Just like the classic Beach Boys song, we’re focusing our attention on sound. Nothing fancy, just sound. How do we hear sound? Simple – vibrations!
Sound is created when something vibrates. Vocal cords vibrate to create voices, guitar strings vibrate to create music, doors vibrate when someone knocks on them – it all comes down to vibrations. The vibrations are energy and energy can be transferred from one object to another. So in all the above cases, the energy from the vibrations transfers into the air and the air, in turn vibrates until it reaches your ear. Your eardrum then vibrates, causing other structures in your ear to vibrate. All of this, in turn, stimulates nerves that send impulses to your brain which translates it all into how we understand sound.
Sounds complicated, and in the details it is beautifully complicated. But, at the heart of it all, sound is vibrations. Let’s create a visualizer to help see the vibrations as they travel through the air.
What You Need:
- Tone generator – you can download them to a computer/laptop for free at several websites like this one or you can get an app for a smartphone like the free TONE app for iPhone here
- 2 inch, 8Ω, 0.5W speaker with leads (if possible) - I used one that I harvested from the Singing Fish Dissection I did a few months ago, but you can also get them at some electronic supply shops or online like at this website
- 3.5mm mono (or stereo, but mono is easier) male/male audio cable – available at most electronics stores or online like at this website
- Electrical tape
- Masking tape or glue
- 12″ round balloon
- Large plastic cup – the one in the video is from a fast food restaurant that rhymes with “Mindy’s”
- Scissors or Dremel tool
- Wire cutter
- Wire stripper
- Salt – I just used a free package from the same fast food location as I got the cup
- Soldering equipment (optional)
What to Do
- Download the tone generator to your computer or smartphone
- Strip about ½” – 1″ from the lead wires on the speaker.
- Note which wire on the speaker is the ground (-) and put a piece of tape on it to help identify it easier as you continue.
- Cut the 3.5mm audio cable in half (sometimes you can find audio cables with an open end with wires already exposed – this will be much easier if you can find that. If so, skip to #)
- Strip back about 1½” of the outer insulation, exposing the interior wires.
- If you have a mono cable, you will see two wires (go to #7) or a bunch of bare wires and an insulated wire (go to #10).
- If two wires, strip both wires back about ½” – 1″
- Connect the ground (-) wire (usually black) to the ground on the speaker by twisting the two wires together or soldering them together (if you know how). Wrap in electrical tape to insulate.
- Repeat with the second wire to the other speaker lead.
- If you see a bunch of bare wires, twist them all together. That is the ground.
- Connect the wires to the ground lead on the speaker by twisting the two wires together or soldering them together (if you know how). Wrap in electrical tape to insulate.
- Strip the second wire back about ½” – 1″ and connect it to the other speaker lead.
- If you are using a stereo jack, you’ll see two insulated wire and a bunch of bare wires. Tape one of the insulated wires out of the way. Then do instructions #10-12.
- Add some more tape to the connection between the speaker and the audio jack to make sure they can’t get accidentally pulled apart.
- Test your speaker by hooking the audio jack up to your computer or smartphone and playing some tones around 500Hz. If you don’t hear anything, you may have a bad connection or the wires crossed.
- Cut a hole in the bottom of the cup using the scissors or Dremel tool. Make it just slightly smaller than the speaker.
- Cut the nozzle of the balloon off
- Stretch the round part of the balloon over the top of the cup so it is on tight. It helps to have someone hold the cup while you do this.
- Tape or glue the speaker to the bottom of the cup.
- Flip the cup so the balloon is on top and the speaker is on the bottom.
- Pour salt on top of the balloon.
- Connect the speaker to the tone generator.
- I recommend starting with tones in the 500Hz range and then change the values. Watch what happens with the salt.
- If you don’t see the salt bouncing, no matter the setting, try turning up the volume.
NOTE: I’m going to create a different explanation of this with photos and post an update when that is completed.
What’s Happening
As I said at the top of this entry, sound is vibrations. But each sound has its own unique vibrations. A tone generator picks one specific tone at a time and creates that specific type of vibration. The vibrations from the speaker pass into the air and then into the balloon making it vibrate. The vibrations from the balloon make the salt bounce up and down on top of the balloon. Different tones create different vibrations which causes the salt to bounce in different patterns.
Some tones won’t create patterns. Even though you can hear it, the vibrations don’t translate as well into the balloon, so the salt won’t dance around like it does at other tones. This could be due to the speaker or the size of the cup. The air and everything is still vibrating, just not in the way needed to make the salt dance.
