Decibels — dB SPL, dBFS, and why the scale is logarithmic
I bought a cheap SPL meter after a loud gig left my ears ringing for two days. Watching the numbers at different venues taught me more about hearing damage than any warning label ever did.
Decibels are logarithmic. Every 10 dB increase is a 10× increase in sound pressure energy, and roughly a doubling of perceived loudness (perception and energy don't scale identically because ears themselves are logarithmic detectors). So 90 dB isn't 1.5× as loud as 60 dB — it's 8× perceived and 1000× the energy.
The scale is anchored at 0 dB SPL, which is the threshold of human hearing at 1 kHz — the quietest sound a young healthy ear can detect. Negative decibels exist (an anechoic chamber can measure -10 dB or lower) but they mean 'quieter than the threshold of hearing'. Ordinary quiet rooms are 25-30 dB.
Everyday reference points
0 dB SPL: threshold of hearing (young healthy ear).
20 dB: leaves rustling, a very quiet library.
40 dB: a quiet residential neighborhood at night.
60 dB: normal conversation, background music, an office.
70 dB: a busy restaurant, a shower.
80 dB: heavy city traffic, an alarm clock. Prolonged exposure starts risking hearing.
90 dB: a lawnmower, a hairdryer. OSHA limits 8-hour exposure at 90 dB.
100 dB: a subway train, a chainsaw. 2 hours is the safe limit.
110 dB: a rock concert, a jackhammer. 15 minutes is the safe limit.
120 dB: threshold of pain, a jet at 100 feet. Immediate damage possible.
140 dB: a jet engine up close, a firearm without hearing protection. Instant damage.
dBFS is different
Digital audio uses dBFS — decibels below full-scale. 0 dBFS is the loudest a digital system can represent without clipping; everything else is negative. A well-mixed track's peaks sit around -3 to -6 dBFS with the average around -14 to -20 dBFS depending on genre. This is not related to dB SPL in any absolute sense — it depends entirely on where the volume knob is set at playback.
The loudness war of the 2000s was engineers pushing digital averages closer to 0 dBFS to make tracks 'jump out' on radio. Streaming services now normalize to consistent loudness (Spotify targets -14 LUFS, Apple Music -16 LUFS), so hyper-compressing a master is now counterproductive — the platform just turns it down to match.
A-weighting
SPL meters usually offer A-weighting (dBA) and C-weighting (dBC). A-weighting rolls off low and very high frequencies to match how the ear perceives loudness at moderate levels, and it's what OSHA and most noise regulations reference. C-weighting is flatter and matters more for high-SPL sound where the ear's frequency response flattens out. A car stereo at 100 dBA and 115 dBC is thumping so much bass the C measurement is 15 dB higher — you feel that difference in your chest.
The takeaway: if you're checking whether a venue is dangerously loud, use dBA. If you're checking whether the bass is going to rattle the windows, use dBC.
Try the converters mentioned in this article
FAQ
Why do my ears ring after a concert?+
Temporary threshold shift — the hair cells in your inner ear are stunned. If it clears in a day, no permanent damage. If it repeats often, you're accumulating irreversible hearing loss.
Are foam earplugs enough for concerts?+
Yes — well-inserted 30 dB NRR foam plugs drop a 110 dB show to about 90 dB effective, which is safe for hours. Custom musician's earplugs preserve tone better but the foam ones work.
This article was written by The Turbo Unit Converter engineering desk (Applied metrology & engineering units) and last reviewed on 2026-07-22 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.