Inner Construction & Measurements
(2)
The frequency response of 35Hz-20KHz is another matter entirely. This spec
is useless without a tolerance (i.e. plus or minus X decibels). Professional
speakers costing in the thousands of dollars have to struggle to meet either
a reasonable 35Hz or 20KHz output. Measurements revealed still another surprise.
While the 45.2’s couldn’t reproduce 35Hz at any appreciable volume the low-end
curve, relative to 100Hz, dug deep. The –3dB point was 56Hz and the –6dB point
was 50Hz, not only respectable numbers but essentially matching the classic
48’s. Even though the 6.5" woofers appear to be the exact same units,
I expected a more sharply rolled off curve due to the smaller and different
cabinet design. Kudos to Altec again.
The
TDA 7375 audio amplifier chip was specifically designed for car stereos or
any other 4-ohm impedance environment. Downloading the ".pdf" datasheet
from SGS-Thompson yielded the aforementioned max power calculations. I observed
only mild heat from the heatsink at full power output, even when the shiny
aluminum wasn’t mounted in the subwoofer port.
Overall, the power supply and amp chip is very
well designed and should provide for many long, enjoyable years of extended
listening. The 45.2’s didn’t balk at ultra loud volume levels, they easily
met the challenge without the typical distortion or limiting effects caused
by weak internal components or overheating output chips.
Signal to noise (S/N) measurements were
average, calculating to 60 decibels "C" weighted (full spectrum)
into a 4-ohm load. Similar to the ACS-48’s S/N, this figure should be greatly
discounted because most computer fans effectively broadcast a "whooshing"
noise that mask much of the potential hiss that would otherwise be heard.
Specifically, the noise of the TDA 7375 won’t be heard due to the lack of
tweeters in the 45.2’s.
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Satellites
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Surround
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The A2156 midrange driver in the ACS-48’s is
the exact same model number as used in the 45.2’s, sans tweeter. This leads
to forcing the 3" driver to reproduce all the frequencies above it’s
lower crossover point, which is set around 150 Hz.
A 3" driver simply cannot muster the speed necessary to wiggle back and
forth 10,000 to 20,000 times per second and if the satellites have one major
downfall, this would be it.
Quality touches, like full rubber housing
surrounds (similar to weather stripping), keep the plastic satellites from
buzzing at high volumes. The full range units are fully shielded unlike the
subwoofer. Placing the satellites near a 19" monitor evoked no tor degaussing.
