Using Echoes of Light to Turn Walls into Mirrors

using a wall as a mirror

 

[Matthias] recently published a paper he worked on, in which he details how his group managed to reconstruct a hidden scene using a wall as a mirror in a reasonably priced manner. A modified time-of-flight camera (PMD CamBoard Nano) was used to precisely know when short bursts of light were coming back to its sensor. In the picture shown above the blue represents the camera’s field of view. The green box is the 1.5m*1.5m*2.0m scene of interest and we’re quite sure you already know that the source of illumination, a laser, is shown in red.

As you can guess, the main challenge in this experience was to figure out where the three-times reflected light hitting camera was coming from. As the laser needed to be synchronized with the camera’s exposure cycle it is very interesting to note that part of the challenge was to crack the latter open to sniff the correct signals. Illumination conditions have limited impact on their achieved tolerance of +-15cm.

Billiards concepts plied to position acoustic panels

If you know your way around a pool table you should be able to apply those skills to improving the sound of your home theater. [Eric Wolfram] put together a post that discusses the issues caused by unwanted sound reflections and shows how to position acoustic tiles to solve the problem.

This is a companion post to his guide on building your own acoustic tiles. Don’t worry if you haven’t gotten around to doing that yet. With just a wood frame, dense fiberglass, and some fabric they’re simple to build. They’re also easy to hang but until now you might have just guessed on where they should go.

Once you have all of your speakers and seats in position grab a mirror and some post-it notes. Take a seat as the viewer and have a friend operate the mirror as seen above. With it flat against the wall, mark each spot with a sticky-note where you can see a reflection of one of the speakers. Finding the reflection points is just like lining up a bank shot in Billiards. With five speakers (5.1 Surround Sound) and six surfaces (walls, ceiling, and floor) you should be able to mark 30 reflections points. Now decide how wild you plan to go with the project. The best result will address all 30 reflection points, but you can get by with just the front marks if you’re a bit more conservative.