Ideas for those old speakers

March 21, 2011

3 Min Read
Ideas for those old speakers

For some reason I really like projects where someone takes something that is basically junk, like old DVD drives, hard drives, speakers, etc. and turns them into something new and interesting.  This project falls into that category.  Nothinglabs took some speakers he picked up at Goodwill and turned them into a DIY laser light show.

A laser light show usually has two or more galvanometers (or galvos), devices that rotate an amount proportional to the voltage applied.  Two of them, each with a mirror attached, are able to provide displacement in the X and Y dimensions.  In this Instructable, the author used a speaker to provide the displacement.   Briefly, a bamboo skewer is suspended above the voice coil, hot glued to LEGO blocks on each edge of the speaker frame.  A mirror is then hot glued, one edge to the speaker cone and the other edge to the skewer.  When the speaker is powered and the cone moves, the mirror will also move, using the skewer as a hinge.

To make the show, the laser first bounces off one mirror, giving the beam a deflection in the X axis.  The other speaker is set up at right angles to the first so that the beam leaving the first mirror hits the second.  This one moves the beam in the Y axis.

An Arduino completes the project by synchronizing the motion of the mirrors with blanking the laser.  It is able to render text into the appropriate signals to the speakers in order to reproduce the text on a projection screen.  In the video that accompanies the Instructable the laser is able to draw text and simple pictures.  The image is about 2 feet high/wide at a distance of 25 feet, according to the Instructable.


I made a static light show once for a Halloween party in college.  It was just a laser up near the ceiling that illuminated a static path by being bounced off mirrors glued to the walls.  A smoke machine made the laser visible.  It worked OK, but I found that after a few bounces the beam got pretty diffuse due to the mirrors I was using.  Some of the beam bounced off the front surface of the glass, and some bounced off the mirror coating on the back of the glass.  The two beams diverged, making it less bright.  For this reason laser optics always use front surface mirrors, and this project could probably benefit from this as well.

Also, there is not really any hinge the way the project is built.  The skewer is hot glued to the speaker frame, and the mirrors are hot glued  to the cone and to the skewer.  Maybe the displacements aren’t that big, but it seems like eventually one of the glue joints would fail.  I think you could make a hinge pretty easily by wrapping the skewer in plastic wrap or aluminum foil at the points where it is glued, allowing the skewer to rotate within the sheath.  It would also change the dynamic response of the system, although it’s hard to see if it would make it better or worse.  The response of the system does matter, by trial and error the author ended up with a small resistor in series with the speaker to improve the damping.

Another idea, suggested by a commenter, is to simply glue a mirrored ball (like a Christmas tree ornament) to the voice coil.   With two of these and an appropriate geometric arrangement you could have a laser show that is driven by an audio source.  You wouldn’t be able to draw pictures or text (at least not without some complicated math) but it would give you some interesting Lissajous figures that would be visually synchronized to the music.

Steve Ravet

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