Cliffnotes on a Monolith: The Legendary Sennheiser HD6x0 (Part 1)

This is part one in an ongoing series devoted to the audiophile’s most storied reference headphone lineup, Sennheiser’s HD6x0.

Introduction and Background

Sennheiser has long been a household name among audiophiles, musicians, producers, engineers, and even the general public. It is synonymous with high fidelity. From the hallowed Sennheiser Orpheus/HE1 to the MD & MK series of microphones used the world over, to the consumer-facing products like the Momentum series products and AMBEO sound bar, to the ever-famous audiophile gear such as the HD 600, HD800, and IE900... Their pedigree is quality in all aspects. After years of putting their money where their mouth is, that legacy is earned.

This brings us to introducing the headphone that needs no introduction: the Sennheiser HD 6x0 line, consisting of HD 580, HD600, and HD 650 (others like Drop's HD58x and HD660s are excluded intentionally). This group of headphones has withstood the test of time for almost 30 years and, in many spaces, is still the go-to recommendation when someone asks: "What headphone should I get?"

Audio as a whole, but especially in the realm of headphones, is not like the typical technology buzz of today. There is no Moore's law when it comes to audio quality; you don't see new headphones that change the landscape of the market as a whole released every six months. This is because good audio stays good.

When picking a headphone and squaring a product's tonality with its intangibles such as dynamics, headstage, resolution etc., it is often a game of having to accept certain compromises. Finding the balance of strengths is the challenge. Even today, many expensive headphones are often riddled with crippling compromises that do not warrant their price tags. This may include tuning, build, comfort, quality control issues, or deficits in the psychoacoustic intangibles such as dynamics, detail, imaging, stage, etc. Often different headphones rely on so-called "party tricks" such as elevation in bass and/or treble, soundstage or imaging idiosyncrasies, or even esoteric methods of build/fit/coupling (such as the Abyss headphones) to create interest or even a selling point. These new headphones are often not guaranteed better performance than their predecessors.

One piece of wisdom in audio often shared by long-time hobbyists is that the price of headphones isn’t correlated to performance. A cheaper headphone can outperform a headphone 2 times or even 20 times its price tag. An older headphone can have technical prowess that outdoes current releases, and this is seen with the aforementioned HD 580, as well as vintage Stax and Yamaha orthodynamic headphones, though even the latter two here have significant compromises which, to many, could make their strengths untenable or irrelevant.

If finding the balance of strengths and compromises is the challenge, the greatness of the HD 6x0 comes from balancing all aspects into a reasonably affordable package.

History of the HD6x0

At the start of the 1990s, a young engineer named Axel Grell began his career at the well-respected Sennheiser audio company. It was an exciting time at Sennheiser. In 1991, the legendary electrostatic headphone system HE90 Orpheus was released. The HE90 proved that a headphone system could compete with quality loudspeakers and provide a benchmark in personal audio. Grell, a junior engineer at the time, was tasked with an incredible challenge: creating a dynamic driver Orpheus for the masses. The story of the Sennheiser HD 6x0 starts at Burgdorf, Germany in 1993. The HD580 was made to be a diffuse field-referenced dynamic driver headphone, and you can see if you compare the two where the similarities lie; HD580 is a warmer take on the Diffuse Field target. HD580 was Grell’s first major success of many. HD580 proved that dynamic drivers could provide a step forward in high fidelity for all consumers, even amongst the perhaps more novel or exciting new technologies of the time, such as electrostatic, orthodynamic (or as commonly known as planar magnetic), and mylar diaphragm driver releases. The HD580 brought a natural, engaging sound. The headphones breathed a sense of punch and warmth into the music; this was unique at the time, as many headphones were thinner sounding.

With HD580 being an evident success, for the 50th anniversary, Sennheiser 1995 released a limited edition HD580 Jubilee, wherein they pivoted from the herringbone grill design to a steel-like mesh similarly found in the HE60 "baby Orpheus" of the time. During the HD580 development, Grell originally wanted to have the HE60 type mesh on the HD580, but his original vision was shelved since he was a junior engineer, and so the herringbone grill design stuck. While there’s little doubt the design fit the early 90s style quite well, with the benefit of hindsight we now know that the herringbone grill caused some resonance issues. However, in the HD580 Jubilee and immediately after with the HD600, we see that Grell finally got his vision of more open steel-mesh grills. On top of a new sleek look, it provided a less restrictive, more transparent sound profile, reducing the acoustic impedance and resonances of the rear volume, though the effect may be a subtle improvement to an already stellar headphone.

