Test Bench: B&W CM Series Home Theater Speaker System

Frequency response, port open / port plugged (at 2 meters) front left/right: 39 Hz to 20 kHz ±5 dB / 84 Hz to 20 kHz ±5 dB center: 74 Hz to 20 kHz ±3.5 dB / 74 Hz to 20 kHz ±4.5 dB surround: 78 Hz to 20 kHz ±5.1 dB / 78 Hz to 20 kHz ±4.5 dB subwoofer: 31 to 79 Hz ±1.9 dB

Sensitivity (SPL at 1 meter with 2.8 volts of pink-noise input) front left/right: 86 dB center: 84 dB surround: 83 dB

Impedance (minimum/nominal) front left/right: 3.1 / 7 ohms center: 4.4 / 11 ohms surround: 5.2 / 12 ohms

Bass limits, port open / port plugged (lowest frequency and maximum sound-pressure level with limit of 10% distortion at 2 meters in a large room) front left/right: 40 Hz at 91 dB / 40 Hz at 91 dB center: 40 Hz at 76 dB / 80 Hz at 91 dB surround: 50 Hz at 79 dB / 80 Hz at 86 dB subwoofer: 25 Hz at 92 dB SPL 103 dB average SPL from 25 to 62 Hz 109 dB maximum SPL at 62 Hz

All of the curves in the frequency-response graph are weighted to reflect how sound arrives at a listener's ears with normal speaker placement. The curve for the left/right front channels reflects the CM7's response with the speaker standing on the floor and averaged over a ±30° window, with double weight at 30° (the most typical listening angle). The center-channel curve reflects the CM Centre's response averaged over ±45°, with double weight directly on-axis of the primary listener. The surround-channel curve shows the CM1's response averaged over ±60°.

Because the CM7 tower will always be used on a floor, measurements were taken with it in that position. I measured both the CM Centre and CM1 on a 6-foot stand which gives anechoic results to approximately 200 Hz. Except for the subwoofer, all measurements (front left/right, center, left/right surrounds) 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.

I measured all the speakers except the subwoofer twice, with their foam port plugs in (to reflect how the speakers were subjectively evaluated) and with the plugs out (to reflect the frequency response and low-frequency limits of the "native" design).

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