Balanced headphones?

[Dan LB]

I’ve just bought a pair of Neumann NDH30 headphones. They sound excellent to my ears and I like them a lot.
In the literature it says “the NDH30 is supplied with a cloth covered cable that is internally balanced”.

Now, I’ve heard about balanced headphones, but don’t they require a 4 pin connector of some type?

How does this internally balanced cable work when it is terminated with a TRS jack? The other end where the cable enters the ear cup is a 2.5mm TRRS so I presume the cans can be wired for ‘true’ balanced operation from a balanced headphone amp.

Any thoughts?

Dan

[Hugh Robjohns]

Oookaaayyyy.... are you sitting comfortably? Then I'll begin....

There is no such thing as 'balanced headphones' and no such thing as a 'balanced headphone amplifier', either. There is nothing 'balanced' about any of it. These terms are misppropriations based on a disappointing misunderstanding of basic audio technology. I blame the marketing departments!

In reality, 'balanced headphones' are nothing more than headphones with independently wired earpieces — requiring a four-wire connecting cable (but not necessarily a 4-pin plug)*.

This is in contrast to the conventional arrangement with a three wire connection, where the negative terminals of each earpiece are connected within the headphone and share a common return.

The potential problem with the shared return is that all wire has resistance, and any current flowing through a resistance generates a voltage across it.

Consequently, the signal voltage going to the left earpiece will also generate a small voltage across the common return wire, and that voltage is inherently added to the signal voltage across the right earpiece... and vice versa.

In other words, the commonned return wire creates unwanted crosstalk between the left and right channels.

The thinner and cheaper (ie, more resistive) the wire, and the lower the headphone impedance, the greater the crosstalk.

Running separate wires from each earpiece avoids that crosstalk risk completely, even if the two negative wires are joined in the plug, because at that point they are grounded directly to the amplifier reference, and no crosstalk can arise.

*So using a four-wire cable into a standard TRS plug achieves one of the main elements of the 'balanced headphone' — reducing crosstalk.

The second element is driving each headphone earpiece from a 'balanced amplifier' ... except that it doesn't exist. What they are really describing is a BRIDGED amplifier — meaning two amplifiers are arranged in a push-pull configuration with the earpiece as a shared load. Naturally, this means the amplifiers are generating signals in opposite polarities, and that's why some idiot thought it was 'balanced'.

As I hope we all know, true balanced interfaces dont need opposite polarity signals....

This bridged amp idea is widely used in PA systems, mostly as a practical way of pushing huge power into a low impedance loads like subwoofers.

For headphone applications this approach has the potential benefit of doubling the voltage (and thus slew rate) across the load.

It's a particularly handy solution for a headphone amp where the power rails are inherently low, such as in battery-powered gear. However, it offers little practical benefit in mains-powered equipment where a conventional single-sided amplifier can be built with high power rails and high slew rates anyway.

So the 'balanced amplifier' thing is mostly nonsense too....

The NDH headphones have separately wired earpieces, as evidenced by the TRRS connector where the cable joins the headphone.

The four wires running down to the TRS plug prevent crosstalk. Plug it into a good high-voltage headphone amp and you'll get as perfect a sound as the headphones can ever muster.

If you really want to use a bridged (not balanced) headphone amp, you'd need to change the cable for one that brought each connecting wire to its own terminal, such as dual XLR3s, a 4-pin XLR, a 3.5mm TRRS, or a Pentaconn plug — these being the most common 'balanced' connection formats.

[James Perrett]

In reality, 'balanced headphones' are nothing more than headphones with independently wired earpieces — requiring a four-wire connecting cable (but not necessarily a 4-pin plug)*.

Aren't most Sennheiser headphones wired like this as standard? I can't remember seeing a pair of Sennheiser headphones that didn't have separate cables going to each earpiece.

[Hugh Robjohns]

Yes, I think so. Certainly my HD600 and HD25 'phones both have four-wire cables.

I have XLR4 and Pentaconn adapters for the HD600, acquired to test 'balanced' headphone amps. They don't get much use....

All of my AKGs are three-wire.... but I can't say I've ever noticed crosstalk issues with any of them.

[sonics]

There is no such thing as 'balanced headphones' and no such thing as a 'balanced headphone amplifier', either. There is nothing 'balanced' about any of it.

Go Hugh! Go Hugh!
I'm right behind you, until the audiophool hordes become unconquerable, that is. Then I'm running away.

The only balanced headphones are those that sit nicely on the bonce, without a tendency to slip off in any direction.

So tell me, how is it that a venerable old German audio company is now using this modern, incorrect language? Is it marketing departments at fault, or have the worms burrowed deeper than we thought?

[Hugh Robjohns]

The worms burrowed deep long, long ago.

It's still rare to find anyone who doesn't believe balanced audio means symmetrical, opposite polarity signals on the hot and cold lines.

[Dan LB]

Thanks Hugh! That clears it up perfectly

[Hugh Robjohns]

[ef37a]

In the July/Aug 1972 issue of the AES journal there was a letter to the effect that...
"Whilst the use of the term "rms watts" is to be avoided we must give the advertisers time to change their printing regimes and use the proper terminology"

We are STILL waiting even though changing an ad now costs bog all and takes but a sweep of the qwerty (one assumes of course that the adpuff peeps know WTF they are describing?)

When "balanced" headphone outputs began to appear on kit in SoS reviews I could not understand what it meant electronically. I am grateful to Hugh for pointing out that it was not I that was a dunce but the people who invented the concept! Well, the naming of it at least.

Dave.

[tea for two]

It's still rare to find anyone who doesn't believe balanced audio means symmetrical, opposite polarity signals on the hot and cold lines.

I believe headphones become balanced when we can wear them standing on our head : yoga style lol.