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Satellite Measurements

Power output measurements were possible and not completely surprising. Glancing at the HUGE wall wart provided me with information that automatically contradicts Labtec's power claims. The external transformer and main filter capacitor were hidden inside a case that was unopenable but the specs were plainly printed on the outside. They said "Output : DC 14.4V 1000mA." Now, with a simple calculation (P=IxE), the result is 14.4 watts. That's the total output power to the satellites and subwoofer. We'll see that Labtec's claim of 30 watts RMS comes with quite the caveat.

First, I measured the maximum RMS voltage that the flat panels could stomach before either they or the amps pooped out. With both channels screaming out 1KHz, clipping was distinctly heard at 4.65 volts. The maximum SPL from both panels at 18 inches peaked at a slightly low 100dB, not quite keeping up with sub. Next, I measured the current used to figure out the impedance. The formula used is E=IxR (current is denoted as I). To ward off emails touting the absence of inductive and capacitive reactance, rest assured that these figures were so low as to be practically insignificant.

Satellite Impedance

Frequency
Voltage (E)
Current (I)
Impedance (R)
315Hz
757 mV
117 mA
6.45 Ohms
1.0KHz
885 mV
129 mA
6.63 Ohms
4.0KHz
969 mV
134 mA
7.23 Ohms

Satellite Pics

Front
Rear

The funny thing is that Labtec claims these SLAB panels are 4 ohm units. I would rate them closer to 7 ohms. Why is this important? It affects the power calculations greatly. At 1KHz, the maximum power output to both satellites at the point of clipping (about 3% distortion) works out to be only 3.26 watts RMS each. Since the subwoofer is connected to a pair of amps in a BTL (bridged tied load) arrangement, approximately 2x4.65 or 9.30 volts would be the maximum available to drive the sub. If the sub is an 8 ohm unit, the max power would calculate to just over 10 watts, if the sub really is a 4 ohm unit, the max power would then be just over 21 watts. Due to the weak wall wart, I'm predicting it would be an 8 ohm driver because current demand would far exceed what a 4 ohm boomer would require.





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