KEF Ci4100QL-THX THX Certified Select In-Wall Speaker

THX-Certified In-Wall Sound for a Clean Home Theater Front Stage

The KEF Ci4100QL-THX is a passive in-wall architectural speaker sold individually for left, center, right, and surround-channel use in home theater systems. Its slim rectangular format combines KEF's Uni-Q technology with three additional 4" low-frequency drivers to deliver strong output from a discreet wall installation.

KEF classifies the Ci4100QL-THX as THX Certified Select, making it a strong fit for dedicated theater rooms and media spaces where accurate tonal balance, broad coverage, and a clean architectural finish are priorities.

Key Specifications

• Sold as: One speaker
• Speaker type: Passive in-wall architectural speaker
• THX certification: THX Certified Select
• LF drivers: 3 × 100 mm (4")
• Uni-Q midrange: 100 mm (4")
• HF driver: 19 mm (0.75")
• Nominal impedance: 4 Ω
• Sensitivity: 89 dB (2.83 V / 1 m)
• Frequency response: 55 Hz–28 kHz (±6 dB, open-backed)
• Frequency range: 40 Hz–30 kHz (-10 dB)
• Crossover frequency: 2.2 kHz
• Recommended amplifier power: 10–150 W
• Recommended high-pass filter: 55 Hz
• Nominal coverage: 150°
• Maximum SPL: 104 dB
• Certification: THX Certified Select, IP64

Who Should Choose the Ci4100QL-THX?

Choose the Ci4100QL-THX when you want a discreet in-wall speaker for a serious home theater system without using visible cabinet speakers. It can be used for left, center, right, or surround channels depending on your room layout and processor configuration.

Using matching Ci4100QL-THX speakers across the front stage can help maintain consistent tonal character between left, center, and right channels.

Passive Speaker and Amplifier Requirements

The Ci4100QL-THX is completely passive and requires an external amplifier or AV receiver. It does not include Bluetooth, Wi-Fi, streaming, app control, or built-in amplification.

KEF recommends 10–150 W of amplifier power and specifies a 4-ohm nominal impedance. Use a compatible AV receiver or amplifier that is designed to operate safely with 4-ohm speakers at your intended listening level and channel count.

The 10–150 W figure is KEF's recommended amplifier range, not an RMS or peak power-handling rating.

Four 4-Inch Drivers With Uni-Q

The Ci4100QL-THX uses three 4" low-frequency drivers plus a separate 4" Uni-Q midrange driver with a 0.75" tweeter positioned at its acoustic center.

This arrangement allows KEF to combine broad dispersion from the Uni-Q section with additional low-frequency driver area in a narrow in-wall format.

150-Degree Coverage

KEF specifies approximately 150° nominal coverage, helping the Ci4100QL-THX distribute sound across a broad seating area rather than focusing output into a narrow listening position.

Frequency Response and System Setup

KEF specifies an open-backed frequency response of 55 Hz–28 kHz at ±6 dB and a broader 40 Hz–30 kHz range at -10 dB. KEF recommends a 55 Hz high-pass filter.

For home theater, a dedicated subwoofer is still recommended for low-frequency effects and deeper bass below the speaker's operating range. Browse Subwoofers for compatible options.

Installation Dimensions

• External dimensions: 490 × 128 × 81 mm (19.29" × 5.04" × 3.19")
• Cutout: 476 × 114 mm (18.74" × 4.49")
• Mounting depth: 76 mm (3.0")
• Net weight: 3 kg (6.61 lb)

Confirm stud spacing, wall depth, electrical wiring, plumbing, insulation, and speaker-wire routing before cutting the wall opening.

Optional Rough-In Frame and Rear Volume

KEF lists the RIF4100L as the optional rough-in frame for the Ci4100QL-THX. It is sold separately.

KEF specifies approximately 15 liters as the ideal rear volume and 7 liters as the minimum rear volume.

IP64 Environmental Protection

The Ci4100QL-THX is also IP64 certified. This provides protection against dust and splashing water but does not make the speaker waterproof or suitable for immersion.

Ultra-Thin Bezel and Paintable Grille

KEF's Ultra-Thin Bezel design keeps the visible rim narrow, while the grille can be painted to better match the surrounding wall finish.

What's Included?

• 1 KEF Ci4100QL-THX in-wall speaker
• Paintable grille
• Integrated mounting system
• Product documentation

The amplifier or AV receiver, speaker wire, RIF4100L rough-in frame, subwoofer, and other installation materials are sold separately.

Complete Your Home Theater System

• In-Wall & In-Ceiling Speakers
• AV Receivers & Surround Sound
• Subwoofers

Need Help Planning Your Theater?

Send Bear Security Shop your AV receiver or amplifier model, room dimensions, planned speaker quantity, and front-stage layout. We can help check 4-ohm compatibility, cutout requirements, amplification, and whether the Ci4100QL-THX is the right fit for your system.

Is the KEF Ci4100QL-THX sold individually?

Yes. KEF USA currently lists the Ci4100QL-THX per each.

Is the Ci4100QL-THX THX Select2 certified?

No. KEF's current official terminology is THX Certified Select.

Can it be used as a left, center, or right speaker?

Yes. The Ci4100QL-THX can be used in left, center, right, or surround-channel positions depending on your theater layout.

Is the Ci4100QL-THX powered or passive?

It is passive and requires an external amplifier or AV receiver plus speaker wire.

What amplifier power does KEF recommend?

KEF recommends 10–150 W of amplifier power. This is an amplifier recommendation, not an RMS or peak power-handling rating.

What is the impedance?

The Ci4100QL-THX has a 4-ohm nominal impedance. Confirm that your amplifier or AV receiver supports 4-ohm speakers.

What is the frequency response?

KEF specifies 55 Hz–28 kHz at ±6 dB open-backed and a 40 Hz–30 kHz range at -10 dB.

How wide is the coverage?

KEF specifies approximately 150° nominal coverage.

What is the maximum SPL?

KEF specifies a maximum SPL of 104 dB.

What high-pass filter does KEF recommend?

KEF recommends a 55 Hz high-pass filter.

What cutout size is required?

The Ci4100QL-THX requires an opening approximately 18.74" high × 4.49" wide.

How much mounting depth is required?

KEF specifies approximately 3.0" of mounting depth.

Is a rough-in frame available?

Yes. KEF lists the RIF4100L as the optional rough-in frame. It is sold separately.

What rear volume does KEF recommend?

KEF specifies approximately 15 liters as ideal rear volume and 7 liters as the minimum.

Is the Ci4100QL-THX IP rated?

Yes. KEF's current architectural specification sheet lists the Ci4100QL-THX as IP64. It should not be described as waterproof.

What should I confirm before ordering?

Confirm speaker quantity, 4-ohm amplifier compatibility, the 18.74" × 4.49" cutout, 3.0" mounting depth, available wall cavity volume, and speaker-wire routing.