Bi-amping and Tri-amping: Why and How
Multiple amps for one speaker: bi-amping & tri-amping
The more you learn about stereo and home theater technology, the more you may hear about bi-amping or tri-amping your speakers. As somebody who has a tri-amped setup at home, I can tell you that it does make a big difference to the sound of your system. But I noticed - when I was considering bi-amping and tri-amping my speakers - that there isn't a good, simple guide to how and why to do it.
I referred to the following two excellent Webpages written by Rod Elliott here (part I) and here (part II) when setting up my tri-amped system. But these pages are quite technical, and it's hard to tell which information is really important to the casual home theater (HT) or stereo enthusiast. So, I decided to distill the information I found on these pages (and through my own experience) into this easy-to-read-and-use hub.
Since my explanation of bi- and tri-amping is simpler than Rod's, I won't show you all the options or explain how and why for every choice I recommend. Top be honest, I don't even completely understand everything in Mr. Elliott's articles. But I do have my system tri-amped, and it sounds great, and nothing has caught fire so...trust me :)
Ready for bi- and tri-amp madness? You'll love it! Read on....
poly-amping vs. poly-wiring
As manufacturers of speakers try to sell into a super-saturated market (where new products are actually of lower quality than older products, and there is no important difference between a 10-year-old piece of gear and a brand-new one), one tactic they've employed is to double the number of terminals on the back of their speakers.
Why? because manufacturers know that audiophiles often employ poly-amping (bi- and tri-amping), so by making their speakers bi-ampable (or appear to be bi-ampable), they make them look like the speakers are of higher quality. But most speakers under $400 (for a pair) with two sets of inputs aren't truly poly-ampable. They're poly-wirable. What's the difference? it's all about an important part inside almost all speakers called a crossover. For a very technical definition, you can refer to the two articles by Rod Elliott (linked above), or take a look at this diagram (below):
Understanding crossovers & the benefits of poly-amplifying
Most speakers have at least one passive crossover inside of them. This is why, when you attach a single set of wires from your amp, the full-range signal doesn't come out of all the drivers (cones) in your speaker: the high frequencies (bells, Mariah Carey, cymbals) go to the tweeters, the lows (bass guitar and drums, for example) go to the woofer, et cetera.
The passive crossover inside of most speakers can not be adjusted, and for good reason: the crossover points are matched to the drivers in the speaker. When we poly-amp a speaker, we bypass this internal crossover, and amplify each driver in the speaker with a different amp, sending only the appropriate frequency band straight to the driver.
Poly-amping allows us to tune the crossover frequencies to our room's particular shape, size, and sound-reflective character. It also allows us to adjust the gain (volume) of each frequency band, lending us another tool to fine-tune our stereo or HT to our room. But if the internal crossover inside the speaker isn't bypassed, then none of these adjustments will improve the sound. In fact, the sound will be worse then ever, as our external crossover and the internal crossover will be working on top of each other.
The difference between poly-amping (awesome!) and poly-wiring (pointless)
When a speaker is poly-amped, the internal passive crossover inside the speaker is bypassed. but most of the speakers you'll find in a big-box store - and even products sold in specialty stores - don't allow you to bypass the internal crossover, in spite of the fact that they appear to allow poly-amping by having two or three sets of speaker terminals.
Makers of these speakers (with more than one set of terminals, but no way to bypass the internal crossover) recommend you bi-wire the speakers. Bi-wiring is when you run two sets of leads from a single amp, and into the two sets of terminals on the back of the speaker. The truth is, bi-wiring gives none of the benefits of bi-amping, except the appearance of a more technically-advanced setup, and higher-quality speakers.
To discover if the two pairs of terminals on the back of YOUR speakers are truly bi-ampable (bypassing the internal crossover when both terminals are wired separately), you need to consult your speakers' manual.
So, are your speakers bi-ampable or tri-ampable? then you're ready to begin...Read on!
Setting up a poly-amped system: Step 1
- Step 1: bet a pair of truly bi- or tri-ampable speakers. I use a pair of the original Paradigm Studio Monitors, which are tri-ampable. See the pic at right for a picture of the three pairs of terminals on the back of these speakers.
