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NAD focuses on the concept of “ effective power ” and its amplifiers have been known for delivering generous headroom, meaning that they can deliver dynamic power bursts far in excess of their rated RMS power.

The key to this feature is to use a flexible power supply which stores significant reserve current for quick release at moments of high musical load.

The various incarnations of this design have been associated with different names over the years including Power Envelope and recently PowerDrive.

Additional benefits of this approach include the fact that amplifiers using this technology can handle complex, real-life, lower-impedance loudspeaker loads as compared with the simple 8-ohm resistor typically used to calculate advertised power ratings and the fact that the circuitry in this approach requires less cooling, while maintaining ability to handle complex impedance loads as low as 2 ohms.