Emotiva X-Ref XRT-5.2 loudspeaker Measurements
Sidebar 3: Measurements
I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Emotiva XRT-5.2's frequency response in the farfield; and an Earthworks QTC-40, with its small, ¼" capsule, for the nearfield responses. I left the grille off for the measurements.
My estimate of the XRT-5.2's voltage sensitivity was 87dB(B)/2.83V/m, which is typical of two-way designs. The Emotiva's plot of impedance magnitude and electrical phase angle against frequency (fig.1) indicates that its impedance stays above 6 ohms for much of the midrange and treble, and that the magnitude is always high when the phase angle is extreme, mitigating its effect. Although there is a dip to 3.7 ohms at 4.3kHz, the Emotiva is not a difficult load for the partnering amplifier to drive.
It's not easy, in a slim tower speaker with a port near one end, to keep the speaker's interior from acting as a resonant pipe. The small blip in the XRT-5.2's impedance traces just above 200Hz suggests that some kind of resonance is present in this region; investigating the vibrational behavior of the enclosure's panels with a plastic-tape accelerometer did suggest some pumping of the sidewalls at 215Hz (fig.2), as well as a couple of higher-frequency modes. When I listened to the cabinet walls with a stethoscope while playing the half-stepspaced toneburst track from Editor's Choice (CD, Stereophile STPH016-2), I could easily hear both the lower-frequency behavior and the higher-frequency resonances. The latter, however, appeared to have no negative effect on music when I sat in the listening position.
The saddle centered on 51Hz in the fig.1 magnitude trace suggests that this is the tuning frequency of the rectangular port on the front baffle, which was confirmed by the fact that a minimum-motion notch in the woofers' outputie, when the back pressure from the port resonance holds the woofer cones stationaryoccurs at the same frequency (fig.3, green trace). Though the port's output (red trace) does peak as expected between 40 and 70Hz, a second peak is evident just above 200Hz. This coincides with both the frequency of the impedance anomaly and the resonant mode I found on the sidewalls, which strongly suggests the presence of some kind of internal air-space resonance. This resonance is strong enough to give rise to a dip in the woofer's nearfield output centered on the same frequency.
Higher in frequency in fig.3, the woofers' response is smooth and even before crossing over to the tweeter at 3kHz. However, a peak at 5.5kHz is visible in their output, above which it falls off very rapidly. A cumulative spectral-decay plot (not shown) revealed that this peak was not associated with any delayed resonant energy. The tweeter rolls in sharply and is flat within its passband. Fig.4 shows how these individual responses sum in the farfield, averaged across a 30° horizontal window. The rise in the upper bass is mainly an artifact of the nearfield measurement technique used below 300Hz, but the low-frequency alignment does appear slightly underdamped. The bass rolls off rapidly below the port tuning frequency of 51Hz, suggesting only modest LF extension. But other than a suckout between 6 and 8kHz, the XRT-5.2's upper-frequency response is superbly flat.
Fig.5 shows the Emotiva's horizontal dispersion, normalized to the tweeter-axis response and with the off-axis behavior on the tweeter side of the asymmetric baffle shown in the foreground of the graph. There is the usual off-axis flare at the base of the tweeter's passband, and the usual restricted output to the sides at the top of its passband. All things being equal, the Emotiva might sound a little bright in medium to large rooms, but also lacking a bit of top-octave air. In the vertical plane (fig.6), a suckout appears more than 10° above the tweetergiven that its tweeter is only 32" from the floor when the XRT-5.2 is supported by its shallow spikes, the speaker mustn't be auditioned when the listener is standing, or even sitting on a high seat such as a canvas director's chair. This graph shows that the on-axis suckout in the mid-treble fills in 10° below the tweeter axis, but that will be of interest only to those who like to listen while sitting on the floor.
Because I wanted to compare the Emotiva XRT-5.2 with the similarly priced PSB Imagine Mini, which I review elsewhere in this issue, I was able to measure the Emotivas' spatially averaged response at the listening position in my room. The mirror-imaged speakers were set up with their tweeters on the inside edges of the baffles; the result is shown in fig.7. The midrange and treble are superbly flat for an in-room measurement, meeting ±1dB limits from 400Hz to 6kHz. Above that range, the treble shelves down by a couple of dB; below it are a smaller-than-usual "floor dip" in the lower midrange and almost 5dB too much upper-bass energy, the latter audible as a rather boomy quality with both pink noise and music. The low frequencies roll off quickly below 50Hz. Listening to the 1/3-octave warble tones on Editor's Choice, while the 63 and 50Hz tones were reproduced at full level, the 40, 32, 25, and 20Hz tones were all inaudible.
Turning to the time domain, the XRT-5.2's step response on the tweeter axis (fig.8) indicates that all three drive-units are connected with positive acoustic polarity. Though the tweeter's output leads that of the woofers, the decay of its step smoothly blends with the start of the woofers' step, suggesting optimal crossover design. Other than some low-level hash at the frequency of the on-axis suckout, and some delayed low-level energy at the top of the woofers' passband, the Emotiva's cumulative spectral-decay plot (fig.9) is superbly clean for such an inexpensive loudspeaker. (The black ridge just below 16kHz is the usual interference from the measurement computer's video circuitry and should be ignored.)
Although there are some anomalous results in its measured performance, Emotiva's XRT-5.2 performed well in the lab overall, and appears to be a well-engineered design at an affordable price.John Atkinson