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Tutorial: Bi-Wire, Passive Bi-Amp, Active Bi-Amp


Prodigal Son
Direct attached speakers (typical)
The output of the amplifier is attached directly to the input of the speaker. If the speaker supports bi-wiring, the two sets of posts are hooked together via some sort of metal strap (see picture).


Bi-Wired Speaker
The amplifier has two cables attached to one output and they run to the speaker. The straps used to connect the two sets of posts are removed. The crossovers now have a dedicated set of wires attaching them to the amplifier (see picture):


Passively Bi-Amp Speaker
Two amplifier channels are used, one for the high frequency and another for the low frequency. The straps that connect the posts together on the speaker are removed (very important).


Active Bi-Amp Speaker
The crossovers are removed from the speaker system and an active crossover is placed in front of the amplifier channels. This way the amplifiers are directly coupled to each speaker. It is VERY important the active crossover be used and adjusted correctly for the speakers being used.


The difference between direct and bi-wired setups is not much. Electrically, the only difference between the two is that the bi-wired arrangement has more copper connecting the amp to the speaker. The same thing can be accomplished by using heavier gauge wire or using two wires without removing the straps on the speaker binding posts. I have never heard any difference between the two as long as the total resistance of the wire between the speakers is the same (direct using 10 gauge wire and bi-wire using two runs of about 13 gauge wire).

The difference between direct/bi-wire and passive bi-amp arrangements is more noticeable. First off, using two amplifiers will likely increase the total current capabilities of the system. Also, high demand in the bass signal will not hinder the output of the treble amp nearly as much. However, the each amp is still attempting to drive the full bandwidth of the signal, so if a very loud bass signal drives the amp into over voltage clipping, the treble amp will still clip and distort the tweeter sound even though there is not bass being sent beyond the tweeter's crossover. Passive Bi-Amp Arrangements very often sound better than direct/bi-wire arrangements.

Active Bi-Amp arrangements completely blow away all three of the above solutions, assuming the setup is done properly and everything is calibrated correctly. There are dozens of reasons Active Bi-Amp setups sound better, including:

1. Removal of the Passive Crossovers improves phase shift, delay, voltage ringing in capacitors, inductor compression, complimentary induction between inductors, compression from heat generation in resistors and capacitors, variances in component values (usually +/-10%) and decoupling of the amp from the driver.

2. Each amp only amplifies the signal appropriate for the driver it is attached to. A terribly loud bass frequency will have zero effect on the treble amp and bass induced treble clipping is virtually eliminated.

3. Since the effective damping factor of each amp is greatly increased with the removal of the crossovers, the speakers will respond more accurately to the signals. This is especially noticeable when the signal stops and the cones stop as well. With non-active setups, the cones might continue vibrating from the inertia generated.
Advantages of Actively Bi-Amped Speakers:

o Dynamic range gain. Even if it appears a bit counterintuitive, with wideband audio signals, like music, an active system with two 100 W amplifiers has a maximum SPL which is 3 dB higher than a passive system with a single 200 W amplifier. Usually the difference is even bigger because of the passive crossover losses, that get removed in the active system, and other minor factors, like bass range amp clipping being filtered by the intrinsic limited bandwidth of the woofers. Most of the times the perceived dynamic range gain is in the 6 dB range, i.e. a two way system with two 100 W amplifiers often sound almost as loud as a passive system with a single 800 W amplifier.

o Better loudspeakers control. The series resistance and losses introduced by the passive crossover components reduces the amplifier damping factor seen by the drivers. This becomes audible, especially in the bass range, where big inductors with series resistances up to 1 Ohm are often used and where the speaker self damping is quite low. With the active approach the drivers are connected directly to the amplifiers, with no series resistance introduced by passive components.

o Each amplifier sees a much more constant load

o Amplifier operates in a narrow frequency band, hence lower IMD (intermodulation distortion, where frequencies combine and spurious distortions arise as a result)

o Drivers are physical separated so one cannot influence the other. Back-EMF from one driver goes straight back to the amp and cannot travel back into the sensitive tweeter.

o It's easy to design the crossovers, you just build them for the freq you want and there is no influence from them on the other crossovers

o Amplifiers may be operating at much lower levels for tweeters than woofers - cheaper amps, and amplifier now operating in much lower distortion range

o Digital crossovers offer new and interesting ways to apply crossovers to the input signal, including some techniques which are simply not available with analog crossovers

o Crossovers are operating with small signal levels (0-2v instead of 0-60V), consequently they can be built using much smaller parts with consequently higher tolerances and quality. The change in components also allows much more accurate crossovers to be built.

o It's possible to "time-align" the drivers. i.e. delay the tweeter signal so that it arrives at the same time as the woofer signal

o Physical relocation of drivers is possible! The most extreme form of the above is advocated by TacT where you physically locate the bass speaker (sub woofer) against a wall where it should work more efficiently, and then add a delay to the main speakers so that the sound from the woofer and main speakers arrives perfectly at the listening position!
What about the "white van" diagram? You know... where there is no crossover, just all drivers connected to the input terminal! :scared-eek:

Thanks again Flint.
Hi Flint,

Great job with nice pictures and explanations.

