In the time domain, the speaker's step response (fig.7) reveals that despite the offset of the tweeter, the CDM 1 is still not time-coherent on the HF axis, the tweeter's output arriving at the microphone a small fraction of a millisecond before that of the woofer. Both are connected with positive acoustic polarity, however. The associated cumulative spectral-decay or waterfall plot (fig.8) reveals a very clean decay, with only a small low-level mode apparent in the mid-treble, this presumably a well-suppressed woofer-cone mode.

Fig.7 B&W CDM 1, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

Fig.8 B&W CDM 1, cumulative spectral-decay plot at 50" (0.15ms risetime).

Finally, a waterfall plot (fig.9) calculated from the output of a PVDF accelerometer strip fastened to the center of the cabinet sidewall revealed only a low-level panel resonance at 390Hz. A couple of lower-frequency modes could be found on the cabinet rear and top panels but were still low in level, indicating that the B&W's cabinet is well-designed and -constructed.

Fig.9 B&W CDM 1, cumulative spectral-decay plot of accelerometer output fastened to side of enclosure (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

Overall, this is an excellent set of measurements, correlating well with the B&W's excellent perceived sound quality.—John Atkinson