Over the past few years, balanced headphones have become a thing. Lots of higher end digital audio players and headphone amplifiers now provide outputs for balanced headphones. Some quality headphones come with cables suitable for use with such outputs and for some which don’t, you can buy suitable third-party cables.
So, let’s see first what balanced headphones are, and what they are not. Then briefly go into one of the complications around balanced headphones: the uncertain connection standards. And then we’ll tackle the tricky subject of, are they even worth the bother?
What are balanced headphones
To start, what is “balanced”
Well, the first thing to make clear is that balanced headphones aren’t “balanced” in the way that we normally use the term with regard to high fidelity equipment. Regular hifi connections – you know, the kind with RCA plugs and sockets – are “single-ended”. The driving voltage is applied to the single, central conductor. The other conductor is passive, and is often simply connected to the earth at the equipment end. The signal travels in that conductor solely as driven by the active conductor. And because it is often earthed, much of the time the signal is also being equally driven down the braided shielding conductor (if there is one).
Is this a terrible scheme? No, not at all. I only recently reviewed a magnificent integrated amplifier that uses only those connections, as do perhaps 95% of all other high fidelity devices. With some of these I manage to measure signal to noise ratios of up to 120 decibels (A-weighted).
Balanced connections mostly use pair of three-pin XLR sockets and plugs. They came to high fidelity from the pro audio world. There they were used because the very low signal levels produced by microphones had to travel down long cables – sometimes tens of metres in length – and were thus susceptible to picking up electrical noise. Both signal cables are active in this case and the earth shielding is kept entirely separate. Any noise that makes it through the shielding will affect both signals equally, and thus will cancel at the input.
The balanced connections in high quality audiophile gear lead to independent amplification circuits for both the positive and negative signals. Their benefits aren’t as clear cut as in the pro audio area, simply because cable runs are short. But notionally at least you can see some advantages.
So, what are balanced headphones?
All of that does not necessarily have anything to do with balanced headphones. To explain what these are, we need to first look at the traditional stereo headphone connection. These use either a 6.35mm (quarter inch) or 3.5mm (one eighth inch) plug and socket combination. The plug is a TRS style. That stands for Tip, Ring and Sleeve. The tip is the end, the sleeve is the rear-most conductor on the plug, while the ring is the bit in between.
That means three connections. But we have two drivers, each of which has to have both a positive and a negative connection. (Of course, audio signals are alternating, so there isn’t an absolute positive and negative. The terms are shorthand for active and return, just as is often the case for loudspeaker connections.) So, four signal connections are required, but only three are provided. That’s solved by the tip providing the positive or active signal to one of the drivers, the ring to the other driver, and the sleeve handling the negative or return for both drivers.
Note, as often as not the connector for the sleeve is earthed in the headphone amplifier.
With balanced headphones, one or two extra connections are provided on the plug. In that way, the left and right headphone drivers no longer have to share the same return connection. Thus, the left and right circuits can be entirely separate electrically. And if that’s how they’re implemented, that could possibly yield some measurable benefit in reduced crosstalk between channels.
It also means that such connections may, if so designed, also be balanced in the way described above. That’s not necessarily the case since it involves not just additional connections but doubling the number of amplifiers.
How can you tell if a headphone amplifier with balanced outputs also provides a balanced signal for each driver? If it does, it will typically say something like “full differential balanced amplifier” in its feature list. If it doesn’t say that, check the output specifications. If it is fully balanced, the output voltage into high impedance loads will usually be twice as high for the balanced output as it is for the single-ended output, and the power will be four times higher. (Although this might not apply into low impedance loads for various reasons.)
Here, for example, are the output ratings for the iFi ZEN CAN headphone amplifier into 600 ohms: from the single-ended output (ie. the regular 6.35mm socket) it can deliver 7.6 volts or 98mW, while for the balanced output that goes up to 15.1 volts or 385mW.
But there are always exceptions. Hours after I wrote the previous section, I was part of a webinar with the high-end Canadian equipment maker Simaudio. The presenter noted that the company’s Moon devices are engineered to deliver the same output voltage over their balanced outputs as they are over their single-ended ones. He did note that very few companies did that.
Balanced headphone connections
As is often the case with new innovations, not all standards are set immediately. In the case of balanced headphone connections, they’re taking a while to settle down. Here’s a fairly complete list of the output connections used on headphone amplifiers and other devices supporting balanced headphones:
- 2 x 6.35mm TRS
- 2 x 3-pin XLR
- 1 x 4-pin XLR
- 1 x 2.5mm TRRS
- 1 x 4.4mm Pentaconn TRRRS
I don’t think 3.5mm TRRS connections have been used (although I could be wrong), because the confusion between those and 3.5mm TRRS connections very commonly used for earphone/microphone combinations would be quite problematic.
Remember T stands for tip, R for ring and S for sleeve. The most common balanced headphone outputs are probably 2.5mm TRRS, which have been widely provided on good quality portable digital audio players for some years. 4-pin XLR has often been employed on larger dedicated headphone amplifiers and high-end DAC/headphone amps. Pairing of two regular connections – 6.35mm or XLR – has tended to be in earlier equipment, although the RME ADI-2 PRO FS R BE DAC/ADC I use primarily for measurements can be configured so that its two independent 6.35mm headphone outputs can operate in balanced mode with headphones. Indeed, since it already has two independent high powered stereo headphone amplifiers, in balanced mode it uses a balanced output for each headphone driver.
