Test Report: Monitor Audio Bronze BX Speaker System Page 4

Test Bench

Frequency response (at 2 meters)
left/right 26 Hz to 20 kHz ±3.3 dB
center 33 Hz to 20 kHz ±2.2 dB
surround 29 Hz to 20 kHz ±3.5 dB
sub 21 to 230 Hz ±3 dB

Sensitivity (SPL at 1 meter with 2.8 volts of pink-noise input)
left/right 89 dB
center 90 dB
surround 88 dB

Impedance (minimum/nominal)
left/right 3.2/5 ohms
center 3.2/5 ohms
surround 3.1/5 ohms

Bass limits
left/right 40 Hz at 81.4 dB
center 50 Hz at 81.2 dB
surround 50 Hz at 76.9 dB
Bass output, sub (CEA-2010 standard)
Ultra-low bass (20-31.5 Hz): 103.4 dB
Low bass (40-63 Hz): 89.4 dB

Except for the subwoofer, measurements of the Bronze BX series speakers were made at 2 meters to ensure that full effects of cabinet diffraction and front-panel reflections were included. Measurements of the Bronze BX2 left/right speaker and BX Centre were taken with the speakers mounted atop a 6-foot stand. Measurements of the Bronze BXFX surround were taken with the speaker mounted on a large piece of plywood to simulate the effects of wall-mounting. The measurements shown in the graph were taken with the speaker grilles removed. These tests gave quasi-anechoic results down to about 250 Hz. Response of woofers and ports was close-miked, summed where applicable, and spliced to the quasi-anechoic response. The Bronze BXW-10 subwoofer's driver was close-miked. Except for the subwoofer, the frequency-response curves of each speaker are weighted to reflect how sound arrives at a listener's ears with normal speaker placement - with double weight on the ±30° response curve for the left/right speaker, on the 0° response curve for the center, and on the ±60° response curve for the surround.

Let's deal right away with the question that may be occurring to you from looking at this graph. While these relatively small speakers do deliver measurable output at surprisingly low frequencies when fed with the 2.83-volt (1-watt) sine waves used for frequency response measurements, it's important to understand that this output is accompanied by a large amount of distortion and would therefore not be considered usable. The bass-limit measurements give a more realistic picture of the speakers' bass response - which, despite these caveats, remains impressive. The Bronze BX2 left/right minispeaker measures extremely well. Its on-axis response is largely flat, and its off-axis response is one of the best I've seen. In fact, the off-axis response curves are almost identical to the on-axis curve, just decreasing in level as you move further off-axis. Bass response is excellent for such a small speaker, with usable output down to 40 Hz; one could get fairly satisfying sound from these without a subwoofer. The grille reduces overall output by about -2 dB on average, with dips of -5 dB centered at 5.5 and 9.5 kHz.

On-axis and at 15° off-axis, the Bronze Centre delivers extremely even response. At 30° or further off-axis, it suffers from the usual cancellation effects caused by interference between the two woofers, with dips of about -10 dB appearing at various frequencies between 700 Hz and 4 kHz, depending on the angle of measurement. The grille reduces output remarkably consistently, by -2 to -3 dB in the mids and treble. Usable bass output of 50 Hz is pretty good for a speaker of this size - more than adequate to accommodate the usual 80-Hz subwoofer crossover point.

Response of the Bronze BXFX is good for a wall-mounted nondirectional surround speaker. (The chart reflects a measurement taken with the speaker set for bipolar response; switching it to the dipolar mode has the effect of reducing average output by about -2 dB between 3 kHz and 7 kHz.) The dip centered at 475 Hz and the corresponding bump at 730 Hz are the result of wall-mounting. Deepest clean bass output is pretty good for a little surround speaker at 50 Hz, although there's not much of it at that low frequency.

Sensitivity of all models is very good, measuring between 88 and 90 dB. However, the impedance curves run low. They're almost identical, with a minimum impedance of about 3.2 ohms in the neighborhood of 180 Hz, and about half the curves running at or below 5 ohms. The phase curves are all exceptionally mild, though, never exceeding ±30° and usually running pretty close to 0°, so I doubt even a bottom-of-the-line A/V receiver would have a problem driving the Bronze BX series to reasonably high levels.

The response curve of the BXW-10 subwoofer that you see here is with the low-pass filter (or crossover) in the circuit set to its maximum frequency of 150 Hz, using the left-channel input. The response with the filter bypassed, using the LFE input, is flat to 1.3 kHz - an unusual result, but one that doesn't offer any useful advantage because you'll be crossing the subwoofer over to the other Bronze BX series speakers at around 80 Hz. The measured frequency response limit of 21 Hz is extremely low for such a small driver and cabinet; I assume this is the result of equalization, not the natural response of the driver and cabinet. Measured by the CEA-2010 standard, average output was 89.4 dB between 20 and 31.5 Hz and 103.4 dB from 40 to 63 Hz. The ultra-low bass output is impressive for the BXW-10's size, and there's a measurable CEA-2010 response down to 20 Hz, although it's 9.9 dB down from the 25-Hz output. The low-pass function of the internal crossover is 24 dB/octave.
-Brent Butterworth