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Assessing Room Correction Products: Dirac And Acourate

Examining the reality of tools designed to counter low frequency acoustic problems with equalization or processing.

When I pointed out the worsened null, my friend said “Dr. Uli Brueggeman, inventor of Acourate, purposely ignores these narrow spikes.”

I’m sure he does! But I disagree that narrow nulls aren’t important. Obviously a narrow null (or peak) does less damage than a broad null because fewer frequencies are affected. But even a very narrow null is a serious problem if it aligns with a note frequency in the music currently playing.

Rather than explain here, this short article explains more about the audibility of narrow nulls, and why some people wrongly believe they’re not important and can be ignored.

Next, let’s look at the rear middle seat (Figure 5). You can see that the EQ cut at 68 Hz that flattened the main seat brought down the rear seat by about 7 dB too much. And the added boost in the range centered at 170 Hz raised the rear seat by about 8 dB too much! This reinforces the “physics truth” that the more correction you apply to improve one location, the worse the response might become elsewhere.

Figure 5: This compares the main seat with the After response at the rear middle seat.

Next let’s consider the other nearby seat at front left (Figure 6). Here the boost at 38 Hz that improved the main seat null makes the response much worse only one seat away. You can see the added 13 dB peak, though we don’t know how much of that is from Acourate and how much was there before Acourate was engaged. This is why it’s best to have Before and After sweeps at every location. You can also see that the boost Acourate added around 170 Hz to improve the main seat raised this seat way too much too.

Figure 6: This compares the main seat with the After response at the front left seat.

Finally, we’ll look at waterfall plots that show how modal ringing is affected by the application of EQ. In this type of graph, the peaks are shown as mountains that come forward over time as they decay. Most room EQ vendors claim their products improve time-based problems as well as frequency response, but my experience is the opposite.

Figure 7 shows waterfalls of the main seat Before and After, overlaid to better see the decay time differences. Yes, the blue corrected response is flatter, but the ringing is much worse (longer) over most of the range below 50 Hz.

Figure 7: This shows the Before and After ringing decay times at the main listening seat.
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