Setting up a poly-amped system: Step 2
- Step 2: get a good active crossover. You can buy crossovers for home stereo and HT use, but I am wary of the cost of these, since they are being sold to people who clearly are willing to spend a LOT of money on their stereo. Instead, I opted for a DBX active crossover designed for pro-audio use (live music and engineering). Pro-audio pieces tend to be well-built, competitively priced, and have a good mix of quality and price. See the pic of my DBX 3-way stereo active crossover. NOTE: you will need cables that go from 1/4" TRS or XLR (pro-audio connections) to RCA (home audio connections).
- For bi-amping, you need a two-way stereo crossover. For tri-amping, you need a 3-way crossover. Make sure the crossover you buy allows you to adjust all the crossover frequencies, reverse the polarity of each output channel (low, mid, and high for each right/left channel), and set gain for each output channel.
Setting up a poly-amped system: Steps 3, 4, and 5
- Step 3: get a good pre-amp. You can use an HT pre-amp (with 5.1, 6.1, or 7.1 outputs) or a stereo pre. Either way, since we're talking about poly-amping the main speakers, the outputs in question are the Left and Right front speaker outputs. Run regular RCA cable from the left and right main outputs on your pre-amp to the left and right inputs of your crossover.
- Step 4: Find the crossover frequencies used by the passive crossover inside of your speakers (you can find this in the manual). Set the crossover (x-over) points of your active x-over to match the factory settings of the internal crossovers.
- Step 5: Run RCA cable from each of the x-over outputs to the appropriate amp. Take a look at a few ways to set this up, depending on your speakers and amps (below):
Step 6: Choosing Amps
The whole reason we are talking about poly-amping is because the sound is better when you do it. We already talked about how being able to fine-tune the x-over frequencies and gain of each frequency band helps adjust the sound for your particular room. The benefits of this are enormous and are reason enough to poly-amp.
But there's another reason audiophiles do this: it lets you choose the right amp for the job. For example, in my system, I use a tube amp (a Dynaco ST-70) putting out 35 watts per channel for my tweeters. Tube amps are well known to be a good match for tweeters because they are good at amplifying high frequencies and make tweeters sound their best. Some say tube amps are "warm" sounding, and can smooth-out harsh high frequencies. I am doubtful about that - but tubes DO make tweeters sound better. If your tweeters sound harsh, however, try adjusting the crossover gain or x-over point . Better yet, get sound panels on your walls, where the tweeter sound would bounce off the wall.
With the tube amp up top, I use an Adcom GFA 535 II for the mid and low drivers on the paradigm main speakers. As you can see in the picture above, I left a copper bridge between the mid and bass terminals on the back of the Paradigms, meaning that the midrage frequencies from the x-over are being split by the Paradigm's low frequency crossover, but the high-frequency crossover in the paradigms has been bypassed.
I don't tri-amp the paradigms because I am using two powered subs to augment the bass. Therefore, the low frequency band (bass sounds) from the x-over go straight to my subwoofers, which have their own amp. this is the second setup diagrammed above.
Each amp in its place! Take a look a the sub and Paradigm tower together:
Last Step: Adjust and enjoy!
Last Step: I put "adjust and enjoy" in the same section because for people like us, adjusting and tweaking is part of the fun! (right?). Once you have your system wired (making sure not to confuse which outputs from the x-over go to which amp, and which speaker wires go from which amp to which set of terminals on your speaker), and the x-over points set to the factory settings, you can start to tweak:
Tweaking x-over points and frequency band gain:
Each room is different, and - as opposed to what most salespeople will usually admit - your room makes a HUGE difference to your sound. Also unlike what you may have heard, a speaker, no matter how "good" it is, needs to be adjusted and equalized to compensate for room shape, size, and acoustic-reflective properties. An equalizer (EQ) is essential for the best sound, no matter how good your speakers are.
Poly-amping with an adjustable active x-over goes one step beyond regular EQ'ing, allowing you to adjust the x-over points and gain for each driver in your speakers.
To adjust the sound to your room, start by "wiggling" the mid/low x-over point until the sound is "right". Listen. Then adjust the mid/high x-over point. Listen. Next, adjust the gain of each band, listen, and repeat. Eventually, you will have a sound perfectly tweaked to your room!
Good luck and enjoy!
Also, visit some of my other articles and website (listed below):
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