Paradigm Reference Studio/60 v.3 loudspeaker Measurements

Sidebar 3: Measurements

The Reference Studio/60 v.3 is of above-average voltage sensitivity, at an estimated 89dB/2.83V/m. Its impedance doesn't drop below 4 ohms, and remains above 6 ohms for much of the audioband (fig.1), implying that it will work well with modestly specified amplifiers and receivers.

Fig.1 Paradigm Reference Studio/60 v.3, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

The traces in fig.1 are free from the midrange wrinkles and small discontinuities that would hint at the presence of panel resonances. Investigating the cabinet's vibrational behavior with an accelerometer confirmed that, despite the panels' relatively large size, they are effectively braced and stiffened, pushing up resonances to higher frequencies where they will be less annoying. Fig.2, for example, is a cumulative spectral-decay plot calculated from the output of the accelerometer when it was fastened to the center of the side wall 12" from the top of the speaker. Two ridges of delayed energy can be seen, the highest lying at 422Hz, but both are commendably low in level.

Fig.2 Paradigm Reference Studio/60 v.3, cumulative spectral-decay plot calculated from the output of an accelerometer fastened to the cabinet's side panel 12" from top (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

The saddle centered at 35Hz in the impedance magnitude trace (fig.1) suggests that this is the tuning frequency of the Studio/60's twin ports. To the left of fig.3 are shown the nearfield responses of the midrange unit (red trace), the woofer (blue), the front port (magenta), and the rear port (green), as well as the sum of these responses, taking into account radiating area and distance from a nominal farfield microphone position (black). While the outputs of the ports peak in a bandpass centered between 25Hz and 60Hz, the midrange unit and woofer differ slightly: the former's minimum-motion point occurs at 35Hz, the latter's at 31Hz. Overall, however, these curves suggest that the Studio/60 offers excellent low-frequency extension. In-room, with the usual boundary reinforcement, the Paradigm should offer a full measure of bass down to the 31.5Hz band, as Kal found.

Fig.3 Paradigm Reference Studio/60 v.3, acoustic crossover (without grille) on HF axis at 50", with the complex sum of the woofer, midrange, and port nearfield responses (black). Also plotted are the nearfield responses of the midrange unit (red), woofer (blue), front port (magenta), and rear port (green), weighted in the ratio of the square roots of the radiating areas.

To the right of fig.3, the individual farfield responses of the midrange unit and woofer and the tweeter reveal smooth rolloffs out-of-band and confirm that the crossover is set at 2kHz, a little lower than is usual for a 1" dome; this should optimize lateral dispersion. These measurements were taken with the grille off, which makes the speaker's response look peaky and uneven. Adding the grille, which eliminates sharp discontinuities in the dome's acoustic environment, smooths the tweeter's output. This can be seen in fig.4, which shows that the Studio/60's farfield response is impressively smooth and flat up to 10kHz. Fig.5 shows the effect on the Paradigm's response when the grille is removed: an audible peak appears in the mid-treble. As attractive as the Studio/60 looks without its grille, you must listen to this speaker with its grille in place if you are to get the treble smoothness you've paid for.

Fig.4 Paradigm Reference Studio/60 v.3, anechoic response with grille on HF axis at 50", averaged across 30 degrees horizontal window and corrected for microphone response, with the complex sum of the nearfield woofer and port responses, taking into account acoustic phase and distance from the nominal farfield point, plotted below 300Hz.

Fig.5 Paradigm Reference Studio/60 v.3, effect of removing the grille on the farfield response on the HF axis (5dB/vertical div.).

The contouring of the baffle provided by the grille also optimizes the speaker's dispersion, evidenced by the smooth, even contour lines in the graph of the Paradigm's lateral dispersion (fig.6). Even with the grille, a slight flare in the off-axis behavior can be seen between 3kHz and 6kHz, which might make the speaker sound slightly bright in small or underdamped rooms. The apparent off-axis peak at 12kHz in this graph is actually due to the on-axis notch at this frequency filling in to the speaker's sides—note that the graph shows only the changes in response off-axis, compared with the response on the tweeter axis. In the vertical plane (fig.7), the Studio/60s's balance doesn't change very much over a wide 10 degrees listening window centered on the tweeter axis—this is desirable, considering that the tweeter is a high 39" from the floor.

Fig.6 Paradigm Reference Studio/60 v.3, lateral response family at 50", normalized to response on HF 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.

Fig.7 Paradigm Reference Studio/60 v.3, vertical response family at 50", normalized to response on HF 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.

In the time domain, the speaker's step response (fig.8) reveals that all three drive-units are connected in positive acoustic polarity. The farfield cumulative spectral-decay plot (fig.9) is fairly clean, though a low-level ridge of delayed energy can be seen at 4.4kHz, this presumably emanating from a breakup mode of some kind in the midrange cone. (This graph was taken with the grille removed.)

Fig.8 Paradigm Reference Studio/60 v.3, step response on HF axis at 50" (5ms time window, 30kHz bandwidth).

Fig.9 Paradigm Reference Studio/60 v.3, cumulative spectral-decay plot at 50" (0.15ms risetime).

The Paradigm Reference Studio/60 v.3 offers excellent measured performance for an affordable price, contradicting the conventional wisdom that, dollar for dollar "big speakers have bigger problems" than small speakers.—John Atkinson

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