In 1997, the world of audio was irrevocably changed and the now legendary HD600 was released, with better build materials (adorned with the famous "granite-counter top" finish) and reportedly improved voice coil structure. The "warm-tilted Diffuse Field" target that Grell aimed for with HD580 was made even warmer, to the benefit of many who were beginning to want warmer and warmer headphones. Though many were pleased enough to crown HD600 the new king of dynamic drivers, an unfortunate discourse centering around what many called the "Sennheiser veil" arose.

Important to note here: with the benefit of understanding wider context of the market as a whole in hindsight, as well as modern research, we now know that this was likely due largely to Sennheiser's foremost contemporaries, AKG and Beyerdynamic, having a much brighter sound profile overall (especially when compared to modern headphones, targeting much more conservative, warmer targets). Though some may have thought the HD600 lacked excitement in the treble, the praise for it was unanimous enough upon release (and in the years that followed) that it is arguably the single most famous audiophile headphone ever made.

In 2003, Sennheiser did extensive research and consulted a diverse group of people, from sound engineers and trade journalists to enthusiasts, to develop better headphones. The key finding from their intensive research showed "Today, people prefer to "feel" the music rather than to analyze it. The result was the the last entry in the HD 6x0 lineup— the HD650—a headphone meant to captivate the listener with the ultimate in lifelike reproduction while still maintaining absolute precision." (Sennheiser, official HD650 press release).

Added bass extension, as well as an additional mid-bass elevation on HD650, created a pleasing coloration that afforded the listener an intimate, engaging warmth, and HD650 is arguably the most accessible headphone in an already incredibly accessible lineup because of this. HD650 spent 6 years as Sennheiser’s flagship, and though it was eventually supplanted by HD800, many would say that Sennheiser’s greatest run of headphones ended in 2003 with the 650.

In 2016, Sennheiser and Drop (then called Massdrop) released the now legendary HD6XX collaboration, which brought the HD650 sound to an even broader audience; this move brought an already legendary, previously flagship headphone into a downright affordable price range, right around $200 USD. This was the final move that established the HD650/HD6XX as many people's default recommendation at any price point, as its value was nearly unimpeachable. In 2019, production shifted to Romania, along with new frames being designed and implemented for the HD600 and 650. In 2022, production has now shifted back to Ireland after the acquisition of Sennheiser by Sonova. Axel Grell went on and became the lead engineer and played a role in creating more legendary Sennheiser headphones, notably the $50,000 USD Sennheiser HE-1 and HD800, both of which are often regarded as some of the finest headphones in the world and are deserving of lengthy historical commendations in their own right.

Grell moved on from Sennheiser and started his own audio company, Grell Audio, and released his first product: a true wireless in-ear monitor, the TWS/1. Still today, Grell uses his personal pair of HD 650 as a reference point for his listening and current projects.

The Why

The HD6x0 is beloved by many. At its price, it provides a balanced sound profile in an affordable package. As a result, we see that the HD6x0 is often preferred to much more expensive headphones, even in the summit-fi range. The love for this headphone is not unwarranted; it comes with a rich history of design, research, community feedback, and the focus on providing a natural, dynamic and engaging sound. With its roots stemming from the famous Orpheus and recent Harman research confirming tuning choices, we can see why these reference headphones are loved by many and why even today are still a formidable choice in any audiophile’s arsenal.

There are countless reasons to own any one (or multiple) of the HD6x0 series of headphones, such that, in our opinion, we think that they deserve more than one article. To that effect, we will be publishing more articles about HD6x0 in the coming months to delve deeper into what about the sound so excites or engages us, as well as the role 6x0 plays in our collections, why it earns its place as the de facto recommendation for anyone entering hi-fi, why HD660S isn't a continuation of the legacy, and much more. Stay tuned for that, and thanks for reading.

References:

Sennheiser 2011 Press release
Headfonia 6x0 Breakdown
OverEarMania HD580 Breakdown
Tyll from InnerFidelity's HD6x0 Breakdown