The sonic benefits of an active crossover. A discussion.

treitz3

Super Moderator
#1
Good evening ladies and gentlemen of the WBF. Moving on to the next topic in the "Dissecting a speaker series", this discussion will be concentrated solely on the sonic benefits of using an active crossover, ways to implement the use thereof, different configurations and why one would want to do something like this in the first place. Some folks love passive, some like external but on the flip side, one might venture to say that a vast majority of those who have tried or heard an active speaker think that this is the way to go. Simply put, why?

What would the sonic benefits be?

What other benefits would those who are interested in active crossovers want to know?

This discussion is not only limited to the sonic benefits and the positive things about an active crossover but some of the deficiencies or drawbacks, if they exist as well. Anything and everything having to do with an active crossover can be discussed here. What say you?

Tom
 
Feb 11, 2012
1,286
0
0
Hangzhou, China
#2
I wonder if 'active crossover' is the right descriptive term? How about 'line level crossover' (as opposed to 'speaker level crossover') because the option I currently prefer is building a passive crossover (using inductors and capacitors) but at signal levels. This stems from the hypothesis which I currently have that its active electronics' intermodulation distortion which is the limitation on SQ. I reckon passive components generate less IMD than active circuits.

With this hypothesis, line level crossovers make life easier for poweramps because by bandlimiting the signals prior to being amplified, the amps generate less IMD by virtue of handling a narrower bandwidth. Their power supplies are also less stressed because the total output power is spread across more than one amplifier. Designing an amp to handle a narrower bandwidth is easier than one handling the whole audio spectrum, line level crossovers allow an amp to be optimized to handle driving only a tweeter (for example).
 

Kal Rubinson

Active Member
May 5, 2010
1,449
2
38
NYC/CT
www.stereophile.com
#3
I wonder if 'active crossover' is the right descriptive term? How about 'line level crossover' (as opposed to 'speaker level crossover') because the option I currently prefer is building a passive crossover (using inductors and capacitors) but at signal levels. This stems from the hypothesis which I currently have that its active electronics' intermodulation distortion which is the limitation on SQ. I reckon passive components generate less IMD than active circuits.

With this hypothesis, line level crossovers make life easier for poweramps because by bandlimiting the signals prior to being amplified, the amps generate less IMD by virtue of handling a narrower bandwidth. Their power supplies are also less stressed because the total output power is spread across more than one amplifier. Designing an amp to handle a narrower bandwidth is easier than one handling the whole audio spectrum, line level crossovers allow an amp to be optimized to handle driving only a tweeter (for example).
I've done this inspired by a wonderful old article in "Audio" magazine. Do you know it or should start digging into my closets?
 

JackD201

[WBF Founding Member]
Apr 21, 2010
11,031
22
38
Manila, Philippines
#5
IMO

Pros: Efficiency, flexibility

Cons: Space, more signal and power wiring

Thing to watch out for: sonic signature of the active crossover unit itself, obviously the less the better
 
Feb 11, 2012
1,286
0
0
Hangzhou, China
#6
Yes - agree that the signature of the active (I prefer to call it line-level) XO is a major issue. In the current way of building systems, its a separate box, with separate mains power supply, another set of cables to introduce degradation.

As a designer my currently preferred way of building a no-compromise digital system is to have one DAC per drive unit, and implement the crossover passively right after the I/V stage of each DAC. This is because multibit DACs already need to have passive filters after them anyway, to cut off the OOB signals, so why have two filters there when one will do (for the bass/mid at least) ? I haven't built a whole system like this yet, but perhaps for the tweeter we'd do better to implement a digital high pass filter prior to the DAC and keep the anti-imaging low pass passive filter. Since to my ears NOS delivers the sweetest sound in future I'd like to play with fractional oversampling (aka undersampling) for bass/mid units - perhaps even running as low as 11.05kHz sample rate where the crossover frequency is 3kHz.
 
