What do you think of passive crossovers?

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I've built identical speakers active and passive and they sound the same. Properly done there is no difference between a passive crossover and an active one. Audibly that is - the active costs a lot more.

Amplifier damping does not cause distortion and if it did then its a bad amplifier design. A decent amp can just as easily drive a loudspeaker with a crossover in front of it as it can just the loudspeaker itself.

Active has some appeal in some situations, like DIY, its ideal, or where you can incorporate some necessary EQ into the crossover, but unless there are some clearly identified reasons to go active, passive is just as good.
 
I on the other hand have compared and converted a few passives and actives, from Dynaudio (DynaudioAcoustics BM5 passive and active plus the equivalent consumer model, the differences were two different passives and one active. Drivers and cabs remained the same.) to my own Tannoys.
To my ears passives don't get close to actives, with regards to bass reproduction particularly.
And for the Tannoys the improvement gained from going active is far greater than in passive mode going from a crappy Arcam Alpha 8 amp to a rather decent MC2 Audio MC450.
 
Half of the problem with comparing active vs passive is making sure that you are actually comparing apples vs apples. It is all too easy to turn a bad situation (mediocre passive implementation) into a better one (mediocre active implementation) and then say that active is better - note that I am not implying here Charles Darwin that this was the situation with yourself.

Passive crossovers have their strengths and their weaknesses as do active ones.

If you want to do a direct comparison between an active and a passive loudspeaker then one has to ensure that the end acoustic responses of both the active and the passive loudspeakers are identical in every which way. This includes both in their amplitude and in their phase response, don't go sneaking in a delay network to sweaten the deal or fine tune the xover/tilt the primary lobe otherwise it's not identical.

Another thing that has to be considered is what load does the passive loudspeaker present to the amplifier? All to often we see passive loudspeakers reviewed and the multi-way versions tend to be quite hard to drive. These demand an amplifier that can cope with the load, try driving them with something inadequate and the performance suffers. If one changed that passive loudspeaker into an active one, even with identical filter transfer functions, there's a high chance that you'll easily prefer the active one because the mid and tweeter amplifiers have been freed of the demanding load that the bass probably presents.

Personally if a passive crossover presents a horrible load to the amplifier then I consider it poorly designed. There are tricks one can use to help keep the load benign but they often cost a bit of extra money. Also audiophile loudspeaker brands don't tend to seem phased with producing loudspeakers that dip to 2 ohms with severe phase angles plastered all of the place.

As Earl has stated, if a passive loudspeaker is appropriately designed then its active counterpart should sound pretty much identical within the limits of the system and this I believe is where the distinction between the two comes into play.

Active crossovers (especially digital ones) are inherently more capable and far more flexible then their passive counterparts. This allows you to do things with the active that you cannot do with the passive and this is almost always to the benefit of the end system design. This is especially true where low frequencies are concerned.

Another benefit of the active design is that it frees the tweeter and midrange amplifiers from the load presented by the bass and frees the designer from sensitivity limitations between drive units. This means you can use a 96dB sensitive midrange driver with an 84dB bass driver and not have to pad down the midrange resistively. In other words you can reap the benefit of having an efficient midrange driver, whereas in the passive version you could not.

In the active design this would mean that you're probably never going to need more then 10 watts to drive the midrange. If the crossover is active those 10 watts would buy you a max midrange SPL of around 106dB. In the passive system if you wanted to use that same midrange driver with the 84dB bass you'd need an amplifier capable of delivering around 150 watts to reach the same SPL. 150 watts doesn't sound that much, but lets say we've got a 100 watt amplifier on the midrange giving a max SPL of 116dB, then you'd need an amplifier capable of delivering more then 1500 watts for a similar SPL in the passive loudspeaker. Some would say you need a transient, peak SPL capability of a system of around 115dB but hardly anyone has an amplifier giving out the 1500 watts capable of providing that, so on peaks you're 300 watt amp will clip and if the bass happened to clip the amplifier in the passive loudspeaker the midrange and tweeter would start sounding terrible, yet in the active one the bass amplifier might clip, but the mid and tweeter amplifiers would not and still sound clean.

