February 8, 2011

Should I bi-amp my speakers?

This question comes up frequently on audio forums, where the original poster asks:

"Should I bi-amp my speakers. I have extra channels in my AV receiver that aren't doing anything. Is it a good idea?"

The short answer is "no, you shouldn't."

Just to clarify, here we will talk about passive bi-amping, where the existing passive crossover remains and one channel drives the tweeter while the other drives the mid. This is different to active bi-amping, in which an active crossover is used and replaces a passive crossover. Each driver has it's own amplifier and the crossover is inserted at line level before the amplifiers. This is a good idea if done correctly, but requires measurement tools to implement.

Reason no.1 - there is no advantage

No extra power is delivered, since the passive crossover remains in the signal chain. While your receiver might in fact deliver 2 x 100w instead of 1 x 100w to each speaker, the extra 100w is still lost in the passive crossover. One channel feeds the tweeter, and about 85% of the power that would normally have gone to the mid is filtered out. The other channel feeds the mid, and about 15% of the power that would have gone to the tweeter is filtered out. The net result is no different.

Some who have misunderstood passive bi-amping, may claim that clipping can be avoided. This is an advantage of active systems, but with passive bi-amping, both amps if identical will clip at the same time.

There are no magical benefits to passive bi-amping and there are no real ones either. 

Reason no.2 - there is a downside

The extra channels in your AV receiver that are not used are not wasted. Affordable receivers are not well designed to deliver a continuous signal to all channels at the same time, the power supplies and heatsinks are simply not up to the task.They are counting on surround channels having an easier task. If some of those channels are not used, that adds headroom the reduces the load. This is a good thing, not an idle waste of resources. If those channels are made to passively bi-amp the mains, they will not only use up that headroom, but they will present a heavier load than was intended for those channels. When pushed, the amp will clip sooner.

Less is more

If you don't need any of the surround channels, give your receiver a break and let them remain unused. Less in this case is definitely more. You will no doubt hear some report benefits and subjective improvements, as you will with many tweaks, snake oil or otherwise. The simple truth is that we are easily tricked, especially when we want to believe. The appeal of this tweak is that it's so easy to do, and if you've asked this question, you are probably looking for a simple easy way to get an improvement. I suggest instead that you have a look around here, and I will show you other ways to get a very real improvement. If you are new to the world of audio, then some of the improvements you can experience are startling. Let me suggest a few things that just might make your jaw drop:
  • DIY subs - suddenly the sub you couldn't afford looks quite unimpressive
  • Learn the tricks of integrating your sub
  • Add some serious bass traps - what you thought was good bass will soon sound like rubbish in comparison and you will be surprised how good your existing sub can sound
  • Consider building some good DIY speakers - the result could be a real eye opener
  • Pay careful attention to speaker placement - small changes can have dramatic results
  • Build some acoustic treatment - the difference is not subtle
Some of the biggest improvements you will ever experience are there and in relative terms they are not exceptionally expensive. 


  1. Hi, thanks for this article. But i have a question. You write about power loss, no extra power is delivered. But without bi-amping this loss is also there right? Why does bi-amping cause more loss? I am aware of the fact that doubling the wattage from 2x100 to 4x100 will not double the dB, but there should be an increase of at least 2 dB and 3 dB at most? I have an Arcam A80 2x65 watt and I am seriously concidering buying a second one, and then I have 4x 65 watt and I can't imagine it wont do anything to volume or experience.



  2. Passive bi-amping takes two amps and yields the output you would get with juse one of them without bi-amping. Let me give you an example. Let's say you have passive 2 way speakers, with 20% of the power going to the tweeter and 80% to the midwoofer. Now let's simplify things and say you have a 100w amp delivering 100w into the speaker. The tweeter sees 20w and the midwoofer 80w.

    Now you are thinking that adding another amp must surely give you a little bit more, right? You would be wrong.

    The first amp drives the tweeter network, after the passive crossover filters out everything but the treble. The tweeter still only sees 20w. Normally the amp would have the midwoofer network connected in parallel, so that the other 80% then goes to the midwoofer. However, now that you have it configured with passive bi-amping, 80% of the power is now wasted.

    The second amp drives the midwoofer network, with 80% of the power going to the midwoofer, the rest is simply wasted.

    In an active system, the crossover takes place before the amplifier, so the signal is already bandwidth limited. As a result, less power is wasted and you have a system with more headroom.

    My advice is save your money and spend it on something that will offer real performance. Don't throw it away!

  3. Hi thanks for the comment and reply. Well now I have the Arcam P80 & A80 together. With my A80 only with a certain song the display starts to dim on the bass in the beat, draining power, and this happens at volume setting 62 and I can hear the sound being altered / distorted due to overload. When I ad my P80, on LF, the sound is more clear, and louder and not distorted at 62, and the volume knob is progressive, but now it starts to distort at 71, and the display dimming starts also at 71! So while the A80 produces bass tones it is not drained from the speaker by it. The sound is really more dynamic, more headroom and more detailed. It is not a placebo effect, since I really know what I am hearing, and can pick out bi-amp or not in a blind test.

    I think this all has to do with the way we think about speakers and amplifiers. The tendency is to think that the bass takes some, and the high takes some. But in reality it is more like this. Power is distributed equally between LF and HF and the LF filter filters out the highs, and the HF filter filters out the low. With bi-amp there is twice the power and the same ratio of filtering. Besides this we have to concider also that 2X50 watts is allready very loud, and 2X100 watts is not two times as loud. Soon I will borrow a decible meter from work so I can prove the volume does increase by about 1,3 dB.

    And I also hooked on the more expensive A85 but this amp is easily beaten by the bi-amp combo, and with the A80 alone compared to the A90 it is almost a tie.

    And in this pricerange sound quality improvement is achieved only by spending huge ammounts of money, and the law of diminishing returns is applied. I am not sure if there is an amp below €3000 that can do what this biamp combo does.

    And my speakers are perfect for biamping because one amp goes to the LF, and the other goes to the MF & the HF, resulting in a more balanced power output from both amps. I have Canton Karats 790.2.

    Anyway thanks, hope I don't annoy you. But please give it some thought, bi amping is terrific!


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