#7
If we are going to talk about crossovers, we should be quite clear about what we are talking about. This has already caused some confusion in the other thread and I see the beginnings of it here :) These are standard industry definitions:

- PHLXO - Passive, high level crossover. These are speaker level crossovers installed in the majority of speakers.
- PLLXO - Passive, line level crossover. These are preamp level crossovers and require multiple power amps. These are a rarity but can be found in some speakers, e.g. B&W Nautilus.
- ALLXO - Active, line level crossover. Preamp level crossovers which are powered, and require multiple power amps. These can be either analog or digital.

The confusion comes because some people refer to all systems with line level crossovers as "active speakers" or "active systems", because the speakers are directly powered by the amplifier. Active speakers are still enough of a rarity in the high end world that some people make the mistake of lumping them all in the same category with no consideration of the nuances between them. I much prefer the more precise terms as used by the industry.

The advantages and disadvantages of PLLXO vs. ALLXO is similar to those between a passive preamp and an active preamp. Some might say that the simpler electronics of a PLLXO provide a more pure experience, others believe the better impedance matching and greater versatility of ALLXO's outweigh the negatives.

Furthermore, ALLXO's come in analog or digital varieties. In addition to the simple crossover function, digital XO's are very easy to tune - you simply change the settings through the front knobs or through a laptop computer, and can correct phase, group delay, and compensate for frequency response anomalies in the speaker and the room. The downside is that the signal needs to be re-digitized if you are not already feeding it a digital signal directly off your transport. Some people think that this is completely inaudible, or argue that the sonic advantages outweigh the disadvantages. My position on this is that it is system dependent.

The other downside is the learning curve - if you fail to take care when obtaining your measurements, you will be telling your crossover to do all sorts of horrible things to your sound. I know some people whose systems are in a constant state of flux because they can't help but keep fiddling with their digital crossovers. That might be OK if your hobby is tuning your system, but my hobby is listening to music and not fooling around with microphones and laptops.
 
Feb 11, 2012
1,286
0
0
Hangzhou, China
#8
The original B&W Nautilus used an active line-level crossover, not passive.

To add to the confusion over nomenclature, I've designed an active crossover using DACs which isn't digital in the sense it doesn't use a DSP, rather an array of DACs to build a hardware-based FIR filter, aka a transversal filter. This has a potential dynamic range advantage over the more traditional digital filters followed by DACs.
 
Jul 25, 2012
2,554
0
36
NY
#9
Oh boy. I don't know if I can do this again.:eek: :eek: :eek:

Just to cast my vote, I'll say that active crossovers and multi-amping is the way to go.

For the most part, I'll second what Keith says. Based on other threads, he and I seem to be pretty much on the same page with this topic.


With regard to definitions, I like to use "active crossovers" to describe an active line level crossover between the preamp and power amps, "passive crossovers" are the common high level crossovers inside the speaker, and I prefer "POWERED speakers" to "active speakers" when the speaker contains the amplifiers, which may also contain an active line level crossover and multiple amplifier channels. Yeah, I know, people have their own preferences with definitions. We should try to get a consensus.
 
Feb 11, 2012
1,286
0
0
Hangzhou, China
#10
I second Keith's suggestions but would like to extend them a little. Rather than 'ALLXO' for active line level crossover, let's keep this monika to mean 'analog (meaning active analog) line level XO'. Then let's add 'DLLXO' for 'digital line level XO' and 'HLLXO' for hybrid (digital) line level XO (which is my transversal filter).
 
Jul 25, 2012
2,554
0
36
NY
#11
I guess we're in for a lot of definitions!:p


What's a hybrid digital transversal filter?
 
Feb 11, 2012
1,286
0
0
Hangzhou, China
#12
What's a hybrid digital transversal filter?
This could get a bit messy in explaining, so bear with me...

Its basic structure is an FIR filter - that means its built out of delays and multipliers with a final adder to combine all the product terms.

