Joseph Audio RM33si Signature loudspeaker Measurements part 2

It is extremely difficult to predict the subjective effect of this measured behavior, as this is also the region where room resonances have a major effect on a speaker's balance. But if you're bothered by any lack of upper-bass power with the RM33si, the solution might well involve minor changes in speaker position in the room.

The RM33si's lateral dispersion plot (fig.4) implies a wide, even radiation pattern, with only a slight flare at the bottom of the tweeter's passband that might brighten the perceived balance in a lively room. Against that must be placed the 1" tweeter's restricted dispersion in its top octave. In the vertical plane (fig.5), the use of a crossover with very high slopes results in a balance that hardly changes over a wide range of listening positions.

Fig.4 Joseph RM33si, lateral response family at 50", from back to front: differences in response 90 degrees-5 degrees off-axis, reference response, differences in responses 5 degrees-90 degrees off-axis.

Fig.5 Joseph RM33si, 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-10 degrees below tweeter axis.

In the time domain, the speaker's step response (fig.6) indicates that all three drive-units are connected with the same positive acoustic polarity, though the speaker is far from being time-coherent. But when we examine the RM33si's cumulative spectral-decay, or waterfall, plot (fig.7), there is nothing to see! This is one of the cleanest waterfall plots I have seen, without a hint of delayed energy though the entire midrange and treble. (Earlier Infinite Slope designs had featured some delayed energy in the crossover region.) Couple this with its flat, even balance, and it's no wonder Chip Stern was so impressed by the Joseph Audio RM33si Signature.—John Atkinson

Fig.6 Joseph RM33si, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

Fig.7 Joseph RM33si, cumulative spectral-decay plot at 50" (0.15ms risetime).

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