This is a review and detailed measurements of the KEF Reference 4C Center home theater speaker. It was kindly purchased new by a member and drop shipped to me. 4C costs US $7,500.
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Apology for using stock picture. Speaker weighs 100 pounds and I got interrupted mid-review with our home flooding so still in measurement room. I had finished the measurements though and hence this write up. You can't tell from above picture but this speaker is deep, very deep. The finish is gorgeous but I found a tiny blemish which was disappointing. Back bindings are custom tool metal ones and the best I have seen and felt. No question KEF has targeted high level of execution with this speaker.
A coaxial driver handles midrange and tweeter responsibility. Woofers then bring the bass along (3-way total).
Measurements that you are about to see were performed using the
Klippel Near-field Scanner (NFS). This is a robotic measurement system that analyzes the speaker all around and is able (using advanced mathematics and dual scan) to subtract room reflections (so where I measure it doesn't matter). It also measures the speaker at close distance ("near-field") which sharply reduces the impact of room noise.
Both of these factors enable testing in ordinary rooms yet results that can be more accurate than an anechoic chamber. In a nutshell, the measurements show the actual sound coming out of the speaker independent of the room.
Measurements are compliant with latest speaker research into what can predict the speaker preference and is standardized in CEA/CTA-2034 ANSI specifications. Likewise listening tests are performed per research that shows mono listening is much more revealing of differences between speakers than stereo or multichannel.
Reference axis was the center of the tweeter (aligned by eye). Measurement room was at 10 degrees C which may lower bass output a bit. I used a higher resolution scan than normal which turned out to not be necessary as the speaker is very well behaved in higher frequencies. Accuracy is better than 1% as a result in most of the frequency spectrum.
KEF 4C Measurements
Acoustic measurements can be grouped in a way that can be perceptually analyzed to determine how good a speaker is and how it can be used in a room. This so called spinorama shows us just about everything we need to know about the speaker with respect to tonality and some flaws:
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While not ruler flan, on-axis response is very good. Even better is directivity index (dashed blue at the bottom) showing that important early reflections are similar to on-axis response which you can see better here:
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Bass response is stepped down due to port tuning being low. We can see this in the near-field response:
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Cabinet/port resonances are kept at bay so don't cause coloration in upper midrange as they usually do in ported speakers.
Predicted in-room response is excellent:
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BTW, sensitivity is also excellent at 90 dB although you better have an amplifier that doesn't mind the very low impedance dip of just 2.9 ohm:
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The quad bass drivers and capable mid-range translate into incredibly low distortion and power capability:
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The biggest issue with the design of most center speakers is that the doubled up woofer/mid-woofer causes horizontal dispersion to narrow due to timing differential between them. Is that solved here with the coaxial mid-range/mid-woofer? Let's see:
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Speaker is so wide that there is still good bit of distance between the woofers causing some cancellation. But generally, this is way better than most center speakers we have tested.
The vertical response though shows how good this could be if all the drivers were aligned horizontally:
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For fan of timing analysis, here are the rest of the measurements of that type:
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Listening Tests
I was in the process of wiring up the speaker to listen to it in the measurement lab when my worried wife ran into the room and said: "downstairs bathroom is flooding!" I rushed out to deal with that and have not had a chance to listen to the 4C yet. I hope to still get a chance to do so and report back.
Conclusions
The fit and finish, design and capabilities of the 4C clearly show that this is a very serious engineering effort by KEF to produce a highly capable center speaker. Physics of sound wavelengths still attack it a bit causing slight narrowing of directivity but otherwise, it is very hard to find fault with this speaker.
I am going to recommend the KEF 4C based on objective data and subjective look and feel of the unit. I expect it to be a super capable center speaker and a great one for 2-channel listening if you use it vertically.
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As always, questions, comments, recommendations, etc. are welcome.
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