Canton Vento 809 DC loudspeaker Measurements

Sidebar 3: Measurements

My estimate of the Canton Vento 809 DC's voltage sensitivity was 92dB(B)/2.83V/m, which is both high in absolute terms and 3.5dB higher than the specified figure. The speaker's impedance remained between 4 and 6 ohms for most of the audioband (fig.1); though the electrical phase angle was mainly moderate, the Canton will need to be driven with an amplifier rated at 4 ohms.

Fig.1 Canton Vento 809 DC, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

The smoothness of the traces in fig.1 is marred by glitches at 130Hz, 450Hz, and 21kHz. The final one is due to the metal-dome tweeter's fundamental diaphragm resonance, which will not have audible consequences. However, the two lower in frequency will be due to cabinet resonances of some kind. Exploring the vibrational behavior of the sleek, metal-sheathed enclosure with a plastic-tape accelerometer revealed a strong resonance at 130Hz. This could be detected on all the cabinet surfaces, but was strongest on the curved sidewall level with the reflex port (fig.2). A weaker mode was present at 180Hz on all surfaces, but I didn't find a vibrational mode between 400Hz and 500Hz, the region where the other impedance glitch occurred. I did find a serious glitch at 450Hz in the midrange unit's nearfield response (not shown), which implies the existence of some kind of internal air-space resonance at this frequency. However, I note that Wes Phillips didn't note any midrange confusion that could be laid at the feet of these resonances.

Fig.2 Canton Vento 809 DC, cumulative spectral-decay plot calculated from the output of an accelerometer fastened to the cabinet's side panel level with the port (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

Though the Vento 809's woofers are reflex-loaded with a port, the speaker's impedance graph was somewhat different in the bass from the usual double-peaked reflex plot. This is due to Canton's "DC" technology, which adds a series capacitor in the feed to the woofers and results in the increase in both impedance magnitude and electrical phase angle below 40Hz in fig.1. This graph suggests that the port is tuned to 42Hz; however, nearfield measurements of the woofers' outputs revealed the usual minimum-motion notches to lie lower in frequency, clustered around 30Hz (not shown). The port's output actually peaks an octave higher. The crossover between the twin woofers and the midrange unit appears to lie at around 250Hz, as specified, with symmetrical 12dB/octave initial rolloff slopes, also as specified. The midrange's high-pass slope increases to 24dB/octave below 100Hz.

The complex sum of the Vento 809's midrange, woofer, and port low-frequency responses, taking into account acoustic phase and scaling each radiator's output in the proportion of the square root of its diameter, is shown to the left of fig.3. The speaker is flat down to 60Hz, with then a steep high-pass rolloff evident at close to 30dB/octave, which is what I would have expected when the 6dB/octave from the series capacitor is added to the fourth-order reflex rolloff. Wes did comment on the speaker's balance being a "tad" lightweight, though he was impressed by its bass definition. I suspect that not only was he reacting to the LF rolloff, but also to the overdamped nature of its alignment—note that the usual 3dB boost in the upper bass that results from the nearfield measurement technique is virtually absent from this graph.

Fig.3 Canton Vento 809 DC, anechoic response on tweeter axis at 50", averaged across 30º horizontal window and corrected for microphone response, with the complex sum of the nearfield woofer, midrange, and port responses, taking into account acoustic phase and distance from the nominal farfield point, plotted below 300Hz.

Higher in frequency, the Vento 809 is reasonably flat in both the midrange and the treble, but a discontinuity between these two regions at 2kHz can be seen in fig.3. The crossover to the tweeter occurs a half-octave higher, at 3.2kHz; otherwise, I would have conjectured that this character is simply due to the tweeter being 2–3dB too high in level. Even so, I am sure this behavior lies at the root of Wes's reaction to the Canton's treble. In his auditioning notes, Wes commented often on the Canton's "clarity" and drew specific attention to the tweeter as adding "an unusual amount of sparkle and air in the harmonic overtones of the piano strings and cymbals." This, rather than brightness per se, is what I would expect from the response shown in fig.3.

On-axis, the tweeter resonance at 21kHz manifests itself as a peak/notch combination rather than the usual peak. This notch fills in to the speaker's sides, as can be seen from the Canton's lateral-dispersion plot (fig.4). Note the narrowing of the speaker's radiation pattern below 2kHz, due to the increasing directionality of the midrange unit at the top of its passband. In live rooms, this will make the tweeter sound even more forward. The tweeter itself also gets a little more directional than usual between 6kHz and 12kHz, which will also make the mid-treble sound a bit more forward in very large or very-well-damped rooms. In the vertical plane (fig.5), the Canton's tonal balance remains consistent as long as the listener's ears stay between the midrange axis and the top of the upper woofer. Above and below that region, a suckout develops at the upper crossover frequency.

Fig.4 Canton Vento 809 DC, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90–5º off-axis, reference response, differences in response 5–90º off-axis.

Fig.5 Canton Vento 809 DC, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 15–5º above axis, reference response, differences in response 5–15º below axis.

In the time domain, the Vento 809's step response (fig.6) indicates that the tweeter and midrange unit are connected in inverted acoustic polarity, the woofers in positive polarity, with the slow rise of the latters' step coinciding with the positive-going overshoot above the time axis of the midrange unit's step. All things being equal, the smooth integration between the drive-unit steps implies similarly good integration in the frequency domain. The Canton's cumulative spectral-decay plot (fig.7) reveals a very clean decay in the treble, but some delayed energy associated with the on-axis discontinuity at 2kHz. This might make the speaker sound bright or hard at high playback levels.

Fig.6 Canton Vento 809 DC, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

Fig.7 Canton Vento 809 DC, cumulative spectral-decay plot at 50" (0.15ms risetime).

When I reviewed Canton's Karat Reference 2 DC loudspeaker in January 2003, I was impressed by its level of engineering. Though not to the degree found in the half-the-price Vento 809 DC, the Karat's treble was also a little elevated, so I must assume that this balance is a deliberate choice on the part of Canton's design team. Apart from that and its rather lively cabinet, the Vento 809 DC offers basically good measured performance.—John Atkinson

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