Sennheiser HD650
The completeness that has been cherished as a reference headphone for over 20 years is truly authentic. Its acoustic design is scientifically rational and boasts top-class technology level even by today's standards. Reliability and support systems are also perfect. The only factor that makes the cost-performance evaluation harsh is the existence of the 'Drop HD 6XX' with nearly identical performance at a lower price. However, its absolute performance and reliability continue to be one of the best choices for many audio enthusiasts.
Overview
The Sennheiser HD650 is an open-back headphone that has reigned as a “reference” in the audio community for over 20 years since its release in 2003. Based on the acoustic design of the HD600 but tuned in a warmer, more musical direction, its sound signature remains timelessly relevant and continues to be beloved by audiophiles and music producers even after many years since its launch.
What’s particularly noteworthy is the rationality of its design. The high impedance design of 300Ω, precisely tuned acoustic damping, and robust construction that withstands long-term use represent a level of completeness truly worthy of being called “heirloom quality.”
Scientific Validity
\[\Large \text{1.0}\]The acoustic design of the HD650 is an excellent example where objective measurement data and subjective sound quality evaluation align at an extremely high level. The frequency response is very flat from bass to midrange, with the treble gently rolling off after 12kHz - a characteristic optimized for long-term listening. THD+N is extremely low at under 0.05%, and IMD characteristics are also excellent.
What’s important is that this measurement data completely matches the actual listening experience. In numerous blind tests, the HD650’s sound quality has been consistently rated highly, and its acoustic characteristics (warm midrange, smooth treble, tight bass) can be clearly read from the measurement data. This represents a successful example of a scientific approach in an industry where “measurements and listening impressions often diverge.”
Technology Level
\[\Large \text{1.0}\]The technical completion of the HD650 is at the industry’s highest level. The design of the 300Ω dynamic driver achieves both low distortion and excellent transient characteristics, remaining technically excellent even by current standards. Everything from the placement of acoustic damping materials, internal acoustic design of the housing, to the distinctive metal grille has been optimized based on acoustic engineering.
What’s particularly impressive is that despite being a design from over 20 years ago, it maintains a technology level that’s competitive with modern high-end headphones. This is proof that Sennheiser pursued “essence” rather than “trends” at the time, demonstrating true technical prowess. The modular design that allows easy replacement of consumables like ear pads and cables also shows practical technical excellence.
Cost-Performance
\[\Large \text{0.5}\]The biggest weakness of the HD650 is its cost-performance. The fact that the “Drop HD 6XX” with nearly equivalent performance to the HD650, currently selling for about USD 350, is available for around USD 220 makes this evaluation harsh. Measurement-wise, the difference between the two is within margin of error, and blind discrimination is difficult. This gives us CP = 220/350 = 0.63, resulting in a low score by our evaluation criteria.
However, this is purely from a performance-to-price perspective and doesn’t consider added values like “Sennheiser brand,” “original,” and “long-term support.” Also, considering the value retention rate in the used market, the practical cost-performance could be better than the score suggests.
Reliability & Support
\[\Large \text{1.0}\]The reliability of the HD650 is at a legendary level in the industry. Despite over 20 years having passed since its release, it continues to be manufactured, and replacement parts are abundantly supplied. Particularly, consumables like ear pads, cables, and headband pads are easily available as genuine manufacturer parts.
There are many cases of professional studios using them continuously for over 10 years, and the reliability of “once purchased, usable for life” is unmatched. Sennheiser’s after-sales support is also excellent, often providing repair services even for products long after discontinuation, which is a great reassurance for users.
Rationality of Design Philosophy
\[\Large \text{1.0}\]The design of the HD650 is thoroughly rational, with all unscientific elements completely eliminated. The high impedance design has the disadvantage of “being picky about amplifiers,” but this is a rational choice to achieve low distortion and stable characteristics. The open-back design is also a result of pursuing natural soundstage, showing a stance that prioritizes sound quality even while accepting the tradeoff of “sound leakage.”
Material choices are also extremely practical. While the plastic housing may look “cheap,” it has superior acoustic characteristics compared to metal. Velour ear pads are also the optimal solution that balances breathability and comfort. All design decisions are optimized toward the ultimate goal of “sound quality,” with no compromises visible due to appearance or sales considerations.
Advice
The HD650 is not for those seeking “cheap and good,” but it’s one of the best choices for those who want to “use something truly good for a long time.”
- Beginners to Intermediates: We recommend starting with used units or the “Drop HD 6XX.” Cost-efficient alternatives are sufficient until you can distinguish the differences in sound.
- Music Producers: Its reliability as a reference is guaranteed. The fact that it’s used in studios worldwide vouches for its capabilities.
- Classical Music Enthusiasts: The HD650’s sound signature pairs particularly well with classical music, beautifully reproducing orchestral textures and instrument separation.
- Long-term Investment Minded: This product has the potential to remain active 20 years from now, truly becoming a “lifelong companion.”
What’s important is that the HD650 is not a “perfect” product but one with a clear personality. Whether that personality matches the sound you’re seeking will be the biggest factor determining your satisfaction.
(2025.07.05)