DYNAMIC POWER MEASUREMENTS
About the Dynamic Power Measurements
The Audio Graph PowerCube is a test instrument used to measure the output of an amplifier in accordance with IHF-202 industry standards. The IHF-202 standard is a Dynamic power measurement and was developed as a means of measuring power in a manner that best repre- sents the Real World operation of an amplifier. Many manufacturers, including Rockford Fosgate, at times will measure amplifier power into a fixed resistor (4 ohm, 2 ohm). While this method is useful in some types of evaluation and testing, it is not representative of an amplifier that is connected up to a speaker and playing music.
Music
Music is dynamic; the sound waves are complex and constantly changing. In order to simulate this, the IHF-202 standard calls for the input signal to the amplifier to be a 1kHz bursted tone. This signal is input (on) for a short period of time and then off for a “rested” period. The signal is gradually increased in level until the amplifier's output exceeds 1% Total Harmonic Distortion (THD). At 1% distortion becomes audible, therefore, any power pro- duced above that level is considered not usable. Many manufacturers represent their amplifiers' output power in excess of 10% distortion. They use many names for this measurement, such as Total Maximum Power or Maxi- mum Output Power. This is not indicative of the actual usable output power.
Listening to Loudspeakers - Not Resistors
A loudspeaker is not a resistor. A resistor's value (resis- tance measured in ohms) is fixed. A loudspeaker's im- pedance is dynamic. It is constantly changing in value, dependent upon the frequency of the input signal. There- fore, measuring power with the amplifier loaded into a 4 ohm resistor is not the same as measuring power with the amplifier connected to a 4 ohm speaker. Most people do not listen to music through a resistor.
