Sound waves travel through air at a measurable speed — and you can time them the same way you time a runner on a track. Fire a starter's pistol while starting a stopwatch, then stop the watch the moment the echo returns from a wall a known distance away. Divide twice the distance by the time, and you get the speed. At room temperature, that works out to about 344 meters per second. At freezing, the speed drops to around 331 meters per second. Through water, sound moves far faster — roughly 1480 meters per second.

Sound waves vibrate at different frequencies, and the enclosure around a speaker shapes how those vibrations reach your ears. To measure this, three sealed plywood enclosures — 500 mm, 400 mm, and 300 mm deep — each hold the same 8-inch speaker. Test tones from 30 Hz to 600 Hz play through each box in turn. A decibel meter placed one meter away records the volume at each frequency. Smaller boxes boost certain frequencies above the flat baseline that larger boxes maintain, and the data makes those differences visible.

Vibrations change depending on what material they travel through. To see this, a battery-powered siren goes inside a plywood box with a removable front panel. Swapping that panel between four materials — plywood, bakelite, glass, and marble, each cut to equal thickness — changes how much sound escapes. A decibel meter placed 500 mm away records the volume through each one. The results show whether the densest materials consistently reduce the most noise.

Sound waves vibrate through solid materials, but denser solids slow and absorb more of that vibration. When a siren plays inside a plywood box, a decibel meter outside records how much sound passes through each panel. Denser materials like glass and marble block the most noise, while plywood, the least dense, lets the most sound through.

Sound starts as vibration, and a drinking glass can show that directly. Fill a piece of stemware halfway with water, wet your finger, and run it slowly around the rim. The glass vibrates and produces a clear tone. Change the water level and repeat — with less water the pitch shifts one way, with more it shifts the other. The water level controls the note.