Crossovers, why so few options?

You bring up a good question, why not more use of active crossovers? It solves so many issues and makes for truly superior performance. For anyone who is *truly* serious, active is the only choice, yet for some unknown reason most audiophiles are either unaware or just want plug & play convenience.

As far as selection, there's not enough demand, but what you need is out there. Several ready made ones, as you've mentioned, and also custom made are available.

The problem is that no "off-the-shelf" active crossover is really suitable for any serious loudspeaker. The crossover must be customized to the the specific speaker system in order to account for amplitude/phase issues in and out of each driver's pass-band. This means that a great deal of flexibility is required in the filters and, more critically, more sophistication is required of the user. The former can be bought but the latter demands some learning and experience.

So, in principle, using an active crossover (and not a passive inbuilt one) can afford real advantages but this is most easily realized with speakers that are designed and marketed that way.

Kal

Just to clarify, I'm talking about using an external crossover to split the signal between sub/mains.

??? Why didn't you say so??!! That's an easy one.

The reason is that such are built into most subs and into all preamp/processors. The need for an external crossover is quite limited today.

Kal

Don't most stereo preamps not have a built-in crossover?

Additionally, outputs from subwoofers usually have a high-pass filter that isn't adjustable; I know that on REL subs, this is as high as 120 Hz for line-level outputs. Most people (I would think) don't want to use such a high crossover frequency.