Overview

The HD 620S is Sennheiser’s May 2024 closed-back audiophile headphone that merges DNA from the HD 600 and 500 series. Featuring reference-grade 42mm angled transducers with 38mm diaphragms and ultra-light 150-ohm aluminum voice coils manufactured at Sennheiser’s Tullamore, Ireland facility, the HD 620S attempts to replicate open-back spatial imaging in a closed design. The angled baffle design encourages air movement to model open-back transducer behavior while maintaining isolation, targeting audio enthusiasts seeking distraction-free listening without compromising natural sound character.

Scientific Validity

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Measurement data demonstrates above-average performance with THD <0.05% at 1 kHz/90 dB SPL, well below the 0.5% problematic threshold for headphones [1][2]. Frequency response spans 6 Hz - 30 kHz with narrow peaks and dips, exhibiting elevated mid and upper treble regions while maintaining acceptable deviation from neutral [1][3]. Third-party measurements show the HD 620S addresses the HD 600’s bass limitations with more extended low-frequency response, though bass distortion increases at higher SPLs with non-linearity factors entering around 95 dB SPL [2]. The 150Ω impedance (159Ω measured) provides high sensitivity at 112 dB/V, making it technically easy to drive despite high impedance [2]. Sound pressure level capability reaches 110 dB SPL according to manufacturer specifications [1].

Technology Level

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The HD 620S demonstrates contemporary engineering with proprietary angled 42mm transducer technology designed to replicate loudspeaker spatial imaging in closed-back format. The custom-tuned drivers feature 38mm diaphragms and ultra-light aluminum voice coils manufactured in-house at Sennheiser’s state-of-the-art Ireland facility, representing genuine technical innovation for closed-back spatial reproduction. However, cost optimization is evident in the adoption of the existing 5-series chassis rather than developing purpose-built housing, with reviewers noting this decision appears driven by cost-saving rather than technical advancement. The angled baffle design encouraging free air movement while maintaining closed-back isolation represents meaningful acoustic engineering innovation.

Cost-Performance

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At 349.95 USD, the HD 620S faces significant cost-performance pressure from equivalent alternatives. The Beyerdynamic DT 770 PRO (80Ω version) provides comparable closed-back performance with similar impedance characteristics at 176 USD, described as “ridiculously good for the price” [4]. Equipped with closed-back design and frequency response performance equivalent to the HD 620S, the DT 770 PRO offers substantially better value. CP calculation: 176 USD ÷ 349.95 USD = 0.503, rounded to 0.5.

Reliability & Support

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Sennheiser provides standard 2-year warranty coverage with established global support infrastructure and repair services ranging 1-4 weeks [5]. The HD 620S benefits from robust driver technology proven in the HD 600 series lineage, with steel-reinforced headband components and drivers manufactured at Sennheiser’s established Ireland facility. However, build quality feedback indicates concerns with extensive plastic construction, strong clamping force, and comfort issues during extended listening sessions [6]. The artificial leather earpads may cause heat buildup, and the 5-series chassis lacks the satisfying click adjustments found in premium models.

Rationality of Design Philosophy

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Sennheiser demonstrates strong scientific approach with measurement-focused development and clear technical specifications. The angled transducer innovation directly addresses real acoustic challenges in closed-back design, attempting to achieve open-back spatial characteristics while maintaining isolation benefits. The design philosophy emphasizes function over form with practical engineering solutions, consistent with Sennheiser’s 75-year commitment to technical excellence and neutral sound reproduction. However, the purely analog/mechanical approach foregoes potential digital enhancement technologies that could further optimize performance. The HD 620S represents logical progression from HD 600 series limitations while maintaining core strengths, showing rational development direction focused on measurable acoustic improvements.

Advice

The HD 620S targets audiophiles seeking closed-back isolation with open-back spatial characteristics, representing genuine innovation in transducer design. However, at 349.95 USD, strong alternatives like the DT 770 PRO offer comparable performance at significantly lower cost. The HD 620S justifies its premium primarily through spatial imaging innovation and Sennheiser’s established reputation. Potential buyers should consider whether the angled transducer technology and brand heritage justify the price premium over well-established alternatives. Those prioritizing cost-effectiveness may find better value elsewhere, while those valuing Sennheiser’s specific acoustic approach and spatial imaging innovation may find the premium worthwhile.

References

[1] Sennheiser Official Specifications, HD 620S Product Page, https://www.sennheiser-hearing.com/en-US/p/hd-620s/, accessed 2025-09-03

[2] Audio Science Review, Sennheiser HD 620S Headphone Review, https://www.audiosciencereview.com/forum/index.php?threads/sennheiser-hd-620s-headphone-review.57952/, 2024

[3] DIY-Audio-Heaven, HD620S Measurements, https://diyaudioheaven.wordpress.com/headphones/measurements/brands-s-se/hd620s/, May 9, 2024

[4] RTINGS, Beyerdynamic DT 770 PRO vs Sennheiser HD 560S Comparison, https://www.rtings.com/headphones/tools/compare/beyerdynamic-dt-770-pro-vs-sennheiser-hd-560s/440/18492, accessed 2025-09-03

[5] Sennheiser Support, General Terms & Conditions for Warranty, https://www.sennheiser.com/en-us/support/terms-conditions-warranty, accessed 2025-09-03

[6] Headphones.com, Sennheiser HD 620S Review, https://headphones.com/blogs/reviews/sennheiser-hd-620s-review, accessed 2025-09-03

(2025.9.3)