August 2017

There’s only one headphone model whose sudden disappearance would literally change the world of audio: Sony’s MDR-7506. Introduced in 1991, the MDR-7506es have become something of a standard for audio and video production. I’ve worked in and visited innumerable recording studios across the country, as well as quite a few radio and TV stations, and I can’t remember ever not seeing a set of ’7506es -- more likely, several pairs -- either in use or easily within the engineers’ reach.

Brent Butterworth

Professional sound engineers have embraced the MDR-7506es mostly because of their neutral, natural, uncolored sound. If, for example, they were to monitor sound on headphones with a big treble peak (as some audiophile-oriented headphones have), they’d turn the treble down and end up with mixes that through most systems would sound dull.

The MDR-7506es’ excellence was recently reconfirmed by famed audio researcher Sean Olive, of Harman International, who noted on Facebook that “a professional headphone costing less than $100 comes close to our preferred target curve.” That’s saying a lot, considering that Harman’s target curve is the result of what has probably been the most extensive and influential research ever into headphone sound. Even in recent shoot-outs involving the very latest headphones, the ’7506es have remained competitive with anything in their price range, and often come out on top.

What’s so special about this 26-year-old design? Considering the MDR-7506es’ price -- currently as low as $79 on Amazon -- their advantage clearly does not lie in expensive drivers, exotic enclosure materials, or “audiophile-grade” cables. It comes from a meticulous attention to what matters more than anything else in sound reproduction: frequency response.

It can be appealing to think of sound reproduction as a mystery so complex and unfathomable that no one can confidently say which practices are certain to deliver excellent sound. “ALL parts of a system matter!” a recent post from another Facebook acquaintance of mine recently insisted, implying that the quality of the electronics influence the sound of a system as much as does the tuning of the headphones or speakers. Yet this notion is demonstrably false.

As clearly shown by experiments conducted by Olive and his colleagues Elisabeth McMullin and Todd Welti, the most reliable predictor of which headphones listeners will prefer is the headphones’ frequency response. In their 2013 AES paper “Listener Preferences for In-Room Loudspeaker and Headphone Target Responses,” they learned that there’s no magic or mystery behind choosing the most desirable frequency response. Their tests found that “The preferred in-room loudspeaker target response is not flat but has a bass boost of about 6.6dB below 105Hz and a treble cut of -2.4dB above 2.5kHz. The preferred headphone target response closely approximates the preferred in-room loudspeaker response with about 2dB less bass and treble.” Which, as it turns out, pretty much describes the way the MDR-7506es are tuned.

I often see audiophiles and manufacturers talk about what effects different types and levels of distortion might have on headphone sound quality, but except in extreme cases -- maybe one headphone model in 30 or 40 -- I haven’t found a correlation between measured distortion and listener perceptions of headphones. Olive and his colleagues (all of the above as well as Steve Temme, founder of audio-measurement-gear company Listen, Inc.; and Steve Tatarunis), came to a similar conclusion in a 2014 paper, “The Correlation between Distortion Audibility and Listener Preference in Headphones.” As the authors stated, “The linear [frequency response] distortions in headphones are orders of magnitude higher and more audible than the nonlinear ones [i.e., harmonic distortion].”

Likewise, you’re not going to find any research that shows consistent listener preferences for a certain type of DAC, a particular type of headphone amp, or any specific materials used in headphone construction. Audiophiles may have opinions about these things, and manufacturers may advertise them as advantages, but they can’t back up those statements with research. They’re just opinions, based on casual, uncontrolled listening, and likely to evaporate when subjected to controlled, blind testing.

Sony MDR-7506

The Sony MDR-7506es just reinforce these conclusions. Sony, probably because of its extensive experience in professional audio, knew way back then what research has only recently proven: If you get the frequency response right, you’ll have a good audio product that can last through generations of technological changes.

This isn’t to say that there are no better headphones than the MDR-7506es. In my opinion, there are many, most notably the best of the large, open-back audiophile designs. But the best headphones don’t sound radically different from the MDR-7506es. They just reveal more detail, and have an even more natural sense of space. And in my view, if a set of headphones does sound radically different from the MDR-7506es, it’s changing the sound of the music into something that is not faithful to the original. In other words, it’s not high fidelity -- no matter how much it costs, how exotic its materials, or how esteemed its brand name.

. . . Brent Butterworth