The decibel (dB) is a commonly used and seen unit on audio product sales and spec sheets. But what is it and what does the decibel scale mean exactly?
Simply put, a decibel (dB) is a unit of measurement that describes loudness of a sound, though decibels are sometimes used to measure other things that have similar mathematical behavior, like electrical power.
The decibel system was not invented by a single person, but rather was developed by a group of scientists and engineers at Bell Telephone Laboratories in the early 20th century. The bel unit (a decibel is one-tenth of a bel) was named after Alexander Graham Bell, inventor of the telephone. The subsequent decibel scale was mainly created to help people understand which noises can damage hearing.
A decibel is what’s called a logarithmic unit. For those who don’t remember or would rather forget their high school math classes, here’s a basic explanation of what that means:
A logarithm (short for logical arithmetic) is just an exponent in reverse, and one thing logarithmic units are good at doing is visually condensing and representing exponential trends, or in other words things that become increasingly large at increasingly very fast rates, like the force of sound:
A rough rule of thumb is that a 10 dB increase in a sound will double its volume.
What is The Difference Between Decibels and Sound Pressure Level? (SPL)
When a company describes a speaker or headphone’s output potential, you might see something like Max dB = 110 or Max SPL = 110 dB. Sound pressure level is the amount of actual measurable physical force that sound waves exert over a given area via the pressure difference between the sound wave and whatever it’s travelling through, which is generally just the air in the atmosphere. SPL is formally measured in Pascals (Pa), but in the audio world it’s just converted to decibels.
A rough rule of thumb is that a 3 dB increase in a sound will double its pressure. What this means is that as perceived volume steadily increases, the physical force the sound waves are exerting on your eardrums exponentially increases, and by quite a lot.
What Decibel Level of Sound Can Start to Cause Hearing Damage?
It can vary from person to person, the specific type of sound, and how long a person is continuously exposed to it, but the threshold for permanent hearing damage is lower than a lot of people think or realize. The following data is sourced from the US Occupational Safety and Health Administration and National Institute for Occupational Safety and Health (OSHA/NIOSH):
| Exposure Time | OSHA | NIOSH |
|---|---|---|
| dB/SPL | dB/SPL | |
| 8 hr | 85 | 85 |
| 4 hr | 88 | 90 |
| 2 hr | 91 | 95 |
| 1 hr | 94 | 100 |
| 30 min | 97 | 105 |
| 15 min | 100 | 110 |
| 7.5 min | 103 | 115 |
| >3.75 min | 106 | 120 |
| >2 min | 109 | – |
| >1 min | 111 | – |
Intuitively Understanding How Much Louder More Decibels is by Comparing Levels to Familiar Sounds
There are a lot of people who ask some form of the question “what does [x] decibels sound like?” as a way to get an intuitive reference, so we’ve compiled a list of these, sourced from the US CDC and other official organizations.
How Loud is 1 dB and What Does it Sound Like?
1 decibel is roughly the base potential of healthy human hearing, and is the quietest sound a human ear can pick up. For example: hearing test at a doctors office.
How Loud is 25-35 dB and What Does it Sound Like?
25-35 dB is a relatively quiet sound but still noticeable without competing noise. For example: soft whisper from someone 5-10 feet nearby
How Loud is 35-55 dB and What Does it Sound Like?
35-55 dB is fairly audible in a normal sized room, but is something most people will subconsciously stop noticing over time. For example: a plug-in fan, light rain outside, refrigerator hum.
How Loud is 55-65 dB and What Does it Sound Like?
55-65 dB is definitely noticeable in a normal sized room, and a level that starts to become involuntarily distracting. For example: normal conversation, large/window air conditioner, inside a car driving on the freeway.
How Loud is 75-85 dB and What Does it Sound Like?
75-85 dB will start to feel intrusive and is practically not able to be ignored. For example: near a washer, dryer, dish washer, vacuum cleaner.
How Loud is 85-95 dB and What Does it Sound Like?
85-95 dB is the point where most people think “this is getting loud” and where sudden noises can startle someone. For example: nearby car horn, hairdryer, blender. This is also a common benchmark of speaker sensitivity and the volume a bookshelf speaker will produce at 1 meter away with 1 watt of incoming power.
How Loud is 95-105 dB and What Does it Sound Like?
95-105 dB is the point where most people will feel discomfort and might instinctively cover their ears. For example: gas powered lawnmower, leaf blower, chainsaw, motorcycle driving by.
How Loud is 105-115 dB and What Does it Sound Like?
This is the point where people will start to feel physical discomfort or pain. For example: dog barking in your ear, trumpet, full fledged concert (always bring hearing protection!). This is also the max volume that most decent in ear headphones can achieve (but that should absolutely not be listened to at!).
How Loud is 115-125 dB and What Does it Sound Like?
115-125 dB is the point loud enough that a person simply cannot continue what they are doing and just has to cover their ears, but will still feel significant pain. For example: ambulance siren, smoke detector, fire alarm.
How Loud is 125-150 dB and What Does it Sound Like?
125-150 dB is the point where someone will immediately suffer from temporarily hearing loss and severe tinnitus (ringing of the ears). For example: gunshot, firecrackers, jet engine taking off.
How Loud is 150+ dB and What Does it Sound Like?
150+ dB sounds will likely rupture a human eardrum, immediately causing permanent hearing damage and possible deafness. Sound of this magnitude can be felt and is possibly forceful enough to knock people down. For example: explosives, NASA rocket launch. The theoretically loudest possible sound that can be created in earth’s atmosphere is about 195 dB and would be instantly lethal and level trees and buildings for that matter.
Common Insidiously Loud Noise Sources
There are a lot of things that cross the threshold of hearing damage risk that aren’t so well known or obvious, but that many people unwittingly use repeatedly without hearing protection. Here’s a running list, in no particular order:
Landscaping devices – lawn mower, leaf blower, etc.
Power tools – table saw, shop vac, other construction equipment.
Headphones – especially when the volume is raised to try drowning out ambient noise. Consider active noise cancellation headphones as an alternative, they are safe and there are now many that aren’t too expensive.
Live Music – Concerts, clubs, etc.
