Test Bench: KEF Q-Series Home Theater Speaker System
Frequency response (at 2 meters) front left/right: 51 Hz to 20 kHz ±8.0 dB center: 96 Hz to 16.6 kHz ±5.6 dB surround: 100 Hz to 8.0 kHz ±2.8 dB subwoofer: 35 to 150 Hz ±2.3 dB
Sensitivity (SPL at 1 meter with 2.8 volts of pink-noise input) front left/right: 90 dB center: 89 dB surround: 85 dB
Impedance (minimum/nominal) front left/right: 3.5/6 ohms center: 4.1/7 ohms surround: 3.2 /7 ohms
Bass limits (lowest frequency and maximum SPL with limit of 10% distortion at 2 meters in a large room) front left/right: 40 Hz at 91 dB center: 62 Hz at 70 dB surround: 50 Hz at 76 dB subwoofer: 20 Hz at 80 dB SPL 102 dB average SPL from 25 to 62 Hz 110 dB maximum SPL at 62 Hz bandwidth uniformity 93%
All of the curves in the frequency-response graph are weighted to reflect how sound arrives at a listeners ears with normal speaker placement. The curve for the left/right front channels reflects the iQ9's response with the speaker standing on the floor, averaged over a ±30º window with double weight at 30º (the most typical listening angle). The center-channel curve reflects the iQ6c's response averaged over ±45º, with double weight directly on-axis of the primary listener. The surround-channel curve shows the iQ8ds's response averaged over ±60º. The center and surround responses were measured with the speakers on a 6-foot stand, which gives anechoic results to approximately 200 Hz. Except for the subwoofer, all measurements are taken at a full 2 meters, which emulates a typical listening distance, allows the outputs of large speakers to fully integrate acoustically, and, unlike near-field measurements, fully includes front panel-reflections and cabinet diffraction.
Front & Surround Speakers
The KEF iQ9 tower has wide, well controlled directivity but relatively rough response above the 250-Hz floor-bounce notch often encountered with floorstanding speakers. It also exhibits multiple ripples in the top two octaves that most likely are caused by the coaxial driver's tweeter output reflecting up its midrange cone.
The iQ6c center channel shares the same basic response character as the towers, with multiple ripples at very high frequencies. Its response also suffers moderate lobing at the widest radiating angles.
The iQ8ds dipole surround speaker's high-frequency output is attenuated when measured (or heard) directly on axis, which is common to speakers with multiple radiating planes and a design goal for dipole surrounds. On the other hand, this model has limited bass output and low sensitivity.
I measured the PSW3500 subwoofer's bass limits with it set to maximum bandwidth and placed in the optimal corner of a 7,500-cubic-foot room. In a smaller room you could expect 2 to 3 Hz deeper extension and as much as 3 dB greater sound-pressure level (SPL).
The PSW3500 clocked an impressive 110 dB output at 62 Hz and will produce an honest 20 Hz, but with only 80 dB output at that frequency; dynamic capability falls at 15 dB per octave below 62 Hz. The sub's Cinema mode increased output below 60 Hz by 1.4 dB with a corresponding reduction of 1 dB above 70 Hz.
Through its LFE input the subwoofer has a 150-Hz upper limit with a 12-dB-per-octave rolloff above. Using the Low Pass control reduced the cutoff frequency to 80 Hz when it was set to maximum (rolloff slope unchanged). When I set the control to minimum the cutoff dropped to 60 Hz and overall level was reduced by 12 dB. Switching to the 24-dB-per-octave setting cut level by 2 dB but did not change the crossover slope.