Overview

The Sennheiser HD 599SE is an open-back headphone from the German audio manufacturer, Sennheiser. It incorporates the company’s proprietary E.A.R. (Ergonomic Acoustic Refinement) technology and is offered as an Amazon.co.jp exclusive model. Positioned as a higher-tier model in the HD 500 series, it is designed with the goal of achieving low distortion and high efficiency through its proprietary transducer technology. The black-based design reflects Sennheiser’s design philosophy, which emphasizes functionality.

Scientific Validity

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The HD 599SE shows good results in measurement performance. While the nominal specification for THD (Total Harmonic Distortion) is less than 0.1% (at 1kHz, 100dB), third-party measurements indicate that it can exceed this value in the low frequencies and at high volumes. The frequency response covers a wide range of 12-38,500Hz. With a sensitivity of SPL 106dB (1kHz/1Vrms) and an impedance of 50Ω, it can achieve sufficient volume with most devices. However, some measurements also show deviations from these nominal specifications. The spatial representation from the open-back design is physically effective, but due to its construction, sound isolation cannot be expected. Overall, it demonstrates high performance across many metrics, and its acoustic performance in the audible range can be judged as scientifically valid.

Technology Level

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The E.A.R. technology is a design philosophy that aims to optimize acoustics by angling the drivers to align with the ear’s shape. The use of aluminum voice coils contributes to high efficiency and low distortion, but these are a combination of technologies widely adopted in modern headphones. Detailed technical specifications of the proprietary transducers are not disclosed, and no innovative elements that significantly surpass industry standards can be confirmed. The open-back design itself is an established technology, and there are no notable technical advantages compared to competing products in the same price range. Practical design elements such as velour earpads and a detachable cable are commendable, but the technology level is rated as slightly above the industry average.

Cost-Performance

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As of this review (August 2025), we select Philips SHP9500 as the comparison target. Using USD for CP per policy, we assume typical street prices of 95 USD for the HD 599SE and 75 USD for the SHP9500. Calculation: 75 USD ÷ 95 USD = 0.79 → rounded to 0.8. Both offer low distortion and wide bandwidth with no meaningful gap in basic acoustic performance. Excluding E.A.R. and brand factors, the HD 599SE remains somewhat overpriced from a pure functionality and measurement standpoint.

Reliability & Support

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Sennheiser offers a 24-month product warranty, and the local subsidiary provides support. The repair RMA process is handled online, and support via chat/email is available. The product construction is primarily plastic to emphasize low weight. Public data for failure rate and MTBF (Mean Time Between Failures) is limited. The warranty period and support structure are above the industry average.

Rationality of Design Philosophy

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The design philosophy of the HD 599SE adopts a rational approach based on acoustic engineering principles. It incorporates elements that contribute to measurable sound quality improvements, such as an expanded soundstage through the open-back design, ease of driving via appropriate impedance matching, and a low-distortion design aiming for under 0.1% THD. E.A.R. technology is also an attempt to optimize acoustic characteristics based on ergonomics and has a physical basis. However, the overall package is a solid implementation of existing technologies rather than a showcase of market-disrupting innovation. While the design direction is rational, it is a somewhat conservative approach that does not establish a clear advantage over competitors.

Advice

While the HD 599SE is an excellent product in terms of measurement performance, buyers prioritizing cost-performance are advised to consider the Philips SHP9500, which offers equivalent or better performance. It is difficult to find a sonic advantage that justifies the price difference of approximately 20 USD, and a careful decision is required, especially for audio beginners. It can be a viable choice for those who value the Sennheiser brand, extensive domestic support in Japan, or the 2-year long-term warranty. Due to the open-back design, it leaks a significant amount of sound and offers poor isolation, making it suitable only for use in quiet, private environments. For those purely seeking a balance between sound quality and price, comparing other alternatives would be a rational decision.

(2025.8.7)