The ability of an amplifier to control woofer cone inertia is referenced by a numerical factor which is the ratio of the loudspeaker load impedance divided by the amplifier’s output impedance. The lower an amp’s output impedance, the better it can control the cone’s “ringing” or “time smearing.” Higher damping factors are associated with tight bass.
Amplifier sensitivity, quoted in either volts or decibels, refers to the input voltage needed to reach full power. Most amps provide the user with two or more choices, allowing it to be matched with various sources or other amplifiers. Lower voltage or decibel values make the amp seem louder, though it will still clip at the same level.
For amplifiers with a 0.775 V setting, this corresponds to a 0 dBu level. 1.4 volts relates to a +4 dBu level. Many amps have a 26 dB “fixed gain” position, which often provides the lowest gain, and usually works well with output levels of 2.5 volts and higher (+10 dBu), allowing systems to be mixed across models and even manufacturers.
Frequently misunderstood is that amplifier front panel rotary controls don’t change the available power, but rather simply reduce the input sensitivity. Other common rear-panel switch functions include parallel or bridged-mono input, high-pass filters and limiters.
Neutrik Speakon output connectors are a nearly standard feature, and not just on tour class amplifiers. It’s standard to find a pair of Speakon connectors, plus sometimes a third across both channels, for bridged mode applications.
Some manufacturers have eliminated “five-way” binding post outputs, and models with Euroblock connectors – a modular terminal block connector favored by installers for their ease of use – are becoming more common on amps and other types of audio equipment that can be networked.
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Mark Frink is Associate Editor for Live Sound International.