Bi-Amping for Dummies...and Smarties?

It is often the case that, in the realm of pro audio, you’ll encounter three types of people: the gear heads (people who live and breathe in the technical elements of things and who love to tinker and experiment with components and audio theory); the pragmatics (people who care about pro audio concepts only as far as they need in order to produce the desired effect, often musicians or performers); and then, nutcases - plain and simple nutcases.  

If I were to place myself in one of these three (and granted, I’m a nutcase in almost every other area of life), my relationship with pro audio concepts have been almost strictly utilitarian. I’m not a gear head or much of a tech-minded person at all. My natural approach to pro audio has always been, “I want to make these sounds louder. How little do I need to know in order to do that?” Electrical theory and audio sciences have only been as useful to me as the gig I’m performing at or the little bits of recording and studio work I happen to be involved in; rarely have I ever been interested in the concepts for their own sake. That is, until I got this job.

When I write these blogs, I know I am writing for a mixed audience (gear heads, pragmatics, and nutcases alike), and that I am writing from a pragmatic perspective: “How can I make this abstract concept or somewhat complicated idea useful for the average musician/performer?” So, when Ryan asked me to do a blog on the concept of bi-amping, my immediate approach was to write about it with the hope of taking a rather sophisticated pro audio concept useful. No debates, no theory, just plain ol’ how to’s.

Then I did some research.

…and I fell down the rabbit hole.

Turns out, bi-amping is a commonly misunderstood concept, and the people out there who do understand it often don’t go as far as to make the information accessible to non-techies. My goal with this article is to make the concept simple enough for the average musician/performer, but accurate enough for the techies out there and, hopefully, clear up a few misconceptions.

So. Here we go.

What in the Name of Sam Hill is Bi-amping anyway?

Whether you’re dealing with your own home stereo system, a studio recording and mixing system, or a large live venue, you’ll find that a bi-amped (or even a tri-amped) system is the pro audio industry’s standard for sound. In simplest terms, bi-amping is taking a single line level signal, splitting it up into different frequencies (in most cases, highs and lows) and then separately powering and driving those respective frequencies. Take a look at this particularly snazzy drawing of a typical P.A. speaker. Notice that it actually incorporates two different kinds of speakers, or drivers:










In a typical bi-amped speaker, you’ll have two drivers commonly called “Tweeters” and “Woofers” (or “sub-woofers”). These two different drivers are designed to carry different frequencies of the sound's signal respectively; tweeters are often responsible for reproducing the signal’s higher frequencies, whereas woofers and sub-woofers are responsible for the lows, or mids and lows. This divide-and-conquer method of sound reproduction actually provides several advantages to the more straight-forward “send-the-whole-dang-signal-through-one-driver” approach that was standard in the past. Mainly:

  1. It’s a significantly more efficient use of power
  2. It provides a more accurate reproduction of the original sound

The term bi-amping really just means that the system incorporates two separate amplifiers, one to power each part of the signal through the drivers. So that means your higher frequencies have its own power source and your low frequencies have their own power source. However, in order to do any of this there has to be some way in which to split the signal and sort the frequencies into their proper amps. How is this done? Why, with a crossover, of course!

Crossovers: Active vs Passive

In the most basic terms, a crossover is simply an electronic device that splits a signal into different frequencies. Ta-da.



 My favorite analogy is to think of a crossover as a sonic traffic cop, directing certain frequency bands one way and other frequency bands another way. All trucks and heavy-duty SUVs are sent to the woofer, and Geo Metros and Ford Escorts are sent to the tweeter. Simple, right?

Oh, but it doesn’t end there. In the P.A. world, there are actually two different types of crossovers – Active and Passive – and when it comes to biamping, they are the thing that makes all the difference.

Passive crossovers split frequencies after the amplifier in the signal chain, requiring that they use components rugged and beefy enough to handle the higher output levels. Using mainly inductors and capacitors, a passive crossover takes in the amplified signal and filters out the different frequencies by virtue of impedance: certain components impede (filter out) higher frequencies, allowing the lower frequencies to pass through, while other components impede lower frequencies, allowing the higher ones to pass through.



