Revel Concerta F12 loudspeaker Measurements
The Revel Concerta F12's voltage sensitivity was both to specification and higher than average at 90dB(B)/2.83V/m. Its impedance remained between 4 and 8 ohms over most of the audioband (fig.1), but did drop to 2.9 ohms in the low treble. This, together with the combination of 5.2 ohms and –45° electrical phase angle at 90Hz, means that a good amplifier rated at 4 ohms will be required to drive the F12 to high levels.
Fig.1 Revel Concerta F12, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)
A small glitch just below 300Hz in the impedance traces correlates with a cabinet vibrational mode at 285Hz that could be detected on all surfaces. However, there were also strong resonant modes evident at 492Hz (fig.2), 313Hz, and 350Hz. Given Kal Rubinson's enthusiasm for the Concerta F12's midrange quality, it is probable that these cabinet resonances look worse than they sound. (While they can be detected with an accelerometer, their audibility also depends on the radiating areas of the affected panels. As always, the ear is the best judge.)
Fig.2 Revel Concerta F12, cumulative spectral-decay plot calculated from the output of an accelerometer fastened to the cabinet's side panel level with the midrange unit (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).
Turning to the Concerta F12's frequency response (fig.3), the impedance saddle centered at 33Hz suggests that this is the tuning frequency of the large port on the rear panel. While there is a notch just above this frequency in the summed nearfield response of the woofers (fig.3, red trace), the port's nearfield response (blue trace) actually peaks a little lower in frequency. This is free from higher-frequency problems, however. The woofers behave identically; the sum of their nearfield outputs with that of the midrange (green) and that of the port, taking into account both acoustic phase and the distances from a nominal farfield microphone position, is also plotted in fig.3 (black trace below 300Hz). Most of the apparent rise in response between 50Hz and 200Hz will be due to the nearfield measurement technique, though the F12 is still a little rich in absolute terms, as KR found in his auditioning.
Fig.3 Revel Concerta F12, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the nearfield responses of the woofers (red) and port (blue) and their complex sum (black), together with the farfield responses of the woofers (red) and midrange (green).
Higher in frequency in fig.3, the Revel's response, averaged across a 30° horizontal angle centered on the tweeter axis, is basically flat, though with a slight boost in the mid-treble. The F12's lateral dispersion (fig.4) is wide and even, and the tweeter's output doesn't fall off to the sides above 10kHz quite as much as is usually found with 1" domes. The usual flare in the tweeter's bottom octave is absent from this graph, meaning that the on-axis energy excess in this region will not be accentuated in-room. I am not sure, therefore, why KR found toe-in to be critical with this design. Vertically (fig.5), the Revel's balance doesn't change appreciably over quite a wide window.
Fig.4 Revel Concerta F12, 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.5 Revel Concerta F12, 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 step response on the F12's tweeter axis (fig.6) indicates that all four drive-units are connected with the same, positive acoustic polarity. The step of each melds smoothly into that of the one next lower in frequency, correlating with the good frequency-domain integration seen in fig.3. The farfield cumulative spectral-decay plot (fig.7) is impressively clean, correlating with the speaker's grain-free presentation.
Fig.6 Revel Concerta F12, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).
Fig.7 Revel Concerta F12, cumulative spectral-decay plot at 50" (0.15ms risetime).
Overall, the Revel Concerta F12's excellent measured performance gives no hint of the speaker's very affordable price. It raises the bar for what should be expected from a design in this very competitive price region.—John Atkinson