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KEF ci250RRM-THX In-ceiling Speaker Review

Rate this In-ceiling Speaker

  • 1. Poor (headless panther)

    Votes: 5 2.9%
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    Votes: 3 1.8%
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    Votes: 71 41.8%
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  • Total voters
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amirm

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This is a review and detailed measurements of the KEF ci250RRM-THX 3-way home theater speaker. It was sent to me by the company and costs US $2,499.
KEF ci250RRM-THX in-ceiling high-end home theater speaker coaxial 3-way measurement.jpg

Please excuse the stock picture. Mine in the plywood baffle doesn't look very pretty.

I must say, I was not prepared for how substantial this speaker it is. It feels and looks a lot larger than typical round in-ceiling speaker. The design is unusual with foams stuffed below the vents. Speaker is THX certified (see a bit more later).

I tested my sample using Klippel NFS Baffle system which creates anechoic measurements from a speaker mounted in a square panel. It automatically excludes edge diffractions and back energy in addition to its standard reflection elimination. The result is a "2 pi" response of the speaker as if it is mounted in a very large panel.

You can learn more about my speaker measurements by watching my tutorial:
[And subscribe to the channel :) ]

KEF ci250RRM-THX Speaker Measurements
The CEA/CTAS-2034 standard unfortunately does not apply to this class of speaker well but let's start with it anyway:
KEF ci250RRM-THX in-ceiling high-end home theater speaker anechoic frequency response measurem...png

The on-axis response rises in treble. I ran this by the company and they stated that the design axis, as per THX, is actually 45 degrees, not 0. This makes sense as the front speakers are mounted close to the screen and you sit back from them. Likewise height and side speakers would be at certain angle. I will compensate for this shortly but company also said that they are seeing higher sensitivity in bass (which otherwise agrees with their measurements).

Fortunately Klippel CEA-2034 module computes the response at 10 degree intervals so we can look at that in both horizontal and vertical axis (which happen to be similar due to coaxial nature of this speaker):
KEF ci250RRM-THX in-ceiling high-end home theater speaker anechoic horizontal 40 degrees frequ...png

KEF ci250RRM-THX in-ceiling high-end home theater speaker anechoic vertical 40 degrees frequen...png


Other than a slight rise around 1 to 1.5 kHz, we now have a flat response "on axis" at 40 degrees so company is correct. Nicely, the ripple in the treble response is much reduced at that angle as well.

You can see this effect as well in the directivity plots:
KEF ci250RRM-THX in-ceiling high-end home theater Horizontal Beamwidth measurement.png

KEF ci250RRM-THX in-ceiling high-end home theater Horizontal directivity measurement.png

KEF ci250RRM-THX in-ceiling high-end home theater Vertical directivity measurement.png


As noted, you don't want to go too far as the response starts to narrow in treble above 50 to 60 degrees. So be mindful of this as you design your theater.

Courtesy of robust design and 2-Pi efficiency, response goes way deep as mentioned on the graph. Combined with very low distortion for the class, this speaker should be able to play quite loud and clean:

KEF ci250RRM-THX in-ceiling high-end home theater THD Distortion Percentage measurement.png

KEF ci250RRM-THX in-ceiling high-end home theater THD Distortion measurement.png


Minimum impedance in bass is above average:
KEF ci250RRM-THX in-ceiling high-end home theater speaker impedance and phase measurement.png

Impedance dips fairly low at higher frequencies but level of energy is low there so I am not worried.

We naturally see some resonances in waterfall:
KEF ci250RRM-THX in-ceiling high-end home theater speaker csd waterfall measurement.png


Step response shows the three peaks for each driver:
KEF ci250RRM-THX in-ceiling high-end home theater speaker Step Response measurement.png


Conclusions
It has been difficult to find an ultra-clean in-wall/in-ceiling speaker. The limitations put on the design is quite severe. KEF seems to have done a heroic job here, producing a high-power speaker that has essentially flat design axis response together with excellent power handling. The price is up there so it is for people who value the best performance in a speaker that you barely see. I also appreciate the extensive white paper on the design of this speaker which far exceeds what we see from almost any manufacturer.

