It is simply JBL's way of telling you that the design calls for a 300Hz crossover. There is an internal crossover set to that frequency, when you go into bi-amp mode, that circuit is removed, and you replace it with your active crossover and two amps. The other crossover components that divide the frequencies to the compression drivers are all still in the circuit as they should be. Simplistically what you do is send all frequencies above 300Hz to the top pair of binding posts and all frequencies below 300Hz to the bottom pair of posts.
This is the simple part... read on!On my shelves of gear in the basement I have at least 5 electronic crossovers. I have bi-amped and tri-amped many of my systems over the years... so no, I am not inherently against bi-amping.
That's a good reason, and it is possible to improve the sound of these speakers by bi-amping.
So you are prepared to trust a bunch of strangers you have never met?
First off, just because a pile a yahoos on the internet tell you that X will happen if you do Y, it just doesn't make it so. That said, I'll give you this yahoo's opinion on the matter.
As Rich said, there is cost and complexity involved in going with a multi-amped system. Is it worth it and will it improve the sound of your system? Not necessarily. As a newbie, the likelihood of your nailing it and getting it right the first time is low. How do all of these other newbies do it? There is a lot of placebo effect out there in audioland. I bet if many owners heard their systems in a blind comparison, they'd prefer the factory crossover to their "improved" system, but it is a hobby, and if they "think" it sounds better, then I guess it does.
OK, so on to the complexity. Obviously you will be adding an amp and the crossover. This adds the inconvenience of power on/off sequence and number of switches to fool with, but all in all not a big deal. What typically is a bigger deal is that with a multi-amped system you also increase the likelihood of adding a grounding issue, gain structure issue or both. Most multi-amped systems I have heard have gain structure issues and many have grounding issues. Both of these mean noise. If you set up the system correctly and you are using high quality gear, you should be able to add these bits and not increase the noise floor... but it just isn't that simple. It gets worse when you start mixing home audio and pro audio gear... they have different grounding schemes and different line levels.
OK, the cost. If your primary system is made up of a decent preamp and a good power amp, and you add a Rane, or an old JBL pro unit, or a digital Behringer, or even the pretty decent Ashly XR-1001, you have just taken the output of your pre and run it through a grunge circuit... why would you want to do that? Now if you are not using a decent preamp and amp, STOP! Stop reading this, and go improve your electronics before proceeding. And don't short change your source. Assuming you are using CDs, I recently bought a new DAC... a much bigger improvement than adding an active crossover.
OK, so you want to continue... I would get a Marchand, Pass Labs, or Bryston crossover. All of these are moderately expensive, but if you don't go this route you are stepping backwards. There are a couple of vintage alternatives that I have had excellent results with, and they are relatively inexpensive, but relatively rare (with patience they are available). My first choice is the John Curl designed Symmetry ACS-1 or ACS-2. Second choice is the Dahlquist DQ-LP1. Both of these vintage (all vintage pieces should be as well) should be checked out by a tech and old caps replaced as needed. I am sure there are some other older crossovers that are good, perhaps the old Crown units, the old Luxmans and Pioneers might be good choices too, but I have never heard them myself. (Just writing this I remembered two more crossovers I have downstairs
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After the crossover is chosen, the next step up is the new amp. This is likely the area of greatest improvement. Here you get to pick an amp that will handle the mids and upper end without being burdened by the bass. I would continue using a big beefy SS amp for the woofer and get a nice tube amp for the top end. This can be a wonderful upgrade.
Now, the next downside... setting it all up. Without test gear, really good ears or both, setting up a multi-amped system is not trivial. You need to pick the frequency and slope that best matches your system, second order (12dB/octave) at 300Hz? That is suggested. Will it be best? Maybe... testing and listening come in here... and then, you need to balance the drivers. Carefully listening you should be able to do this, but you also need to balance them left and right. Even the simple task of getting these levels all balanced isn't trivial.
Is this whole process fun or painful? It can be both... I set up my first tri-amped JBL system about 30 years ago and have had a hell of a great time screwing up ever since.
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