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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 45.2ís couldnít reproduce 35Hz at any appreciable volume the low-end curve, relative to 100Hz, dug deep. The Ė3dB point was 56Hz and the Ė6dB point was 50Hz, not only respectable numbers but essentially matching the classic 48ís. 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 wasnít 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 45.2ís didnít 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-48ís 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 wonít be heard due to the lack of tweeters in the 45.2ís.

Satellites
Surround

The A2156 midrange driver in the ACS-48ís is the exact same model number as used in the 45.2ís, sans tweeter. This leads to forcing the 3" driver to reproduce all the frequencies above itís 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.







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