ZMF Caldera Closed: A Technical & Musical Analysis
(Photo source: ZMF official page)
Introduction & Context
Transparency in audio reviewing requires proper context. I've known Zach Mehrbach, ZMF's founder, for several years, initially as a customer before developing a professional relationship through forum interactions and eventual friendship. This connection, while common in our specialized audio community, warrants disclosure as we examine these headphones.
The Caldera Closed under review is a standard production unit on loan from ZMF. Over two and half months, I've accumulated approximately 200 hours with them through systematic evaluation: protocol-based analytical sessions, comparative listening, pad rolling experiments, and amplifier pairing tests. My evaluation aims to present findings that would help readers make informed decisions about a significant investment.
Technical Framework
- Design: Closed-back planar magnetic headphones
- Impedance: 60Ω
- Sensitivity: ~94dB/mW
- Weight: 545g (without cables)
- Price: $3,500 (as reviewed)
Physical Analysis
Design & Construction
Initial examination of the Caldera Closed reveals two significant aspects. The Shou Sugi Ban ash wood cups represent a departure from typical ZMF aesthetics. This Japanese wood-charring treatment creates distinct visual patterns and potentially serves acoustic purposes, though the latter would require objective verification.
The distinctive raised triangular section on the cups warrants analysis. While visually striking compared to ZMF's typically organic designs, its functional aspects deserve consideration. The shape provides natural grip points for handling and may contribute to acoustic management, though without access to development data, such conclusions remain speculative.
The build emphasizes serviceability – all wear components (pads, strap, cables) are user-replaceable. The aluminum frame provides structural integrity while controlling overall mass, though the rod blocks require more frequent adjustment than lighter models.
The mini-XLR connectors demonstrate proper strain relief and maintain connection integrity through repeated cable changes. Both provided cables (balanced and single-ended OFC) offer adequate flexibility and strain relief, with the balanced option showing marginally better handling characteristics.
Comfort & Ergonomics
The 545g (w/o cable) mass presents definite ergonomic considerations. Extended testing reveals how weight distribution affects long-term wearability. The suspension strap system (standard version tested) manages mass distribution effectively, though not completely. After approximately 50 hours of use, adaptation to the weight occurs, but awareness of it remains.
The stock hybrid pads employ an asymmetrical design: thicker rear sections create natural angles for head anatomy. Their dual-material construction (leather exterior, suede interior) demonstrates reasonable thermal management for a closed design, though heat buildup during extended sessions remains noticeable.
Temperature management represents an inherent challenge of the closed architecture. Regular breaks (every 2-3 hours) prove beneficial during long sessions, particularly in warmer environments. The cup design's raised sections provide practical benefits for handling and positioning adjustments.
Technical Implementation
The Caldera Closed's development presents interesting technical challenges. Converting an open planar magnetic design to closed-back architecture involves more than simple enclosure. Key engineering hurdles include:
- Managing resonances in the closed chamber
- Controlling internal reflections
- Maintaining planar driver speed characteristics
- Achieving effective isolation without compromising dynamics
Measurements
(Note: I am planning to disseminate measurements and analyses in separate reports. Hence, only summary is provided in this review.)
Using calibrated testing equipment under controlled conditions reveals several key characteristics. Frequency response shows controlled behavior with slight lower-midrange dip (250-400 hz) and some brilliance emphasis (around 6.5 khz). Distortion remains very low at normal to very loud listening levels, increasing predictably but not dramatically at higher volumes. The extended high-frequency response matches category expectations, while impedance behavior indicates good amplifier compatibility.
Sound Performance
Frequency Response & Tonal Balance
The low frequency performance, assessed through Massive Attack's "Paradise Circus," demonstrates the closed-back implementation's bass control capabilities. The descending bass line maintains clear definition while coexisting harmoniously with vocals, suggesting effective management of the closed chamber's typical resonance challenges. Bass presents with full frequency extension without resorting to obvious emphasis of any particular region.
Christian McBride's "Night Train" provides deeper insight into the planar driver's transient behavior. String attacks show clear articulation, while the resonant body of the acoustic bass maintains natural decay characteristics. The distinction between fingered notes and thumb-played passages remains clear throughout, indicating capable speed characteristics without artificial emphasis of leading edges.
Midrange evaluation through Diana Krall's "Peel Me A Grape" reveals interesting characteristics. Vocals occupy a slightly less forward position compared to some competitors, though they maintain proper scale and timbral accuracy. Piano harmonics demonstrate good resolution, albeit with somewhat less immediacy than observed in the open-back version. During analysis of Leonard Cohen's "You Want It Darker," male vocals exhibit proper fundamental weight and chest resonance. The closed architecture appears well-damped, avoiding both the artificial emphasis that can affect closed-backs and the thinness that can compromise vocal authenticity.
