It was in 2008 that we started hearing about the SPL Phonitor, a high end headphone amplifier developed by professional recording equipment company SPL in Germany. SPL coined a nice name for the stereo imaging issue that plagued virtually all headphones, even the K1000: the super-stereo effect. What we mean by super-stereo effect is that with headphones, the left ear hears only the sound coming from the left transducer and the right ear hears only the sound coming from the right transducer. Well, isn’t it supposed to be like that? Apparently not, because even in stereo loudspeaker set ups, some of the sound coming from the left speakers would be captured by the right ear, and vica versa. Pictures would explain better:

This is a loudspeaker set up. Both ears actually receive direct and indirect waves from both left and right speakers.

This is a headphone set up. The left transducer sends waves to the left ear, and the right transducer sends waves to the right ear. There is no mixture of the soundwaves like what we get with speakers, thus the super-stereo effect.

We are all aware of the super-stereo problem created by headphones, and there have been a lot of different techniques developed to help attenuate the problem. Before the introduction of the Phonitor, Dr. Meier’s crossfeed circuit was probably the most widely known answer to headphone enthusiats. Even the Grace m902 amplifier utilizes Meier’s crossfeed, and though it was a very good crossfeed circuit, there are no adjustment capabilities built into it. For headphone enthusiasts, we may think that crossfeed is really not that necessary. After all, many fine headphone amplifier comes without any crossfeed circuitry. Not to mention purists who fear that adding more circuitry will introduce distortions and sound degradations. Besides, we have adjusted to the super-stereo effect, and most of us resort to other techniques such as a technically superior headphone or a better DAC to give us better imaging. So, we simply ignore the super stereo effect and accept is as a fact of life.

For recording engineers, the existing solutions were not enough. While monitoring speakers technology is constantly getting better, headphones are still best for “zooming in” into a particular mix. Hence, they want to be able to use headphones for mixing. Here is an excerpt from the Phonitor User Manual:

On one hand the analytical headphone monitoring is like working with an acoustic magnifier but without external room influences; on the other hand, as with loudspeaker monitoring, forgoing the microscopic effect, but with room ambiance.
Working with the magnifier effect on headphones has the advantage of safely hearing clicks or similar defects and helps in fine tuning crossfades or to judge tonal problems in individual tracks.
On loudspeakers such analysis is much more difficult, as such problems just are not as apparent as when working without being able to “zoom in” aurally.

So, there has got to be a better way to deal with the super stereo effect. Again, from the Phonitor’s User Manual:

Traditional headphone reproduction produces 180-degree stereo width in the middle of the head, and it is exactly this which creates the very problematic-to-impossible headphone mixing environment. An essential reason for such unnatural ambiance is the complete separation of the channels, which does not exist either in natural hearing or in stereo loudspeaker reproduction. This makes it nearly impossible to judge tonal balance, a stereo image and the phantom centre level. Panorama adjustments as well as related EQ settings that one attempts with headphones, typically just do not function on loudspeakers.

In short, the Phonitor was created in an attempt to give the most complete control over recreating a proper loudspeaker imaging.