Revel Ultima Studio2 loudspeaker Measurements
The Revel Studio2's bulk meant that I wasn't able to lift it very far off the floor for measuring. The resolution of the data in the midrange will therefore not be as fine as I usually achieve. All the farfield measurements were performed on the tweeter axis, which is a high 43" from the floor. My estimate of the Revel's voltage sensitivity was 89dB(B)/2.83V/m, which is within experimental error of the specification.
I measured the Studio2's impedance with all of its controls set to Normal (fig.1). The magnitude ranges between 4 and 6 ohms for much of the audioband, with a minimum value of 3.6 ohms at 338Hz. There is a demanding combination of 5.5 ohms and –44° electrical phase angle at 23Hz, but other than organ and house music, it is rare for there to be much energy in this region, which will ameliorate any drive problems this load might cause an optimistically specified amplifier.
Fig.1 Revel Ultima Studio2, electrical impedance (solid) and phase (dashed), switches set to Normal (2 ohms/vertical div.).
There is a slight discontinuity in the impedance traces around 150Hz, but I found no panel resonances in this region. I did find a moderately strong mode at 523Hz on the side panel level with the woofer (fig.2), and a lower-level mode at 370Hz. However, the exact levels of these modes varied considerably according to where I placed the accelerometer, and it's probable that the areas of the affected areas are small enough and the transmission of the vibrational energy to the air is inefficient enough for this behavior to look worse than it sounds. The Revel's enclosure felt solid enough when I rapped it with a calibrated knuckle.
Fig.2 Revel Ultima Studio2, cumulative spectral-decay plot calculated from the output of an accelerometer fastened to the center of the main cabinet's sidewall level with the lower woofer (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).
Fig.3 is a composite made up from the farfield response of the tweeter and midrange unit on the tweeter axis (blue trace above 400Hz), the nearfield response of the midrange unit below 400Hz (blue), the summed nearfield response of the woofers (black), and the nearfield response of the downward-firing port (red). The two woofers measured identically, and the minimum-motion point in their output, which is where the cones are held motionless by the port resonance's back pressure, lay at 31Hz. This is a little higher in frequency than the middle of the low-frequency saddle in the impedance-magnitude trace, and it can be seen in fig.3 that the port's maximum output does lie a little lower in frequency than the notch in the woofers' output. There is a slight peak in the port's output at the same frequency as the impedance discontinuity, suggesting the existence of some sort of acoustic mode. However, this mode is low in level and will be further suppressed by the fact that the port fires downward.
Fig.3 Revel Ultima Studio2, nearfield responses of port (red), woofers (black), and midrange unit (blue below 400Hz), all plotted in the ratios of the square roots of their radiating areas, with the farfield responses of the midrange unit and tweeter (blue above 400Hz).
The crossover between the woofers and the midrange unit appears to lie around 230Hz, as specified, and the acoustical slopes are textbook 24dB/octave, fourth-order, with only the very slightest hint of out-of-band misbehavior from the woofers. These inverted titanium domes are true pistons! The midrange and tweeter's response on the tweeter axis is basically flat. Well, yes, there is a slight bulge between 2 and 3kHz, and the top octave is shelved up by 2dB or so. But the ±1.6dB of adjustment provided by the treble control (fig.4) allows the latter to be compensated for, if the listener feels it necessary.
Fig.4 Revel Ultima Studio2, anechoic response without grille on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the complex sum of the nearfield responses plotted below 300Hz.
The Studio2's overall response, averaged across a 30° horizontal window on the tweeter axis, is shown in fig.5, spliced to the complex sum of the nearfield responses at 300Hz. While there are some small peaks and dips, these are evenly spaced to either side of what is basically a flat line up to 10kHz. This is extraordinary speaker engineering! The top octave is still slightly shelved up, despite the spatial averaging, but again, this can be adjusted with the treble control. At the low end, there is only a hint of the usual nearfield exaggeration, implying that the speaker's port tuning is overdamped. This will optimize the speaker's low-frequency definition, but the port doesn't quite fully reinforce the woofers' output. However, the usual room gain in this region will provide some useful boost to its bottom-octave output.
Fig.5 Revel Ultima Studio2, effect of HF control set to ±1dB on tweeter-axis response.
As difficult as it might be for a speaker's designer to achieve, a flat on-axis response does not ensure a neutral perceived balance in-room, because that will also depend on the speaker's dispersion. Fig.6 plots the Studio2's lateral dispersion on the tweeter axis in 5° increments. Each trace has been subtracted from the on-axis response so that just the changes are shown. Below 9kHz, the Studio2's dispersion is superbly even and well controlled. Again, this is textbook behavior, and will ensure that the room sidewalls' reflections of the speaker's sound will not color the balance. Above 9kHz, the waveguide in front of the tweeter dome does restrict the unit's dispersion so that its output falls rapidly more than 15° to the speaker's sides. All things being equal, this would make the Revel sound a little airless in all but small rooms. In rooms of normal size, however, this will to some extent be compensated for by the shelved-up on-axis output in the same region. I note that Kal didn't feel the need to adjust the Studio2's tweeter level with the rear-panel control, though he did experiment with toe-in. The tweeter's increasing directivity above 10kHz can also be seen in its plot of vertical dispersion (fig.7). Below that frequency, however, the Revel is remarkably tolerant of exact listening axis.
Fig.6 Revel Ultima Studio2, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90–5° off axis, reference response, differences in response 5–90° off axis.
Fig.7 Revel Ultima Studio2, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 15–5° above axis, reference response, differences in response 5–15° below axis.
In the time domain, the Studio2's step response (fig.8) indicates that all four drive-units are connected in the same positive acoustic polarity, but that the speaker is time-coherent rather than time-coincident: each drive-unit's step smoothly hands over to the next lower in frequency. This correlates with the superb frequency-domain integration between their outputs seen in fig.5 and heard by Kal in his auditioning. The Revel's cumulative spectral-decay plot on the tweeter axis (fig.9) is clean overall, particularly in the top octaves, though some low-level hash is evident in the mid-treble.
Fig.8 Revel Ultima Studio2, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).
Fig.9 Revel Ultima Studio2, cumulative spectral-decay plot at 50" (0.15ms risetime).
The Revel Ultima Studio2 offers superb engineering and measured performance for which no apology need be made. It is a worthy successor to the original Ultima Studio, which has been one of my speaker references for the past seven years.—John Atkinson