Hearing protection is a topic we talk about a lot in any job. Hearing loss is one of those things that happens over time, so it's not always a priority for young people. But that scene where the old lady yells at her husband is only cute in movies and TV. This sucks in real life. With this in mind, we decided to put together a quick guide to understanding sound pressure level (SPL) and the decibel scale (or dB scale).
Since the goal is to understand at a functional level, not to prepare you for a final exam, I'll skip some details and focus on general concepts.
Sound pressure level or SPL is a measurement of sound pressure using Pascals (Pa) as the unit of measurement. We convert this to the more popular decibel scale, or dB scale.
Sound pressure is the difference between the pressure created by a sound wave and the pressure of the environment (usually air for our purposes) in which the sound travels.
The reason sound pressure level and decibels are so important is because it gives us a numerical scale to help prevent hearing loss.
Sound pressure level and decibel scale
There are two important points to keep in mind when it comes to the dB scale: the actual Sound pressure level and loudness of sound .
There are plenty of decibel equivalence examples to give you an idea of how loud something is at a certain decibel level, like we provide.
How Sound Pressure Level Works
When it comes to sound pressure levels (and remember, sound pressure can cause real damage), every 3 decibels of sound pressure level doubles, and every 10 decibels of sound pressure level increases by a factor of 10.
To put this into practice, let's consider a conversation with 60 on the decibel scale (60 dB). A loud conversation at 63 decibels is twice the SPL, a conversation at 66 decibels is four times the SPL, and a group of people talking at 70 decibels is 10 times the SPL.
Compared to 60 decibels of sound…
- 63 dB is twice the SPL
- 66 dB is 4 times the SPL
- 69 dB is 8 times the SPL
- 70 dB is 10 times the SPL
- 72 dB is 12 times SPL and so on…
How Perceived Loudness Works
It's a slightly different ballgame when it comes to how loud something is, but we can still use the decibel scale to make sense of it. This one is a bit more straightforward: when you boost it by 10 decibels, the noise sounds twice as loud.
Compared to 60 decibels of sound…
- 70 dB sounds twice as loud
- 80 decibels is 4 times louder
- 90 dB sounds 8 times louder, and so on…
How Sound Pressure Level and the Decibel Scale Affect Jobs
OSHA defines the amount of noise you can be exposed to during a certain period of time. For example, you can work for 8 hours with your ears hearing 90 decibels, or 1 hour with 105 decibels. Both of these are daily limits.
Hearing protection allows us to work longer in noisier environments without violating these OSHA restrictions. When you're shopping for hearing protection, look for the NRR value – the noise reduction rating. It very simply tells you how many decibels your device has lowered.
If you work in an environment with a fairly constant 105dB and use earmuffs with an NRR of 25, your ears will only be exposed to 80dB. this is very simple!