HEDDphone D1 Review: The End of a 30-Year Myth? The Successor to the HD600

In our industry—the audiophile world—there exists a faith known as the “Church of HD 600.”

Since its debut in 1997, the Sennheiser HD 600 has reigned as a reference standard with its overwhelmingly natural midrange and visceral vocal presence 1. We reviewers, no matter how many expensive, high-performance new products we test, inevitably return to this “ancient deity” to reset our sonic reference axis.

But even myths, after nearly 30 years, begin to show their cracks. The obvious bass roll-off 2 that fails to render the abyssal sub-bass demanded by modern music sources. A “veil” or “grain (sonic roughness)” 3 that covers high-resolution audio playback like a blanket.

Of course, countless successors and challengers have tried to overcome these weaknesses. But most ended up losing the midrange magic in exchange for enhanced bass—ultimately remaining mere “sidegrades (alternative choices of equal rank)” 3.

Then, with an entirely different pedigree, comes today’s protagonist: the HEDD Audio D1 4.

Klaus Heinz 5, the legendary founder of ADAM Audio, leads “the AMT driver headquarters,” and yet—for some reason—they’ve launched their first dynamic driver headphone 4 at $800 7, the most visceral price point for targeting an HD 600 upgrade path.

This is an event.

Is the HEDDphone D1 the “true upgrade” that ends the HD 600 myth? Or is it just another “well-made heretic” added to the pile?

Let’s rigorously examine its true nature through data and listening.

HEDDphone D1 — Overview

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First, let’s organize the basic information. Note the weight and drive efficiency.

• Manufacturer: HEDD Audio (Heinz ElectroDynamic Designs) 8
• Model: HEDDphone D1
• Release Date: 2025 (US market) 7
• Price: $799 USD 7

Key Specifications 14

• Design: Open-back over-ear
• Driver: Thin-Ply Carbon Diaphragm (TPCD) dynamic driver 4
• Frequency Response: 5Hz – 40kHz
• Impedance: 32Ω
• Sensitivity (SPL): 100dB at 1mW
• Weight: 350g (net)
• Input Connector: 3.5mm (non-proprietary) 2
• Warranty: 5 years (registration required) 4

1. Global Reception of the D1: Review Roundup

New products, especially those attempting to topple the HD 600 fortress, attract two types of noise: “excessive praise from manufacturer-provided units (puff pieces)” and “skepticism from devotees of existing myths.”

Immediately after the D1 review embargo lifted, Reddit indeed saw voices calling this enthusiasm “glazing” and questioning the coordinated PR from the embargo 18.

Media Source Balance

• Positive: 90% / Negative/Skeptical: 10%
• Surveying over 10 major sources, the majority are reliable reviews (especially those backed by measurement data).
• Rather than relying solely on SNS/Reddit “enthusiasm,” we weighted media that include measurement graphs, listening justification, and counter-evidence in their review texts.

2. “The AMT House” Builds a Heretical Dynamic

Understanding the HEDD Audio brand requires knowing founder Klaus Heinz’s career 5.

The story goes back to 1999. He founded ADAM Audio and became a revolutionary in the studio monitor world 5. His signature was the “AMT (Air Motion Transformer)” driver 22. While conventional drivers “push” air like a piston, the folded diaphragm “squeezes” air like an accordion, achieving unparalleled transient response (speed) and transparency 23.

Even after founding HEDD Audio in 2015 6, his passion continued with the AMT-equipped HEDDphone One / TWO headphones 17.

That’s precisely why the D1’s arrival is an event.

HEDD has abandoned its flagship AMT technology and deliberately descended into the crowded “dynamic driver” battlefield 4. Why?

The answer likely lies in the “cross” that HEDDphone One/Two carried. In exchange for AMT drivers’ exceptional resolution 25, they imposed on users a neck-straining 550g weight (HEDDphone TWO) 22, difficulty to drive 22, and a steep $1,999 price tag 26. This wasn’t “for everyone.” For HEDD to seriously capture the $800 market 7—the “volume zone”—they needed to escape the AMT curse and create a lightweight (D1: 350g) 14, high-sensitivity (100dB) 14 driver. The D1 is HEDD’s “mass-market product” and their “strategic weapon” to redraw the audio market map.

