In-ceiling Speakers

KEF Expands Its Extreme Home Theater Line With In-Ceiling MAT-Enabled Speaker and Subwoofer

So if you are looking for a new, small, discrete THX-certified Ultra in-ceiling speaker or subwoofer for your home theater, rejoice! Because KEF has expanded its Extreme Home Theater line with a new MAT-enabled in-ceiling speaker plus an in-ceiling subwoofer. The new Ci250RRM-THX is a three-way, THX-certified coaxial speaker, and their Ci250RRb-THX is a high output, in-ceiling architectural THX-certified subwoofer. And as a reminder, Kef uses MAT (Metamaterial Absorption Technology) in its LS50/LS60 Meta and Reference and Blade series. And right now MAT is one of the hot “must-have’s” in the high-end audio world. Very timely for this new series.

So should these be on your shopping list? Let’s discuss.

KEF Ci250RRM-THX In-Ceiling

The Ci250RRM-THX ($2200 ea) is KEF’s first architectural speaker with MAT or Metamaterial Absorption Technology. KEF claims that MAT will absorb up to 99% of unwanted sound within the speaker, translating to deeper and richer sound. For an in-ceiling speaker, I can see this being a great benefit. 

KEF also paired MAT with their patent-pending Cavity Radiation Control and Low Diffraction LF Aperture. KEF claims that Cavity Radiation Control has solved the midrange issues in typical three-way coaxial loudspeakers. Its unique open-backed midrange with acoustically absorptive foam design eliminates midrange issues. This includes frequency response dips of up to 30dB in magnitude – a reduction of 99.9% SPL. With Cavity Radiation Control, Ci250RRM-THX promises to deliver the highest midrange acoustic realism among three-way coaxial loudspeakers.

Low Diffraction LF Aperture is “a carefully profiled, smoothed housing design with an outer acoustically absorptive foam ring that reduces resonance and diffraction. As a result, it delivers exceptional MF/HF performance while preserving a tremendous bass output.” So the long and short of the new tech is absorbing unwanted noise and creating a more precise and realistic sound.

And because this is a KEF speaker, it uses their Uni-Q Array. The 12th Generation driver uses a 10″ driver, paired with a 4″ midrange and 0.75″ tweeter. The speaker is 89dB sensitive and claims an open-backed frequency response of 28Hz to 20kHz. 


Model Ci250RRM-THX
Series Ci-R Series
Nominal impedance 
Sensitivity (2.83V/1m) 89dB 
Frequency response (±6dB) open-backed 28Hz – 20kHz 
Frequency range (-10dB) 20Hz – 45kHz 
Nominal coverage 120° 
Max SPL 111dB 
Crossover frequency 540Hz, 2.6kHz 
LF Driver250mm (10 inch) 
MF Driver100mm (4 inch) Uni-Q 
HF Driver19mm (0.75 inch) vented aluminum dome with Metamaterial Absorption Technology
Recommended amplifier power 50 – 250W 
Recommended high-pass filter (Hz) 30 – 60Hz 
Product external dimensions 346mm (13.62 inches.) 
Cut-out dimensions 175mm (6.89 inches.) 
Net Weight  6kg (13.2lbs) 
Mounting depth from surface 168mm (6.62in.) 
Optional rough in frame 
Ideal rear volume 150L
Minimum rear volume 80L
THX certification THX® Certified Ultra
Safety and Regulatory Compliance IP64
Ceiling thickness (Maximum) 30mm (1.18 inches) 
Ceiling thickness (Minimum) 6mm (0.24 inches) 

Ci250RRb-THX In-Ceiling Subwoofer

The KEF Ci250RRb-THX Subwoofer ($1500 ea) claims to deliver accurate and powerful bass. The Ci250RRb-THX features a 10″ bass driver with a 150oz magnet with a throw distance of 10″. KEF claims a low-frequency extension of 20Hz. So what does that mean for you? This driver will move a lot of air inside your attic and should hit like a sledgehammer! Just remember that this is a passive subwoofer. You’ll need to add an amp. KEF has an amp that can power up to two of these subs for $1100. If you power just one, it will achieve THX Ultra output. If you power two, it can only get loud enough to receive THX-Select certification. For more information on THX certification, check out our article here.

Designed with an ultra-thin bezel and a magnetic, paintable grill like the Ci250RRM-THX, the Ci250RRb-THX should blend in with any decor. And like the Ci250RRM-THX, both are IP64 certified, dust-proof, and splash-resistant. I would never have thought I wanted a splash-proof speaker until I had kids (and friends who like to party)! With the possibility of roof leaks, a water-resistant speaker makes sense.


Model Ci250RRb-THX
Series Ci-R Series
Frequency response (±6dB) open-backed 20Hz – KASA setting
Frequency range (-10dB) 16Hz – KASA setting 
Max SPL (dB) 109dB 
LF Driver250mm (10in.) 
Recommended amplifier KEF KASA500 
Recommended low-pass filter (Hz) 50Hz – 120Hz 
Diameter346mm (13.62in.) 
Depth153mm (6in.) 
Cut-out dimensions 300mm (11.81in.) 
Net Weight 5.6kg (12.3lbs) 
Mounting depth from surface 147mm (5.8in.) 
Ideal rear volume 140L
Minimum rear volume 70L
THX certification THX® Certified Ultra
Safety and Regulatory Compliance IP64
Ceiling thickness (Maximum) 30mm (1.18in.)
Ceiling thickness (Minimum) 6mm (0.24in.) 

Our Take 

So KEF’s new additions to its THX-Certified Extreme Home Theater are not cheap. That said, for the price, both offer solid performance and are in-ceiling solutions for those who want to hide their speakers and not their sound. And the in-ceiling subwoofer is particularly unique as there are not a lot of in-ceiling sub solutions on the market. So while the Ci250RRM-THX might be great performers, they are certainly overkill for Atmos speakers. Because we never recommend in-ceiling speakers for your floor level speakers, these would only be recommended by us when traditional speakers or in-wall options are impossible.

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