Paradigm Reference Studio/20 loudspeaker Measurements
The Paradigm was quite sensitive, at an estimated 86.5dB/2.83V/m (B-weighted). Its impedance (fig.1) dropped to 4 ohms briefly in the lower midrange, but was otherwise benign. The timing of the rear-firing port is indicated by the "saddle" in the magnitude curve at 42Hz, the frequency of the lowest note of the 4-string double bass and bass guitar. Other than a small wrinkle in the traces at 25kHz, indicating the presence of an ultrasonic tweeter resonance, there are no artefacts due to cabinet resonances apparent.
Fig.1 Paradigm Reference Studio/20, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).
Fig.2 shows the responses of the Studio/20's drive-units and port. The crossover between the tweeter and woofer can be seen to be set at 1.5kHz, meeting the specification. This is lower than usual for a two-way design, but typical of Paradigm designs, I have found. As expected from the impedance plot, the port peaks between 40Hz and 50Hz. Though there is some kind of resonance in its output at 900Hz, this is low in level and its audibility will be further reduced by the fact that the port faces away from the listener.
Fig.2 Paradigm Reference Studio/20 acoustic crossover on tweeter axis at 50", corrected for microphone response, with the nearfield woofer and port responses plotted below 300Hz and 1kHz, respectively.
How these individual responses add on the tweeter axis is shown in fig.3. (The grille was in place for all the measurements.) The Studio/20's upper-bass appear to be balanced a little on the generous side with this nearfield measurement. This is not something that any audiophile will complain about and the benefit is, as Bob Reina found, that a relatively small speaker can have a more extended bass response than might be expected.
Fig.3 Paradigm Reference Studio/20, anechoic response on tweeter axis at 50", averaged across 30 degrees horizontal window and corrected for microphone response, with complex sum of the nearfield woofer and port responses plotted below 300Hz.
In the midrange and treble, the Paradigm is impressively flat, with just a small amount of excess energy between 7kHz and 12kHz that might correlate with BJR's finding the speaker a little "metallic"-sounding. Interestingly, the measured response of the very similar Paradigm Active/20 (fig.2, November 1997, p.116.), which sounded flat through the treble actually featured a slight depression in this region.
All things being equal, the lowish crossover frequency means that the speaker's lateral dispersion (fig.4) is wide and well controlled. This is always associated with excellent, stable, well-defined stereo imaging, in my experience. Vertically (fig.5), the speaker offers pretty much the same balance as long as the listener's ear is between the top of the cabinet and the center of the woofer, meaning that tall stands are better than short stands.
Fig.4 Paradigm Reference Studio/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.
Fig.5 Paradigm Reference Studio/20, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 45 degrees-5 degrees above-axis; reference response; differences in response 5 degrees-45 degrees below-axis.
The Paradigm's step response (fig.6) is tyical of the genre, with both units connected with the same polarity. Like the Active/20, the Studio/20's waterfall plot (fig.7) is astonishingly clean, implying excellent presentation of low-level detail.
Fig.6 Paradigm Reference Studio/20, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).
Fig.7 Paradigm Reference Studio/20, cumulative spectral-decay plot at 50" (0.15ms risetime).
Although the impedance plot was free from wrinkles, the cabinet did feature a single resonant mode, present on all surfaces but highest in amplitude on the side panel (fig.8). However, this is high enough in frequency that its subjective effect will probably be minimal.—John Atkinson
Fig.8 Paradigm Reference Studio/20, cumulative spectral-decay plot of accelerometer output fastened to cabinet side. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)