Meadowlark HotRod Shearwater loudspeaker Measurements part 2
Fig.6 Meadowlark Shearwater, vertical response family at 50", from back to front: differences in response 15 degrees-5 degrees above tweeter axis, reference response, differences in response 5 degrees-15 degrees below tweeter axis.
In the time domain, the Meadowlark's step response (fig.7) is remarkably time-coherent, with an excellent right-triangle shape. The drive-units appear to be connected with the same positive acoustic polarity, and the setback of the tweeter and the phase behavior of the first-order crossover are just right to give time coherence. The small spike at the beginning of the step, however, suggests that my measuring microphone was very slightly higher than the optimal axis. This is confirmed by fig.8, which shows the individual drive-unit steps on the tweeter axis.
Fig.7 Meadowlark Shearwater, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).
Fig.8 Meadowlark Shearwater, step responses of woofer and tweeter on tweeter axis at 50" (5ms time window, 30kHz bandwidth).
Finally, the Shearwater's waterfall plot (fig.9) indicates the presence of some delayed energy at the top of the woofer's passband (the cursor position). All things being equal, this will again make the sound a little aggressive in this region, and the associated step in the on-axis behavior might also add a slightly nasal character to the speaker's tonal balance. Again, however, it must be noted that CS was not disturbed by problems in this region.
Fig.9 Meadowlark Shearwater, cumulative spectral-decay plot at 50" (0.15ms risetime).
Overall, the design decisions to go with a time-coherent crossover and quasi-transmission-line woofer loading go a long way to explaining the measured problems I found. The question must be: Do the subjective benefits of the former outweigh the downside? Chip obviously felt the answer was "Yes."—John Atkinson