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Objective Measurements


Data acquired and reported of this type is done without any opinion or bias whatsoever. For a quickie brush up course on audio terminology and measurements, point your browser to the Audio Reproduction Systems article.

Rated R.M.S. Power Output

As I griped earlier, a high distortion power rating is nearly useless when contemplating higher end audio. Possibly a few teenagers, especially those with some hearing to spare might enjoy massively distorted sound, but this reviewer cringes at anything much over the 1% mark (which is plenty detectable). For the purposes of all my audio reviews, I chose the generous 3% rating, which was traditionally utilized for cassette deck/reel-to-reel testing until the early 1990's. At 3%, the waveform when viewed on an oscilloscope starts to visually "flat-top" or clip.

The main voltage rails of the two 4700uF 35V capacitors measured 23.6 VDC at no load. With nearly 48 Volts peak-to-peak, the following estimations were calculated (not directly measured due to time constraints). The amplifier chips are higher quality ICs, namely two TDA7296 chips and one TDA7294 chip. Based on the .pdf files and assuming peak power (for a fraction of a second) ratings, this would give rise to 60 Watts (at 0.5% THD and a 4 Ohm load) per satellite and 58 Watts (at 0.5% THD and a 4 Ohm load) for the subwoofer. Thus, a total peak power rating at a low distortion would be 178 Watts. I'd venture to extrapolate that at 10% THD, the entire package could pump out well in excess of the 200 Watts claimed by Altec. Fancy that, a manufacturer that under-rates their gear. Kudos Altec.

Miscellaneous Measurements

Input impedance is important because if your sound card can't drive the input of the speakers, distorted or low levels of sound can be the result. Measuring slightly low for my tastes, the 621s have an input impedance of 7.40 KOhms. I'd rather see at least 10 KOhms, but better sound cards like the Sound Blaster Live! series won't have many issues driving this model.

Cord length has been an issue in past reviews. Why make a great set of speakers and then prohibit/impede typical hookup scenarios by providing cables that are two feet too short? The 621s had no such problems, giving the user generous lengths in all key areas:

Satellite Cable
Controller Cable
Power Cord
Input Cable
>9.5 ft
> 9.5 ft
6.5 ft
6.5 ft


ACS-48 & 621 Sat
No Covers
Factory Pic
Sat Stand
Sub Bottom
Sub Front
Amp Module
Amp Chip
Factory Pic


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