Now it used to be that passive crossovers were all that were ever used in P.A. speakers, mainly because they are cheaper and less sophisticated than active ones. Today this is changing, since passive crossovers are inherently less efficient than active crossovers. Because a passive crossover receives the signal after amplification, it wastes power when it filters the frequencies and the excess is burned off as heat. Imagine the traffic cop, if you will: picture a dude standing in the middle of a busy intersection, but instead of blowing his whistle and making a bunch of hand gestures and communicating with the cars where the best place is to go before they start accelerating, you have a guy running around attempting to block traffic to certain places with his body. Instead of telling the Geo Metro to head left, he instead runs out in front of the Geo Metro and blocks the right lane, attempting to force traffic in the opposite direction. Not efficient. In a sense, that’s kind of how a passive crossover approaches a signal: it suppresses the unwanted stuff and allows the other stuff to pass without resistance.

The approach of the Active Crossover is much different, being that it addresses the signal before power is applied to it. Before the signal ever reaches the amplifiers, the crossover sorts the frequencies at line-level, thereby saving a lot of power that otherwise would have been burned off and wasted. It’s a traffic cop with a plan! Instead of throwing a bunch of obstacles in the way of a powered-up signal in order to only let the wanted stuff just squeak on by to the driver, an active crossover is able to sort out the signals ahead of time.

This approach, while being much more energy efficient, also affords us the ability to dial in our frequency bands more accurately. A signal in a passive crossover is at the mercy of the impedance levels of the components therein, even though impedance changes from when the speaker is in use to when it isn’t. An active crossover can ensure that a particular frequency (and only that frequency) can make it to its respective driver in order to provide the most accurate sound, whereas a passive crossover’s frequency response winds up all over the place since impedance is an ever-changing factor.

Simply put: a passive crossover comes into play after amplification, whereas an active crossover takes care of things before they get too loud to deal with efficiently. So naturally, an active crossover is required in order to truly bi-amp a sound system.

So, what does Bi-amping get me sound-wise?

In a word, accuracy. In a couple words, efficiency AND accuracy.

Given that we have a way in which we can sort frequencies into their own individual machinery, with their own power source and are able to calibrate said power sources and crossover points in order to best compliment all of the components involved, the result is a more accurate reproduction of the original sound source for our pathetic human ears. Think of it this way: if I were to take the entire dynamic range of a human vocal note, with all of its fluctuations and peaks and valleys and complex overtones, and then try to stuff all of it into a single 12” speaker and hope for the best, the result will be less than accurate. Speakers have limitations and no one speaker can handle all frequencies equally well (sorry audiophiles, it doesn’t matter what those magical catalogs say). So, to have the option of splitting up the work of one driver into several different drivers, each one suited to handle a specific frequency band at its best, is ideal and now consider quite necessary in pro audio.

The principal is evident whenever you go to a live concert venue and you take a look (and listen) at their sound system. A common P.A. set-up for a live band may look something like this:






















You know how it sounds, don’t you? The main speaker cabinets handle the higher-to-middle frequencies, giving you all that trebly goodness, while the subs are the giant, earth-shattering boxes that thump your heart around in your chest. Two different types of speakers both handling different parts of the same total signal! The result is better efficiency due to the fact that one amp can be solely allocated to power one half of the signal for optimum sensitivity to its speaker-mates, while the other amp can focus all its power solely on making sure the other half reaches all of its audible potential. If you tried to do the same thing using only one amp and then split the signal later (like in a passive system), that amp is having to spread its power across the entire dynamic range of the signal, resulting it less practical output and wasted energy by the time the crossover is finished with it. Two amps mean a lighter load for each and a more effective use of power within each frequency band.

