Review: PSB Speakers Imagine Mini Speaker System Page 4
If you want true high-end sound quality in a truly tiny speaker, the PSB Imagine Mini I clearly one of the best options going. Match it up with a good subwoofer like the SubSonic 1 (and add more Minis and an Imagine C if you want surround sound) and you’ll have a system that sounds like something much bigger and much more expensive.
• minispeaker 82 Hz to 20 kHz ±3.0 dB
• center 61 Hz to 20 kHz ±3.8 dB
• subwoofer 36 to 145 Hz ±3 dB
Sensitivity (SPL at 1 meter/1 watt)
• minispeaker 84.6 dB
• center 86.7 dB
• minispeaker 3.1/8 ohms
• center 4.8/8 ohms
• minispeaker 63 Hz at 91 dB
• center 40 Hz at 103 dB
Bass output, subwoofer (CEA-2010 standard)
• Ultra-low bass (20-31.5 Hz) average: 79.4 dB
20 Hz: NA
25 Hz: 78.0 dB
31.5 Hz: 100.2 dB
• Low bass (40-63 Hz) average: 114.9 dB
40 Hz: 112.7 dB
50 Hz: 118.5 dB
63 Hz: 113.5 dB
I measured the Imagine Mini and Imagine C center speaker without grilles at a distance of 2 meters. Both sat atop a 2-meter-high stand to give quasi-anechoic results down to 250 Hz. The curves in the graph show an averaged response from 0° to 30°, smoothed to 1/12th of an octave. I close-miked the woofers and ports of both speakers, and then scaled and summed the results to get each speaker’s bass response. I then spliced the bass responses to the averaged quasi-anechoic responses to produce the curves you see here. To measure the SubSonic 1 subwoofer’s frequency response, I used a ground-plane measurement at 2 meters.
The Imagine Mini and Imagine C responses are normalized to 0 dB at 1 kHz, and the subwoofer is normalized so that its peak response shows as +3 dB. The Imagine Mini exhibits the classic measured response for a great minispeaker: a slight hump in the bass to give it a little extra oomph, a flat midrange, and a slight downward tilt to the tonal balance to keep it from sounding thin. There’s what seems to be a slight tweeter resonance at 17.5 kHz, but the peak it creates is so narrow and so high in frequency that I’m positive I can’t hear it and I doubt you can, either.
Off-axis response is outstanding. Other than the usual treble rolloff, there are no off-axis anomalies until you get out to 60° off-axis, where a 7-dB dip appears at 1.2 kHz. When measured on-axis, the sole significant effect of the grille is a 5.6-dB dip at 11 kHz. Pretty much ditto for the Imagine C, except the tonal balance is flatter and there’s a bigger bump in the bass; except for that bump, the C would measure flatter than the Mini, which is quite a feat for a two-way center speaker. (This measurement is with the port plug removed.) Off-axis response is very clean out to 30°, but past that, at 45° and 60° off-axis, you see major interference between the two woofers, resulting in 28- to 30-dB dips in the 1-kHz region. These are big and probably audible dips. I wonder if they’re the cause of my perception of a slight midrange emphasis, i.e., the dip made the region from 1 to 2 kHz seem subjectively emphasized. The grille produces a 3.9-dB dip at 11 kHz, but no other significant measurable effects.
Practically any amp or receiver can drive these speakers to reasonably loud levels. Average sensitivity from 300 Hz to 10 kHz at 1 watt (2.83 volts), measured quasi-anechoically at 1 meter, is a little low for the Imagine Mini at 84.6 dB, but about average for the Imagine C at 86.7 dB. Impedance runs 8 ohms nominal for both speakers. While the Imagine Mini drops to a somewhat low 3.1 ohms at 400 Hz, the impedance phase is just +4°, so it shouldn’t present a problem. Minimum impedance for the Imagine C is 4.8 ohms at 200 Hz, with phase of –3°. Maximum phase shift for the Mini is –71° at 132 Hz/9.3 ohms; for the C, it’s –69° at 94 Hz/17 ohms.
I measured the output of the SubSeries 1 using CEA-2010 methodology. Measurements were made on the ground at 2 meters; 6 dB was added to the results to approximate measurements at 1 meter. The SubSeries 1 has amazing output in the low bass (40-63 Hz) region, comparable to that of many much larger subs, but the output in the ultra-low bass (20-31.5 Hz) is weak, with decent output at 31.5 Hz but practically nothing below that. (To get the 20-Hz figure to calculate the ultra-low bass average, I subtracted 18 dB from the 25-Hz figure per CEA-2010 practice.) Combined low-pass function of the crossover, driver, and enclosure is about –16 dB/octave. —B.B.