Overview

The PSB CS850 is a two-way in-ceiling speaker designed to deliver extended bass in large rooms. It uses an 8-inch carbon-loaded polypropylene woofer and a 1-inch titanium tweeter with a waveguide. Developed from over 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, enabling high sensitivity and reduced harmonic distortion at various listening levels.

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Uncompromising acoustic design

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

The 25 mm titanium dome tweeter is a technological feat in itself. 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 uniform sound quality. This waveguide technology, directly derived from research conducted on the Imagine T3 series, minimizes off-axis colorations 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 the tweeter. This carefully chosen crossover frequency allows each transducer to operate within its optimal comfort zone, thereby maximizing overall performance while minimizing intermodulation distortion. The “Open Back” acoustic design facilitates integration in various installation environments, allowing the speaker to naturally adapt to the ceiling’s acoustic characteristics without creating unwanted resonances in the cavity.

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Adjustability and sound customization

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

Two-position switches for the tweeter and woofer offer fine control over tonal balance. Each switch lets you choose between a neutral setting (0 dB) and a boosted setting (+3 dB), allowing four different combinations to tailor the frequency response to the room’s acoustic characteristics or personal preferences. This flexibility helps compensate for variations in acoustic absorption due to construction materials, furnishings, or the specific geometry of the listening space.

The tweeter’s indexed adjustment system deserves special attention. Unlike simple rotating systems, this mechanism locks the tweeter into predefined positions, ensuring precise and repeatable orientation. This precision in acoustic aiming significantly improves stereo imaging and localization of sound sources—crucial aspects for convincing musical reproduction or cinematic surround effects.

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Streamlined professional installation

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

The required 245 mm cutout diameter and 111 mm mounting depth conform to industry standards, making it easier to replace or upgrade existing installations. Spring-loaded terminals accept different connection types: bare wire up to 12 AWG, pin connectors, or single banana plugs, offering maximum flexibility based on installation preferences and existing wiring constraints.

The frameless magnetic grilles are another example of attention 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 firmly 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; spraying is recommended to achieve a professional finish.

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Comparison with the CS810 model

While sharing many features with its CS810 counterpart, the CS850 distinguishes itself with several significant enhancements that justify its premium positioning. The CS850’s cast steel woofer basket, as opposed to the CS810’s stamped basket, offers superior rigidity and better thermal dissipation. This more robust construction results in increased power handling and reduced distortion during demanding dynamic passages.

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

The superior components used in the CS850, directly derived 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 clarity and definition at high listening levels, where less sophisticated speakers would begin to show signs of compression or distortion.

Frequently Asked Questions

What is the main difference between the CS850 and other PSB in-ceiling speakers?

The CS850 stands out with its premium components directly derived from the Imagine T3 series, including its titanium tweeter with ferrofluid and its cast-basket woofer. These elements give it superior sensitivity (86 dB in an anechoic chamber) and the ability to maintain low distortion even at high listening levels. Multiple adjustment options, including indexed tweeter orientation and dual level switches, offer customization not possible with more affordable models.

What amplifier power is recommended for the CS850?

PSB recommends amplifier power between 10 and 100 watts for the CS850. With a nominal impedance of 6 ohms (minimum 4 ohms), the speaker presents a relatively easy load for most amplifiers. A quality amplifier of 30 to 50 watts per channel is more than sufficient for normal home listening, while installations requiring higher sound pressure levels will benefit from more powerful amplifiers, up to 100 watts.

How can I optimize the CS850’s positioning and settings?

Aim the tweeter toward the main listening area using the indexed mechanism. For highly reverberant rooms, start with the level switches in the neutral position (0 dB) and adjust gradually according to your preferences. In heavily damped spaces or with very high ceilings, increasing the tweeter level (+3 dB) can restore lost liveliness. Acoustic measurements with a calibration microphone can help fine-tune the settings precisely.

Can the grilles really be repainted without affecting performance?

The CS850’s steel grilles are specifically designed to be repainted. PSB recommends spraying rather than applying with a brush or roller to maintain the necessary acoustic porosity. A light application in several thin coats preserves the acoustic characteristics while allowing a perfect visual integration. The magnetic grilles make removal for painting and reinstallation easy without risk of damage.

What is the minimum ceiling depth required for installation?

The CS850 requires a mounting depth of 111 mm (4 3/8”). Additional space should also be provided for wiring and ventilation, bringing the total recommended space to about 150 mm minimum. Ceilings with insulation or vapor barriers require special attention to avoid any direct contact with the back of the speaker, which could affect acoustic performance or create unwanted vibrations.

Is the CS850 compatible with modern home automation systems?

While the CS850 is a traditional passive speaker, it integrates perfectly into home automation systems via compatible amplifiers. Multichannel amplifiers with IP control or digital audio matrices make it possible to integrate CS850s into sophisticated systems with app control, intelligent zoning, and DSP processing. The speaker’s superior quality ensures it will fully reveal the benefits of these advanced systems.