Paradigm Reference Active/20 loudspeaker Measurements

Sidebar 3: Measurements

Even with its level control set to the central detented position, the Paradigm Active/20 didn't require much drive to go quite loud. With a 1kHz, 1/3-octave warble tone, 200mV (balanced) was enough to raise an estimated 95dB at 1m. It's hard to conceive of a combination of source components that wouldn't accommodate this speaker. The protection seems quite complex: while 470mV (unbalanced) of the white-spectrum MLS noise was enough to turn on the red warning LED, the indicator remained green when the speaker was driven with more than 1V of 1kHz sinewave.

The 6" woofer is rolled off faster than would be the case with a simple reflex system. Fig.1 shows the nearfield responses of the woofer and the port, together with their complex sum (footnote 1). Both woofer and port roll out with a fourth-order, 24dB/octave slope, while their combined response approaches 27dB/octave. The small woofer is therefore protected from infrasonic overload. The measured response appears to be 6dB down at 35Hz, which is a low frequency for a minimonitor—I assume that some equalization is at work here. The reflex port covers the 30Hz-60Hz octave, but note that its output peaks up again at 800Hz. This is presumably due to some kind of pipe resonance; fortunately, the port opens on the speaker's rear, meaning that the subjective effect of this peak will probably be negligible.

Fig.1 Paradigm Active/20, LF Contour set to "0," nearfield responses of woofer and port responses plotted below 1kHz, with the complex sum of port and woofer responses (top at 70Hz).

To the left of fig.2 is shown the Reference Active/20's bass response with the Low-Frequency Contour set to its maximum and minimum positions: the effect is to move the speaker's -6dB point between 40Hz and 32Hz. The third trace to the left of fig.2 is the low-frequency response with the High-Pass Filter switched into circuit: -3dB at 67Hz. This will allow the Paradigms to be matched with a subwoofer.

Fig.2 Paradigm Active/20 with grille in place, anechoic response on tweeter axis at 50", averaged across 30 degrees horizontal window and corrected for microphone response, with the complex sum of midrange and woofer responses plotted below 300Hz with (L-R): LF Contour set to "+4dB," "-4dB," and "0" with the High-Pass Filter engaged.

Moving higher in frequency in fig.2, the Active/20 features a very smooth response on the tweeter axis, with perhaps a slightly recessed output in the mid-treble. Certainly, this is how it sounded in the listening room. The output returns above the 0dB line above 18kHz, but this should not present any subjective problems. This curve was taken with the grille on. Removing the grille results in a response peak almost 5dB high just below 4kHz (fig.3), presumably because the tweeter no longer sees a clean, nonobstructive acoustic environment. Do not listen to this speaker with its grille removed.

Fig.3 Paradigm Active/20, effect on anechoic response of removing grille (5dB/vertical div.).

The curve in fig.2 was also taken with the High-Frequency Contour control set to its middle, detented position. Fig.4 shows the effect of the control set to its maximum and minimum positions. (For clarity, the on-axis response has been subtracted from both of these curves.) The control can be seen to shelve the speaker's treble above 3kHz up or down by approximately 2dB.

Fig.4 Paradigm Active/20, effect on anechoic response of setting HF Contour to "±2dB."

Fig.5 reveals the Paradigm's vertical dispersion. A crossover suckout appears more than 10 degrees above the tweeter axis, suggesting that tall stands work best. The AudioStream Premier stands supplied by Paradigm for this review are 25" tall including the spikes, bringing the speakers' tweeters level with my ears, which was optimal. Horizontally (fig.6), the use of a small woofer results in superbly controlled dispersion, something that always correlates with good imaging, as I found in my auditioning. (The grille was left on for all of these measurements.)

Fig.5 Paradigm Active/20, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 10 degrees-5 degrees above-axis; reference response; differences in response 5 degrees-15 degrees below-axis.

Fig.6 Paradigm Active 20, horizontal response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90 degrees-5 degrees off-axis; reference response; differences in response 5 degrees-90 degrees off-axis.

Footnote 1: For full details of how I measure loudspeakers for Stereophile reviews, see "Loudspeakers: What Measurements Can Tell Us—And What They Can't Tell Us!," AES Preprint 4608, presented at the 103rd Audio Engineering Society Convention, New York, September 1997, and reprinted as three Stereophile articles.—John Atkinson
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