High frequency behavior, examined through Bill Stewart's "Telepathy," shows thoughtful implementation. Cymbal textures maintain proper metallic character while suggesting effective management of the closed chamber's potential reflection issues. The high-frequency presentation remains extended without introducing artificial edge. Hilary Hahn's Bach Violin Sonatas serve as an effective examination of upper register reproduction. Violin overtones maintain proper brilliance while keeping bow noise proportionate to fundamental tones - a particularly challenging balance for closed-back designs.
Spatial Presentation
Spatial reproduction, observed through Bill Evans' "Sunday at the Village Vanguard," reveals careful attention to imaging characteristics. The recording's complex spatial cues remain intact, with Paul Motian's brushwork and Scott LaFaro's bass lines occupying distinct positions. The presentation shows good organization within closed-back constraints. Hans Zimmer's "Time" from Interstellar tests the design's ability to maintain separation during complex passages. While soundstage width necessarily differs from open-back designs, depth layering remains well-defined. The presentation varies appropriately with different recordings rather than imposing a consistent artificial perspective.
Dynamic Performance
Dynamic response testing through systematic evaluation reveals nuanced performance characteristics. Micro-dynamic capability shows clearly through subtle drum brush work in "Blue in Green," where fine detail remains evident without artificial emphasis. Natural decay characteristics are preserved, with good distinction between similar intensity levels.
Macro-dynamic performance, evaluated through Mahler's Symphony No. 3 (Zander/Philmarmonia Orchestra), demonstrates competent handling of orchestral crescendos without obvious compression. The headphone maintains instrument separation during complex passages, though some amplifier dependency becomes apparent during extreme peaks.
Recording Format Response
Through systematic testing across various source qualities, the Caldera Closed exhibits noteworthy format-dependent behavior. Contemporary high-resolution recordings, such as the 192/24 masters of Keith Jarrett's solo works, reveal the headphone's capability for portraying subtle ambient cues without emphasizing technological artifacts. The ability to maintain musical coherence while exposing recording-chain differences proves particularly useful for critical listening tasks.
Standard commercial releases from the past decade demonstrate the headphone's handling of modern production techniques. Daft Punk's "Random Access Memories" serves as an excellent example, where heavily processed elements coexist with live instrumental recordings. The Caldera Closed maintains separation between these elements while preserving the intended blend of synthetic and organic sounds.
Older recordings, particularly those from the early digital era, expose the headphone's treatment of compromised source material. Early CD releases of Deutsche Grammophon classical recordings retain their fundamental musical value despite their technical limitations. The Caldera Closed reveals these limitations honestly without rendering the recordings unenjoyable - a delicate balance that speaks to thoughtful voicing decisions.
Practical Considerations
Long-Term Usage Patterns
Extended use over two months reveals performance characteristics that might escape notice in shorter evaluation periods. Regular listening sessions averaging 3-4 hours provide particular insight into practical usability patterns.
Morning sessions typically allow longer continuous use, as ambient temperature significantly affects comfort duration. A typical three-hour session might require one brief break, though this pattern varies with room temperature and individual sensitivity.
Professional use scenarios present specific considerations. The isolation proves sufficient for most studio environments, while detail retrieval supports critical listening tasks. However, the physical mass may affect productivity during extended professional sessions. The protective case supports occasional transport between locations, though size and weight suggest these headphones are best suited for dedicated listening spaces rather than frequent movement.
System Integration
Testing with various amplifiers reveals notable characteristics despite moderate specified requirements. Through the Topping DX9's balanced output, performance proves adequate for most material, though complex orchestral crescendos suggest potential benefits from better amplification like higher end tube amplifiers (generally good at large signals).
The Cayin HA-300B MK2's transformer-coupled tube design shows good control despite higher output impedance, surprising me at macrodynamics, though bass definition softens slightly compared to solid-state options. The Pendant SE proves particularly successful with acoustic material in more tasteful and nuanced timbre (one of my favorites in this respect), though the solid-state Topping DX9 and LA90 maintains better control across a broader material range. Perhaps most telling, the Schiit Magnius demonstrates respectable performance despite its price differential, suggesting reasonable amplification flexibility.
Relatively flat impedance (usual for planarmagnetic headphones) may indicates minimal interaction with output impedance, though current delivery (in quality, not quantity) appears more critical than voltage swing for optimal dynamic performance.
