The hearing threshold is the minimum sound intensity that the human ear can perceive. It corresponds to an acoustic pressure of approximately 20 μPa (20 micropascals), defined as 0 dB SPL. This threshold varies considerably depending on the sound frequency and the listener’s age.
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How to measure it in class
With the FizziQ app, it is possible to explore the limits of hearing and raise awareness about auditory health.
Steps:
- Open FizziQ and select the “Sound Level Meter” instrument
- Measure the ambient sound level in different environments
- Compare with the hearing threshold (0 dB) and the pain threshold (approximately 120 to 130 dB)
- Use the synthesizer to generate sounds of different frequencies
- Observe that low-pitched and very high-pitched sounds must be louder to be heard
- Test the frequency limits: 20 Hz (bass) to 20 kHz (treble)
Scientific activities on this topic
Possible extensions with FizziQ: create a simplified audiogram with different frequencies and measure the sound levels of everyday life.
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Variation with frequency:
The ear does not have the same sensitivity at all frequencies. It is maximum between 1000 and 4000 Hz (the speech zone). Low-pitched and very high-pitched sounds must be more intense to reach the same level of perception.
Equal-loudness contours (Fletcher-Munson):
These curves show the pressure levels necessary to perceive sounds of the same subjective loudness (in phons) at different frequencies. At 100 Hz, it takes about 40 dB more than at 1000 Hz for the same sensation.
Variation with age (presbycusis):
Sensitivity to high frequencies naturally decreases with age:
- Children: hearing up to 20 kHz
- Adults 30-40 years: up to 15-17 kHz
- Seniors > 60 years: often limited to 8-12 kHz
Dangers and prevention:
Prolonged exposure above 85 dB can irreversibly damage hearing. The pain threshold lies around 120 to 130 dB; beyond 140 dB, the risk of immediate hearing damage becomes very high.
Formula
The reference hearing threshold corresponds to:
I₀ = 10⁻¹² W/m² (acoustic intensity)
p₀ = 2 × 10⁻⁵ Pa = 20 μPa (acoustic pressure)
Sound level in dB SPL:
L = 20 × log₁₀(p/p₀) = 10 × log₁₀(I/I₀)
Application examples
- The silence of an anechoic chamber approaches -10 dB (below the average hearing threshold)
- A normal conversation is at 60-65 dB, well above the threshold
- A rock concert can reach 110 dB, close to the pain threshold
- Hearing tests (audiograms) measure the individual threshold at each frequency
FAQ
Q: Why is the threshold defined at 0 dB and not at true silence? A: It is a practical convention. 0 dB SPL corresponds to the average human hearing threshold at 1000 Hz. Negative values are possible (sounds below the average threshold).
Q: Can my smartphone detect sounds below the hearing threshold? A: No, the smartphone microphone has its own sensitivity limits, generally higher than the human hearing threshold.
Q: Is the hearing threshold the same for everyone? A: No, it varies according to age, past noise exposure, and individual characteristics. An audiogram measures the personal threshold at each frequency.
Q: How long can you listen to loud music without risk? A: At 85 dB: 8 h max/day. At 100 dB: 15 min. At 110 dB: 1 min. The risk depends on both the level and the duration.
Related concepts
Decibel - Sound Intensity - Sound Level - Frequency