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Old 28th September 2011, 08:50 PM   #1
Boscoe is offline Boscoe  United Kingdom
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Default What do you think of passive crossovers?

Some hate them and will never use anything other than active, they say due to high distortion brought on by amplifier damping.

What do you think? Do you like the sound of active over passive?
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Old 28th September 2011, 09:10 PM   #2
gedlee is offline gedlee  United States
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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.
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Old 28th September 2011, 09:13 PM   #3
Boscoe is offline Boscoe  United Kingdom
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I personally think exactly the same, the argument is that in worst case scenario damping is high so shift crossover frequencies creating peaks in FR. Also that passive generally adds to distortion.

If you want HiFi don't use poorly designed amps I say!
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Old 28th September 2011, 09:44 PM   #4
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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.
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Old 28th September 2011, 11:09 PM   #5
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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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Old 28th September 2011, 11:11 PM   #6
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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.
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Old 28th September 2011, 11:16 PM   #7
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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.

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Old 28th September 2011, 11:40 PM   #8
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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.
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Old 28th September 2011, 11:51 PM   #9
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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.

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Old 28th September 2011, 11:52 PM   #10
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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.

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