Dynaudio Excite X12 loudspeaker Measurements
I performed the quasi-anechoic measurements of the Dynaudio Excite X12 with DRA Labs' MLSSA system and a calibrated DPA 4006 microphone. The speaker's rather clumsy grille was left off for the measurements. The Excite X12's specified voltage sensitivity is 86dB/2.83V/m; my estimate of its sensitivity was a bit lower than that, at 84.8dB(B)/2.83V/m, which is below average. This speaker will work better with relatively high-powered amplifiers, such as the Creek integrated and Audio Research power amp BJR used for his auditioning. However, while Dynaudio specifies the X12 as having a nominal 4 ohm impedance, its plot of impedance magnitude and phase (fig.1) reveals that it doesn't drop below 6 ohms, and then only in the lower midrange, when it reaches a minimum value of 4.8 ohmswhich, like the combination of 6.6 ohms and 30° capacitive phase angle at 125Hz, will not tax any well-designed amplifier.
Fig.1 Dynaudio Excite X12, electrical impedance (solid) and phase (dashed) with port open (2 ohms/vertical div.).
The traces in fig.1 were taken with the rear port open; the saddle between the twin magnitude peaks in the impedance curve between 50 and 60Hz suggests that the port is tuned to this region. With the port closed with the supplied foam plug, the impedance curve resembles that of a conventional sealed box in the bass, with a single peak of 15 ohms at 80Hz (fig.1).
Fig.2 Dynaudio Excite X12, electrical impedance (solid) and phase (dashed) with port open (2 ohms/vertical div.).
The traces in the impedance graph are free from the small discontinuities that would indicate the presence of cabinet resonances. Nevertheless, when I investigated the panels' vibrational behavior with a simple plastic-tape accelerometer (similar to a piezo guitar pickup), I found two fairly strong resonances on the cabinet's sidewalls, at 590 and 711Hz (fig.3), as well as a lower-level mode at 109Hz that was present on all surfaces. The audibility of any such modes depends on a number of factors besides their amplitudes, including: the size of the area affected, its phase relationship with the primary source, its frequency, and its Quality Factor, or Q. In general, the higher in frequency the mode and the higher its Q, which means it covers a smaller frequency range, the less likely it is to be excited. The two upper-frequency modes present in fig.2 thus might well not affect the Excite X12's sound quality, especially as the radiating area of the panel is small.
Fig.3 Dynaudio Excite X12, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of side panel (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).
Turning to the Dynaudio's frequency-domain behavior, the black curve below 300Hz in fig.4 shows the complex sum of the woofer (green trace) and port (blue trace) nearfield responses. ("Complex" means that the sum takes into account both acoustic phase and the different distances of the two radiators from a nominal farfield microphone point.) The broad hump in the upper bass is almost entirely due to the nearfield measurement technique, which assumes a 2-pi acoustic environment for the radiators; ie, one that extends to infinity in all directions. As Bob Reina noted, the Excite X12 does have relatively extended low frequencies for such a small loudspeaker; allowing for the nearfield boost, the speaker's bass output is down 6dB at the port tuning frequency, which, as shown by the minimum-motion notch in the woofer's output, occurs at 55Hz. The port's output does have a peak evident in the midrange, but as it fires to the speaker's rear, it's possible that this mode will not affect the sound quality. The red trace in fig.4 shows the woofer's nearfield output with the port blocked. In this condition the Excite X12 rolls off below 100Hz, which might be preferable if the speaker is to be used near a room boundary, the reflex tuning being perhaps a touch on the rich side.
Fig.4 Dynaudio Excite X12, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with nearfield responses of port (blue), woofer with port open (green) and closed (red), and complex sum of woofer and port (black), plotted below 2kHz, 300Hz, 300Hz, 300Hz, respectively.
Higher in frequency in fig.4, the black trace shows the Dynaudio's farfield response, averaged across a 30° horizontal window centered on the tweeter axis. It is superbly flat overall, though with perhaps a slight trough evident in the presence region (25kHz). As this is the region where the ear is most sensitive, it's possible that the Excite X12 might sound a touch laid-back as a result. However, the Dynaudio's plot of lateral dispersion, normalized to the tweeter-axis response (fig.5), indicates that there is a slight off-axis flare in the same region. In a typical room, this will counteract the on-axis behavior to give a flat tonal balance in the treble. As is usual with a 1" tweeter on a flat baffle, the Excite X12 gets more directional above 12kHz or so, though not to any serious degree. In the vertical plane (fig.6), a hefty suckout develops in the crossover region more than 5° below the tweeter axis; 515° above that axis, the presence region is boosted a little. Both of these phenomena suggest that shorter stands will work better than tall ones to get the most neutral tonal balance in-room. BJR's 24" Celestion stands will be ideal.
Fig.5 Dynaudio Excite X12, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 905° off axis, reference response, differences in response 590° off axis.
Fig.6 Dynaudio Excite X12, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 455° above axis, reference response, differences in response 545° below axis.
In the time domain, the Excite X12's step response on the tweeter axis (fig.7) indicates that the two drive-units are connected in positive acoustic polarity, the tweeter's output leading that of the woofer. However, the decay of the tweeter's step smoothly blends into the woofer's step, correlating with the good frequency-domain integration of their outputs seen in fig.4. Other than a slight ridge of delayed energy at 5.2kHzmost likely a woofer-cone mode of some kindthe Dynaudio's cumulative spectral-decay plot on the same axis (fig.8) is superbly clean.
Fig.7 Dynaudio Excite X12, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).
Fig.8 Dynaudio Excite X12, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).
In his conclusion, Bob Reina mentioned that the Dynaudio Excite X12 has become his new benchmark for loudspeakers costing under $2000/pair. I am not surprised. For $1200/pair, a well-engineered speaker like this makes it hard to justify spending more on a bookshelf speaker unless you can afford one of the cost-no-object models.John Atkinson