Extended testing with various components reveals specific matching characteristics. DAC pairing shows solid synergy with both ESS-based and AKM-based delta-sigma designs, while the differences to advanced R2R (Rockna Wavedream Signature) or Pulse-Array (Chord Dave) implementations remain audible. Output impedance sensitivity proves relatively low, though current delivery capability in amplification proves more critical than pure voltage swing. Experience suggests optimal performance with output impedance below 2 ohms.
Cable response reveals subtle subjective differences but are unmeasurable with my devices. The balanced connection appears to demonstrate some advantages in perception, while shield quality shows correlation with presumably achieved noise floor. Overall, these differences, while present, remain subtle compared to amplification changes.
Pad Variants
Systematic pad variant testing reveals consistent effects on performance. The stock hybrid configuration, combining leather and suede, achieves the most balanced frequency response while maintaining good isolation characteristics and consistent seal. Protein leather variants increase bass impact and push the upper mids slightly forward, though at the cost of higher thermal buildup. Full suede options relax the upper midrange and improve thermal characteristics but require more frequent positioning adjustments to maintain optimal seal.
Market Context
Competitive Analysis
Direct comparison with contemporary alternatives reveals different approaches to similar challenges. The Dan Clark Audio Stealth, positioned slightly higher at $4,000, demonstrates an alternative solution to closed-back planar magnetic design. Each shows distinct priorities in resolution, dynamics, and comfort implementation. The Caldera Closed might be preferred if you want more tight, punchy, and less damped sounding while the Stealth have some merits on neutral balance and are marginally better in detail retrievals. Comparison with dynamic driver alternatives like the ZMF Verite Closed (at $2,500) or Focal Stellia (at $3,000) highlights CC's technical excellence of planar drivers in resolving details and spatial cues at a cost of weight.
Value Proposition
The current market position of the Caldera Closed warrants careful examination. At $3,500, these headphones compete in a segment where technical excellence is expected. The build quality and material choices align with price expectations, while the serviceable design supports long-term ownership value. The inclusion of multiple pad options and potential future mesh variations suggests a product ecosystem that extends beyond initial purchase.
Within ZMF's own lineup, the Caldera Closed represents a distinct technical approach from their dynamic driver designs. The price positioning above the Verite Closed reflects increased manufacturing complexity and different performance priorities rather than strictly hierarchical improvement.
Conclusion
The Caldera Closed demonstrates successful implementation of planar magnetic technology within closed architecture constraints. Rather than attempting to completely overcome the inherent challenges of closed-back design, it presents thoughtful compromises that maintain musical engagement while providing practical isolation.
Primary strengths emerge in low-frequency control, coherent frequency balance, and effective isolation without severe technical compromise. The build quality and serviceability support long-term ownership, while pad options allow meaningful user adjustment. Thermal and weight characteristics require accommodation but prove manageable with appropriate usage patterns.
For prospective buyers, the decision framework should consider several factors. The intended usage environment impacts the value of isolation versus potential comfort adaptation. System matching, particularly in amplification, influences the realization of performance capabilities. Climate considerations affect comfort during extended sessions, while the long-term ownership perspective might justify the premium price position.
The Caldera Closed serves as a statement about balancing multiple technical challenges while maintaining musical engagement. Its success lies not in achieving ultimate performance in any single criterion, but in presenting a carefully considered set of compromises that serve practical listening needs without severe technical limitations.
Reference
Associated Equipment Used
- Primary Chain: Topping DX9 DAC/Amplifier
- Alternative Amplification: Topping LA90 Integrated Amplifier, Cayin HA-300B MK2, ZMF Pendant SE, Schiit Magnius
- Alternative Digital Source Converter: Chord Dave, Rockna Wavedream Signature
- Other Headphones: ZMF Caldera (open), Dan Clark Audio Stealth, Hifiman Susvara
- Measurement Equipment: MiniDSP EARS, SMSL M500 Mk3, SMSL HO200
Key Reference Recordings
- Diana Krall - "Peel Me A Grape"
- Massive Attack - "Paradise Circus"
- Bill Evans - "Sunday at the Village Vanguard"
- Mahler Symphony No. 3 (Zander/Philmarmonia Orchestra)
- Tool - "Fear Inoculum"
- Christian McBride - "Night Train"
- Hilary Hahn - Bach Violin Sonatas
- Hans Zimmer - "Time" (Interstellar)
- Leonard Cohen - "You Want It Darker"
- Bill Stewart - "Telepathy"