Floor Loudspeaker Reviews

I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone with an Earthworks microphone preamplifier to measure the Audiovector QR 7's farfield frequency response and dispersion. I used an Earthworks QTC-40 mike for the nearfield and in-room responses and Dayton Audio's DATS V2 system to measure the impedance magnitude and electrical phase angle.

Audiovector specifies the QR 7's anechoic sensitivity as 90.5dB/W/m. My estimate was slightly lower, at 88.7dB/2.83V/m, though this is still higher than average. The QR 7's impedance is specified as 6 ohms. The impedance magnitude (fig.1, solid trace) varied between 5 ohms and 12 ohms in the midrange and treble, with a minimum value of 4.3 ohms between 120Hz and 130Hz. The electrical phase angle (dotted trace) is generally benign, though it does reach –59.75° at 57Hz. Fortunately, the magnitude is high at this frequency, but the effective resistance, or EPDR (footnote 1), still drops below 3 ohms between 57Hz and 140Hz, with a minimum value of 1.8 ohms at 76Hz. As long as the partnering amplifier can drive 4 ohms, the QR 7 shouldn't present it with any drive problems.

The traces in fig.1 are free from the small discontinuities that would imply the existence of cabinet resonances of various kinds. Nevertheless, when I investigated the enclosure's vibrational behavior with a plastic-tape accelerometer, I found a resonant mode at 367Hz that was present on all the panels. This was highest in level on the front baffle midway between the bottom woofer and the base (fig.2). This mode has a high Q (Quality Factor), which will work against audibility—the rule of thumb is that a resonance needs to be excited by the same number of cycles as its Q for it to be fully excited.

The saddle at 28Hz in the magnitude trace reveals that this is the tuning frequency of the rectangular port on the speaker's base, which implies extended low frequencies. The red trace in fig.3 shows the response of the port, measured in the nearfield. The output reaches its maximum just below the tuning frequency, and while the upper-frequency rollout is disturbed by some peaks in the midrange, the fact that the port fires downward should ameliorate the audibility of this behavior. The woofers' nearfield output (blue trace) has the expected minimum-motion notch at the port-tuning frequency, and their upper-frequency rolloff is initially gentle. There is therefore a broad overlap between the output of the woofers and the midrange unit (green trace) in the crossover region. The midrange unit's output has a small peak at 80Hz.

The complex sum of the midrange, woofer, and port responses is shown as the black trace below 300Hz in fig.3. The slight rise in the midbass response is due to the nearfield measurement technique, which assumes that the drive units are mounted in a true infinite baffle. The black trace above 300Hz in fig.3 shows the QR 7's quasi-anechoic farfield response averaged across a 30° horizontal window centered on the tweeter axis. A peak in the speaker's upper midrange is accompanied by a slightly shelved-down response in the mid-treble. The pair matching between the two samples was excellent, meeting ±0.25dB limits between 400Hz and 20kHz except that the right-hand speaker output was 1.5dB lower than the left in a narrow band centered on 3kHz.

Fig.4 shows the QR 7's horizontal dispersion, normalized to the response on the tweeter axis, which thus appears as a straight line. The contour lines in this graph are even, though there is slightly more mid-treble output to the speaker's sides, which will tend to compensate for the lack of energy in the same region in the on-axis output. (This balance between a speaker's on-axis and off-axis behavior is often referred to as "voicing.") The tweeter starts to become directional above 10kHz, implying that the optimal top-octave response will be obtained when the speakers are toed-in to the listening position.

Fig.5 shows the speaker's dispersion in the vertical plane. The tweeter-axis response is maintained over a ±5° window, which is a good thing considering that the QR 7's tweeter is 42" from the floor. A suckout develops in the upper crossover region 15° above the reference axis. Don't listen to this speaker while standing.

The red trace in fig.6 shows the Audiovector QR 7s' spatially averaged response (footnote 2) in my listening room. Other than a slight excess of energy in the upper midrange, the in-room response is reasonably even from 150Hz to 3kHz, with then the expected gentle downward slope, due primarily to the increased absorption of the room's furnishings as the frequency increases. For reference, the blue trace in fig.6 shows the spatially averaged response of the Q Acoustics Concept 50s, which I reviewed in the August 2022 issue. The QR 7s extend lower in frequency than the Concept 50s, and their mids and upper bass are in better balance. (As I explained in my review, I wasn't able to position the Q Acoustics speakers as close to the wall behind them as they needed.) Both speakers offer similar behavior in the treble, though the Audiovectors have more top-octave energy.

Turning to the time domain, the QR 7's step response (fig.7) indicates that the tweeter and midrange unit are connected in positive acoustic polarity, the woofers in negative polarity. The decay of the tweeter's step, which arrives first at the microphone, blends smoothly with the start of the midrange unit's step, and the decay of that unit's step blends smoothly with the negative-going step of the woofers. Some ripples can be seen in the decay of the step response, which correlates with some delayed energy in the upper midrange in the QR 7's cumulative spectral-decay plot (fig.8). Other than that, this graph has a very clean decay overall.

Other than a slight (but audible) excess of energy in the midrange, the Audiovector QR 7 performed well on the test bench.—John Atkinson

Footnote 2: Using the FuzzMeasure 3.0 program, a Metric Halo MIO2882 FireWire-connected audio interface, and a 96kHz sample rate, I average 20 1/6-octave–smoothed spectra, individually taken for the left and right speakers, in a rectangular grid 36" wide by 18" high and centered on the positions of my ears.