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.
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:
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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:
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):
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:
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:
Minimum impedance in bass is above average:
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:
Step response shows the three peaks for each driver:
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/
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:
]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:
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):
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:
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:
Minimum impedance in bass is above average:
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:
Step response shows the three peaks for each driver:
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/
