Author:
Douglas Bruce
Lead Audio Test Engineer and Technical Support, US Amps

US Amps Impact 1000.1 Audio Testing Results

When it comes to a monoblock amplifier designed to drive subwoofers, simply knowing the rated wattage doesn’t tell the entire story.

We also want to know how the amplifier behaves across the frequencies where a subwoofer actually operates. How much distortion is present? What happens to the noise floor as output increases? How well does the amplifier maintain control over the connected load? And perhaps most importantly, does it continue producing strong power as frequency changes?

I recently put the US Amps Impact 1000.1 through a series of bench tests to answer those questions.

The purpose of this testing was not simply to produce the biggest wattage number possible. The goal was to look deeper into the amplifier’s actual audio performance under controlled conditions.

Test Conditions

The Impact 1000.1 was tested at approximately 12.6 volts into a 1-ohm mono load.

Primary audio measurements were taken at three output levels:

1 watt
10 watts
100 watts

Testing at several power levels gives us a better picture of how the amplifier behaves as output increases instead of relying on a single measurement taken at one operating point.

Frequency Response: 20 Hz to 320 Hz

Across all three tested output levels, the Impact 1000.1 produced a measured frequency response of:

20 Hz to 320 Hz ±2 dB

That result remained consistent at 1 watt, 10 watts, and 100 watts.

For a monoblock amplifier intended for low-frequency reproduction, consistency across the operating range is important. We want the amplifier to reproduce the incoming bass signal predictably instead of dramatically changing its response as output increases.

The Impact 1000.1 maintained the same measured frequency range throughout all three test levels.

Total Harmonic Distortion + Noise

THD+N allows us to look at the amount of unwanted distortion and noise present relative to the original signal.

Minimum measured THD+N was:

1 watt: 0.7%
10 watts: 0.2%
100 watts: 0.4%

Maximum measured THD+N was:

1 watt: 0.8%
10 watts: 0.6%
100 watts: 0.8%

Looking at distortion at several different output levels helps show how the amplifier behaves during normal operation rather than judging it solely at maximum output.

Signal-to-Noise Ratio

The Impact 1000.1 showed a significant improvement in measured signal-to-noise ratio as output increased.

Measured SNR was:

74.2 dB at 1 watt
82.2 dB at 10 watts
90.2 dB at 100 watts

At the 100-watt test level, the amplifier reached a measured 90.2 dB signal-to-noise ratio.

As the desired audio signal becomes stronger relative to the amplifier’s noise floor, the measured SNR increases. This gives us another useful way to examine amplifier performance beyond power output alone.

Slew Rate

Measured slew rate remained completely consistent throughout the three tested output levels:

22 V/µs at 1 watt
22 V/µs at 10 watts
22 V/µs at 100 watts

Slew rate describes how quickly an amplifier’s output can respond to changes in the incoming signal.

Even with bass reproduction, the signal is constantly changing. Kick drums, bass transients, and rapid changes in program material require the amplifier to follow the input signal accurately.

The consistency of the Impact 1000.1 across all three test levels is one of the measurements worth noting.

Output Impedance and Damping Factor

Measured output impedance was:

0.01818 ohms at 1 watt
0.01818 ohms at 10 watts
0.01923 ohms at 100 watts

The corresponding measured damping factor was:

55 at 1 watt
55 at 10 watts
52 at 100 watts

Damping factor is particularly relevant when we are talking about subwoofer control.

A subwoofer cone has physical mass and momentum. Once it begins moving, the amplifier must maintain electrical control of the driver. Output impedance and damping factor help us understand that relationship between the amplifier and the connected speaker load.

FFT Harmonic Analysis

The next stage of testing used a Fast Fourier Transform, or FFT, to examine harmonic content.

The fundamental reference frequency was set to:

40 Hz at 0 dB

The second harmonic at 80 Hz measured:

-55 dB at 1 watt
-53 dB at 10 watts
-47 dB at 100 watts

The third harmonic at 120 Hz measured:

-83 dB at 1 watt
-79 dB at 10 watts
-75 dB at 100 watts

FFT analysis gives us more information than a single distortion percentage because it allows us to see where harmonic energy appears in relation to the original 40 Hz test signal.

As output increased, the harmonic components became more prominent relative to the fundamental, which is exactly the type of behavior this testing is designed to document.

Continuous Power Across Frequency

For a subwoofer amplifier, this is one of the most interesting parts of the test.

Instead of measuring power at only one frequency, I tested the Impact 1000.1 from 10 Hz through 60 Hz into a 1-ohm mono load at a minimum of 12.6 volts, with output measured at approximately 0.5% THD.

The results were:

Frequency	Continuous Power
10 Hz	553 watts
20 Hz	640 watts
30 Hz	667 watts
40 Hz	830 watts
50 Hz	835 watts
60 Hz	840 watts

The amplifier produced 830 watts at 40 Hz, 835 watts at 50 Hz, and reached its highest measured output of 840 watts at 60 Hz.

What stands out is how consistent the amplifier became once it reached the 40 to 60 Hz range.

There is only a 10-watt difference between 40 Hz and 60 Hz.

At the lower end of the spectrum, the Impact 1000.1 still produced 640 watts continuously at 20 Hz and 553 watts at 10 Hz under the test conditions.

A 10 Hz signal is well below the primary musical bass range in most systems, but testing there gives us useful information about how the amplifier behaves as frequency continues to fall.

Why We Test Amplifiers This Way

A single wattage number is easy to advertise.

It is much harder, and much more useful, to document how an amplifier actually behaves across frequency and output levels.

The Impact 1000.1 maintained a measured 20 Hz to 320 Hz ±2 dB frequency response, reached a measured 90.2 dB SNR at 100 watts, maintained a 22 V/µs slew rate across all three test levels, and produced up to 840 watts of continuous power into the tested 1-ohm load at 12.6 volts.

More importantly, the testing gives us a deeper view into the amplifier’s behavior through THD+N measurements, FFT harmonic analysis, output impedance, damping factor, and power across frequency.

That is the kind of information we want to continue providing at US Amps.

Not just what the amplifier says on the box.

What does it actually do on the test bench?

— Douglas Bruce
Lead Audio Test Engineer and Technical Support
US Amps