Sennheiser's HD 600 series headphones are reference standards in audio. Three current options exist in similar price territory: HD 600 ($330), HD 6XX ($220, Drop exclusive), and HD 660S2 ($600). Each has specific characteristics that distinguish them, and the choice between them depends on specific use cases.
This comparison documents the differences and provides specific recommendations.
The shared heritage
All three headphones share substantial heritage:
Open-back, dynamic-driver design.
Sennheiser's HD 6X0 series tuning developed since the late 1990s.
Similar physical form factor and weight.
Generally accurate, slightly warm sound signature.
Excellent comfort for long listening sessions.
Replaceable cables and pads.
Substantial production track record across decades.
The shared heritage means all three are known quantities with consistent quality.
HD 600 (0) — the reference
The HD 600 is the canonical reference of the lineup. In production since 1997.
Sound signature: Neutral with slight warmth. Excellent midrange clarity. Smooth treble. Modest bass extension. Wide soundstage for closed-back style design.
Best at: Critical listening, mixing reference, classical and acoustic music, vocal-prominent material.
Less ideal for: Bass-heavy genres at high volumes. Critical bass content.
Why it remains relevant: The reference standard against which other headphones are measured. Many engineers and audiophiles consider it the price-performance sweet spot.
HD 6XX (0) — the value play
The HD 6XX is a Drop-exclusive version of the HD 650, sold at substantially below regular HD 650 pricing.
Sound signature: Slightly warmer than HD 600. Slightly more emphasis in lower midrange. Generally similar character to HD 600 with subtle differences.
Best at: Same use cases as HD 600. Particularly good for long listening sessions due to slightly relaxed character.
Less ideal for: Studio reference (slightly less neutral than HD 600).
Why it represents value: Same essential character as HD 650 ($430 retail) at $220. The price difference is substantial without commensurate sound difference.
HD 660S2 (0) — the upgrade
The HD 660S2 is the most recent and most expensive of the three. Released 2023.
Sound signature: Similar overall character to HD 600 but with more bass extension, slightly improved detail retrieval, and somewhat increased dynamics.
Best at: All HD 600 use cases plus better bass-heavy music handling. Critical listening at higher levels.
Less ideal for: Pure budget-conscious purchases. The price premium over HD 600 is substantial.
What the upgrade is: Modest but real improvements in specific areas. Whether these improvements justify the price premium depends on individual use cases.
The amplification consideration
All three headphones have similar amplification needs:
300 ohm impedance (HD 600, HD 6XX). 150 ohm impedance (HD 660S2).
All benefit from substantial amplification with adequate voltage swing.
Smartphone outputs are typically inadequate. Decent amplification produces noticeable improvement.
None require expensive amplification — competent $200-300 amps are sufficient.
The amplification considerations are similar across the three. Budget for amplification regardless of which headphone you choose.
The sound differences in detail
Specific sonic comparison:
Bass response. HD 660S2 has noticeably better bass extension and impact. HD 600 and HD 6XX have similar bass quantity with HD 6XX being slightly more present in lower midrange.
Midrange. All three have excellent midrange. HD 600 is slightly more neutral; HD 6XX is slightly warmer; HD 660S2 has somewhat more sparkle.
Treble. HD 600 has slightly more treble presence than HD 6XX. HD 660S2 has somewhat more treble extension and detail.
Detail retrieval. HD 660S2 retrieves slightly more detail than HD 600 or HD 6XX. The difference is subtle.
Soundstage. All three have similar soundstage width. None is particularly wide; all are appropriate for headphones.
Dynamics. HD 660S2 handles dynamic transitions slightly better than HD 600 or HD 6XX.
The differences are real but not dramatic. All three are excellent headphones with subtle differences.
The build quality
Build quality across the three:
Materials are similar — primarily plastic with metal grilles and replaceable cables and pads.
HD 600 and HD 6XX use essentially identical construction (HD 6XX is HD 650 manufacturing).
HD 660S2 has slightly improved materials and finish.
All three are durable for sustained use across years.
Replaceable parts are available for all three from Sennheiser.
The build quality differences are modest. None of the three is fragile.
The use case recommendations
For specific use cases:
Studio reference / mixing: HD 600. The most neutral of the three. The reference standard.
Long listening sessions / general enjoyment: HD 6XX. Slightly relaxed character is comfortable for hours.
Best overall sound (price no object): HD 660S2. The improvements are real even if modest.
Best value: HD 6XX. Same essential character as more expensive alternatives at substantially lower price.
First serious headphone: HD 6XX. Outstanding value introduction to quality audio.
Bass-heavy music focus: HD 660S2. The improved bass response matters for this use case.
Acoustic / classical / vocal music focus: HD 600 or HD 6XX. The neutral midrange is excellent for this material.
Each scenario has a clear preferred choice.
Common questions
Q: Is the HD 6XX really the same as HD 650?
Yes. The HD 6XX is the HD 650 manufactured for Drop and sold at lower price. The internal design is identical.
Q: Why is HD 660S2 so much more expensive?
Newer release with somewhat better performance. Pricing reflects current Sennheiser positioning rather than dramatic improvement.
Q: Should I buy the HD 6XX over the HD 600?
If you don't need absolute neutrality, yes. The HD 6XX is essentially HD 650 sound at substantially lower price than either HD 600 or HD 650.
Q: Is the HD 660S2 worth the upgrade from HD 600?
For most listeners, no. The improvements are real but modest. The price premium is substantial.
Q: What about HD 800S?
Substantially different design (very wide soundstage, more analytical character). Different use case rather than upgrade in this lineup.
The honest assessment
All three headphones are excellent. The differences are real but modest.
For most buyers, HD 6XX represents the best value. The Drop exclusivity makes it require some additional planning, but the price-to-quality ratio is exceptional.
For buyers wanting maximum neutrality (mixing engineers, studio reference users), HD 600 remains canonical despite being older than HD 660S2.
For buyers wanting current-generation Sennheiser performance and willing to pay for it, HD 660S2 is the appropriate choice.
None of the three is a wrong choice. The decision depends on specific use case and budget.
Where to buy
For purchasing:
HD 600: Authorized Sennheiser dealers (B&H, Sweetwater, etc.) at consistent pricing.
HD 6XX: Drop exclusively. Drops periodically; sometimes on backorder.
HD 660S2: Authorized Sennheiser dealers.
Used markets have all three available, often at substantial savings. Verify condition and authenticity.
Long-term ownership
Considerations for long-term ownership:
All three benefit from periodic pad and cable replacement. Pads compress over time; cables can develop intermittent connection issues.
Sennheiser provides parts for sustained use across years.
The headphones themselves have no consumable components beyond pads and cables. Driver longevity is excellent.
Resale value is strong for all three. Used HD 600s from years ago still command meaningful prices.
Long-term ownership produces excellent value across decades of use.
The honest summary
Three excellent headphones with subtle differences. Each appropriate for different scenarios.
HD 6XX represents the best value of the three for most users. Same essential character as more expensive alternatives at lower price.
HD 600 remains the reference standard for buyers wanting maximum neutrality.
HD 660S2 is the appropriate current-generation choice for buyers wanting modest improvements at substantial price premium.
None of the three is a wrong choice. The choice depends on specific use case, budget, and whether Drop's exclusivity is acceptable.
Buy with confidence. The Sennheiser HD 6X0 series remains among the best headphone lines available regardless of price level.
That's the comparison. Pick the one that fits and stop overthinking.
