Test Bench: JBL Cinema Sound Speaker System
In the lab
Frequency response (at 2 meters) front left/right: 87 Hz to 20 kHz ±6.8 dB center: 94 Hz to 20 kHz ±3.5 dB surround: 87 Hz to 20 kHz ±6.7 dB subwoofer: 35 Hz to 80 Hz ±2.5 dB
Sensitivity (SPL at 1 meter with 2.8 volts of pink-noise input) front left/right/surround: 89 dB center: 88 dB
Impedance (minimum/nominal) front left/right/surround: 4.3/6 ohms center: 4.9/6 ohms
Bass limits (lowest frequency and maximum SPL with limit of 10% distortion at 2 meters in a large room) front left/right/surround: 40 Hz at 81 dB center: 80 Hz at 87 dB subwoofer: 20 Hz at 83 dB SPL 104 dB average SPL from 25 to 62 Hz 107.1 dB maximum SPL at 62 Hz bandwidth uniformity: 97%
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 CST55's response with the speaker standing on the floor averaged over a ±30-degree window, with double weight at 30 degrees (the most typical listening angle). The center-channel curve reflects the CSC55's response averaged over ±45 degrees, with double weight directly on-axis of the primary listener. The surround-channel curve shows the CST55's response, again standing on a floor, averaged over ±60 degrees. The CSC55 was measured 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.
TOWERS & CENTER
The CST55 left/right and surround-channel speakers have a floor bounce notch (-8 dB at 180 Hz) that is common to floorstanding speakers with woofers located well up in the cabinet. Because the speaker has very uniform directivity, the traces for the two applications are nearly identical, with each showing octave-wide anomalies (a 4 dB peak at 1.5 to 2.5 kHz and a 5 dB dip between 6 and 12 kHz.).
The CSC55 center speaker has the same basic response as the towers, which should yield good timbre-matching for centered listeners. But lobing begins immediately when the microphone is moved off dead center and becomes increasingly severe at wider listening angles.
Although both these speakers have relatively limited bass extension when measured with a 1-watt input (the subwoofer is necessary for truly full-range sound), they have better low-frequency dynamic output capability than this measurement suggests.
I measured the CSS10 subwoofer's bass limits with it placed in the optimal corner of a 7,500-cubic-foot room. In smaller rooms users can expect 2 to 3 Hz deeper extension and up to 3 dB greater sound-pressure level (SPL). The crossover frequency is fixed at 80 Hz with an 18 dB per octave slope. When the LFE input is used, the CSS10 has usable output (-6 dB) up to 180 Hz with no out-of-band artifacts. Dynamic capability is remarkably good for subwoofer with a single 10-inch driver. It delivers 83 dB at 20 Hz and a minimum of 105 dB SPL at 2 meters from 32 Hz up. This helps ensure that listeners hear all the bass that's actually on the recording, nothing less (or more).