How to play Decibel Meter
- Choose a test and read the levels, the distances, or the intensity on the card.
- Use L = 10·log(I ÷ I₀): +10 dB for ten times the intensity, and −6 dB for each doubling of the distance.
- Type your prediction and press Start. Watch the dial as the sound changes.
- Compare the orange needle or mark with the meter's reading and the graph.
Sound levels in decibels
Our ears handle an enormous range: the loudest sound we can bear carries about a million million times more power than the faintest we can hear. So sound levels use a logarithmic scale, the decibel: L = 10·log(I ÷ I₀), with I₀ = 10⁻¹² W/m². Every 10 dB is ten times the intensity: a quiet room is about 30 dB, conversation 60 dB, a busy street 70 dB, a rock concert 110 dB, and pain starts around 120 dB. Doubling the intensity, two speakers instead of one, adds only 3 dB, and we hear a sound as twice as loud only when it is about 10 dB louder. Moving away from a small source spreads its sound over a bigger sphere, so the intensity falls as 1 ÷ r² and the level drops by about 6 dB each time the distance doubles. Long exposure above about 85 dB can damage hearing, which is why people working with loud machines wear ear protection.
A focused learning model
The threshold of hearing is I₀ = 10⁻¹² W/m². The speakers are identical and their intensities add. The distance tests treat the source as a point in open air, so the intensity falls exactly as 1 ÷ r², with no echoes and no absorption by the air. Each run changes one thing over 3.5 s and then holds the reading. Answers within 2% are right.