Can you help me understand "balanced" in the headphone world?

[MrC]

As this site is based on measurable facts and not subjective comments such as “it makes it sound better” (I have enough of my own subjective opinions ), I was wondering if you could help me out a little understanding this.

I apologize in advance for what may be a lengthy post but I am seriously interested in getting a grip on the facts.

I am new to the headphone hifi world, actually, new to the whole audiophile world. However, I have been working in the audio industry (live, studio and permanent install) for over 20 years. Although I am actually in management, you don’t spend this much time without at least learning something about how things work, so let´s say that my audio knowledge is of a medium level.

Now, stepping into the headphone world, it seems that it is the same... but different. Things that are called the same may not actually be the same. I also get confused by many “reviewers” as to what is their opinion and what is actual fact (which is why I am enjoying reading this site!!).

So, on to the subject that I am trying to get a grasp on... balanced headphones, headphone amps and DACs.

First let me explain what (I think) I understand.

I get the balanced headphones part (although I am not sure why it is referred to as balanced, as all it means is that it has a separate ground for each side, like any other speaker I have ever installed) so let’s skip that part, unless there is something else I need to know.

On to the balanced amplifiers…

I also understand the balanced output section of the amp, which refers to the above, providing a separate ground reference to each side, again, like any normal amplifier in the PA world, which is basically two separate amplifier modules, one for each channel. Again, the nomenclature is confusing to me but that is the least of my worries.

When talking about the balanced inputs of the amp, it is my understanding that this is exactly the same as the balanced input on any other amp, it takes a balanced signal to feed it into amplifier. This is again normal in the PA world. In a lot of cases amplifiers may offer a balanced and unbalanced input for each channel which are treated equally once they hit the actual amplification part (after passing through the internal preamp part of the amplifier). Basically there is no difference in amplification between the balanced and unbalanced inputs, the balanced inputs are their to facilitate the connection of balanced cables which are used to prevent exterior interference over their run, not because they are a “better signal”.

Finally, balanced DACs…

Again, unless I am mistaken in the headphone/audiophile world, their should be no difference in signal quality between an unbalanced and balanced output on a DAC, as long as it is obviously the same DAC, the only difference is again to be able to prevent interference over the cable run between the DAC and the destination of the signal (in this case the amplifier).

So, my questions…

Why is it so common to see that reviewers say that the audio quality is much better when using a balanced output from a DAC to a balanced input on a headphone amp?

Why is it so common to hear/read them state that the audio quality is better when using the balanced input of the amplifier rather than the SE, when connecting balanced headphones to the output?

Why do I see that most recommend either using the unbalanced input and SE output or the Balanced input and Balanced output and not using the unbalanced input to feed the balanced output?

Is there some disconnection inside headphone amplifiers that is not common in PA amplifiers?

Are most of these statements (from reviewers) based on subjective opinions or are there facts to back them up?

I sincerely apologize for all the questions and the sheer length of the post but I am seriously interested in knowing the facts behind all this.

 

[RayDunzl]

I also understand the balanced output section of the amp, which refers to the above, providing a separate ground reference to each side, again, like any normal amplifier in the PA world, which is basically two separate amplifier modules, one for each channel.

Balanced to me in part means "differential drive". One signal lead follows the input waveform, the other is the inverse of that.

A balanced amplifier would have what looks/acts like two amplifiers per channel, working in opposition across the load. Neither output lead is ground.

What bastardizations the headphone folks have dreamed up, I don't know.

 

[MRC01]

Consider Ray's intuitive explanation: each output channel has 2 signals, each the mirror image of the other (inverted amplitude). That means at any given instant in time, the sum of the two voltages is 0, and the difference between them is twice either one.

Now I'll risk having some of the EEs here criticize my intuitive explanations, and apply this to some of the OP's questions:

A speaker or headphone responds to the difference between 2 wires. It doesn't have a ground reference, so it can't tell whether they're balanced. But if they are balanced, the difference between them is twice the amplitude of either. So it sees twice the voltage (6 dB bigger signal), which draws twice the current, which is 4x the power. That's compared to an unbalanced output having the same voltage as either of the 2 balanced wires.

Because at every instant in time their voltage sum is zero, the cable carrying the 2 signal wires has no net EMF.

Any spurious signal that is the same in both wires doesn't change the output. For example, if the cable passes through an external EMF that distorts the signal, it affects both equally, so the difference between them doesn't change, and since the headphone responds to the difference between them, that distortion is rejected.

Theoretically, when the amp delivers a spurt of electrons its ground voltage could temporarily change slightly, which would create distortion. I speculate that balanced output might eliminate this effect because the output voltages (and currents) are instantaneously equal and opposite. The analogy is if you go outside and jump up and down, the Earth moves a little bit. Theoretically, if somebody else on the opposite side of the Earth is jumping up and down at the same time you are, your impacts cancel each other and the Earth doesn't move at all. But your mass is so much less than the Earth, the effect is too small to measure even without that other person. And it's debatable whether this theoretical concern would make any practical or measurable difference in an amplifier. For all pragmatic purposes, the ground absorbs all electrons without its voltage changing.

In summary, balanced can give higher S/N ratio and output power, and it can reduce or eliminate ground noise or hum. It's ideal for low level signals that travel on long wires, through noisy EMF areas -- like microphones, which have millivolt signals with long cables that pass through recording studios having amps and power cables. But balanced requires dual symmetric amplification for each channel which adds expense & complexity. Typical consumer audio involves signals around 1V (not millivolts) with short cable runs, so the benefits of balanced could be marginal to nonexistent.

 

[solderdude]

... preamble ...

So, my questions…

Why is it so common to see that reviewers say that the audio quality is much better when using a balanced output from a DAC to a balanced input on a headphone amp?

Because they believe it is the case. Reviewers KNOW what they review and how it is connected.
Maybe in some rare occasions they may have gotten rid of groundloop issues.

Why is it so common to hear/read them state that the audio quality is better when using the balanced input of the amplifier rather than the SE, when connecting balanced headphones to the output?

A: Because they believe it is the case. Reviewers KNOW what they review and how it is connected.
B: In some cases there might be up to 6dB more headroom (power) available which in some cases might be welcome.
C: Because technically the single return wire with low impedance headphones can make a measurable difference

Why do I see that most recommend either using the unbalanced input and SE output or the Balanced input and Balanced output and not using the unbalanced input to feed the balanced output?

A: Because they believe it is the case. Reviewers KNOW what they review and how it is connected.
B: In some cases there might be up to 6dB more headroom (power) available which in some cases might be welcome.
C: Because technically the single return wire with low impedance headphones can make a measurable difference

Is there some disconnection inside headphone amplifiers that is not common in PA amplifiers?

PA amplifiers are designed to provide LOTS of power in low impedances, headphone amplifiers are low power devices designed to drive higher impedances.

Are most of these statements (from reviewers) based on subjective opinions or are there facts to back them up?

Most are based on subjective opinions and maybe a handfull are based on more scientific facts.