Now using low sensitivity drivers is not Earls cup of tea and there are very good reasons for this. Even if you're using a passive crossover and even if the loudspeakers are horrible to drive, if they are sensitive you might only ever need 25 @ 2 ohm watts to cause hearing damage. This however isn't representative of the majority of hifi drivers out there, that often require large amounts of power to hit decent SPLs. Using an active crossover in these situations, where some of their specific advantages can be exploited makes far better sense and will provide you with better sound. This is especially true where people want small boxes capable of producing deep bass, here you need to use active equalisation to arrive at that goal and you often need a lot of amplifier power to get there too. In situations like these, where you're throwing around and paying for a large number of watts, then you most certainly don't want to lose a dB of SPL to the inherent resistance of a monster inductor in a passive crossover - one more bonus to using high sensitivity designs.

Both active and passive have their place and if you don't need the additional capabilities of an active crossover then it is a waste of time/money implementing one.
 
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I generally agree with Earl and 5th E's statements. Done right, they don't sound much different to me.
Sometimes I find the passives a bit more "organic" or "integrated" sounding - like part of a whole thing. Active can have superb detail but can also sound forced or artificial (to me.) Kinda Hyper-Fidelity.

Those subject impressions may have more to do with the choices made in the crossover than the active/passive thing.
 
Some very good loudspeakers with passive xovers have been made. But it is an outdated technology.

The only way to realize real progress in sound reproduction i.m.o. is to mate optimal amplification with individual drivers, and to design active xovers that take accoustic driver specifics into account. With passive xovers, you have to deal with both accoustic and electrical specifics (Le, resonant peaks, thermal effects). You avoid all that electrical hassle by going active. Plus, the sort of compensations you would want to make because of driver accoustics, are 10 times easier realized in silicon sprinkled with some passives, than in big copper coils and fat caps. Think about the cost too.

vac
 
Perhaps the question should be when to use active.

Earl Geddes makes somewhat unusual speakers which may benefit somewhat less from going active. Earl's speakers need subwoofers since they are not asked to produce much bass.
Gedlee speakers are large closed box units with very high sensitivity drive units, these very high sensitivity drive units use very large motor systems in closed boxes, this is very good for control and low distortion. These speakers are not pushed to produce deep bass and again this helps with control.
These speakers will benefit from very low drive unit excursion. The cones do not have to move very much to produce a big sound due to large diaphragms and high sensitivity compression drive units. careful matching of drive unit sensitivity also means relatively simple crossovers too.

These speakers do not require a lot of equalization, this doesn't mean they are inherently superior or worse just that they suit his design parameters. His designs are of the no compromise school, very large yet still needing bass reinforcement. Perhaps they are cutting edge for the right home, by which i mean a large enough listening room with extremely understanding spouse or dedicated listening room!

In sharp contrast I use the active Linkwitz Pluto's which are heavily equalized and use a drive unit combination rather unsuitable for sensible passive design. These speakers are truly superb but could not be more different. This is a different animal though, designed for small spaces and listening in close quarters.

Pluto is an exceptional speaker, really good and incredibly natural sounding, free from hardness and artifice. driver integration is seamless. You will be hard pressed to find its equal in a small speaker. The bass is impressive from such a small enclosure tuneful too, due to well designed long throw driver and linkwitz transform circuit increasing deep bass. Subjectively distortion is low at surprising volume given such a small bass mid.

I hope products like Pluto point to a brave new active future for domestically friendly designs. Of course there are many truly excellent passive designs but I think passive is ultimately restrictive and backwards looking.
 
You must tailor the system SPL to the lowest sensitivity driver with a passive crossover. Try boosting signal/power delivery using a passive circuit, e.g. EQ - you can't! All you can do is direct or dispose of the power coming out of the amplifier.

Try implementing something like a Linkwitz Transform (e.g. for bass boost on a subwoofer) using a passive circuit without throwing away lots and lots of power.

