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
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.
