PSB CS850

The PSB CS850 is a two-way in-ceiling speaker designed to deliver extended bass in large rooms. It uses an 8-inch carbon-filled polypropylene woofer and a 1-inch titanium tweeter with waveguide. Developed based on more than 45 years of acoustic research in the anechoic chambers of the National Research Council of Canada, it shares certain components with the Imagine T3 floorstanding speaker, delivering high sensitivity and reduced harmonic distortion at different listening levels.

Uncompromising acoustic design

The CS850 stands out with its 203 mm carbon-filled polypropylene woofer, mounted on a stamped steel basket with foam surround. This combination of carefully selected materials provides optimal cone rigidity while minimizing unwanted resonances. Carbon-filled polypropylene offers a particularly favorable stiffness-to-weight ratio, allowing the cone to respond accurately to transient signals while maintaining excellent power handling. The foam surround contributes to linear cone movement, ensuring faithful low-frequency reproduction down to 45 Hz.

The 25 mm titanium dome tweeter is a technological achievement in its own right. Ferrofluid-cooled and equipped with a high-temperature neodymium magnet, it reproduces high frequencies up to 20 kHz with remarkable clarity. The integrated waveguide optimizes horizontal and vertical dispersion, creating an expanded listening area where every listener benefits from consistent sound quality. This waveguide technology, derived directly from research conducted for the Imagine T3 series, minimizes off-axis coloration while maintaining exemplary tonal consistency throughout the room.

The 3,100 Hz crossover uses a fourth-order Linkwitz-Riley (LR4) topology, ensuring perfectly smooth transitions between the woofer and tweeter. This carefully selected crossover frequency allows each driver to operate within its optimal comfort zone, maximizing overall performance while minimizing intermodulation distortion. The “Open Back” acoustic design facilitates integration into different installation environments, allowing the speaker to adapt naturally to the acoustic characteristics of the ceiling without creating unwanted resonances in the cavity.

Adjustability and sound customization

One of the CS850’s most remarkable features lies in its sophisticated adjustment options. The tweeter features an indexed positioning mechanism that allows the acoustic axis to be precisely aimed toward the listening area. This feature is particularly useful in configurations where the speakers cannot be positioned directly above listeners, or when increased directivity is desired for certain home theater applications.

Two-position switches for the tweeter and woofer provide fine control over tonal balance. Each switch allows you to choose between a neutral position (0 dB) and a boosted position (+3 dB), enabling four different combinations to adapt the frequency response to the room’s acoustic characteristics or personal preferences. This flexibility makes it possible to compensate for variations in acoustic absorption caused by building materials, furniture, or the specific geometry of the listening space.

The tweeter’s indexed adjustment system deserves special attention. Unlike simple rotary systems, this mechanism allows the tweeter to be locked into predefined positions, ensuring precise and repeatable orientation. This accuracy in acoustic aiming significantly improves stereo imaging and sound source localization, crucial aspects for convincing music reproduction or cinematic surround effects.

Simplified professional installation

PSB has paid particular attention to the CS850’s ease of installation. The mounting system uses high-strength Delrin rotating mounting tabs (doglegs), operated by a rotary cam mechanism. This ingenious design enables secure installation with a simple screwdriver, with the cams locking firmly against the rear surface of the ceiling. The system’s robustness ensures long-lasting fastening, even with the speaker’s substantial weight (2.67 kg).

The required 245 mm diameter cutout and 111 mm mounting depth meet industry standards, making replacements or upgrades to existing installations easier. The spring terminals accept different types of connections: bare wire up to 12 AWG, pin connectors, or single banana plugs, offering maximum flexibility depending on installation preferences and existing wiring constraints.

Frameless magnetic grilles are another example of the attention given to practical details. Available in round (270 mm diameter) and square (272 mm) versions, they suit different aesthetic preferences. High-strength magnets hold the grilles securely in place while allowing easy removal for access to adjustments or maintenance. Made of painted steel, these grilles can be repainted to blend perfectly with the ceiling, with spray painting recommended for a professional finish.

Comparison with the CS810 model

Although it shares many characteristics with its CS810 counterpart, the CS850 stands out through several significant improvements that justify its premium positioning. The CS850 woofer’s cast steel basket, as opposed to the CS810’s stamped basket, offers greater rigidity and better heat dissipation. This more robust construction results in increased power handling and reduced distortion during demanding dynamic passages.

The CS850’s ferrofluid-cooled titanium tweeter also surpasses the CS810’s aluminum tweeter in terms of high-frequency extension and heat dissipation capability. Ferrofluid not only improves voice coil cooling but also contributes to mechanical damping, reducing unwanted resonances and improving response linearity.

The higher-quality components used in the CS850, derived directly from Imagine T3 technology, achieve higher sensitivity and lower harmonic distortion than other models in the CustomSound 800 series. This difference is particularly evident in the CS850’s ability to maintain its clarity and definition at high listening levels, where less sophisticated speakers would begin to show signs of compression or distortion.

Technical Specifications

Highlights

• Deep bass: 203 mm polypropylene/carbon woofer with foam surround
• Detailed treble: 25 mm titanium tweeter with ferrofluid and waveguide
• Wide frequency response: 45 Hz – 20 kHz
• Precise tuning: switches for woofer and tweeter, indexed tweeter positioning
• 3,100 Hz LR4 crossover: smooth, balanced transitions
• Easy installation: sturdy mounting clamps, round and square magnetic grilles
• Discreet design: blends seamlessly into the ceiling

Acoustic Performance

• On-axis frequency response at 0° ±3 dB: 45 – 20,000 Hz
• Sensitivity
  • Anechoic: 86 dB
  • Listening room: 88 dB

Electrical Specifications

• Impedance
  • Nominal: 6 Ω
  • Minimum: 4 Ω
• Recommended amplifier power: 10 – 100 W

Acoustic Design

• Tweeter: 25 mm titanium dome with ferrofluid
• Woofer: 203 mm black polypropylene cone, stamped steel basket, foam surround
• Crossover: 3,100 Hz, LR4
• Type: open-back

Dimensions and Installation

• Ceiling cutout: 245 mm
• Mounting depth: 111 mm
• Round grille: 270 mm
• Net weight: 1.47 kg per speaker

Finish

• White with included round and square paintable grilles