Decibels Explained — Measure Sound Levels & Stay Safe
The decibel scale is the one everyone has met and almost everyone misreads: it is logarithmic, so 90 dB is not "a bit more" than 80 dB — it is ten times the sound energy, and the difference between a safe workday and mandatory hearing protection. A sound meter makes the invisible audible-numbered. Here is how to read those numbers, which ones threaten your ears, and what a phone microphone can honestly tell you.
Decibels — the scale that multiplies
Sound pressure spans an enormous range — the threshold of pain carries about a trillion times the energy of the threshold of hearing — so we compress it logarithmically. Each +10 dB means ten times the sound energy: 70 dB is ten times 60 dB, and 100 dB is a thousand times 70 dB. Two consequences everyone should internalise: everyday differences are huge (a 3 dB change is a doubling of energy but barely perceptible), and combining sources does not add — two identical machines running together measure ~3 dB louder than one, not double.
| Level | Example |
|---|---|
| 30 dB | Quiet library, whisper |
| 60 dB | Conversation, office |
| 70–80 dB | Traffic, vacuum cleaner, busy restaurant |
| 90–100 dB | Motorcycle, subway train, loud headphones |
| 110–120 dB | Concert front rows, chainsaw, nightclub |
| 130 dB+ | Jet takeoff at distance — pain threshold |
The numbers that protect your ears
Hearing damage is a function of dose — level × time. Occupational standards converge on the same shape: 85 dB for 8 hours is the ceiling for repeated daily exposure, and every +3 dB halves the safe time — 88 dB buys 4 hours, 100 dB about 15 minutes, 110 dB around 90 seconds. The quiet danger is headphones: at full volume many pairs deliver 100–110 dB straight down the ear canal, meaning a single commute can spend the whole day’s allowance. The insidious part of noise-induced hearing loss is that it accumulates painlessly and does not recover — hair cells do not regenerate.
How accurate is a phone sound meter?
Honest answer: good enough for awareness, not for compliance. Phone microphones and their automatic gain control introduce a few dB of uncertainty, and the phone’s own noise floor limits low readings. In practice they track changes reliably — a room getting 5 dB louder registers as 5 dB louder — and land within a few dB of the truth in the 40–100 dB range where life happens. Regulatory or professional measurements need a calibrated Type-class meter; deciding whether your workspace or headphone habit is hazardous does not.
- Measure where your ears are — not the source, not the corner.
- Watch the average, not peaks — dose is driven by sustained level.
- Hold the phone freely — cupping the mic with your hand inflates readings.
- Compare, don’t litigate — treat phone readings as a map with a compass rose, not surveyor-grade coordinates.
Using LND AI Sound Meter
- Open the toolGo to namansoni.in/sound-meter — completely free, no sign-up; it needs microphone access and computes locally.
- Grant microphoneThe browser asks; the meter reads the live level in your tab only.
- Measure your real environmentPlace the phone where your ears actually are and watch the dB readout settle.
- Check the mapCompare against the loudness map above — a workspace sustained above 85 dB deserves attention.
- Fix what you measureVolume discipline, earplugs, or distance — the measurement exists to change behaviour, not decorate it.
Frequently asked questions
What is a decibel?
A logarithmic unit of sound pressure — necessary because audible sound spans a trillion-fold energy range. Each +10 dB is ten times the sound energy: 90 dB carries ten times the energy of 80 dB. A 3 dB increase is a doubling of energy but barely perceptible, which is why "only 3 dB louder" matters physically even when your ears shrug.
How loud is too loud?
Dose is level × time. The occupational ceiling is about 85 dB for a full 8-hour day, and every +3 dB halves the safe duration: 88 dB buys 4 hours, 100 dB roughly 15 minutes, 110 dB about 90 seconds. Headphones at full volume often deliver 100–110 dB directly into the ear — one commute can spend the day’s entire allowance.
Is noise-induced hearing loss reversible?
No. Loud sound destroys the inner ear’s hair cells, which do not regenerate — the loss accumulates painlessly over years and is permanent. Prevention (volume discipline, earplugs, distance from sources) is the entire treatment arsenal, which is what makes measuring your real exposure levels worthwhile.
How accurate is a phone decibel meter?
Good enough for awareness, not for compliance: expect a few dB of uncertainty from phone microphones and gain control, with the most reliable zone around 40–100 dB. Changes track faithfully — a 5 dB rise registers as 5 dB — so phone meters excel at comparisons and self-audit. Regulatory measurement requires a calibrated Type-class meter.
Why do two noise sources not double the decibels?
Because dB is logarithmic. Two identical sources together carry twice the energy, which is +3 dB — audible as a small increase, not a doubling of loudness. Ten identical machines raise the level 10 dB. This is also why adding one more machine to an already loud room changes the risk far less than intuition suggests — and why removing one changes little; the level, not the count, governs.