Triad Design System Seven satellite/subwoofer loudspeaker Measurements

Sidebar 3: Measurements

Fig.1 shows the satellite's impedance magnitude and phase angle. (Note that electrical phase is presented with inductive angles to the bottom of this graph, the opposite of our usual convention.) Since the impedance is generally above 6 ohms, the System Seven should be an easy load for an amplifier to drive. The narrow impedance peak is centered on the frequency that the midrange begins rolling off.

Fig.1 Triad System Seven satellite, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

The System Seven's frequency response, averaged over a 30° lateral window, is shown in fig.2. (The woofer's nearfield response, measured separately, is shown to the left of the graph.) It reveals a smooth midband with a rising treble response, as suggested by the auditioning. As the measurement microphone is moved off-axis, the response flattens considerably. The sharp dip at 7kHz is greatly reduced, as is the treble energy, when measured off-axis. In addition, the amount of HF level is more in line with the rest of the spectrum off-axis, also suggested by the auditioning. The System Seven is remarkably flat through the entire midband to about 4kHz, an area where the ear is most sensitive to amplitude irregularities. The woofer response shows the System Seven's ability to produce low frequencies and the fact that its energy output is centered around the octave from 40–80Hz.

Fig.2 Triad System Seven satellite, anechoic response on tweeter axis at 44", averaged across 30° horizontal window and corrected for microphone response, with the nearfield response of the System Seven woofer plotted below 600Hz.

Also indicated by the measurement is the woofer's rapid rolloff above 100Hz. It is about 10dB down at 150Hz, the very lowest frequency we could expect the satellite to produce at full level. These measurements suggest the System Seven may well have a dip in the overall response between the woofer and satellites. This correlates very well with my impression of a leanness through the mid/upper bass coupled with ample output in the low bass.

Moving to the time domain, the satellite's impulse response is shown in fig.3. The response is clean, but with a little overhang. The step response (fig.4) indicates that all the drive-units are connected in the same positive acoustic polarity, but that the tweeter's output is a little too much ahead of that of the midrange unit for optimal integration on this axis.

Fig.3 Triad System Seven satellite, impulse response on tweeter axis at 44" (5ms time window, 30kHz bandwidth).

Fig.4 Triad System Seven satellite, step response on tweeter axis at 44" (5ms time window, 30kHz bandwidth).

The System Seven's cumulative spectral-decay plot (fig.5) is among the best I've seen. It reveals a very rapid decrease of energy after the drive signal has been removed. The only evidence of any overhang is the ridge at 3kHz, but this is very minor. (The ridge at 16kHz is the computer monitor's scanning frequency, not a loudspeaker anomaly.) Compare the System Seven's waterfall plot with others taken over the past few months: it is among the best measured.—Robert Harley

Fig.5 Triad System Seven satellite, cumulative spectral-decay plot on tweeter axis at 44" (0.15ms risetime).

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Triad Speakers, Inc.
15835 NE Cameron Blvd.
Portland, OR 97230
(877) 264.6315
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