Triangle Esprit Comete Ex loudspeaker Measurements

Sidebar 3: Measurements

The Triangle Esprit Comete Ex is significantly more sensitive than the norm, my estimate of its voltage sensitivity coming in at 91dB(B)/2.83V/m. While its impedance magnitude drops below 5 ohms in the lower midrange and mid-treble (fig.1, solid trace), and the electrical phase angle is occasionally extreme, overall the speaker will be fairly easy to drive.

Fig.1 Triangle Esprit Comete Ex, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

There are two sharp discontinuities in the impedance traces, one at 620Hz, the other between 800 and 900Hz. Investigating the cabinet's vibrational behavior with a plastic-tape accelerometer, I found some strong resonances. Fig.2, for example, shows a cumulative spectral-decay plot calculated from the output of the accelerometer when fastened to the center of one of the sidewalls. There is a strong mode at 355Hz, along with some higher in frequency. This mode, which I detected on all surfaces, is high enough in level and low enough in frequency that I would be surprised if it didn't affect the speaker's sound quality, yet in his auditioning Art Dudley noted nothing untoward in this region. I did find a strong mode at 900Hz on the top panel; this could correlate with the discontinuity in the impedance traces at the same frequency. But I was surprised that the mode at 355Hz didn't affect the impedance measurement.

Fig.2 Triangle Esprit Comete Ex, cumulative spectral-decay plot calculated from the output of an accelerometer fastened to the center of the sidewall (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

The impedance glitch at 620Hz correlates with a very strong resonance at that frequency in the port's output (fig.3, blue trace). There is also a suspicious-looking peak in the woofer's output close to the same frequency (fig.3, black), though this graph lacks the resolution to indicate if this peak occurs at exactly the same frequency as the port resonance. The saddle centered on 62Hz in the impedance-magnitude trace indicates that that is the tuning frequency of the port. There is, indeed, a minimum-motion notch in the woofer's nearfield output at that frequency, though the port's output broadly peaks a little higher in frequency. The woofer rolls off quite sharply above 2kHz, though what would otherwise be a well-controlled rolloff is disturbed by a small peak at 4kHz. The tweeter (fig.3, red) is rolled off very steeply below 2kHz. While its output is relatively uniform in its passband, it appears to be balanced about 5dB too high in level.

Fig.3 Triangle Esprit Comete Ex, acoustic crossover on tweeter axis, corrected for microphone response, with farfield responses of tweeter (red) and woofer (black), with the summed nearfield responses of the port (blue) and woofer (black) plotted in the ratio of their radiating diameters.

Fig.4 shows how these individual measurements sum on the tweeter axis in the farfield. While the woofer and tweeter outputs integrate nicely, the Comete Ex's response rises through the mid- and high treble. The peak around 700Hz is still evident, and the speaker's output in the upper bass peaks up by 7dB. Some of this boost will be due to the nearfield measurement technique, which assumes a 2pi acoustic environment for the low-frequency radiators, but the speaker does have a somewhat underdamped low-frequency alignment. Subjectively, this will tend to balance the hot top octaves, but as AD noted, it does add "a bit more drumminess on some notes than the recording would seem to call for."

Fig.4 Triangle Esprit Comete Ex, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the complex sum of the nearfield responses plotted below 300Hz.

The Esprit Comete Ex's lateral dispersion on the tweeter axis is well-controlled and even (fig.5), which correlates with the excellent stereo imaging noted in the review. There is only the slightest hint of off-axis flare at the bottom of the tweeter's passband. The horn loading for the tweeter may increase the unit's sensitivity, but it appears that the primary benefit is to match the unit's dispersion to that of the woofer in the crossover region. The tradeoff is that the speaker becomes more directional in the top two audio octaves, but, as AD found, that does enable the listener to adjust the toe-in angle to obtain a more neutrally balanced treble. In the vertical plane (fig.6), a deep suckout develops immediately above and more than 10° below the tweeter axis. The stands should be chosen to place the listener's ears close to the tweeter axis, if the Comete Ex is not to sound a little hollow.

Fig.5 Triangle Esprit Comete Ex, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90–5° off axis, reference response, differences in response 5–90° off axis.

Fig.6 Triangle Esprit Comete Ex, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 45–5° above axis, reference response, differences in response 5–45° below axis.

In the time domain, the Triangle's step response (fig.7) reveals that both drive-units are connected with the same positive acoustic polarity and that the tweeter step smoothly hands over to the woofer step. The tail of the latter's step, however, is overlaid with some gentle undulations with a period equivalent to a frequency of 710Hz, the same as the small peak in the on-axis frequency response. A ridge of delayed energy can therefore be seen in the speaker's cumulative spectral-decay plot (fig.8), though the initial decay of the speaker's sound is otherwise impressively clean. The tweeter's dome resonance occurs just below 20kHz, which is a bit close to the audible band for comfort for younger listeners.

Fig.7 Triangle Esprit Comete Ex, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

Fig.8 Triangle Esprit Comete Ex, cumulative spectral-decay plot at 50" (0.15ms risetime).

The Comete Ex's measurements are not at all bad considering its price, and suggest that the speaker's owner can experiment with toe-in and placement to get the optimal balance between the high- and low-frequency regions. Its high sensitivity will also allow it to work well with low-powered amplifiers. But I am suspicious of the fact that the port resonance, the cabinet panel resonance, and the slight peak in the farfield response coincide within a quite narrow region of 620–900Hz.—John Atkinson

COMPANY INFO
Triangle Electroacoustique
US distributor: VMAX Services
P.O. Box 570
Chazy, NY 12921
(800) 771-8279
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