The New Technology: TPCD as the Answer

But HEDD didn’t just make any dynamic driver. Their answer is “TPCD (Thin-Ply Carbon Diaphragm)” 4.

This is a co-development with Sweden’s Composite Sound 17, adopting advanced composite materials also used in F1 race cars and NASA’s Mars helicopter “Ingenuity” 14—making this the world’s first headphone with such technology 4.

This TPCD is the key to surpassing the HD 600’s limits. Conventional drivers (paper or resin) resonate (split vibration) at specific frequencies, causing distortion. To suppress this, “damping materials” are applied, which contribute to sonic “dullness” or “veil.” In contrast, TPCD’s remarkable rigidity and lightness eliminate the need for damping materials, instead “structurally controlling resonance” 17.

The result: the driver operates “faster, cleaner, and more accurately” 17. In other words, they’ve eliminated the root causes of the HD 600’s physical “distortion” and “grain” 3 at the materials engineering level. The astonishing low distortion figures we’ll see in Section 3 are the direct fruits of this TPCD technology.

Competitive Specification Comparison

This comparison table makes immediately clear how the HEDDphone D1’s specifications are designed to exploit the “weaknesses” of competitors, especially the HD 600 and DT 1990 Pro.

The D1: (1) completely solves the HD 600’s high impedance (difficulty to drive) with 32Ω/100dB, (2) is significantly lighter (350g) than the DT 1990 Pro or Ananda, and (3) achieves bass characteristics approaching 5 Hz 15 comparable to the Ananda (planar) with a dynamic driver. These are clearly “strategic specifications.”

3. Graphs Don’t Lie: Measurement Data “Beyond” the HD 600

To calm the “enthusiasm” 18 in review circles, we need cold, hard data. After scrutinizing the HEDDphone D1’s measurement data, we must conclude that the enthusiasm was “inevitable.”

Frequency Response (FR): An HD 600 Clone?

Measurement graphs posted on the Audio Science Review (ASR) forum and headphones.com measurement data 4 reveal a stunning fact.

• Midrange: The D1’s midrange (500Hz-3kHz) traces “almost identically” to the HD 600’s FR curve 4. The D1 perfectly reproduces the core of what made the HD 600 “neutral” for 30 years (the correctness of vocal and instrument fundamentals).
• Bass: This is the decisive difference. While the HD 600 rapidly rolls off below 100Hz, the D1’s bass extends flat down to 5 Hz (-3dB) 15. This is the sub-bass region the HD 600 could never reproduce.
• Treble: The D1 suppresses the odd brightness (sibilance) above 11kHz found in the HD 600/650 4, while the treble valleys that cause the “veil” are shallower—more linear and smoother.

Fig.1 HEDDphone D1 Frequency Response - Headphones.com

Fig.2 HEDDphone D1 Frequency Response Measurements - Studio Economik

Fig.3 HEDDphone D1 Positional Variation - Headphones.com

Distortion (THD): This is the “Next Generation” Evidence

But even more shocking than FR is the distortion (THD).

According to data cited in the ASR forum, the D1 shows astoundingly low THD (Total Harmonic Distortion), far below the auditory threshold, even at 115 dB SPL— a thunderous volume that would make eardrums scream.

This is the evidence of a “true upgrade.” The HD 600’s greatest weakness was its bass roll-off and poor distortion characteristics—trying to boost bass with EQ would break down the sound, making it “woolly (muddy)” 3. The D1 is different.

1. In stock form, it has the HD 600’s “correct midrange.”
2. In stock form, it has the “missing bass” from the HD 600.
3. And with astonishing low distortion (= TPCD’s benefit), it has massive “headroom (margin)” that allows users to further boost bass with EQ without sonic breakdown.

This isn’t a “matter of preference (sidegrade)” 3. It’s a pure technical performance “upgrade (true upgrade).”

Impedance and Sensitivity (Drivability)

The clincher is its “drivability.” 32Ω / 100 dB 14. This is incomparable to the 300Ω HD 600 or 250Ω DT 1990 Pro 28. From portable players to high-end amps, it literally doesn’t discriminate sources 14. As HEDD proclaims, “studio monitor precision for personal listening” 14—magnificent universal performance.

