Paradigm Reference Studio/20 loudspeaker Measurements

Sidebar 3: Measurements

The Paradigm Reference Studio/20's voltage sensitivity on its tweeter axis was to specification at an estimated 87dB(B)/2.83V/m. Its impedance magnitude (fig.1, solid trace) remained above 6 ohms in the upper midrange and treble, but dropped to 3.5 ohms in the lower midrange. This, together with the combination of 5.1 ohms magnitude and –37° electrical phase angle at 110Hz (a frequency where music has a lot of energy), implies that the Paradigm will work best with good amplifiers rated at 4 ohms.

Fig.1 Paradigm Reference Studio/20, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

The impedance traces are free from the small wrinkles that would hint at the existence of cabinet resonances. Investigating the panels' vibrational behavior with a plastic-tape accelerometer uncovered very little to be concerned about. The strongest mode was present on the sidewalls, at 414Hz (fig.2), but this is high enough in frequency and low enough in level not to lead to coloration.

Fig.2 Paradigm Reference Studio/20, 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 saddle centered at 45Hz in the impedance-magnitude trace suggests that this is the frequency of the reflex port mounted on the front baffle. The woofer's response, measured in the nearfield, does indeed show the expected notch at this frequency (fig.3, bottom-left trace), while the port's output broadly peaks between 30 and 100Hz. The port's upper-frequency rolloff is commendably free from resonant peaks. The woofer crosses over to the tweeter at 2kHz, as specified. Though the crossover filters are said to be second-order "electro-acoustic," the tweeter's acoustic high-pass slope appears steeper than the second-order's 12dB/octave. The woofer's low-pass rollout is approximately second-order, but is broken by some slight peaks due to cone-breakup modes. The tweeter's output is flat within the audioband, but a large ultrasonic peak develops on axis between 20 and 30kHz that might bother bats and other small mammals.

Fig.3 Paradigm Reference Studio/20, acoustic crossover on tweeter axis at 50" (with grille), corrected for microphone response, with nearfield responses of woofer and port, plotted in the ratios of the square roots of their radiating areas below 350Hz and 700Hz, respectively.

Fig.4 shows the Studio/20's farfield response, averaged across a 30° horizontal angle on the tweeter axis, spliced at 300Hz to the complex sum of the nearfield woofer and port outputs. The response is superbly flat from the middle of the midrange to the top of the audioband, but the ultrasonic peak in the tweeter's output again makes an appearance. The broad rise in the Paradigm's upper-bass output will be due in part to the nearfield measurement technique, but the bass alignment appears to be somewhat underdamped. Bob Reina did remark on a "a sense of bloom" in the lower midrange, which is what I would have expected from this measured behavior.

Fig.4 Paradigm Reference Studio/20, anechoic response on listening axis at 50" (with grille), averaged across 30° horizontal window and corrected for microphone response, with the complex sum of the nearfield responses plotted below 300Hz.

The response measurements that went into the trace in fig.4 were taken with the Paradigm's grille in place, as this has plastic moldings that continue the smoothly curved acoustic environment presented to the drive-units by the front baffle. Fig.5 shows what happens when the grille is added: the main effect is to reduce the speaker's output by 3dB in the low treble. In other words, if you listen to the Paradigm without its grille, an octave-wide, 3dB peak appears in the low treble. Again, as BJR noted: "I listened to them briefly with the grilles off, and I agree: the highs sounded too prominent, and detached from the midrange."

Fig.5 Paradigm Reference Studio/20, difference in tweeter-axis response made by adding grille.

The Studio/20 also needs the grille to optimize its dispersion. Fig.6 shows the lateral dispersion with the grille in place, referenced to the response on the tweeter axis. There appears to be a small off-axis flare between 6 and 9kHz, but if you look at the on-axis response in fig.4, this is actually due to a small suckout filling in to the speaker's sides. The Studio/20 offers textbook-perfect lateral dispersion, with the contour lines in fig.6 smooth and uniformly spaced. In the vertical plane (fig.7), a suckout develops in the crossover region above the top of the cabinet. Tall stands will work better with this speaker than short ones.

Fig.6 Paradigm Reference Studio/20, lateral response family at 50" (with grille), 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.7 Paradigm Reference Studio/20, vertical response family at 50", normalized to response on tweeter axis (with grille), from back to front: differences in response 15–5° above axis, reference response, differences in response 5–15° below axis.

Turning to the time domain, the Studio/20's step response (fig.8) indicates that both drive-units are connected with positive acoustic polarity but that the tweeter step smoothly hands over to the woofer's. This correlates with the good frequency-domain integration of their outputs seen in fig.4. The cumulative spectral-decay plot (fig.9) is superbly clean except for a couple of low-level modes in the mid-treble. These are most likely due to woofer-cone breakup, and although they are low in level, I do wonder if they led to BJR's occasional concern about the Studio/20's high frequencies.

Fig.8 Paradigm Reference Studio/20, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

Fig.9 Paradigm Reference Studio/20, cumulative spectral-decay plot at 50" (0.15ms risetime).

Even without taking its relatively affordable price into account, the Paradigm Reference Studio/20 offers superb measured performance. Just be sure to use it with its grille on, and placed on a stand that brings its tweeter up to ear level.—John Atkinson

Company Info
Paradigm Electronics Inc.
205 Annagem Boulevard
Mississauga, Ontario L5T 2V1
Canada
(905) 564-1994
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