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
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).
Towers, Center, and Surrounds
This system is attractively styled, but its measured performance was mediocre. The CM7, CM Centre, and CM1 all show a depression between 1.4 and 4 kHz at every radiating angle and that worsens as the angle gets wider. With the port plugs out, all three show a bump between 100 and 200 Hz, and the CM7 also has a 3-dB floor-bounce notch at 300 Hz.
Inserting the supplied foam plug into the CM7 tower's port (which partially blocks it) dramatically changes the cabinet tuning, cutting low-frequency output starting around 200 Hz: The speaker's output was reduced by 2 dB at 100 Hz and 10 dB at 60 Hz, and the low end of its usable frequency response went from 39 to 84 Hz. Interestingly, inserting the plugs for the other speakers had little effect on their static frequency response, perhaps a function of their much smaller cabinet volumes. But the measured bass limit, which was practically unaffected by plugging the port in the CM7 (less than a full dB), was altered by the plug in the two smaller speakers, presumably because of the loss of the port's output, which normally would reduce the woofer excursion required at very low frequencies.
Subwoofer
I measured the ASW 750 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, users can expect 2 to 3 Hz deeper extension and up to 3 dB greater sound-pressure level (SPL).
SPL capability is impressive in the critical 40- to 62-Hz frequency range, and the subwoofer maxed out at 109 dB (within our 10% distortion limit) at 62 Hz. Output fell at 21 dB/octave below this point, however. For its low-end bass limit (again, with 10% maximum distortion), it produced a true 25 Hz at 92 dB.
The ASW 750 has limited upper-frequency response, with the half-power point at 103 Hz when the low-pass filter is bypassed and only 79 Hz when the crossover is set to a marked 180 Hz. Measurements showed that the true acoustical range of the crossover-frequency control is only 50 to 79 Hz, despite dial markings that run from 40 to 180 Hz. There is significant level interaction as the control is moved downward in frequency (over 10 dB), so users must be sure to double check and adjust the level after making adjustments to the crossover. The sub's EQ option cuts output starting at 50 Hz and below, attenuating by up to 10 dB at 20 Hz. The protection circuit on the subwoofer also limits the output, with loud cracking noises emitted when the subwoofer is driven into overload.
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