Rockford Fosgate® - PowerCube®

PowerCube®

The AudioGraph® PowerCube® illustrates dynamic power capabilities of an amplifier. The PowerCube® tests an amplifier's ability to deliver linearly short term current into capacitive and inductive (not just resistive) speaker loads. These tests are designed to mimic an amplifier's ability to perform under real-world 4-ohm speaker loads. DO NOT follow the impedance loads illustrated in the charts - refer to your amplifier's owners manual for minimum "ohm" loads.

Series:

Model:

*discontinued model

READING THE TEST AND CUBE QUICKLY

Figures 1 - 6 are taken from the PowerCube owners manual. All amplifiers should strive for Figure 1, the Perfect Amplifier. It's very hard to achieve a Figure 1 type cube. Look for them, perfection is rare.

Figure 1.
Perfect Amplifier
This amplifier works as a perfect voltage generator and is not affected by battery voltage, impedance or current demand.

Figure 4.
Current Limiting
This amplifier probably has too few output devices. To protect them, the amplifier has an electronic protection circuit which turns off the amplifier at "dangerous loads."

Figure 2.
Good Example
This is an amplifier with typically good behavior. There are some low impedances losses, but the PowerCube is still cubic.

Figure 5.
Oscillating
This amplifier is not stable at certain reactive loads. As a result, the distortion is always over 1% THD and the resulting output power is 0 watts.

Figure 3.
Poor Power Supply
This amplifier's power supply is too small or has too few output devices and cannot produce enough current in low impedances. As a result, the dynamic output power gets lower in these impedances.

Figure 6.
Poor Protection Circuitry
This amplifier is designed for higher impedance application. Subsequently, it shuts down into low impedance loads.

What is a PowerCube®? The PowerCube by AudioGraph is a specially designed test device that simulates a real speaker load playing a musical signal. Rockford Fosgate utilizes the PowerCube to show our customers an amplifier's performance in a real world environment, NOT an amplifier's unrealistic power rating into a laboratory load resistor. It is not possible to "tweak" the test to make an amplifier look beter or worse.

The device tests at (20) different impedances, not to see if the amplifier can drive those impedances of a loudspeaker, but to get the current draw on the amplifier to a level where it approximates the current requirements of a single 8Ω speaker. If an amplifier's PowerCube shows obvious problems and is not "cubic" in appearance, then that amplifier really will not drive an 8Ω speaker correctly, let alone a 4Ω or lower impedance load. This should be an easy test for a high quality amplifier to "pass". The test asks the amplifier to deliver high current for 20 milliseconds.

An amplifier that will not produce a "cubic" appearing cube almost always has power supply, protection circuitry or other circuit design problems or shortcomings.

If the PowerCube is relatively "cubic" in appearance, and the power expressed almost doubles as the load impedance is halved, then the amp should be able to adequately drive a normal loudspeaker, and will obviously be a better choice for lower impedances as well, when compared to an amplifier that does not produce a "cubic" cube. RF beleives that the information gleaned from testing with the PowerCube is valuable because it accurately predicts the output capabilities of a given amplifier, and perhaps even more importantly, the ability of an amplifier to drive a loudspeaker correctly. It shows problems in areas of amplifier design such as oscillations due to reactive loads, or inhibitive protection schemes that are not obvious during other test methods.

The PowerCube is Fair, unbiased and always accurate!

For more detailed information regarding the PowerCube visit www.audiograph.se
AudioGraph® & PowerCube® are registered trademarks of AudioGraph AB, Sweden.

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