Since I can't listen to the KEF ci250RRM-THX, I can't provide a recommendation. But will say that I am impressed and will steer people towards it for in-ceiling applications.
------------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

Attachments

  • KEF ci250RRM-THX.zip
    40.3 KB · Views: 56
Reserved for @AdamG to kindly post the specs.

Manufacturer Specifications:

IMG_0997.jpeg

Link to further product description and information:
 
Last edited by a moderator:
Wow, what a great job by KEF. Impressive. The price tag is justified when you know that they will not be sold in large numbers, so R&D costs must be spread over a smaller number.
 
KEF also provides a set of measurements for this speaker:

newplot (6).png

The on axis measurement is close esp. above 100Hz.
 
Last edited:
KEF seems to have done a heroic job here, producing a high-power speaker that has essentially flat design axis response together with excellent power handling.
It seems so... as you say pricey, but for an in-ceiling speaker this is a solid option. Thanks for the measurements, a few pics for the thread;

1740642009598.png


1740642027751.png


1740642137910.png


1740642201336.png



JSmith
 
It's hard to ignore the price on this one, amazing design or not.
The thing to not ignore is they bothered making it . Undertook the considerable engineering challenge , possibly just because they thought they could.

I doubt the company are going to make huge profits from this plus it might just inspire a few others to join in thusly improving the in ceiling speaker market as a whole. A win for everyone!

So they took the risk , invested their money likely knowing its never really going to make a huge positive impression on the KEF bottom line , possibly even a negative one .., one has to also remember they have to engineer and tool up the subsequent manufacturing process too , it's not just let's build a prototype.

Even KEF engineers have to eat .
 
Unusual impedance dip at highs, a consistent 3 to 2 Ohm from 3kHz all the way to 20kHz.

Really nice, this one.

Thanks Amir!
 
I've always suspected that the Uni-Q would be the perfect design for Atmos/DTS-X/AURO 3D overheads. Its uniform radiation in both the horizontal and vertical planes make it a better option for positioning that just about anything else. I suspect a budget version of this might involve buying some Kef Egg Speakers and placing them near the ceiling mounted on long vertical poles. They of course would not give the volume output of these things, but is that kind of output needed for the height effects? I, for one, don't think so. Something less elaborate with lower output levels would probably work just fine in smaller home theater set-ups at lower volume levels. After all, we're looking at $10 k for four height speakers in a 7.1.4 set up or maybe a cool $15 k for a 9.1.6 setup. That's a lot of money to put into heights which are a nice effect, but hardly the most important even in Atmos.
 
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Wow. First KEF I'm really impressed with.
Bass - measured at least - is better than R3 and even R5-R7 produce lol.

Oh, it's simple - size matters:
Drive Units
LF: 250mm (10in.)
MF: 100mm (4in.) Uni-Q
HF: 19mm (0.75in.) vented aluminium dome
 
I'm thinking that design might be a whole lot cheaper without the woofer. Most home theaters are using subs anyway. A version with just the Mid-High unit which would be something like a ceiling mounted LS 50 Meta might just be the ticket for most aspiring home theater owners.

Those speakers are indeed a heroic effort by KEF, and if I ever win Powerball, and want something to pair with my 8 Blade Metas plus whatever center Ker recommends, they would certainly my choice.

Still don't know how I'm going to get a house in Big Sur with floor to ceiling windows overlooking the Pacific and still have a good sounding home theater in it, though. Maybe have to settle for headphones for that use case and build the theater in the bunker, Guess you can't have it all, no matter what.

Very good review, Amir.
 
Fantastic review and measurements! I agree, it's rare to find an in-ceiling speaker that combines both high power handling and excellent performance, especially with such a clean frequency response and low distortion. The THX certification adds an extra layer of assurance for anyone looking for a top-tier home theater experience. It’s great to see KEF pushing the limits of in-ceiling speaker design, and your thorough analysis helps potential buyers understand exactly what they’re getting. While the price is certainly a factor, it seems like a worthy investment for those who prioritize the best quality for their home theater setup.
 
I see that price is a main subject here but think of it the other way around:

Say you built something like that.
How much a good quality 10" driver costs (not Purifi or Scan-Speak distortion grade, let's say lower stuff) ? How much for the Uni-Q? How much for a decent x-over to blend those as nicely as we see here?

I think it's cheap for what it offers.
 
