Canton Vento Reference 1 DC loudspeaker Measurements

Sidebar 3: Measurements

My estimate of the Canton Vento Reference 1 DC's voltage sensitivity was 89.7dB(B)/2.83V/m, a little higher than the specified 88.5dB and a good 3dB higher than average. Its impedance, however, was generally on the low side, ranging mainly between 4 and 8 ohms, with a minimum value of 3.8 ohms at 29Hz (fig.1). The electrical phase angle is moderate except at infrasonic frequencies, suggesting that the speaker will be relatively easy to drive despite its lowish magnitude (and daunting appearance).

Fig.1 Canton Vento Reference 1 DC, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

A small wrinkle just above 20kHz in each of the impedance traces suggests that this is the primary resonance frequency of the metal-dome tweeter's diaphragm. Another discontinuity visible around 125Hz implies that some sort of cabinet resonance exists in this region. Despite the large areas of the Vento Reference 1's cabinet, these all seem very inert with respect to vibrational resonant modes. The only well-defined mode I could find was on the sidewall level with the lower woofer (fig.2), but this was well down in level.

Fig.2 Canton Vento Reference 1 DC, cumulative spectral-decay plot calculated from the output of an accelerometer fastened to the cabinet's side panel level with the lower woofer (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

I usually measure a speaker's farfield frequency response on its tweeter axis, but the big Canton's tweeter is 47" from the floor—well above the head of a seated listener. (The typical seated listener's ears are 36" from the floor, which is midway between the lower midrange unit and the upper woofer on the Vento's front baffle.) Canton's PR rep, the affable Gordon Sell, told me that the intended listening axis is midway between the lower midrange and the tweeter, or 43" from the floor. Fig.3 shows how the Canton's balance changes according to listening height, referenced to the response on the tweeter axis. Despite the vertical spacing of its drive-units, the Vento Reference 1 doesn't seem that fussy about listening axis. I therefore did all the rest of my measurements on the recommended 43"-high axis.

Fig.3 Canton Vento Reference 1 DC, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 10–5° above axis, reference response, differences in response 5–15° below axis.

The black trace in fig.4 shows the Canton's farfield response averaged across a 30° horizontal window centered on the listening axis, spliced at 300Hz to the sum of the nearfield woofer, midrange, and port responses and taking into account acoustic phase. The balance is even, with a degree of forwardness in the low treble and slight lifts at the two frequency extremes. The apparent bass boost will be mainly due to the nearfield measurement technique, which assumes a 2pi (half-space, or 180° solid-angle) acoustic environment for the drive-units. The top-octave lift was greater exactly on-axis, which is why I assume Canton recommends listening to these speakers 15° to the side of the primary axis. Peculiarly, the tweeter's dome resonance doesn't manifest itself as the usual peak but as a mathematical transform of a peak, with a sharp rise followed by an almost vertical drop to a sharp suckout.

Fig.4 Canton Vento Reference 1 DC, anechoic response on listening axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the nearfield responses of the port (blue), woofers (red), and midrange units (green), and their complex sum plotted below 300Hz.

To the left of fig.4 are shown the nearfield responses of the port (blue trace), the sum of the woofers (red), and the sum of the midrange units (green). The port peaks a little higher in frequency than the woofers' minimum-motion point, this at a very low 22Hz, but the speaker will have extended bass performance, as Wes Phillips found in his auditioning. The woofers have identical outputs and smoothly roll off above 150Hz with an ultimate third-order slope. There is a sharp peak at 125Hz in the port's response, this probably not coincidentally the frequency of the impedance glitch. Fortunately, the facts that the port faces the floor and that its output is suppressed a little may minimize any coloration due to this behavior. However, the woofers do feature a very slight peak in their output at the same frequency. The midrange units both roll out below 150Hz with an ultimate fourth-order slope, but the upper unit starts to roll off gently above 500Hz (not shown). The lower midrange unit continues up in frequency to 2.8kHz, which is where fig.3 suggests it crosses over to the tweeter.

Lateral dispersion is wide and even below 7kHz (fig.5), though the radiation pattern narrows a little above that frequency before widening again in the top octave. I performed a spatially averaged measurement of the Canton's output in WP's listening room, in a 36"-wide, 18"-high window centered on the positions of his ears as he sat in his listening chair. However, instead of using pink noise and my usual 1/3-octave spectrum analyzer, I used a "chirp" method implemented in Christopher Liscio's new FuzzMeasure 2.0 program (SMUG Software) running on my Mac PowerBook, which is a very much faster means of capturing an in-room response "on location."

Fig.5 Canton Vento Reference 1 DC, lateral response family at 50", normalized to response on listening axis, from back to front: differences in response 90–5° off axis, reference response, differences in response 5–90° off axis.

The result—a 1/6-octave–smoothed, FFT-derived spectrum extending up to 30kHz—is shown in fig.6. A strong peak can be seen between 70Hz and 100Hz, this the result of room modes that have not been eliminated by the spatial averaging. But note the well-extended low frequencies, down to almost 20Hz, and the smooth response overall, which slowly slopes down at high frequencies due to the increased room absorption in the treble. (The sharp rolloff above 20kHz is real; my measuring microphone, an Earthworks QTC40, has a flat response to well above 30kHz.) You can also see a slight excess of energy centered on 2kHz, this correlating with the small peak at the same frequency seen in the quasi-anechoic farfield response. This kind of response won't necessarily be heard as coloration, but it may have added to the sense of detail Wes noticed at less-than-loud listening levels.

Fig.6 Canton Vento Reference 1 DC, spatially averaged, 1/6-octave response in WP's listening room.

In the time domain, the Vento Reference 1's step response (fig.7) suggests that the tweeter and midrange units are connected in inverted acoustic polarity, the woofers in positive polarity, which I confirmed by looking at the steps of the individual drivers (not shown). More important, the step of each unit hands over smoothly to the next lower in frequency, correlating with the excellent frequency-domain integration noted earlier. Finally, apart from a strong ridge of delayed energy at an inaudible 20kHz, this the result of the tweeter's dome resonance, the Canton's cumulative spectral-decay plot (fig.8) is very clean, correlating with WP's finding that the speaker's sound was free of grain.

Fig.7 Canton Vento Reference 1 DC, step response on listening axis at 50" (5ms time window, 30kHz bandwidth).

Fig.8 Canton Vento Reference 1 DC, cumulative spectral-decay plot at 50" (0.15ms risetime).

Overall, this is a fine set of measurements that reveals some excellent audio engineering behind Canton's Vento Reference 1.—John Atkinson

Canton Electronics Corp.
504 Malcolm Avenue SE, Suite 400
Minneapolis, MN 55414
(612) 706-9250