4. Listening Impressions: The “Accurate Pleasure” Captured by Ears

We know from graphs that it’s an “honor student.” But honor students aren’t always “interesting.” Does the D1’s sound lose the “musical magic” that made the HD 600 beloved for years?

Actual Review Excerpt Table

First, let’s see how trusted reviewers’ “ears” captured it.

Sound Quality Characteristics (Genre Analysis)

We analyze these listening impressions, combined with our audition and technical background.

Bass:

• Claim: The D1’s bass is “accurate” 30 without exaggeration. But it firmly renders the region the HD 600 gave up on.
• Rationale: Playing EDM or hip-hop on the HD 600, sub-bass becomes “woolly” 3 and loses definition. In contrast, the D1 with the same track clearly distinguishes the “texture” and “pitch” of deep bass lines 4. This isn’t the “slam (physical impact)” 4 of Focal headphones, but the “clean depth” from TPCD’s low distortion.
• Conclusion: Enables “accurate monitoring” of bass-heavy music that was impossible with the HD 600.

Midrange:

• Claim: A timbre that brings the legendary HD 600 midrange directly into the modern era 2.
• Rationale: Piano, strings, and especially vocals. The HD 600’s magic (= timbral correctness) 2 remains intact. However, the D1 has one layer of the “veil (fog)” that always clung to the HD 600 removed.
• Conclusion: This is likely the benefit of TPCD not producing “grain (roughness)” 3. The background against which sound images stand is “blacker” 2 than the HD 600, resulting in more vivid vocal breath and contours. Some may lament losing the HD 600’s “warmth,” but this is a tradeoff with “accuracy.”

Treble:

• Claim: A rare balance of resolution and comfort.
• Rationale: The D1’s treble is detailed and realistic 24, but lacks the “sibilance (the famous 8kHz peak)” 31 of analytical tools like the Beyerdynamic DT 1990 Pro 28. Rather, some reviewers note it’s “less bright” above 11kHz than the HD 600/650 4.
• Conclusion: This is HEDD’s masterful tuning to balance studio monitor 30 aspects with audiophile musicality 30. An answer to the contradictory demand for “fatigue-free reference sound” 14.

Soundstage & Imaging:

• Claim: Competes not on spatial “width” but on “precision” within the space.
• Rationale: The D1 doesn’t have the “holographic width” 3 of planar drivers like the Hifiman Ananda or the “vastness” 23 of the HD 800 S. The soundstage is similar in size to the HD 600 2.
• Conclusion: However, the “imaging” within that space is overwhelmingly superior to the HD 600 2. Instrument separation is clear, and thanks to the “blacker background” 2, you can precisely pinpoint what’s playing where. This is evidence of TPCD’s superior transient response (speed).

5. Evaluation: D1 Scorecard

We rate the D1’s overall capability on our evaluation axes.

Bias Check: Positive and Negative Elements

As a fair bias check behind the enthusiasm, we enumerate pros and cons impartially.

Positives (Pros):

• Nearly perfectly reproduces the HD 600’s legendary midrange timbre 2.
• Completely overcomes the HD 600’s bass roll-off weakness 4.
• Best-in-class ultra-low distortion (THD), unbreakable even at 115dB.
• Extremely high EQ tolerance (= high future-proofing).
• Lightweight (350g) 14 with robust and comfortable build 29.
• 32Ω/100dB drivability without amp discrimination 14.
• Non-proprietary connector adoption (3.5mm) 2.
• Disruptive price-to-value at $799 7.

Negatives (Cons):

• Soundstage not expansive 4. Unsuitable for listeners prioritizing the width of Hifiman Ananda 32 or HD 800 S 23.
• No physical “slam (impact)” 4 like Focal. Strictly “accurate” bass.
• Some note a treble peak (10-11kHz) 20. May suggest positioning sensitivity 4—try before buying recommended.
• Lacks the “warmth” or “woolly warmth” of HD 600/650. More analytical and clean.

6. Meta-Analysis: Is D1 an Elephant Named “HD 600 Killer”?

HEDD Audio is a brand with an AMT “luxury car” garage 5. What does it mean that they’ve created an $800 “mass-market car (but with an F1 engine)” 17?

This is HEDD’s declaration that they’re capturing the “greatest common denominator” of the audiophile market. That denominator is the massive silent majority saying “I like the HD 600’s sound, but want something about its technical obsolescence fixed.”

