PSB New Stratus Mini Measurements

Sidebar 3: Measurements

The New Stratus Mini's B-weighted sensitivity weighed in at a calculated 85dB/2.83V/m, an inconsequential 1dB below the specification (probably due to differences in measurement technique). The impedance plot (fig.1) indicated the New Mini to be a moderately demanding load, with an amplitude dipping below 4 ohms in the lower midrange. The variation of impedance with frequency is mild, however.

Fig.1 indicates that the New Mini's port appears to be tuned to 39Hz or so, this confirmed by the nearfield response plots (fig.2), which show the port's maximum output coincident with the woofer's minimum output, this typical of a reflex design. The woofer's output appears to be slightly exaggerated in the upper bass but otherwise evenly balanced in its passband. It rolls off steeply above 2kHz, as does the tweeter below the same frequency, though there seems to be a little too much overlap between the two drive-units in the crossover region.

Fig.1 PSB New Stratus Mini, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

Fig.2 PSB New Stratus Mini with grille, acoustic crossover on listening axis at 50", corrected for microphone response, with nearfield woofer and port responses plotted below 300Hz.

This gives rise to a very small peak at 2kHz, as can be seen in the New Mini's overall response (fig.3) measured across a ±15 degrees horizontal window centered on an axis level with the top of the enclosure (which I understand to be the intended listening axis). This small peak might have contributed to the occasional, music-dependent sense of brightness I detected in the upper midrange. There is a slight lack of energy in the bottom of the tweeter's passband, this correlating with the laid-back balance, and a slight excess at the bottom of the woofer's, but overall the New Stratus Mini's balance is impressively smooth and flat. Paul Barton—a master at measuring loudspeakers—had supplied me with a full set of swept-sinewave measurements for the review samples, taken in the Canadian NRC's anechoic chamber. I was gratified to see that his listening-window measurement (not shown) generally agreed with the plot shown in fig.3. What differences there were could be attributed to the differences in technique and measuring conditions.

Fig.3 PSB New Stratus Mini with grille, anechoic response on listening axis at 50", averaged across 30 degrees horizontal window and corrected for microphone response, with complex sum of nearfield woofer and port responses plotted below 300Hz.

The PSB sounded significantly worse without the grille. Fig.4 shows the effect on the fig.3 response of removing the grille: severe peaks up to 4.5dB appear in the mid- and high-treble regions.

Fig.4 PSB New Stratus Mini, effect of removing grille on anechoic response on listening axis at 50" (only the difference in response is shown).

The PSB's lateral dispersion (fig.5) revealed some moderate beaming at the top of the woofer's passband (the cursor position). Overall, however, this is good performance. In the vertical plane (fig.6), the Mini's balance doesn't change too much as long as you sit within a ±5 degrees window centered on the top of the cabinet. On the 25" stand, this gives a listening height of between 34" and 46" at a typical listening distance. Above or below that, however, suckouts and peaks appear in the response.

Fig.5 PSB New Stratus Mini with grille, horizontal response family at 50", normalized to response on listening 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.6 PSB New Stratus Mini with grille, vertical response family at 50", normalized to response on listening axis, from back to front: differences in response 90 degrees-5 degrees above listening axis; reference response; differences in response 5 degrees-90 degrees below listening axis.

COMPANY INFO
PSB
The Lenbrook Group
633 Granite Court
Pickering, Ontario L1W 3K1, Canada
(905) 831-6333
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