But with heavyweights like Sony behind it, the 4.4mm Pentaconn connection seems to be advancing rapidly. The lastest Astell&Kern portable digital audio player models incorporate it, as does a lot of top-notch iFi Audio gear. I hope that this connection prevails. It is compact enough for portable gear, provides a larger contact area than 2.5mm, and has five separate contact areas, so you can have hot and cold, positive and negative for both headphones along with a separate earth/shield connection. I expect that the 4-pin XLR will persist for higher-end applications where size isn’t a problem.
This uncertain field for connections can lead to problems. For example, as recently as 2020 I was looking for something as seemingly simple as an adaptor so that I could use headphones with a 4.4mm plug in a DAP with a 2.5mm socket. But I couldn’t find anything locally at the time. The only adaptor I could find was via Alibaba from a shop in China. I bought it. But that difficulty is being rapidly overcome by much readier availability of adaptors and replacement cables in both 4.4mm and 4-pin XLR configurations.
Oh, one quirk of the 4-pin XLR connection of which you should be aware: it reverses the usual XLR conventions. With other XLR applications, the pins point in the direction of the signal. So, the microphone has pins in its base and the microphone cable has a socket on its end to plug into the microphone. At the other end it has three pins which plug into the socket on the mixer or whatever. And so the connections always go, with the pins pointing from source to receiver.
4-pin XLR connections used for balanced headphones reverse this, with a socket on the front panel and the headphone cable sporting a four-pin connection.
Are balanced headphones worth it?
As with all manner of audiophile things, in the end you will need to judge for yourself according to what you hear. Me? I can’t say I’ve been able to hear any difference that I’ve been able to clearly identify. Although I should note that it’s hard to do seamless A/B testing when you’re unplugging a cable from headphones between each listen.
So what differences might balanced headphone outputs offer compared to single ended ones, considered from a technical point of view.
Well, it’s hard to see what they might be. Reduced noise? Well, there’s no differential amplifier at the headphone end of the cable to cancel out line interference. Let’s compare balanced and unbalanced headphone outputs in the real world.
We’ll start with the iFi Audio iDSD Diablo DAC and headphone amplifier. It managed a noise level of -115.7dBA via the standard 6.35mm single-ended output, and a less impressive – but still well-beyond-the-limits-of-human-hearing – -109.4dBA from its 4.4mm Pentaconn output. I should note at this point that I don’t really trust those measurements because, as I remarked in my review, some kind of weird interaction between this device and my measurement rig produced what looked like unrepresentative graphs. Still, it is data. The frequency response from both was identical. The THD in both cases was virtually identical at less than 0.0005%. The balanced output pipped the unbalanced in IMD: 0.00132% vs 0.00170%. If you can hear that difference, I bow to you.
Next, the Topping A30 Pro headphone amplifier (fed via a balanced connection by the Topping D30 Pro DAC). The resulting figures were starkly different … in the other direction. Via single-ended, the noise level was an impressive -112.1dBA. But the balanced output pushed that up by 9.5dB to an astonishing -121.6dBA:
As you can see from the graph, much of that increase is from the elimination of mains (and mains harmonic) breakthrough into the signal. That sharp reduction also affects the distortion measurements, THD down from 0.0036% to 0.00006% and IMD down from 0.0045% to 0.0004%.
Finally, the iFi ZEN CAN headphone amplifier (fed by a Topping E30 DAC), again via both the 6.35mm single ended headphone output and the 4.4mm balanced. I had to increase the gain for the former by around 6dB since the balanced headphone output is delivered by a pair of amplifiers. The results? The same headline noise, THD and IMD. There’s only a slight difference in mains breakthrough shown on the noise graph:
So, clearly, in the real world sometimes balanced headphone outputs measure better than single-ended, sometimes worse, sometimes the same. It looks a lot like it’s more a case of implementation than balanced or single-ended.
And I must stress, than in none of those six cases was any noise audible in the slightest. We’re talking about performance levels way beyond the ability of the human ear to detect the differences.
Hermann Gier from the German electronics maker SPL notes that in all the professional audio gear produced by his and many other companies, and all of it marketed to people who are extremely picky about sound quality, virtually none includes balanced headphone outputs. Given that his company does indeed sell high quality headphone amplifiers into the consumer space and that these are fitted with balanced headphone outputs, you can see that he was arguing against his own interest.
So I’m somewhat sceptical of the superiority of balanced headphone connections. Indeed, as I’m writing this I’m using a Topping A30 Pro headphone amplifier mentioned earlier, but I’m listening via the 6.35mm regular headphone output using the Final Audio D8000 headphones, and it’s sounding pretty magnificent.
I think it’s likely that balanced headphone connections and cables and adapters are here to stay, regardless of their objective merits. As we saw, even a pro-audio company sceptical of merits of balanced headphone connections incorporates them in its premium consumer product. Even if no-one used balanced headphones, the ability to work in balanced mode has become a strong mark of quality.
If you are interested in experimenting, make sure that your next headphones come with both single-ended or balanced connections. Or that they use a removable cable so you can buy an after-market balanced cable. And have a listen for yourself.