theaudiotweak
On the cd topper I would say that the change is electromagnetic shielding or absorption and it could also be absorbing stray light bouncing off the cd edges and bouncing around inside the chassis. Less light emission inside means there will be less error correction required and and a less corrupted signal which means better sound. I have a cd topper that covers the top and the edges to virtually eliminate light scatter being read.
A couple of things. One is that much of the scattered light problem occurs right next to the laser on the data side of the disc.which is why coloring the data side near the spindle hole of the CD is effective. Of course, one could line the entire inside of the transport with absorbing material, you know, like turquoise colored paper.
>>>>>>Black actually is not that great an absorber of infrared light (above 700 nm) which is invisible. Colors don’t absorb outside the visible part of the spectrum. And turquoise or green absorbs visible RED scattered light, which is somewhat below the nominal wavelength of the CD laser, 780 nm. So what about the scattered light above red, above around 700 nm? The band between say, 700 nm and 850 nm.
The turquoise won’t work for near infrared. Nor will black. Not to mention the color black should never be used on the label side or the outer edge, only on the inner edge, the part that touches the spindle. It should also be mentioned that the color of the CD label graphics also affects the sound. Thus, a lot of experimentation is actually necessary to arrive at the ideal combination of colors for each CD, depending on colors used in the label graphics. Too much experimentation for this dude. I just use Green, Black and Orange.