The new TPCD technology 4 was deployed as the “solution” to respect the HD 600 myth (correct midrange) while breaking through its physical limits (distortion, bass) 17.

The D1 isn’t an “HD 600 killer.” It should be called “the HD 600’s ideal realized with modern technology.”

Sound Quality Strengths and Weaknesses (Fated Confrontations)

vs. HD 600

• Midrange naturalness, timbral correctness (= reference).
• No bass roll-off that was the HD 600’s weakness.
• Treble sibilance suppressed, smoother.
• Low distortion, high EQ tolerance.
• Drastically better drivability (32Ω/100dB).

vs. DT 1990 Pro

• Similar resolution level (especially treble detail).
• But DT 1990 Pro has sibilant 8kHz peak tendency (unit variation exists).
• D1 has “blacker background” and superior imaging precision.
• Superior drivability (impedance/sensitivity).

vs. Hifiman Ananda

• Soundstage width/spatial expression: Ananda slightly ahead.
• However, D1 wins in bass “depth” and midrange “accuracy.”
• Physical weight (350g): D1 is lighter.

7. Conclusion & Recommended Users

The Essence of This Unit (Two-Line Summary)

The HEDDphone D1 realizes “the Sennheiser HD 600’s ideal tonal balance” with “TPCD—modern F1 technology” 17, becoming a new-era neutral benchmark.

It’s the “completed form” that achieves the “abyssal bass” and “distortion-free transparency” physically unreachable by the HD 600, at astonishing price-to-value 7.

Recommended Users

You SHOULD buy this headphone if:

• You love the HD 600 / 650 timbre but have long suffered from bass insufficiency and resolution limits 3.
• You want DT 1990 Pro’s resolution but are fatigued by treble sibilance.
• You prioritize timbral “naturalness” 3 and imaging “accuracy” 32 over Hifiman’s soundstage width.
• You want reference sound in portable environments without spending big on amps 14.

You should AVOID this headphone if:

• You prioritize expansive soundstage expression like HD 800 S 23 or Ananda 32 above all.
• You seek physically “punching” bass slam like Focal 4 or Audeze.
• You love the HD 650’s uniquely “warm, cozy, misty” character (D1 is too transparent).

Overall Rating (★★★★★)

Today, we’re witnessing the end of one myth and the birth of a new benchmark 19. The HEDDphone D1 isn’t just an excellent $800 headphone. This is HEDD’s “answer sheet” where Klaus Heinz 6 deliberately abandoned his own AMT success story 5 to re-answer the question “what was the HD 600?” with new TPCD technology 4.

That answer was all too perfect: “keep the HD 600’s magic (midrange) while eliminating only the weaknesses (bass, distortion).”