This is a review and detailed measurements of the KEF ci250RRM-THX 3-way home theater speaker. It was sent to me by the company and costs US $2,499.
View attachment 431878
Please excuse the stock picture. Mine in the plywood baffle doesn't look very pretty.

I must say, I was not prepared for how substantial this speaker it is. It feels and looks a lot larger than typical round in-ceiling speaker. The design is unusual with foams stuffed below the vents. Speaker is THX certified (see a bit more later).

I tested my sample using Klippel NFS Baffle system which creates anechoic measurements from a speaker mounted in a square panel. It automatically excludes edge diffractions and back energy in addition to its standard reflection elimination. The result is a "2 pi" response of the speaker as if it is mounted in a very large panel.

You can learn more about my speaker measurements by watching my tutorial:
[And subscribe to the channel :) ]

KEF ci250RRM-THX Speaker Measurements
The CEA/CTAS-2034 standard unfortunately does not apply to this class of speaker well but let's start with it anyway:
View attachment 431881
The on-axis response rises in treble. I ran this by the company and they stated that the design axis, as per THX, is actually 45 degrees, not 0. This makes sense as the front speakers are mounted close to the screen and you sit back from them. Likewise height and side speakers would be at certain angle. I will compensate for this shortly but company also said that they are seeing higher sensitivity in bass (which otherwise agrees with their measurements).

Fortunately Klippel CEA-2034 module computes the response at 10 degree intervals so we can look at that in both horizontal and vertical axis (which happen to be similar due to coaxial nature of this speaker):
View attachment 431882
View attachment 431883

Other than a slight rise around 1 to 1.5 kHz, we now have a flat response "on axis" at 40 degrees so company is correct. Nicely, the ripple in the treble response is much reduced at that angle as well.

You can see this effect as well in the directivity plots:
View attachment 431884
View attachment 431885
View attachment 431886

As noted, you don't want to go too far as the response starts to narrow in treble above 50 to 60 degrees. So be mindful of this as you design your theater.

Courtesy of robust design and 2-Pi efficiency, response goes way deep as mentioned on the graph. Combined with very low distortion for the class, this speaker should be able to play quite loud and clean:

View attachment 431887
View attachment 431888

Minimum impedance in bass is above average:
View attachment 431889
Impedance dips fairly low at higher frequencies but level of energy is low there so I am not worried.

We naturally see some resonances in waterfall:
View attachment 431890

Step response shows the three peaks for each driver:
View attachment 431891

Conclusions
It has been difficult to find an ultra-clean in-wall/in-ceiling speaker. The limitations put on the design is quite severe. KEF seems to have done a heroic job here, producing a high-power speaker that has essentially flat design axis response together with excellent power handling. The price is up there so it is for people who value the best performance in a speaker that you barely see. I also appreciate the extensive white paper on the design of this speaker which far exceeds what we see from almost any manufacturer.

Since I can't listen to the KEF ci250RRM-THX, I can't provide a recommendation. But will say that I am impressed and will steer people towards it for in-ceiling applications.
------------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
Wouldn't it be interesting and possible to build a very simple wooden housing with the appropriate volume and then listen to and measure the loudspeaker?
 
Is the mid cone back essentially open, other than the white foam? I don't see a full enclosure there. Or maybe that foam is solid, like polystyrene, doing double duty of sealing the mid and filling a cavity space that would otherwise cause resonance?
 
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Is the mid cone back essentially open, other than the white foam? I don't see a full enclosure there. Or maybe that foam is solid, like polystyrene, doing double duty of sealing the mid and filling a cavity space that would otherwise cause resonance?
Hi @ssashton , the details of this aspect of the design are explained in the white paper. It's downloadable from the specification table on the product page: https://uk.kef.com/products/ci250rrm-thx
 
KEF ci250RRM-THX in-ceiling high-end home theater Horizontal directivity measurement.png

KEF ci250RRM-THX in-ceiling high-end home theater Vertical directivity measurement.png


As noted, you don't want to go too far as the response starts to narrow in treble above 50 to 60 degrees. So be mindful of this as you design your theater.
Hm but these are plotted relative to the on-axis response, right?

If we take 45° as reference axis like intended, then the e.g. -6dB line would be further off-axis (with a +x dB "hot" center of course).

Can Klippel plot it like this?
 
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