Measured results obtained with Dolby Digital test signals.
Subwoofer-output frequency response (crossover set to 80 Hz): -24 dB/octave above -6-dB rolloff point of 80 Hz
High-pass-filter frequency response (crossover set to 80 Hz): -12 dB/octave below -3-dB rolloff point of 80 Hz
Maximum unclipped subwoofer output (trim at 0): 6.6 volts
Subwoofer distortion (from 6-channel, 30-Hz, 0-dBFS signal; subwoofer trim set to 0): 0.03%
Crossover consistency: bass crossover frequency and slope were consistent for all sources and formats
Signal-format consistency: consistent for all applicable formats
Speaker-size selection: all channels can be set to "small"
Speaker-distance compensation: available for all main channels.
Yamaha's RX-V661 yielded some very good numbers, including superbly low noise and distortion through its analog multichannel inputs. The digital inputs' S/N, linearity, and noise-modulation results together suggest a digital-to-analog conversion error involving the magnitude of the least-significant bit. But this was not enough to induce any audible effects on our several dithered-noise listening signals, even over headphones at reference-plus levels.
The Yamaha is equipped with a setup-menu 8-ohm/6-ohm speaker-impedance switch (I'd still like to know where they're buying these "6-ohm" speakers). The latter position apparently takes the Yamaha's supply voltage down to reduce the maximum current drawn through the output transistors, restricting output power by roughly half. (I had no problems running high-power tests of single and paired channels into 4-ohm loads with the switch set to "8-ohm," but I'm not suggesting that anyone disregard Yamaha's directives. Honest.) Power results otherwise were generally fine, though 5- and 6-channels-driven tests fell well short of the unit's single-channel/stereo spec of 90 watts, suggesting that total power-supply current is not sufficient to service all channels fully at the same time even when unchecked by the protection circuitry. This is not uncommon among all but the most expensive receivers, and the fact that I observed ample power in listening tests confirms that such all-channels tests, while a useful benchmark of overall potential, are not a particularly real-world model.
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