In this implementation though the multipliers are current-output DACs with different resistor values giving the multiplicand and the final addition is just summing all the voltages together by putting them in series. The delay elements are still digital - shift registers.
 
Jul 1, 2010
8,713
0
0
#13
We've already complicated the thing beyond reason, and unless I missed it, haven't answered the question. The advantages of an active crossover, before a separate amplifier for each driver in the speaker system (regardless of whether or not the crossover components are analog or digital)?

Headroom
Driver control (damping)
The transient needs of one driver (usually the bass) do not take from another
The designer can match amplification to specific drivers

Those are the high points, anyway. The sonic results? Lower distortion. Tighter bass (passive users often think active speakers are "lean." They're used to bad bass control), cleaner highs, more transparent mids, incredibly clear, precise imaging, better dynamic range....

But I personally don't think this is a DIY endeavor. If you're an audio engineer, go for it. You'll still have to live with the negative effects of all the wire and connections, the boxes full of redundant, noise-making components inherent in a user-built active system, but you should be able to put together a system that works well and gets you way ahead of the same system executed passively. If you're not an engineer, buy good active speakers. The amps the crossovers, the drivers will all have been chosen, if not designed by, the design team to work together -- Synergy by design instead of trial and error! -- All the interconnects will be soldered, all the wire extremely short (I'll take a 6" copper wire over a 10' silver one all day, every day). Buy active speakers and subs, and enjoy.

Personally, I think the magic is in 2-way systems consisting of a primary driver of approximately 6" and either a dome or ribbon tweeter...and lots of power. With a sub or two it'll handle a decent-sized room and give you incredible clarity and imaging. I think you lose some of that when you get mid-bass drivers in the 8" and above range. I think you lose more of it when you add the second crossover and attempt to go too deep in the mains with a 3-way. I don't have a technical explanation for that, I just hear it. But if you have a huge listening room, or just want a larger than life sound, the industry makes some big actives for you; they're out there. But engineered active systems are, IMO, the way to go for most music lovers.

99% of the available product is in pro audio. See Adams, Events, JBLs, Genelecs, Dynaudio, Tannoy...the list is long. Anyone who is really interested has a journey ahead of them. And if you're not prepared to accept more for less -- substantially less -- if you're not prepared to believe that an active speaker system could replace not only your speakers, but your amps and preamp and cables, and sound better doing it, for a fraction of what audiophiles commonly pay for speakers alone, don't bother going out the door. You're also going to have to be prepared for a relatively transparent view into your recordings. You may not like it.

Tim
 
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#14
Tim nails most of the benefits above.

I'll reinforce that to me, the biggest advantage is lowered distortion.

Time and phase aligning the drivers delivers a clean impulse response, giving an active XO system outstanding imaging compared to the same speaker on passives.

My experience is based on using the same set of speakers (MartinLogan Monoliths) in the same room driven by the same amps over a decade where the major changes were the following progression:
  • Factory passive 2-way crossover in external box
  • Bi-amp via factory passive crossover - Noticeable improvement, especially in the bass as the amp is not modulated by the ESL panel
  • Bi-amp via analog active crossover - Big step up in quality but time alignment between panel and woofer still not right
  • Bi-amp via cheap DSP active crossover - Huge step up in all dimensions except noise floor of XO, soundfield now focused and smooth.
  • Replace woofers with units optimized for 60 - 500Hz , reset crossover points to 60 and 314Hz. Much improved mid-bass.
  • Bi-amp via DBX 260 active crossover - much lower noise floor, more granular time-alignment helps focus.
  • Bi-amp via DBX 4800 speaker processor - absolutely silent, adjustable gain structure optimizes amp performance, high quality algos are very transparent.

All these steps were supported by careful measurements and tuning. Not for the novice as note above. But results are astounding and totally tuned to your speaker and room. One of the things that gets overlooked is in-room performance. By tuning the XO to not only close-miked speaker performance but also to total in-room results, the overall 'synergy' people talk about it raised significantly.

