Balanced Audio Guide
Surf Cables LLC Guide to Balanced Audio
1. What is balanced audio?
Balanced audio circuitry operates on balanced signals. A balanced signal is made up of an original signal and another, "inverse signal" that is the opposite of the original signal. This is opposed to a traditional "single ended" audio circuit that operates on a signal that is compared to a never-changing ground signal.
The overall output signal of a balanced system is the original signal minus the inverse signal. Since the inverse signal is supposed to be an inverted copy of the original signal, you have a subtraction of a negative value, i.e., x - (-x) = 2x. The output of a balanced system is therefore twice as much as a single ended system, meaning the gain is twice as much.
Please refer to the following online tutorials which are excellent.
2. What are the advantages of balanced audio?
When a balanced audio signal picks up noise, (say a positive blip of some type), the noise appears in the original signal (as a positive blip) and in the inverted signal as (a positive blip). This noise is carried along and when the output signal is taken, the noise is cancelled! Think of our equation, x is the signal and n is a blip of positive noise. We have (x+n) - (-x + n) = x+n+x-n = 2x. The noise has subtracted out and our signal is twice as big!
Cables: balanced audio cables are used in the pro audio market for microphones and long cable runs because if cables pick up noise from the environment, the noise is canceled.
Amplifiers: All amplifier topologies are imperfect and add some noise. If we use an amplifier to amplify the original signal, and a different amplifier of the exact same type to amplify the inverted signal, the noise and distortion that each amplifier adds to its signal will be identical, and this noise will be canceled out by the balanced system. The amount of noise in common is called common mode noise, and the amount of rejection in a balanced system is often called the common mode noise rejection ratio or CMNRR or CMR for short.
System Design: Think of a balanced source such as a media player, a balanced cable to an amplifier and a balanced cable to a balanced set of headphones. In this system the original and inverted copy of the original signal are treated separately from the source all the way to the headphone drivers. The noise added in the source, the noise picked up by the first set of cables, the noise added by the amplifier, and the noise added by the second set of cables will all be added to the original and inverted signals through the chain until the signal arrives at the headphone driver. The signal could be completely dirty with noise but this noise will be effectively canceled out at the headphone driver due to the nature of balanced signals. Thus, the more balanced equipment the better as it daisy-chains from beginning to end.
Speakers and Headphones: The good thing about speakers and headphones is that they are usually inherently balanced, a driver is typically caused to move by applying a + signal and a - signal across a driver or coil. In a balanced system this will be an original signal and an inverted copy of the same signal, providing twice the output and canceling noise in the process, making balanced drive very suitable for audio purposes. The speaker and headphone actually perform the subtraction needed to have a balanced output.
3. What are the disadvantages of balanced audio?
Complexity: Balanced audio circuitry has to amplify or process the L+, L-, R+ and R- signals separately from each other, where typical single ended circuitry just amplify or processes an L and R signal. Think more complex, more costly, more difficult.
Nose: balanced circuits need to be precisely matched so that the noise added by the + circuit is the same as the noise added by the - circuit. This further adds to the complexity and cost. In the end if the noise is not identical there will be no cancellation and thus all this extra circuitry was not worth it (although you still have double the gain).
4. Are my headphones balanced?
Yes, all headphones are balanced since each driver setup in each ear can be driven separately. But wait! In most cases the manufacturer has destroyed the balanced nature of the headphones by connecting the negative input on the left earpiece with a wire over the headband to the negative input on the right earpiece. They have tied the negative signal (grounds) to each other thus destroying the balanced nature of the headset! Why? Because they want to use a cheap 3 conductor cable in one earpiece to connect the headset to the music player instead of using a 4 conductor cable or two cables (one to each earpiece).
Even if the two earpieces have their own wires, such as with IEMs, manufacturers join the negative signals either at the junction stress relief structure at the neckline cable split, or at the TRS unbalanced plug at the very end of the cable. Why? Most people simply don't use balanced equipment so its not something they worry about.
Faced with unbalanced headsets, "Modders" and DIY enthusiasts will take the headsets apart to add separate inputs to each earcup, or change the connector to accept 4 independent signals (L+, L-, R+ R-).
Sometimes you get lucky and the headphones are balanced with removable cables so that a true balanced solution can be easily achieved by only adding a single cable.
The Oppo PM-3 and Sennheiser HD598/ HD558/ HD515 use a balanced TRRS receptacle on one earpiece with separate wires over the headband, preserving the balanced nature of the headphones, but these ship with TRS cables that destroy the balanced nature of the headsets. However, since the cables unplug, you just need a balanced TRRS cable and you are in business!
Other manufacturers have used separate removeable inputs in each earpiece, preserving the balanced nature of the headsets as no wires connect the left and right earpieces, but ship these headsets with mostly unbalanced cables. These include Sony (MDR-Z7), Oppo (PM-1/ PM-2, Audeze (all models), Sennheiser HD600/650 type, and HiFiMan (all headphones). If these ship with unbalanced cables you can simply plug in balanced cables to enjoy fully balanced operation.
Please see our balanced headphone chart for an updated list of natively balanced headphones.
5. Where are the balanced music players and amplifiers?
They are all around.
Pono Players operate in balanced mode.
HiFiMan players have a balanced amplifier module, providing balanced output.
Many higher end amplifiers have balanced outputs and balanced operation is common in pro audio equipment.
6. I have XLR Audio Equipment, do I have balanced audio?
It is true that XLR connectors are designed for balanced audio. However, just because your equipment has balanced XLR connectors does not mean that the internal circuitry is balanced. Many manufacturers include XLR connectors for convenience, so that if you have other balanced equipment it will connect to their equipment. It may disregard the balanced signal (using only the positive signal for example) or it my convert the signal to unbalanced immediately, and process or amplify the signal from then on unbalanced. Look for a CMR or CMNRR specification or "fully balanced" or "truly balanced" to ensure the equipment is balanced from input to output.
7. I have RCA Audio Equipment, can I do balanced audio?
No. Audio equipment with RCA connectors is not balanced, it is not possible to connect balanced signals to an RCA connector. This is because the grounds (outer metal shell of the RCA) of every RCA are shorted to every other RCA. Balanced audio needs the grounds to be disconnected from each other in order to process the inverse signals separately. It is not possible to use a cable to turn your RCA equipment into a balanced system.
8. What Are the Balanced Headphone Amplifiers?
We can make headphone cables for most any balanced headphone amplifier. Here is a list of some balanced headphone amplifiers.
|Balanced Headphone Amplifiers - Portable (Battery Powered)||Comments|
|Pono Player and Sony PHA-3||Dual 3.5mm connectors|
|HiFiMan HM901s||3.5mm TRRS|
|Cayin N5, Onkyo DP-X1, Astell & Kern players||2.5mm connector|
|Ray Samuels Audio ("RSA") or ALO Audio balanced amps||4 pin plug|