Is bi amping worth it ?

Bi-amping can be complex, but it doesn’t have to be just to get  your feet wet.  You don’t have to start by realizing every theoretical benefit for bi-amping that exists for it to be beneficial.  There are many options, but each situation is different, so you really need to forge your own path.  I’d hate for people not to try bi-amping because of being intimidated by the choices....you’ll learn as you go.  You can start with something very simple....like adding an active subwoofer....just like that you’re bi-amping horizontally, very possibly with a benefit in SQ, relatively low cost, and minimal effort.

With the right active sub, you can run a high pass filter to the main amps to relieve them (and the main woofers) of some of the low bass duty.  You can experiment with running them through the HP filter, or full range, while you play around with placement, gain, polarity, and crossover frequency.  That offers  a very good opportunity to improve midrange via both the amp and the woofer’s new found freedom from the rigors of handling low bass.  Your sub (or subs) are better suited for the bottom octaves)  Just be cautious about featuring your thumping new sub over the rest of your system.

 
It’s not mandatory that you bypass your entire passive crossover (if  you have one), but it is something you can explore.  Removing a well designed high quality passive crossover and replacing it with an active crossover involves some serious challenges that not everyone will be up for. Even though there are advantages with active x-overs, there’s no guarantee you will like it better..it’s always subjective. If you’re starting from scratch there are a lot of advantages in choosing active crossovers, but there are some very fine passive crossovers out there too.  If it sounds good now with a single stereo amp, it will very likely sound good bi-amped, and has potential to sound better if an active crossover is executed well. 

Choosing the right frequencies, gain levels, polarity and slopes isn’t typically first-timer territory, but neither is it an insurmountable task.   My rig uses a combination of active and passive crossovers in a horizontal bi-amp configuration with an SS amp to the woofers, and tube monoblocks to the midbass and tweeters.  I bypassed the main woofer’s passive crossover, and replaced it with an active low pass filter that feeds a BK solid state amp below 63hz. It was pretty straight forward, simple to do, and came with some notable benefits. For the midbass/tweeters I use an inline high pass filter for the tube amps, but kept the passive crossovers in that section. I have some concerns about being able to replicate the coherency and blend I’m getting from the passive crossover, in spite of their known disadvantages.  They’re well executed with top notch parts, and sound right to me.   Maybe some day I’ll try bypassing them, and going full active, but it’s an ambicous move for a guy who’s pretty content with the way things are now.

Biamping has multiple benefits when properly done. That means using an electronic crossover and bypassing the existing crossover entirely. By removing the lowpass series inductor, you also remove the resistance that kills bass damping. It can also add up to 6dB dynamic range simply due to how amp level voltages sum up, so a 2x50W biamped system has the same dynamic range as a 200W non-biamped speaker. That opens up a whole different approach to powering (and taming) things like Klipsch KHorns and Cornwalls. In pro audio this isn't news - biamped studio monitors were common 50 years ago, and I designed triamped and even quad-amped live sound systems back then as well. 

As for "3. The following is my preferred solution which is to use a source (DAC) that has some DSP.  Purists will hate this idea but that's ok.  The DSP allows you to tailor the sound to your liking.  Adding a few dB of gain in the low bass region can really make a difference.  Again, I'd recommend auditioning something and playing with it for a weekend to see if it solves your issue." I couldnt agree more. Get a WiiM Ultra Music Streamer & Digital Preamp for a whopping $329(!) and you get not only a better than decent streamer and DAC, but a very nice graphic/parametric equalizer as well as DSP tuning. I just swapped one into my office system to help a bass-shy  but otherwise spectacular pair of Focals and am very pleased with the results. 

an interesting thread. as others have posted. Bi-amping has a lot of plus and minus and it all depends on what you are targeting to solve or improve. 

for me, I had the weird idea of biamping the ATC speakers. what I did was to use the X150 to drive the mains and XA25 to drive the tweeters, 

I personally did not find a major improvement, there was some change, I would like to point out a better dynamic, but not enough to justify the extra cost of an amp.

YMMV though ..

Very good explanation russbutton!  I started my multi-amp journey with a Lafayette integrated amp and a homemade Sanken amp using a couple 30watt hybrids.  As mentioned previously, two key points are the electronic crossover to limit the amplifiers demands and eliminating the passive speaker crossover parts entirely.

@billpete  Active crossovers and equalizers are totally different animals.  Let's first understand the difference between active and passive crossovers.  A passive crossover is an electronic circuit that has no power supply.  It is just a circuit that sits between the output of your amplifier and the loudspeaker drivers.  

An active crossover has a power supply like your preamp and power amp, and sits between your preamp and multiple power amps.

An equalizer is a device with a power supply, that typically is located on an extermal processor loop on your preamp, or a tape recorder loop on your preamp. 

The do very different things.  An equalizer alters the system response.  Typically the operate on ten bands across the audio spectrum.  

A crossover, either passive or active, is designed to separate out the signals being sent to the loudspeaker drivers.  High frequencies for the tweeter and low frequencies for the bass driver.  If you have a 3-way system, then the crossover has the added function of allowing only an intended band of signals for the mid-range driver.

Most loudspeakers use a passive crossover.  The user has a preamp & power amp, or an intergrated amp or receiver, and run one speaker line to the speaker.

In a system with an active crossover, the preamp sends a line level signal to the active crossover, which then outputs line level signals that have only those frequencies suitable for the given driver.  If you had a 3-way system, then on each side, the active crossover would have 3 line level output signals for 3 separate amplifiers, each of which powers a single driver.

The more expensive amplifiers are very good at managing the very complex impedances typical of loudspeakers with passive crossovers.  

Less expensive amplifiers can do a very good job if they are only powering a single driver and do not have to cope with the complex loads that a passive crossover have.

I run a set of Linkwitz Orion loudspeakers, which have an active crossover.  I use a B&K AV1260 power amp which has 12 channels at 60 watts/channel.  Each side of my speaker has two tweeters run in parallel, a mid-bass driver and two 10" bass drivers.  There is one amp channel for the tweeters, the mid-bass driver and each of the 10" bass drivers.  B&K made MOSFET amps that were well thought of in their day, but was never seen in the same class as Mark Levinson, Bryston, McIntosh, etc.  Being that my amp channels don't have to deal with a passive crossover, they do a very good job.  I *LOVE* my system.