I am firmly in the camp that a highly flexible DSP XO yields better overall performance from a speaker than any passive XO can ever hope for. Any deficiencies in the DSP or extra D/A steps pale in comparison to the benefits achieved in overall in-room system performance.
 
#15
thought it might be good to hear from an actual speaker designer as well.

Roger Sanders, from Sanders Sound Systems is a person I deeply admire and whose opinion on ESL and audio topics in general I deeply respect.
In an interview, he clearly explains his position on active vs passive and some of the benefits of actives:

"Passive crossovers have dreadful performance. This is another extensive topic that I cannot address adequately in this interview. So just allow me to summarize by saying that passive crossovers have the well-known problems of phase shift, hysteresis losses, group delay, inadequately steep crossover slopes, and distortion. Less appreciated is the fact that they insert inductors, capacitors, and resistors between the amplifier and the speaker's drivers. This isolates the woofer from the amplifier and prevents the amplifier from having tight control of the driver. Or to put it another way, the damping factor of the amplifier is degraded by passive crossovers.

Since it is essential to use the amplifier to control the woofer, the amplifier must be connected directly to its driver without any intervening crossover components. Therefore electronic/active crossovers are essential to obtaining good integration. The amplifier must have a high damping factor. This excludes the use of tube amplifiers for driving woofers because their output impedance is too high. Powerful, well-designed solid state amplifiers have incredibly low output impedance (typically less than 0.1 Ohm), and massive current flow capacity, so they have the high damping factor and power needed to really control a woofer.

It is necessary to use electronic/active crossovers to achieve the best from any speaker system. I continue to be amazed by all the speakers on the market with passive crossovers that claim to be "reference" quality or SOTA systems. The truth is that electronic/active crossovers and multiamplifier systems are superior to any passive crossover system. All speakers will be improved with the proper use of electronic/active crossovers. So any speaker that uses passive crossovers simply cannot be considered the finest available. I am unwilling to compromise and so do not use passive crossovers in any of my current speakers.

There are many diverse types of electronic/active crossovers with many different features. Also, both analog and digital electronic crossovers now are available. I consider digital crossovers to be one of the greatest advances in modern audio. They offer features that I have wanted crossovers to have for years, but which were unavailable. "

From this article: http://www.dagogo.com/View-Article.asp?hArticle=991

Based on all my experience, Roger is 100% correct.
 
Jul 1, 2010
8,713
0
0
#16
thought it might be good to hear from an actual speaker designer as well.

Roger Sanders, from Sanders Sound Systems is a person I deeply admire and whose opinion on ESL and audio topics in general I deeply respect.
In an interview, he clearly explains his position on active vs passive and some of the benefits of actives:

"Passive crossovers have dreadful performance. This is another extensive topic that I cannot address adequately in this interview. So just allow me to summarize by saying that passive crossovers have the well-known problems of phase shift, hysteresis losses, group delay, inadequately steep crossover slopes, and distortion. Less appreciated is the fact that they insert inductors, capacitors, and resistors between the amplifier and the speaker's drivers. This isolates the woofer from the amplifier and prevents the amplifier from having tight control of the driver. Or to put it another way, the damping factor of the amplifier is degraded by passive crossovers.

Since it is essential to use the amplifier to control the woofer, the amplifier must be connected directly to its driver without any intervening crossover components. Therefore electronic/active crossovers are essential to obtaining good integration. The amplifier must have a high damping factor. This excludes the use of tube amplifiers for driving woofers because their output impedance is too high. Powerful, well-designed solid state amplifiers have incredibly low output impedance (typically less than 0.1 Ohm), and massive current flow capacity, so they have the high damping factor and power needed to really control a woofer.

It is necessary to use electronic/active crossovers to achieve the best from any speaker system. I continue to be amazed by all the speakers on the market with passive crossovers that claim to be "reference" quality or SOTA systems. The truth is that electronic/active crossovers and multiamplifier systems are superior to any passive crossover system. All speakers will be improved with the proper use of electronic/active crossovers. So any speaker that uses passive crossovers simply cannot be considered the finest available. I am unwilling to compromise and so do not use passive crossovers in any of my current speakers.

