Laser Representation of Sound Waves and Their Vibrational Forms

This experiment was based from a sound wave experiment using sand to vibrate into forms on a metal plate. The source from both experiments is still the exact same, using a hollow cylinder with an elastic membrane to capture the sound waves. Although instead of a vertical tube with sand forming on the surface of the membrane, the tube is horizontal with a miniature mirror bonded to the membrane. The inspiration for this altered experiment came from Bruce Yeany on YouTube (link will be provided in sources). This concept of sound having mathematical shapes was extremely interesting to me, especially due to my already existing interest in music and sound (my family room sound system might also be a factor in this experiment's success). Most information and testing actually came from Dr. Horner. With much respect she was able to set me on the right track and supply early resources for rough drafts of the project.

Supplies

XL balloon for flexible membrane
Decent quality laser ( for a clear focused beam)
Small mirror piece
Twine or rubber band for security of membrane
Creators choice of hollow cylinder (diameter can vary)
Physical speaker (subwoofer preferred)
Power source for speaker
Sand bags (optional for stability of cylinder)
Adhesive strips

Step 1: Cylinder Diameter

Locate a hollow cylinder with firm structure. The diameter can vary to whatever materials are available. Keep in mind the bigger the diameter, the larger and more sensitive the laser shapes become in the end product. If drums are available, I suggest using them for this experiment. They’re built for sound capture and structure.

Step 2: The Membrane

Once your cylinder diameter is determined, find a balloon that will comfortably stretch around the circumference of the cylinder. I suggest an XL rubber balloon from a party store (cheap, accessible, and simple).

Step 3: Security and Tightness

After balloon is stretched around the circumference of the cylinder, wrap string, twine, zip ties, or any form of line around the balloon securing a tight bind to the cylinder frame. Even an XL rubber band will do the job, although overall security and tightness of the membrane will be lost over time. Tune the membrane to be easily flexible to your finger. The face of the membrane should has no ripples on the surface (as seen in third image of step 3).

Step 4: Mirror Fragment

The mirror fragment should roughly be 1cm by 1 cm. The primary factors of this step are to be very safe when either cracking a mirror or handling the mirror fragment. Please use safe equipment such as safety goggles, gloves, close toed shoes. An alternative to this step is to use a small piece or reflective metal such as tin foil, steal, aluminum etc… but the reflected image from the laser wont come out as clear or strait as preferred. (It can be considered to be equally as challenging to find a 1cm by 1cm square of these materials compared with breaking a mirror fragment safely.

Step 5: Attaching Mirror Fragment

Step 5 is quite simple. Use and adhesive strip to bind the membrane and mirror fragment together in the center of the membrane face. Double sided tape is a great option for this step. The only issue is the stick of the tape over time will eventually dissolve.

Step 6: The Laser

A decent quality laser will do the trick for this experiment. The laser used in this experiment was purchased from amazon with a price of about 30 dollars. I suggest purchasing a laser with a push in button rather than a press and hold button. When the laser can stay on by itself it resolves the issue of weighting the button down or wrapping tape around the button.

Step 7: Stable Laser

A mount for the laser is a vital step in this process. If the laser slides around and or falls out of line with the mirror fragment, it results in a un-win-able cat and mouse game (not fun). Tape can do the trick to temporarily secure the laser to a mount, but a more permanent solution could be to use sand bags to support and hold the laser in a fixed position while still being adjustable. For my exact experiment I used a scope mount with adjustable levels of degrees.

Step 8: Speakers

The bigger the better for this experiment. A subwoofer is an essential part to the success of the experiment. A mid-range speaker will provide some slight movement, but even a small subwoofer (8in) will produce exponentially better results than a mid-range. About 90% of the sound wave designs occur between 15hz - 100hz. For this exact experiment I used a 14 inch subwoofer with a standard amp output.

Step 9: End Set Up Pt 1

Now we are ready for the arrangement of the membrane and laser. In this first part, secure your cylinder about 3-4 inches in front of your speaker. Make sure to secure your cylinder with a tie down method or sand bags in order to produce a solid surface for your laser to hit. Your membrane should be visibly moving, while your cylinder should be rock solid.

Step 10: Set Up Pt 2

The laser set up requires some aiming. You want your cylinder to be completely still as you aim the laser as accurately as possible at the center of the mirror fragment. Secure you laser mount to the surface on your platform with some weights or adhesive stripes. Now we can put the batteries in and test our beam accuracy.

Step 11: Super Cool Laser Machine 3000 Light Show

Now that your beam is accurate and your membrane is sturdy… FLIP OFF THE LIGHTS! Play some of your favorite songs and watch as your laser visually represents sound waves onto your wall. These crazy images are truly fun to watch. If the images from the laser are too small or big to see, then adjust your amplitude (volume) of the speaker. The volume of the speaker directly correlates to how big or small the image becomes. Enjoy!