Test Report: KEF R Series Speaker System Page 3


Frequency response

  • main 54 Hz to 20 kHz ±3.5 dB
  • center 60 Hz to 20 kHz ±4.3 dB
  • surround 69 Hz to 20 kHz ±4.0 dB
  • subwoofer 42 to 141 Hz ±3 dB

Sensitivity (SPL at 1 meter/1 watt)

  • main 82.5 dB
  • center 85.2 dB
  • surround 80.2 dB

Impedance (minimum/nominal)

  • main 3.3/8 ohms
  • center 3.3//7 ohms
  • surround 3.4/8 ohms

Bass output, subwoofer (CEA-2010A standard)

• Ultra-low bass (20-31.5 Hz) average: 95.1 dB

  • 20 Hz        91.8 dB
  • 25 Hz        93.3 dB
  • 31.5 Hz     98.7 dB

• Low bass (40-63 Hz) average: 117.2 dB

  • 40 Hz       113.4 dB
  • 50 Hz       117.5 dB L
  • 63 Hz       119.6 dB L

Bass limits

  • main 93.7 dB at 50 Hz
  • center 106.7 dB at 40 Hz (down 21.9 dB at 31.5 Hz)
  • surround 87.0 dB at 40 Hz

I measured the frequency response of the R-Series speakers using quasi-anechoic technique to remove the effects of reflections from nearby objects. I measured the R100 bookshelf speaker, R200c center speaker, and R800ds surround with each speaker placed atop a 2-meter-high stand, measuring the speaker in both horizontal and vertical positions. The microphone was placed at a distance of 2 meters. I positioned the microphone directly in front of the R100 and R200c tweeters, then averaged the measurements at 0°, ±10°, ±20°, and ±30°. For the R800ds, I positioned the microphone on the same plane as the tweeters, with the mike perpendicular to the length of the speaker (as your ears would be when you listen to the speaker), then averaged the measurements at 0°, ±15°, ±30°, ±45°, and ±60°. All quasi-anechoic measurements were smoothed to 1/12th octave. Bass response of all speakers and the R400b subwoofer was measured using ground plane technique with the microphone on the ground 2 meters from each speaker; this was smoothed to 1/3rd octave, then spliced to the quasi-anechoic measurements at 130 Hz. Results are normalized to 0 dB at 1 kHz. All frequency response measurements were made with a Clio FW audio analyzer and then imported into a LinearX LMS analyzer for post-processing.

The R100 and R200c both measure fairly flat, and both have the consistent off-axis response expected of a concentric woofer/tweeter design. Out to ±30°, you barely see any difference in the frequency response compared with the on-axis measurement, and at ±45° and ±60°, the anomalies (dips at 4.5 and 6.5 kHz, respectively) are mild. As you can see in the chart, both speakers have a mild downward tilt in the tonal balance, so they may sound a little soft in the treble — or they may sound appealingly smooth and forgiving, depending on your taste.

I was most impressed by the R800ds, which delivered much flatter and more even response than a typical multidirectional surround speaker does. Its ±60° averaged response is about as smooth as the R100 and R200c’s ±30° response.

The R-Series speakers shouldn’t be tough for any halfway decent receiver or amp to drive. For the R100 bookshelf speaker, minimum impedance is 3.3 ohms at 255 Hz with a phase angle of +5°. For the R200c center, it’s 3.3 ohms at 160 Hz/+2°; it does drop to 2.6 ohms at 42 Hz, but as long as you keep the speaker size set to “small” in your surround processor or receiver, the R200c won’t be operating in this range anyway. For the R800ds, minimum impedance is 3.4 ohms/300 Hz/-2°.

Sensitivity (measured on-axis outdoors, average output from 300 Hz to 10 kHz at 1 meter with a 2.83-volt RMS signal) is relatively low for the R100 and the R800ds. I would give these guys at least 80 or so watts of juice per channel to get the best performance from them.

The subwoofer frequency response measurement you see here was taken with the EQ switched out, and the result normalized so that peak output measures +3 dB. You can see the effects of the two EQ modes in the accompanying chart. Effects of the EQ modes are centered at 45 Hz. The EQ +6 mode (red trace) boosts the bass at that frequency by 5.7 dB, and the EQ +12 mode (green trace) adds another 5.6 dB. Combined low-pass function of the internal crossover, the driver, and the enclosure measured at -25 dB with the crossover set to 80 Hz.

CEA-2010A output measurements for the R400b subwoofer were taken at 3 meters and then scaled up +9.54 dB per CEA-2010A requirements so that they are equivalent to 1-meter results. Measurements with an L next to them are those in which the maximum output was determined by the sub’s internal limiter. As I’ve said before of many small, stylish, and relatively expensive subs, output of the R400b is good for its size but not its price. The emphasis is on the low bass octave (40-63 Hz), where average output is 117.2 dB. Below 40 Hz, response takes a dive, to an average of 95.1 dB. However, there’s still substantial output at 20 Hz. — Brent Butterworth

Bottom Line

It’s my job to find fault, so if the KEF R Series R100 system has one, it might be a very slightly “drier,” less ambient, and tightly focused two-channel character than most high-end speakers present. (Keep in mind that for multichannel playback, this is more virtue than vice.) And that’s about it.

Of course, most people will consider $5,700 to be a lot of coin for a “compact speaker system,” and in this case at least most people are right. But there’s another way of looking at the KEF suite: with your ears. Is almost 6 grand too much for a speaker array that is entirely without sonic vices; boasts a legitimately full range and full dynamics; can produce?a pure, seamless sphere of surround from the best productions; and is easy on both the eyes and?your room’s floor space? For comfortably employed music and movie devotees, the answer would surely be “No.”

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