There are many diverse types of electronic/active crossovers with many different features. Also, both analog and digital electronic crossovers now are available. I consider digital crossovers to be one of the greatest advances in modern audio. They offer features that I have wanted crossovers to have for years, but which were unavailable. "

From this article: http://www.dagogo.com/View-Article.asp?hArticle=991

Based on all my experience, Roger is 100% correct.
Another inherent advantage. And I agree with Jonathan. The bottom line? The advantage is audibly decreased distortion. Audiophiles spend tens of thousands of dollars and tweaks and upgrades that have nowhere near the impact.

Tim
 

Mike Lavigne

Member Sponsor & WBF Founding Member
Apr 25, 2010
7,133
53
48
#17
IMO

Pros: Efficiency, flexibility

Cons: Space, more signal and power wiring

Thing to watch out for: sonic signature of the active crossover unit itself, obviously the less the better
+1

assuming a desire for true full frequency range performance and given a well thought-out purpose designed room; i prefer a passive crossover for the highs, mids and fairly low into the bass, and then analog active for the deep bass.....MM7's/MM3's/VR9SE/VR11SE.....one totally integrated package.

this approach minimizes the crossover signature effects on levels of refinement optimizing analog sources (when ideally implemented), allows for modestly powered main amplification, maintains an analog signal path for mids and highs, but still allows for room/speaker adjustments in the bass without DSP.
 
Feb 11, 2012
1,286
0
0
Hangzhou, China
#18
The truth is that electronic/active crossovers and multiamplifier systems are superior to any passive crossover system. All speakers will be improved with the proper use of electronic/active crossovers.
This is quite simply, a nonsense claim without knowing the transparency of the electronics involved.

So any speaker that uses passive crossovers simply cannot be considered the finest available. I am unwilling to compromise and so do not use passive crossovers in any of my current speakers.
Yet an active speaker would have to incorporate the finest amplifiers and the most transparent active XOs to be considered the finest available. Do any of them?

There are many diverse types of electronic/active crossovers with many different features. Also, both analog and digital electronic crossovers now are available. I consider digital crossovers to be one of the greatest advances in modern audio. They offer features that I have wanted crossovers to have for years, but which were unavailable. "
They do indeed offer a whole slew of useful features, yet they're normally paired up with DACs which are iPod quality (thinking Behringer here). If there's a DSP XO with decent DACs I'm keen to learn of it.


Based on all my experience, Roger is 100% correct.
Based on my experience as both an active speaker and digital systems designer, he's wide of the mark in many respects.
 
Jul 1, 2010
8,713
0
0
#19
This is quite simply, a nonsense claim without knowing the transparency of the electronics involved.



Yet an active speaker would have to incorporate the finest amplifiers and the most transparent active XOs to be considered the finest available. Do any of them?


They do indeed offer a whole slew of useful features, yet they're normally paired up with DACs which are iPod quality (thinking Behringer here). If there's a DSP XO with decent DACs I'm keen to learn of it.




Based on my experience as both an active speaker and digital systems designer, he's wide of the mark in many respects.
Relative to an active system built with the "finest amplifiers," whatever that means, maybe. Compared to passive systems? It is, perhaps, more effective to look at the problems in passive crossovers than to try to convince people of the advantages of active systems. You could start with the "finest amplifiers" or the purest spring water. Run it through a dirty pipe and its fine beginnings become a moot point.

Tim
 
Feb 11, 2012
1,286
0
0
Hangzhou, China
#20
To have the analogy hold up then there'd need to be some correspondence between a dirty pipe and the capacitors and inductors used in high quality speaker level crossovers. Is there?

Incidentally 'finest amplifiers' means the most transparent ones (for subjectivists), or the ones with lowest IMD with music signals (for objectivists).
 

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