Peak Consult Empress loudspeaker Measurements

Sidebar 3: Measurements

The Peak Consult Empress was too heavy for me to lift it on to a high stand for the farfield acoustic measurements. I therefore had to window out the reflection of its sound from the floor in front of it, which will limit the midrange resolution of the response measurements.

With that caveat in mind, the Empress's sensitivity was slightly higher than average, at an estimated 88.5dB(B)/2.83V/m, though this is less than the specified 90dB. Its impedance remains between unusually narrow limits (fig.1), only rising above 6 ohms above the audioband and never dropping below 4.4 ohms. Its electrical phase angle is also small, with the only questionable combination of low magnitude and high phase angle occurring at 31Hz: 5.4 ohms and –45 degrees. Even then, music rarely has high energy at this frequency, meaning that the Empress will be a relatively easy amplifier load.

Fig.1 Peak Consult Empress, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

The traces in the impedance graph are free from the midrange wrinkles and discontinuities that would indicate the presence of cabinet resonant modes (though something suspicious is happening around 1.2kHz). Examining the vibrational behavior of the cabinet panels—those that weren't covered in textured leather, to which my accelerometer refused to stick—revealed a mode at 453Hz on both the top and side panels (fig.2), though this is not very high in level and at this high a frequency is unlikely to be audible.

Fig.2 Peak Consult Empress, cumulative spectral-decay plot calculated from the output of an accelerometer fastened to the cabinet side panel level with the midrange unit (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

The saddle centered at 37Hz in the impedance-magnitude trace suggested that this was the tuning frequency of the large-diameter port on the rear panel. However, the notch in the woofer's output, measured in the nearfield (fig.3, blue trace), lies slightly higher in frequency, at 40Hz. The port's output (fig.3, red) is a neat bandpass curve centered on the same frequency, implying good if not outstanding low-frequency extension. Though some higher-frequency peaks can be seen in the port output, these are well down in level. The woofer rolls off smoothly above 200Hz, also with very little amiss evident in its upper-frequency response. The midrange output is plotted in green in fig.3, scaled to that of the woofer in the ratio of their radiating diameters, which appears to indicate a crossover frequency slightly higher than the specified 200Hz. Its rollout is initially 12dB/octave but steepens below 80Hz to 24dB/octave.

Fig.3 Peak Consult Empress, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the complex sum of the nearfield tweeter, woofer, and port responses, taking into account acoustic phase and distance from the nominal farfield point, plotted below 300Hz, as well as the nearfield responses of the midrange unit (green), woofer (blue), and port (red).

The top, black trace below 300Hz in fig.3 shows the complex sum of these individual nearfield responses, calculated taking into account acoustic phase and difference in distance from a nominal farfield point. The nearfield measurement technique inevitably exaggerates the upper-bass level, but the Empress can be seen to offer bass extension flat to below 45Hz, with the usual 24dB/octave rolloff of a reflex design resulting in an output down 10dB at a respectable 30Hz.

Above 300Hz, fig.3 shows the farfield response averaged across a 30° horizontal window centered on the tweeter axis. There is the suggestion of a slightly forward midrange, but owing to the limited resolution mentioned earlier, this must remain a suggestion. But above 1kHz the Empress's response on this axis is impressively flat and uniform, which, all things being equal, correlates with a neutral treble balance.

In a room, of course, all things are not equal, and a loudspeaker's dispersion plays as strong a role as its on-axis response in affecting the perceived tonal balance. However, the Peak Consult Empress's horizontal dispersion is textbook in nature, with uniform, evenly spaced contour lines and only the slightest hint of off-axis flare at the bottom of the tweeter's passband (fig.4). However, the speaker does become quite directional above 8kHz, due to the tweeter's fairly large radiating diameter. This will tend to make the speaker sound too mellow in large rooms. In the vertical plane (fig.5), a strong suckout develops more than 5° above and below the tweeter axis.

Fig.4 Peak Consult Empress, 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 Peak Consult Empress, 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 5–10° below axis.

In the time domain, the Empress's step response (fig.6) indicates that the tweeter and woofer are connected with positive acoustic polarity and the midrange unit in inverted polarity, each unit's step smoothly handing off to that of the next lower in frequency. This is associated with the smooth frequency-domain integration already seen between the drive-unit outputs. And other than a low-level mode at 7.1kHz, probably associated with the midrange unit's cone, the spectral-decay waterfall plot on the tweeter axis (fig.7) is simply superb, with a clean, rapid decay of the sound evident in the treble.

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

Fig.7 Peak Consult Empress, cumulative spectral-decay plot at 50" (0.15ms risetime).

The Peak Consult Empress offers impressive measured performance overall, indicating some respectable audio engineering talent. I didn't test the speaker's distortion, but it is fair to conjecture that the dynamic limits of its single 8" woofer probably restrict its overall dynamic range, given how clean the speaker appears to be in the midrange and treble. But in rooms of small to medium size the Empress will be a strong contender.—John Atkinson

Peak Consult
US distributor: Signals SuperFi LLC
Atlanta, GA
(678) 528-8077