those produced by the loudspeaker.

There is something wrong here. The amplifier (unless it's a very very good one), by virtues of typical Class-AB amplifier distortions such as crossover distortion, under/over biasing, thermal issues, power rail modulation, etc*... will produce all sorts of distortions including IMD distortion. And these are audible in the sense that they are removed or diminished by (a) going to a better amplifier like a class-A bjt amplifier, (b) going fully active so the amplifier working bandwidth is narrower, or (c) both.

To put your argument in other terms, a normal, decent phono cartridge with a conical stylus can produce up to 10% of harmonic distortion in the mid-high range and up to 1% of intermodulation distortion, far above what most amplifiers produce. Yet the improvement in IMD is readily audible when using better speakers and better amps.

* not to mention all the problems that are created by driving a reactive load of varying impedance... and an inductance value that is modulated with the signal!!

As far as distortion, any decent amp operated in it's linear range has a tiny fraction of the distortion of the best drivers when run hard,

See my posts above. There is much more to audio than what the THD specification say. See Earl Geddles papers on distortion audibility. Amplifiers that even show little THD under the ancient way of testing still can contribute audible, significant distortion on real-world use.

While some speakers can have rather highish THD on paper, but under the Geddles criteria such harmonic distortion may be non objectionable.

At any rate, if amp distortion and noise sound bad, in my experience it will sound bad with a passive crossover or an active crossover.

Again, if you're using a fully active setup then you're narrowing down each amplifier bandwidth, which should reduce IMD products.
 
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Originally Posted by weltersys
As far as distortion, any decent amp operated in it's linear range has a tiny fraction of the distortion of the best drivers when run hard,

See my posts above. There is much more to audio than what the THD specification say. See Earl Geddles papers on distortion audibility.
I have read Geddes opinions, my previous mention of amplifier crossover distortion was in agreement with that being an objectionable type of distortion that can make low volume listening worse than high volume, as the distortion percentage reduces as power is increased.

As far as IMD and THD audibility in an actively driven driver at low to high drive levels, you can listen for yourself and decide whether it is an audible problem:
http://www.diyaudio.com/forums/multi-way/212240-high-frequency-compression-driver-evaluation.html
A shorter version (only 3000 rather than 8000 words, and a lot less pictures) can be found here:
High Frequency Compression Driver Evaluation

The sound files in the soundforums.net posts do not have the low frequency portion of the music mixed in, listening to the HF horn alone makes it easier to hear the difference in sound quality and distortion between the drivers.

The IMD and THD of the drivers was certainly evident to me at any drive levels approaching the rated power of the drivers.
Earl has yet to comment whether he could hear the difference ;).

Art Welter
 
We are starting to get into the "Amplifier distortions are more audible than speaker distortions" territory - aren't we?

Yes but note that "Distortions" is a veeeery broad generalization where we should discern between very low order HD, higher order HD, intermodulation (and... at which frequencies?) and -more importantly- other non-linear behavior.

Decent driver-makers go through great pains to ensure low, unobjectionable "distortions" proven that the driver is used within a certain bandwidth and below a certain SPL.

After you (or the speaker manufacturer) has selected pretty multiple good quality drivers, the extra "distortions" that blur the sound are to be contributed by the amplifiers.

And it's there that I claim that the "distortions" that are going to matter more are higher-order HD, IMD, and other non-linear stuff. It is on "IMD" and the other "non-linear" stuff where the active setup may bring significant improvements.

I claim that IMD can be significantly reduced simply by narrowing down the operating bandwidth of the amplifier... makes sense, really: narrower frequency range, less multiplication products possible.

I also claim that a fully active speaker setup gives the side effect of requiring significantly less amplifier power, particularly in the critical high frequency range (some tweeters can have more than 100dB sensitivity), which opens up many important routes for improvement, that truly do make a difference to the sound.

When you read a book such as "High performance audio amplifiers" by Duncan, you realize how compromised is a typical (high quality) amplifier when it's asked to drive a 85-91dB sensitivity speaker with a typical passive crossover network. Mainly, the power required for driving the woofer, significantly higher than the power for the sqwawker and tweeter, causes all sorts of things on the amplifier, and those things do destroy the clarity of the high frequencies, which are (sadly) travelling through the same canal.

Most high quality, low distortion, high clarity, no-nonsense studio loudspeakers have a provision for bi-amping...
 
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When you read a book such as "High performance audio amplifiers" by Duncan, you realize how compromised is a typical (high quality) amplifier when it's asked to drive a 85-91dB sensitivity speaker with a typical passive crossover network. Mainly, the power required for driving the woofer, significantly higher than the power for the sqwawker and tweeter, causes all sorts of things on the amplifier, and those things do destroy the clarity of the high frequencies, which are (sadly) travelling through the same canal.
And conversely there are a number of very inexpensive (think LM3886 inexpensive) amplifiers which will drive almost any tweeter with NO audible amplifier distortion of any sort. And by removing the high frequency/high slew rate demand from the "other" amps in the system it becomes much easier to design them to be inexpensive, high power and effectively distortion free (within their working range) as well. Thus spoke Mr Natural . . . "Use the right tool for the job".
 
Whilst these posts are interesting and have given me lots of food for thought, there's still no clear ‘winner’ as far as I can see – even after nearly 700 posts of mainly technical argument.

Perhaps the way to decide whether passive or active offers the best listening experience of recorded music reproduced in the domestic environment is to know what system type (i.e. passive or active) people on this forum choose to listen to with the important proviso that ’serious examples’ of both system types have been used in your home for long enough to be able to express a valid preference.

(A lame idea as this forum doesn’t appear to support polls!)
 
There is something wrong here. The amplifier (unless it's a very very good one), by virtues of typical Class-AB amplifier distortions such as crossover distortion, under/over biasing, thermal issues, power rail modulation, etc*... will produce all sorts of distortions including IMD distortion. And these are audible in the sense that they are removed or diminished by (a) going to a better amplifier like a class-A bjt amplifier, (b) going fully active so the amplifier working bandwidth is narrower, or (c) both.

Yes and this is the point, that if your amplifier isn't suitably designed that going active will reduce the detrimental effects that higher order distortion products could potentially introduce.
 
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...... there's still no clear ‘winner’ as far as I can see – even after nearly 700 posts of mainly technical argument.

Perhaps the way to decide whether passive or active offers the best listening experience......

700 shots, a draw.......and you don't see the obvious conclusion ? there is no winner, never will be, and none needed anyway
the best is whatever works for you :p

lets just say I decide that active would the best for you
but if you can't make it work, what good is for you then
 
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