PSB Image 4T loudspeaker Measurements part 2
Fig.4 PSB Image 4T, anechoic response on-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 plotted below 300Hz.
Fig.5 PSB Image 4T, lateral 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.6 PSB Image 4T, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 15 degrees-5 degrees above reference axis, reference response, differences in response 5 degrees-10 degrees below axis.
In the time domain, the PSB's step response (fig.7) reveals that all three drive-units are connected with the same, positive acoustic polarity, with the tweeter step smoothly handing over to the upper woofer's step. However, some mild ringing can be seen overlaying the tail of the woofer step. Though the waterfall plot (fig.8) is generally very clean, it shows that this ringing is associated with some delayed energy at the top of the upper woofer's passband. Perhaps this is the cause of Bob's "powdery" coloration.
Fig.7 PSB Image 4T, on-axis step response at 50" (5ms time window, 30kHz bandwidth).
Fig.8 PSB Image 4T, cumulative spectral-decay plot at 50" (0.15ms risetime).
All in all, this is excellent measured performance for such an inexpensive loudspeaker.—John Atkinson