ATOHM Sirocco 1.24 Bookshelf Speaker

The Atohm Sirocco 1.24 bookshelf speaker is a study in refined performance, where meticulous French engineering meets timeless design. Crafted for listeners who value nuance as much as power, it delivers an effortlessly natural presentation with exceptional clarity, tonal balance, and dynamic control. Advanced proprietary drivers and a precisely tuned cabinet work in harmony to reveal the full emotional depth of music, from delicate textures to commanding crescendos.

Equipped with a lightweight 20 mm silk dome featuring progressive breakup characteristics, the WSD20DND04F tweeter incorporates an optimized waveguide crafted from die-cast molded aluminum. This construction eliminates vibrations and closely aligns the tweeter’s temporal origin with that of the C150 mid-woofer. Paired with a precisely calibrated phase equalizer, the design improves efficiency and delivers nearly constant directivity across the entire frequency range, ensuring refined and accurate sound reproduction.

The motor assembly, optimized through extensive dynamic simulations (FEA) and prototyping, features a dual neodymium ring made from ultra-high-grade ND52H material, generating a magnetic flux of 14,500 gauss within a tall gap. This configuration ensures excellent linearity (±0.25 mm excursion) and optimal thermal dissipation. A CCAW voice coil, shorter than the magnetic gap, combines low mass with high strength and is mounted on an ultra-thin aluminum former for improved rigidity and heat conduction. Ferrofluid further enhances thermal dissipation while contributing to damping.

The vented motor opens into an injection-molded aluminum rear chamber, which aids in heat dissipation and is precisely calibrated to absorb the rear wave. This design helps control excursion and reduce distortion at low frequencies outside the unit’s operational range.

With a high sensitivity of 97 dB (2.83 V / 1 m), this tweeter is engineered for exceptional performance and reliability. When integrated into a speaker system, its output level is intentionally attenuated by the crossover—by 4 to 8 dB, depending on the rear-panel switch setting—to match the accompanying mid-woofer. Since a tweeter’s thermal power handling is typically two to four times lower than that of a mid-woofer, this attenuation proportionally reduces the power delivered to the tweeter, harmonizing dynamics across the system.

This approach ensures optimal sound reproduction, minimizes distortion and thermal compression in the high-frequency range, and delivers consistent power handling across the full speaker bandwidth, enhancing overall system reliability while preserving signal accuracy.

Each component of this tweeter is manufactured with exceptional precision, and final assembly in our workshops receives meticulous attention to detail. Quality control includes a frequency sweep test and five additional measurements performed in a mini anechoic chamber. These procedures allow the tweeters to be classified by sensitivity and matched to within ±0.25 dB before integration into the loudspeaker system.

One of the earliest ATOHM® drivers, the LD130, was originally developed in 2000–2001. The new C150 DCR units draw inspiration from this landmark design, retaining its fundamental characteristics, including intended application, diameter, basket mounting, membrane type, and ferrite-based motor structure. Building on decades of accumulated expertise and utilizing modern development tools, the driver and all of its components have been completely reengineered to deliver performance that surpasses its predecessor in every respect.

Balancing stiffness, low mass, and effective damping, the new units employ a specialized “paper” cone constructed from oriented short fibers. A dedicated rear treatment complements this design by optimizing and controlling cone breakup at higher frequencies. The result is improved response linearity and a crossover tuning process that is both more precise and more efficient.

The NBR rubber surround integrates LDS™ (Low Diffraction Surrounding) technology, allowing for progressive breakup behavior in the midrange and contributing to a smoother, more linear frequency response. Its carefully optimized geometry maintains symmetrical stiffness during high-excursion operation while simultaneously reducing overall moving mass.

Drawing on extensive experience and advanced electromagnetic simulations (F.E.A.), the motor assembly incorporates an 84 mm ferrite magnet, optimized pole pieces, and a 25 mm voice coil. This geometry maximizes magnetic flux concentration within the gap, ensuring a high, stable, and symmetrical force factor (BL) across a wide excursion range. The result is bass reproduction that is both exceptionally powerful and remarkably clean, free from unwanted artifacts.

• Speaker Type: 2-way bass reflex bookshelf speaker
• Sensitivity: 88 dB (2.83 V / 1 m)
• Nominal Power Handling (IEC 60268, 100 h): 100 W (effective)
• Short-Term Power Handling (IEC 60268, 1 s, 80 Hz–20 kHz): 270 W (effective, 40 V)
• Maximum Short-Term SPL (IEC 60268, 1 s, 80 Hz–20 kHz, 40 V): 110 dB SPL
• Nominal Impedance: 6 Ω (minimum 4.4 Ω @ 200 Hz)
• Frequency Response: 46 Hz – 25 kHz
• Crossover Frequency: 3.5 kHz
• Midbass Driver: C150 DCR 04
• Tweeter: WSD20 DND 04F
• Crossover Slope: First-order with impedance compensation
• Cabinet Construction: 18 mm MDF
• Finish Options: True wood veneer or white satin varnish
• Dimensions (W × H × D): 180 × 345 × 260 mm (7.08 × 13.6 × 10.3 in)
• Weight: 7 kg (15.43 lbs)