Energy Connoisseur C-2 loudspeaker Measurements

Sidebar 3: Measurements

John Atkinson measured the Energy C-2 and provided me with the results after I had completed my listening tests.

The Energy's sensitivity measured to specification at 88dB/W/m (B-weighted). Its impedance characteristic is shown in fig.1. This is an undemanding load, with a minimum impedance of 4.6 ohms at about 160Hz. The port is tuned to 40Hz, visible on the curve as the typical tuned-port saddle dip. The small wrinkles in the curve at just over 200Hz indicate possible cabinet resonances, and the small discontinuity at 23kHz is the ultrasonic tweeter resonance.

Fig.1 Energy C-2, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

Fig.2 shows the FFT-calculated responses of the port and woofer (nearfield) and the on-axis responses of the woofer and tweeter at a microphone distance of 50". The port output shows well-suppressed modes, except for a single slight resonance at 775Hz, down 16dB. The dip in the woofer's response at 40Hz—the point of minimum cone motion—corresponds with the port tuning frequency. The lack of cone breakup modes in the decay of the woofer's response above the 1900Hz crossover frequency is notable, as is the very steep acoustical slope (24dB/octave). The acoustic crossover slope of the tweeter is also steep at about 14dB/octave. Finally, the tweeter resonance peak at 23kHz is high in level, but has no significant effect in the audible range below 20kHz.

Fig.2 Exposure 3010S, frequency response at 2.83V into: simulated loudspeaker load (red), 8 ohms (magenta), 4 ohms (green), 2 ohms (red). (1dB/vertical div.)

The overall response—nearfield port combined with the woofer and tweeter FFT responses averaged across a 30° lateral window, is shown in fig.3. The slight rise in the upper bass was later confirmed by the pink noise curve (not shown). It should add a little richness to the sound without making it bass heavy. Note that the bass response holds up well to below 40Hz (where it is roughly equivalent in level to the output through the midrange) and is down only 6dB at 30Hz. For those who may be wondering at this point what possible advantage there might be in a larger loudspeaker with a similar measured bass response, the answer is output. The C-2 will respond nicely to very low frequencies and produce an impressive measured response. But like virtually all small loudspeakers, it does not have the ability to generate low bass at levels which will produce a powerful, visceral impact.

Fig.3 Energy C-2, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with complex sum of nearfield woofer and port responses plotted below 300Hz.

The remainder of the C-2's response is unusually smooth and flat up to 20kHz. There are a few ripples, but for a loudspeaker these are very benign. The slight rise at 10kHz, inconsequential in the overall smooth trend, may add just a trace of sparkle to the sound.

The horizontal response family of the Energy C-2, with any on-axis response deviations subtracted out so that the on-axis response appears as flat, is shown in fig.4. The off-axis response is as impressive as the on-axis curve in fig.3, with a smoothly increasing rolloff with increasing frequency. This should contribute to good imaging and freedom from performance irregularities at off-axis listening positions. A response which holds up well off-axis at high frequencies should also result in an audibly open, extended response, which is exactly what I heard.

Fig.4 Energy C-2, horizontal 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.

The vertical response family (fig.5) is very linear off-axis also; within an approximately ±10° vertical window, the response remains quite flat. At extreme vertical off-axis angles, however, notches do develop at the crossover frequencies—a not unusual result.

Fig.5 Energy C-2, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 45°–5° above axis; reference response; differences in response 5°–45° below axis.

The step response on the tweeter axis is shown in fig.6. Both drivers are connected in the same (positive) polarity, though the two drivers are not time-coherent. The impulse response taken on the same axis (fig.7) is typical of such a non–time-coherent two-way design. The ringing visible in fig.7 is due to the ultrasonic tweeter resonance, and the ripples in both figs.6 and 7 above 7ms are room reflections.

Fig.6 Energy C-2, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

Fig.7 Energy C-2, impulse response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

The cumulative spectral-decay or "waterfall" plot is shown in fig.8. This would be a truly exceptional result at any price. Except for a very small resonance at just over 8kHz, the high frequency response here is as free of "hash" as any we have seen.

Fig.8 Energy C-2, cumulative spectral-decay plot at 50" (0.15ms risetime).

Fig.9 shows the cabinet vibration measured on the top. The top panel resonance here contributes to the ripples visible in the impedance curve, and may contribute to a little lower-midrange coloration. There are similar resonant responses in the back and side panels, though slightly less pronounced (not shown).

Fig.9 Energy C-2, cumulative spectral-decay plot of accelerometer output fastened to back of enclosure near the top (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

This is an outstanding set of measurements for any loudspeaker, and particularly notable for a moderately-priced, two-way design. The only measurements which were unsurprising at the price are the cabinet resonances. The overall response smoothness and delayed-energy (waterfall) responses, however, are particularly impressive—better than many loudspeakers costing several times the price.—Thomas J. Norton

Energy Loudspeakers, a wholly owned division of Klipsch Group, Inc.
3641 McNicholl Ave.
Scarborough, Ontario
Canada, M1X 1G5
(416) 321-1800