Though you seem to have left out 2 things.

1. The last diagram shows what appears to be vertical bi-amping where one amp is running one speaker. In that case the amps need to be identical. I would have liked another diagram where you show HORIZONTAL bi-amping where one amp drives the bass/mids of both speakers and another amp drives the highs (in a 2 way speaker). This can allow for dissimilar amps.

2. What about passive line level crossovers? Easy to do, cheap and no need for an active crossover.

Again nice job.

Dawnrazor said:
Hi Flint,

Great job with nice pictures and explanations.

Though you seem to have left out 2 things.

1. The last diagram shows what appears to be vertical bi-amping where one amp is running one speaker. In that case the amps need to be identical. I would have liked another diagram where you show HORIZONTAL bi-amping where one amp drives the bass/mids of both speakers and another amp drives the highs (in a 2 way speaker). This can allow for dissimilar amps.

2. What about passive line level crossovers? Easy to do, cheap and no need for an active crossover.

Again nice job.

1) I chose the vertical bi-amp diagram on purpose. For most people, the greatest issue they believe they have is getting enough current from their amp to achieve the output they desire with the most affordable amps they can get. A vertical biamp allows for one channel of a stereo amp to be underutilized for the tweeter channel freeing up the woofer channel to have as much current from the supply as needed. While I personally horizontal bi-amp, most people prefer the simpler vertical bi-amp approach.

2) I am not a fan of passive line level crossovers because of the dozen, or so, I have tested, the actually crossover frequency in any given installation was way off from the printed number. This is caused by the input and output impedance of the preamp and amplifier (respectively) were too varied and not what the passive filter designer planned for. Also, I prefer the accuracy of a variable filter, which to do that properly with the least amount of coloration, requires active components. DIY passive crossovers are a viable option for serious tweakers, but not a simple "intro to tech" tutorial subject.
Hey Flint,

1. Sure lack of current is why people can want to try bi-amping. Though it would be nice to call out the need for identical amps in the text around the diagrams. IMHO just as big a problem to those new to biamping is having 2 identical amps! Who just happens to have that and who would buy that without knowing how great active biamping can be?? Odds are that anyone with a extra amp will have a dissimilar amp and that is why a horizontal diagram would be nice.

2. Ok. You are right about the tweak nature of passive line level crossovers and the need to take the impedances in to account. Though there are companies that can make them for you based on the existing components.
Just want to add, welcome Dawnrazor! This is a place with some knowledgeable folks, kick back and stay a while!

And it seems we have missed the Digital crossover.

One day we will have digital from the source to the amp.

Of course this will not change the flow from what has been described above. It will allow greater flexability depending on the software running the crossover.

PS. Woops sorry Flint saw top and bottom but missed the middle with the reference to digital.

I was talking to a friend the other day about the new Presonus live mixers and the all digital processing. My statement was how nice it would be to give amplifiers an IPV6 address and the channels out the assigned address. That way you could have WiFi broadcast on eithernet and provide 10 or more channels of wireless delivery to various locations in a room. There also is a new Live sound mixer option on the street from SAC, using a card to accept light pipe with 72 ins and 72 outs. Soon we will have fast enough processing to allow the systems to work in sync. I hope the media venders like cable, or Fios, Dish, and such are able to improve there sync between two DVR's.
There are systems out there today which have pure wireless digital links with the amp, crossover, and processing all done in the amp. The only restricting aspect is the need for power for all the electonics in the amp.
I have a Marantz SR6009 running 2.1 with a pair of PSB Synchrony B bookshelf speakers and the Parts Express / Dayton Audio 10" Titanic diy sub kit. The Marantz has a Bi-Amp option but I don't know how the amp(s) work in this config. Would this be passive? Active? Something in between? I'm currently running it in std config with the speaker terminal jumpers. If I removed the jumpers does this remove the speakers' crossovers from the circuit?

I have the extra cable and would only need to install new banana plugs and crawl behind my media cabinet (yet again) to hook it all up. Would it be worth the effort do ya think?

Here's the page from the Marantz manual:

Screen Shot 2016-09-06 at 9.19.40 PM.jpg
That would be passive bi-amping. The crossovers are inside the speaker. To remove them from the circuit you would have to open the cabinet and remove some circuit boards. I wouldn't bother with doing this, but it wouldn't hurt anything to do it. Any improvement in the sound quality, if there were any at all, would be extremely subtle, at best, if you were to go this route.
I have my front two speakers passively bi-amped, and like Flint said, it's not a world of difference, but there is a difference. Even my wife could hear it when I first started playing around with it.