So, that’s an example using external system components. But the same effect can be achieved inside a single speaker cabinet itself. A great example is in the Presonus Eris E5 (available here at the store, by the way!): everything that just occurred here…
























…but on a much smaller scale. Looking at the guts of an Eris E5 also helps to show the technical efficiency of bi-amping in numbers. Here we have two separate amps, the High Frequency Amp valued at 35 watts and the Low Frequency Amp valued at 45 watts, each responsible for powering their respective part of the signal. Notice how, because higher frequencies do not require as much power as lower frequencies, we can actually save power by putting in a smaller-value amp for the tweeter.













The alternative would have been a single amp large enough to power both drivers that then feeds its signal into a passive crossover which would burn off a significant portion of the power anyhow. An active crossover gives us the ability to accurately slope our frequencies and sort them into amps chosen specifically to power those frequencies. The result is cleaner, clearer, more accurate sound, making your home stereo system or studio monitoring system that much more tasty!

Bi-wiring, Passive Bi-amping, and the Misconceptions that Follow

Before I conclude my article on bi-amping, I do want to quickly address a couple of goofy things I found. When I said earlier that I fell down the gear-head/nutcase rabbit hole during my research, it was because I accidentally came into some discussions on “bi-wiring” and “passive bi-amping” and how it all compares to “true” or “active bi-amping”. Turns out this is a big debate among audiophiles and HiFi-guys and I can see how some people get mixed up about pro audio’s outlook on bi-amping when this stuff is all over the Internet.

The HiFi guys and those dudes who obsess over the stereo systems in their cars will argue that the virtues of “bi-wiring” or “passive bi-amping” are equal to that of true P.A.-level bi-amping. I’m here to argue that it is simply not true, for a number of reasons. Let me break it down:

“Bi-wiring” is a concept floating around the audiophile world that some insist will produce a similar if not equal effect to your sound as pro-audio bi-amping. The idea is to take your basic loudspeaker with its two drivers (a tweeter and a woofer) and hook it up to a power amp in such as way as to “optimize signal flow”: to do this, you wire it this way…










…instead of the conventional way…











The claim is that by adding extra cables in the circuit and keeping them segregated into high-frequency and low-frequency sections, it “frees up” the cables in order to focus particular frequencies into a particular path, all of this being grounded in the theory that “signals take the path of least resistance”.

Now on the surface, the idea of giving the HF’s a chance to go this way on their own and the LF’s to go that way on their own seems like an ideal way of making sure the tweeter and the woofer don’t get all muddled up with each other’s frequencies. However, a theory is a theory, and though it may be that higher frequencies can “get by” easier when they don’t have to share a cable’s bandwidth with lower frequencies, bi-wiring doesn’t even come close to having the same dramatic effect as true, active bi-amping. This is because we are attempting to consolidate frequencies by messing around with impedances, not by actively sorting them. Not to mention, we are dealing with a single source of amplification that comes into play before the signal is ever split (which, as you can see, is the very last thing that happens before the signal gets to a driver). Also, instead of adding cables in order to lessen resistance, you could just simply get larger guage wires to handle more load. Just sayin'.

Passive Bi-amping has a weak point when it comes to its amplification approach as well. Here’s the deal: just having two amps does not a bi-amp system make. At least, not in the way P.A. accepts bi-amping. True bi-amping requires an active crossover and power sources allocated to each frequency band. Passive bi-amping claims that it is basically the same thing as active bi-amping, just without an active crossover.



Now, some argue that this does make an audible difference, and they are entitled to their opinions. But again, on a practical level, you aren’t dealing with frequency-sorting so much as impedances again. Two separate amps may lighten the load on each other, but without something to sort the frequencies into their respective amps beforehand, there’s really no advantage as far as power-efficiency or final output. You are still attempting to sort the frequencies after amplification, and that wastes power by burning off as heat inside the components. In the end, if there is a difference, it still doesn’t come close to true bi-amping.

So to sum up, for all you pragmatics (thanks for hanging in there): in the pro audio world, if you have the means to go the multi-amp route with your audio system, do it. You’ll get the best sound and the most efficient set-up and the quality end-result is certainly worth an extra buck or two.

Stay excellent and have a good week!





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