Review: BG Radia's Supersized Surround System Page 3


Bottom Line


In the right setting - a very large living room or custom home theater with the wall space to accommodate 6-foot-high speakers - the LA-550/SS-303 combo delivers some of the finest movie sound you'll hear outside of, say, the Mann Village Theater in Los Angeles. There's no denying that it's a niche product, but if you're in that niche, it's something you should hear.


Test Bench


Frequency response
• left/right 55 Hz to 20 kHz ±5.1 dB
• surround 52 Hz to 6.3 kHz ±9.7 dB
• subwoofer 26 to 183 kHz ±3 dB

Sensitivity (SPL at 1 meter with 2.8 volts of pink-noise input)
• left/right 92 dB
• surround 91 dB

Impedance (minimum/nominal)
• left/right 5.4/8 ohms
• surround 5.9/8 ohms

Bass output, subwoofer (CEA-2010 standard)
• Ultra-low bass (20-31.5 Hz): 88.3 dB
• Low bass (40-63 Hz): 108.1 dB

Bass limits
• left/right 50 Hz at 83 dB
• surround 40 Hz at 85 dB

The BG LA-550 proved extremely difficult to measure because its long driver array doesn't really "add up" acoustically until you're about 15 feet away. It's not practical with my equipment setup and available space to run measurements at this distance. So I ran them at 3 meters, the farthest I could get the speaker from the mike while still being able to remove reflections off nearby objects from the response. As a result, the speaker probably shows more treble rolloff than you'd hear in a normal installation. Take these measurements as an approximation.

For this speaker, I spliced the close-miked response of the woofers to the quasi-anechoic measurements of the speaker, averaged from 0° to 30° off-axis and smoothed to 1/12 octave. The splice point was 600 Hz, much higher than the normal ~240 Hz because of the greater measurement distance. I ran all measurements with the grille in place. The LA-550 was mounted in one of the enclosures BG supplied, with foam attached to the corners to prevent diffraction.

For the SS-303, I was able to run measurements much the same way I usually do with a multipolar surround speaker: averaged quasi-anechoic response at 2 meters from 0° to 60°, smoothed to 1/12 octave and spliced at 400 Hz to a close-miked measurement of the woofers. Again, measurements were made with the grille in place and using a BG-supplied enclosure with foam attached to the corners.

The LA-550 and SS-303 responses are normalized to 0 dB at 1 kHz, the subwoofer normalized so that its peak response shows as +3 dB.

Given the measurement difficulties, the LA-550's frequency response looks fairly smooth. As I suggested, it's not as bass-heavy in a normal application as it appears in this graph. There's a broad dip centered at 1.3 kHz, with small response peaks centered at 2.2, 3.7, 5.8, and 11 kHz. Off-axis response was great: At 45° and 60° off-axis, it looked quite similar to what you see here, just with more treble rolloff and the flattening of that peak at 11 kHz. In case you're curious how it measured from 2 meters, the treble rolloff was much more extreme. The curve looked similar but tilted down on the right (treble) side; I calculated ±13.9 dB from 55 Hz to 20 kHz.

The SS-303's measurements were pretty jagged, as you might expect from the multidirectional driver array. The averaged measurements showed a lot of treble rolloff. As is often the case with complicated, multipolar arrays, the response varied considerably at different angles.

Both speakers will be easy for practically any amplifier to drive because their sensitivity is high - in the low-90-dB range - and their impedance curves never dip very low. This is helped by the ribbon drivers, whose impedance runs fairly high and mostly flat. The impedance phase curves of both speakers are moderate, never exceeding –35°.

The BGX-S6B has the same general characteristics I measured in its big brother, the BGX-S12B: solid punch in the second octave of bass but much less output in the bottom octave. Using CEA-2010 measurement techniques, with four of the subwoofer modules lined up together, I got 110.1 dB from 40 to 63 Hz and 89.3 dB from 20 to 31.5 Hz. Close-miked frequency response shows a –3-dB point at 25 Hz. The measurements here are for the movie mode with the crossover bypassed; the music mode introduced a couple of very tiny changes in frequency response but, more important, brought the subwoofer's overall level down by about –5 dB. The combined low-pass response of the crossover and the drivers' acoustical rolloff is about –18 dB/octave.


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