Try implementing a delay line passively, as part of a crossover... not pretty.

I have to agree that IMHO passive filters are not a great match to the varying impedance load of a driver, but people go to great lengths to make them work, and they do it well for the most part. There are many seasoned passive crossover designers who know little tricks and such to pull off impressive filtering with very few parts on just the "right" drivers.

You might consider combining active a passive crossovers... If you use a powered subwoofer, you are likely already doing that.

-Charlie
 
Active crossovers are great!

Easy to mess around with filters, slopes, overlapping, underlapping and getting the drivers interaction sorted out.

However, the speakers are not speakers anymore--they are a system. 20 years ago I had a set of Carvin 993 PA speakers that had bi-amp inputs and full range inputs through a passive crossover. Generally, I would bi-amp them and change the crossover frequency from the dual 15" woofers going to the dual 6.5 inch cone midranges as the night wore on. At the beginning, I'd lower the XO from the stock 500Hz to around 250Hz for a cleaner sound--later on I'd go to 500Hz or slightly higher if I needed massive SPL. Loved running them bi-amped but sometimes, I'd run a single amp through the passive XO.

The active/passive option was great since one day one of my amps shut down so I finished off with the passive XO. If the active crossover dies, the passive backup is a nice option also. My HT main speakers use an active XO with built-in amplifier crossed at 200 Hz, the mid to tweet is passive at 3 KHz. Nice system but eventually, the amp will fail so I'll build a new speaker with a passive filter network feeding a different woofer combo. The downside of active is eventual failure of the amp/electronics but when it's good--it is very good!

For subwoofer use, I only use active crossovers and their own amplifiers--gotta pay to play. Mid/tweet filters are fairly inexpensive to build and the speaker will connect to many different things as a single unit.

Can I vote active subwoofers and passive mid/tweet filters?
 
Rob, we may have cross-posted, but you go to the heart of the matter: The Pluto, like the other Linkwitz designs I know, rely on active xovers with driver specific compensations to achieve their goals. Linkwitz rules, I have stated it before.

vac


Yes, I have read your post now, I should have edited mine with reference to your post.
I am with you 100%, Linkwitz rules!

He made a speaker out of drain pipe and $20 fullrange drive units as tweeters with active equalization that is so vanishingly smooth that they rival the Heil AT's, ribbons and Seas Excel tweeters I have used in previous passive speakers. I do not even hanker after the Quad Electrostatics I used to use now either.
 
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Geddes speakers big? The Abbeys sure aren't. They're no bigger than most bookshelf speakers.

IMO the reason most folks rave about the advantages of active crossovers is simply because they are easier to get right. That's a huge advantage for the DIY guy. His chances of success are far greater.

I'm tired of the hassle and all the parts of active, I'm going back to passive. Stay tuned to see if I regret it. :D
 
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I originally designed my system with the idea I would some day go active, and designed a quick and dirty passive X-0, it was good enough that I went back and did it right later. These days I have no serious plans for active for the reasons stated above. It's much less trivial when you are running an all tube system..
 
There are a few manufacturers that make otherwise identical speakers in active and passive versions. The ones I have auditioned are by ATC, PMC, and Dynaudio. Not only were the active versions markedly better on all occasions, they were also better value for money. Massive overengineering is needed to make amplifiers that can drive super-speakers with vanishingly low impedance these days. This is sheer folly. Amplifiers that are asked to drive band-limited drivers directly are fairly easy to construct to a very high subjective standard; the more so the higher driver impedance is. High current requirement is the bane of high fidelity (hey, I like this, I'll make it my sig).
 
Passive crossovers are expensive, difficult to implement, and have limited application.

"Difficult to impliment", absolutely, especially with waveguides, way over most DIYs capability, but a walk in the park with my software tools, but "expensive" that is completely ridiculous, they are cheap by comparison with a DSP box and another amplifier - get real! "Limited application", I guess if they are "difficult to impliment" thats true.
 
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