Passive & active crossover sonic differences?

I'm curious if there are sonic differences between these two approaches when the speakers are very much alike. An example would be passive ATC speakers driven by ATC amplification versus active ATC speakers.
I ask this because I've heard people say "I hate active crossovers". I wondered if it was a not well designed example that they were refering to until I read a review in HiFi+ of an active ATC SCM20 which the reviewer didn't like, but also added that his criticism did not apply to the passive models.

 

I think it depends on the complexity of the crossover. If we are talking about a simple passive crossover than I'd think that an active crossover could be setup to be close to sonically identical. That said, many passive crossovers are not that simple and are designed specifically for the speakers networks they are a part of. Crossovers do other things besides just dividing the frequency spectrum. Some have time delays built in, in an attempt to insure that the sound from the different drivers arrive at the listeners ears at the same time.

Most active crossovers are not made specifically for a specific speaker system, so are more general purpose. Now if efficiency is a consideration, as in a PA system or a speaker system that needs to play very loud, an active crossover will have certain advantages. By using an active crossover, separate amplifiers can be used for each driver. This not only can improve efficiency, it can lessen IM distortion and driver to driver interaction. Then again, bi-wiring offers many of the advantages of bi-amping but doesn't necessary improve efficiency.

So it would seem to me that this is not an easy question to answer. I'd imagine most audiophiles would prefer passive crossovers and bi-wiring over bi-amping. IIRC, Steve is on record as saying that he is not a big fan of active crossovers in hi-fi speakers.

 

Thanks Doug.
I was thinking that maybe those who heard an active design and found it unsatisfying could point to a common characteristic. Some fundamental musical difference between active and passive. I'm imagining overly analytical in the active.

 

Mike F,

To see what one proponent of active crossovers says about them look at:

http://linkwitzlab.com/crossovers.htm

If you've heard of Linkwitz-Riley crossovers you've heard of Siegfried Linkwitz. His current designs utilize active crossovers. A previous design of his was Stereophile's 1998 loudspeaker of the year. I own his current ORION loudspeakers which have gathered much praise. See the following page for some reviews:

http://linkwitzlab.com/orion_reviews.htm

I don't see why an active crossover properly implemented would not be equal to or better to a passive one.

-sneak

 

Can someone give a brief explanation of what constitutes an active vs. a passive crossover? Do I understand that typically a passive crossover lives in the speaker cabinet while an active one lives upstream in the signal path somewhere? Are there other differences?

 

The passive crossover is usually located in the speaker cabinet but doesn't have to be. It generally is designed to handle the power output of an amplifier which means that it will use larger components that can handle more current. As a result it usually generates a bit of heat when the sound level is high. This heat is wasted power and part of the reason for loss of effeciency. Also power resistors are generally not considered as sonically pure as many types of lower power resistors.

By definition, an active crossover, or any active device, requires a power source for operation. There are usually gain controls for each output section. With an active crossiver it is easier to change the parameters such as crossover frequency and rolloff slope. As a result, they are more versatile and can be used with various speaker systems so long as each driver in the speaker has accessible terminals.

A passive crossover is generally less efficient than an active crossover. Usually the output of the amplifier is spectrally divided by the passive crossover before being presented to the speaker components. But is is surely possible to use a passive crossover before the amplifier, in which case it functions much like an active crossover, but has less flexibility.

My Dahlquist crossover is a combination of an active and passive crossover, but is used before the amplifiers. The high pass section is just a series capacitor which just cuts the lows from the signal. This is passive and is very kind to the signal. But by being passive it has only a simple 6db per octave rolloff and the crossover frequency can't be changed without changing the value of the capacitor. Since it is designed for subwoofers this is a great solution.

The low pass output of this crossover is active. As a result it can have a much higher rolloff slope, which in my case is 12db per octave. This is important to insure that there are no highs getting into the bass speaker which would interfere with the signal coming out of the higher frequency speaker components. There is also a gain control with this section to esily set the correct level for the subwoofer output. Of course, having this high of a slope is not as important for the high pass output because the passive 6db per octave slope is aided by the natural low frequency roll off of the main woofer.

 

Thanks for the explanation.