Joseph Audio RM7si loudspeaker Big Science part 2
Fig.6 Joseph RM7si, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 45 degrees-5 degrees above axis, reference response, differences in response 5 degrees-45 degrees below axis.
For my in-room spectral analyses I average six measurements at each of 10 separate microphone positions for left and right speakers individually, giving a total of 120 original spectra. These are then averaged to give a curve that, in my room, has proved to give a good correlation with a loudspeaker's perceived balance. I use an Audio Control Industrial SA-3050A spectrum analyzer with its own microphone, which acts as a check on the MLSSA measurements made with the B&K mike. I also used the Goldline DSP-30 automated spectrum analyzer. In-room, the spatially averaged response of the pair (fig.7) is a little rolled-off at the frequency extremes, but otherwise very flat and even. It meets superb ±1.25dB limits over a wide range, from 315Hz to 10kHz.
Fig.7 Joseph RM7si, spatially averaged, 1/3-octave, free-field response in JA's listening room.
In the time domain, the step response (fig.8) reveals that both drive-units are connected with positive polarity, though the tweeter's output leads the woofer's by about 0.6ms. The cumulative spectral-decay or waterfall plot (fig.9) indicates a clean decay through the treble, but some energy hangover in the crossover region, presumably due to the Infinite Slope topology. This is mild in degree, however, and I didn't notice anything amiss in this region during my auditioning.
Fig.8 Joseph RM7si, on-axis step response at 50" (5ms time window, 30kHz bandwidth).
Fig.9 Joseph RM7si, cumulative spectral-decay plot at 50" (0.15ms risetime).
Finally, remember that wrinkle in the impedance plot just above 300Hz. The cabinet resonated quite strongly on both its back and side panels at 375Hz, which can be seen in fig.10, a waterfall plot calculated from the output of a PVDF accelerometer fastened to the center of one of the RM7's side panels.—John Atkinson
Fig.10 Joseph RM7si, cumulative spectral-decay plot calculated from the output of an accelerometer fastened to the cabinet sidewall. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)