How We Measure Sound Intensity 

Humans can hear sounds over an incredible range of intensity.  The difference between a 0 dB SPL sound (threshold of hearing) and a 130 dB SPL sound (painfully-loud) is 10,000,000,000,000.  It isn’t practical to use such enormous numbers so a scale was created to represent this wide range with more manageable numbers – the decibel or dB scale.  

You will often see other letters behind the ‘dB’ level such as dB SPL, dB HL, or dB-A.

dB SPL represents the actual Sound Pressure Level recorded and does not account for the fact that humans hear some pitches better than others.

dB HL accounts for how humans hear different pitches and thus represents the actual Hearing Level that a human would perceive.

dB-A represents a measurement taken using a filter set which accounts for how humans hear different pitches.

All of these dB variations are used when correctly testing and fitting your hearing aid instruments.

Sound Pitch

Humans can hear sounds over a wide range of pitch from 20 Hz to 20,000 Hz (Hz = Hertz = cycles per second).  It is important to understand that humans do not hear all pitches equally well.  We hear the mid pitches (1000 Hz – 4000 Hz) much better than very low or very high pitches.  

Birdsong is often regarded as the highpoint in hearing health. Bird songs vary between 1,000 Hz and 8,000 Hz which is regarded as the human “sweet spot” for hearing. It’s also one of the first things we notice is missing when our high-frequency hearing capabilities start to diminish.

  • Brown Creeper from 3750 to 8000 Hz
  • Cedar Waxwing from 6000 to 8000 Hz
  • Blackpoll Warbler from 8000 to 10,000 Hz

As we age, we also notice that it may be difficult to hear young children’s speech. The average frequency for boys between the ages of 6-10 is 262 Hz, and is higher for girls at 281 Hz on average. Young children having a meltdown can be as high as 1000 Hz. Remember, we hear mid-pitches (1000 Hz – 4000 Hz) most easily.

The average adult speaking voice checks in with a range of 125 Hz – 8000 Hz, which places it comfortably at the average range of our hearing abilities.

The graph shows how humans hear different pitches at different intensities:

Sound Math

When out in the world, we typically do not hear one sound at a time, they are layered on top of each other. We hear the bus turning the corner, the sound of the cars heading to work, and people on the phone walking by all at the same instant. 

Sound pressure, or acoustic pressure, is logarithmic, meaning that it increases by 3x at every measurement point.

When two identical sounds are combined – the overall level is increased by 3 dB SPL (sound pressure level)

A doubling or halving of the distance to the sound source  – subtracts or adds 6 dB SPL. 

This is why working with continuous loud machinery can be damaging to hearing health. Any continuous noise measuring over 85 dBA can lead to tinnitus and hearing loss over time. Musicians, construction, road crew and machinists all work in layers of heavy sound at close range that adds up to damaging levels every day. Hearing protection used while lawn mowing is also recommended for the same reason.