P.M.P.O. (Peak Music Power Output)
What kind of a spec is that? 1000
watts measured how? At 1000% distortion? MidiLand isn’t the only manufacturer
guilty of this meaningless number, almost all brands boast that somehow the
maximum music output is vastly higher (10 times or more) the
R.M.S. (root-mean-square) wattage. Don’t ever be wowed over by the P.M.P.O.
spec. It has no relevance to anything. Besides, as loud and efficient as speakers
are these days, I wouldn’t want to have my eyeballs blown out by a bass peak
of 1000 watts.
Rated R.M.S. Power Output
Without turning
one screw to peer inside the sub box, the giant AC adapter gives a clue as
to the maximum power output of the 490's. Rated at 14.5 VAC at 2.5 Amps this
yields just over 36 watts of input power. MidiLand rates the 490's at 10 watts
for each satellite and 30 watts for the subwoofer. Can a 36-watt transformer
deliver almost double its rated power? The short answer is no.
Partial
disassembly revealed a 6800uF 25 volt capacitor and a mysterious Philips OM8383S
9-pin output semiconductor. Even though Philips denies any knowledge of this
unit, output power can still be calculated. At idle (no signal input), the
measured voltage across the input power capacitor was 16.5 volts DC. Into
a 4-ohm load, this translates to 34 watts rms for the sub and 8.5 watts rms
for each satellite. Of course, no load conditions aren’t practical, so I turned
the 490’s on and cranked the volume until a slight clipping was heard. At
full volume the supply voltage dropped significantly to 13.0 volts DC. The
power calculations now are 21 watts and 5.3 watts for the sub and satellites
respectively.
What can be concluded regarding
the factory rated power? Not really grossly out of spec, the 490’s can pump
out about 42 watts rms and 68 watts for short peaks (100mS or less). Interestingly
enough, the sub had 30W stamped on it and the satellites had 5W stamped on
them.
Miscellaneous Measurements
The crossover frequency, the frequency
in which the sub stops producing sound and the midranges start producing sound,
was measured at 150Hz, typical for speakers of this genre. Signal
to noise measurements were also typical at 62dB "C" weighted relative
to 1 watt into a 4-ohm load (2 volts rms).
Maximum volume for the sub was 107dB
at 18 inches and each pair of satellites could muster 100db of undistorted
sound at my 18 inch standard. The total maximum volume from all 5 pieces was
107db. The maximum output was measured with the satellites at 18 inches from
the listener, while the sub was 36 inches from the listener, placed at the
intersection of two walls.
Frequency response
As I have mentioned in previous articles, I have routinely listened to some
of the best examples available in the professional high-end arena. Some speakers
cost in the ten’s of thousands of dollars, and fall short of the magical 20Hz-20KHz
+3dB specifications. Actual measurements weren’t unreasonable; the
6-1/2 incher dipped moderately low into boom-land. The –3dB point relative
to 100Hz was 63Hz and the –6dB point was 61Hz. This equates to a usable extension
of nearly 60Hz, which, although higher than I expected, may be the best at
this price point.
Since the satellites are single driver
units, the midrange driver must strain to reproduce frequencies in the tweeter
range. Most mid’s flop at trying and so do the 490’s drivers. Extreme highs
simply won’t be available, but as I discovered in my review of the Altec
ACS-45.2’s, this doesn’t equate to unlistenable
highs—just muted ones.
