As noted by Amir earlier in his comments the customer sent him the Aeon 2 Noire without the included tuning pads. As such, the review really only covered a subset of the system's performance options. It's important to note that the tuning system not only affects the frequency domain, but also THD performance. For most users using the tuning kit is recommended as the tuning of the top octaves may sound bright to those looking for a more neutral or more Harman response.
The following shows the effect of various filters on frequency response. For myself I generally use 1 notch white + 1 black as shown in the blue line. The reason the filters reduce the amplitude of the peaks and sometime valleys is they serve to reduce standing waves. Their ability to do so is limited, which led us to develop our Acoustic Metamaterial to give better control of all aspects of upper octave performance.
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As is evident, the blue curve is significantly smoother than the no-pads tuning, and is also therefore easier to PEQ, using the following settings:
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Last of all, as noted above the filters significantly reduce THD, including in the lower midrange. This particular unit I pulled from inventory also has a bit less bass THD, but Amir's unit was within norms. Note the reduction in THD around 700Hz.
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I hope this provides additional insight into both the intended use of the product as well as the performance effects of the tuning system.