Revel Ultima Gem loudspeaker & Ultima Sub-15 subwoofer Measurements Page 2

Fig.3, a waterfall plot calculated from the output of a simple PVDF plastic-tape accelerometer attached to the center of the cabinet sidewall, shows that there is in fact one resonant mode present, and at quite a high level. However, the presence of extensive and well-positioned bracing pushes this up to a very high frequency, 670Hz, which will mean that it will both "fall between the notes" in the musical spectrum and, once excited, not ring for very long. And it should be noted that this measurement was made without the Gem bolted to its stand. When the speaker was attached to the stand, I couldn't hear this mode being excited even with a stethoscope. I could detect it in the stand pillar, which suggests that the speaker and the stand should be regarded as a single mechanical system.

Fig.3 Revel Ultima Gem, cumulative spectral-decay plot of accelerometer output fastened to cabinet sidewall. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)

The LE-1's high- and low-pass functions are shown in fig.4. The top curve to the left is the basic drive signal to the subwoofer, the bottom curve is the subwoofer drive with the boundary compensation EQ switched into circuit. The crossover appears to be set at 80Hz, with a third-order, 18dB/octave high-pass slope and a fourth-order low-pass slope. The LE-1's input impedance at 1kHz was 10k ohms, which should not load down the partnering preamplifier to any great extent; its line-level output to the satellite amplifier was a low 102 ohms. The output impedance at the subwoofer terminals was a very low 0.05 ohms.

Fig.4 Revel LE-1, crossover responses (5dB/vertical div.).

From left to right, fig.5 shows the individual responses of the Gem's port, woofers, and tweeter (with the front-tweeter control set to its flat position). As expected from the impedance plot, the port covers the range centered on 42Hz, the minimum-motion frequency of the woofers. Though there is a slight peak in its output at 850Hz, this shouldn't have any subjective consequences due to the fact that the port faces away from the listener. The woofers are basically flat in their passband, rolling off steeply above 2kHz so that a slight peak at 4.5kHz is well suppressed.

Fig.5 Revel Ultima Gem, acoustic crossover on tweeter axis at 50", corrected for microphone response, with the nearfield woofer and port responses plotted below 300Hz and 1kHz, respectively.