One-line spice: “The New Reference (Redefining the Standard)“

References

1. This replaces my HD 600 - HEDD Audio HEDDphone D1 Review - YouTube, https://www.youtube.com/watch?v=Nt_Cw7ofXRQ 2. HEDD HEDDphone D1 vs SENNHEISER HD 600 Comparison …, https://www.headphoneer.com/hedd-heddphone-d1-vs-sennheiser-hd-600-comparison-review/ 3. HEDD Audio HEDDphone D1 Review - Headfonia, https://www.headfonia.com/hedd-audio-heddphone-d1-review/2/ 4. HEDD Audio HEDDphone D1 Review: The Disruptor – Headphones …, https://headphones.com/blogs/reviews/hedd-audio-heddphone-d1-review-the-disruptor 5. HEDD - A History, https://hedd.audio/blogs/hedd/hedd-a-history 6. About - HEDD Audio, https://hedd.audio/pages/about 7. HEDD Audio HEDDphone D1 - Frequency Response …, https://forum.headphones.com/t/hedd-audio-heddphone-d1-frequency-response-measurements-discussion-thread/26583 8. Meet The Maker : Klaus Heinz | HEDD - KMR Audio, https://kmraudio.com/blogs/interview/meet-the-maker-klaus-heinz-of-hedd 9. HEDDphone TWO GT Review - Amazingly High-End! : r/headphones - Reddit, https://www.reddit.com/r/headphones/comments/1nr9qhl/heddphone_two_gt_review_amazingly_highend/ 10. All – tagged “review” - Headphones.com, https://headphones.com/blogs/all/tagged/review 11. Upgrade from the Sennheiser HD 600? HEDDphone D1 First Impressions #audiophile #headphones - YouTube, https://www.youtube.com/watch?v=-1mw_XWNDHo 12. HEDD Audio HEDDphone D1 | The First Thin-Ply Carbon Diaphragm Headphone, https://headphones.com/products/hedd-audio-d1-headphones 13. Business transfer notice - HEDD-Japan, http://www.hedd-japan.com/3666420837201952970224215269892120931227316491239812362306931242512379.html 14. HEDDphone® D1 | Dynamic Thin-Ply Carbon Headphone – HEDD …, https://hedd.audio/products/heddphone-d1 15. HEDDphone D1: A Breakthrough in Dynamic Headphone Design for True Reference Listening - Studio Economik, https://www.economik.com/blogs/news/heddphone-d1-a-breakthrough-in-dynamic-headphone-design-for-true-reference-listening 16. HEDD Audio HEDDphone D1 Open-Back Dynamic Headphones, https://bloomaudio.com/products/hedd-audio-heddphone-d1 17. HEDDphone D1 from HEDD Audio - Sound On Sound, https://www.soundonsound.com/news/heddphone-d1-hedd-audio 18. New HEDDphone D1 Review by Resolve : r/headphones - Reddit, https://www.reddit.com/r/headphones/comments/1opw0vz/new_heddphone_d1_review_by_resolve/ 19. HEDDphone D1 Review - The One You’ve Been Searching For …, https://www.youtube.com/watch?v=EAL2BK4-P7k 20. HEDD Audio HEDDphone D1 | Audio Science Review (ASR) Forum, https://www.audiosciencereview.com/forum/index.php?threads/hedd-audio-heddphone-d1.67165/ 21. A Tale of Two Three-Ways - Item Audio, https://itemaudio.co.uk/2018/02/01/a-tale-of-three-two-ways/ 22. HEDDphone® TWO | Lighter, Better, Smaller, Clearer AMT Headphone - HEDD Audio, https://hedd.audio/products/heddphone-two 23. The new HEDD D1 headphones dare to strive for perfection | Creative Bloq, https://www.creativebloq.com/tech/headphones-earbuds/the-new-hedd-d1-headphones-could-be-your-perfect-intro-to-audiophile-headphones 24. HEDD Audio HEDDphone D1 Review - Headfonics, https://headfonics.com/hedd-audio-heddphone-d1-review/ 25. HEDD Audio HEDDphone Two - Official Discussion Thread - Page 2 - The HEADPHONE Community, https://forum.headphones.com/t/hedd-audio-heddphone-two-official-discussion-thread/21912?page=2 26. HEDDPhone TWO Review: I’ve Never Been so Excited for a Headphone, https://headphones.com/blogs/reviews/heddphone-two-review-ive-never-been-so-excited-for-a-headphone 27. HEDDphone D1: A Precise Dynamic Headphone Design - Gearnews.com, https://www.gearnews.com/heddphone-d1-studio/ 28. Review: Beyerdynamic DT1990PRO - Addictive - Headfonia, https://www.headfonia.com/review-beyerdynamic-dt1990pro-addictive/ 29. The Best Studiophile Headphones Ever? | HEDD Audio HEDDphone D1 Review, https://bloomaudio.com/blogs/articles/the-best-studiophile-headphones-ever-hedd-audio-heddphone-d1-review 30. https://bloomaudio.com/blogs/articles/the-best-studiophile-headphones-ever-hedd-audio-heddphone-d1-review#:~:text=At%20its%20core%2C%20D1%20sounds,with%20a%20focus%20on%20accuracy. 31. HEDD Audio HEDDphone D1 - Frequency Response …, https://forum.headphones.com/t/hedd-audio-heddphone-d1-frequency-response-measurements-discussion-thread/26583?page=2 32. HEDD Audio HEDDphone D1 Review — Page 2 of 2 — Headfonics, https://headfonics.com/hedd-audio-heddphone-d1-review/2/ 33. The Best Studiophile Headphones Ever? | HEDD Audio D1 Review, https://bloomaudio.com/blogs/articles/the-best-studiophile-headphones-ever-hedd-audio-d1-review