We all have experienced something too loud such as a baby yelling, and we have all experienced something so quiet it was inaudible, like breathing. But how many dB are these things? Knowing that loudness can be measured and represented as a number leads to a range of interesting questions such as, do we interpret sounds differently as we age? And what are the quietest and loudest sounds that you can hear? Read on to learn more.
Table of Contents
What are Decibels?
Decibels, or dB, are a measurement unit to allow the representation of a sound’s amplitude. Decibels are often used to discuss how loud something is, however, using the term “loud” is not 100% factually correct. This is because loudness is referred to as the level that was perceived by the listener, which, as will be discussed, can vary wildly between two people for the same sound!
Bell Telephone Laboratories, now known as Bell Labs, created a unit for sound measurement called the “bel”, after its founder, Alexander Graham Bell. Bell is most famous for his invention of the telephone. The decibel is a scale commonly used today to measure sound loudness. The word decibel is derived from the bel, with the inclusion of “deci-” to signify that a decibel is one-tenth of a bel.
When discussing how loud something is in dB, people are often referring to the dB Sound Pressure Level, which is often shortened to dB SPL. This is a scale where 0 dB SPL is the lowest level sound audible to humans and sounds are louder the greater the dB. The dB scale is logarithmic, meaning that a 10 dB increase actually means that the sound level perceived is doubled and a 10 dB decrease means that the sound level perceived is halved.
Aside from dB SPL, there is also the dBA and dBC weightings. If a professional acoustician were to be investigating the loudness of a workplace, they would likely be following The Control of Noise at Work Regulations 2005 act, which uses both dBA and dBC for measurements. These weightings are used because they represent the level difference at different frequencies similar to the human ear (which will be discussed in more detail later). This way they can more easily test if sounds are too loud for humans.
To allow you to gain a better understanding of the loudness of different sounds, some common sounds you have likely experienced have been grouped together below. Take a look at dB level loudness description to help in your understanding.
The Loudness Description of Different dB Levels:
|Serious Injury||115 – 140|
|Dangerous||85 – 115|
|Normal||40 – 85|
|Barely Audible||10 – 40|
|Inaudible||0 – 10|
Typical Loudness of Sounds Producible from Your Mouth
|Loudest Sound Capable by Human Voice||120|
|Screaming, Yelling, Shouting||90|
|Whispering at 5 ft||20|
Typical Loudness of Sounds in Your Home
|Garbage Disposal, Lawnmower, Toilet Flush||80|
|Vacuum Cleaner, Shower||70|
Typical Loudness of Places You May Visit
|Stock Car Race||130|
|Busy Video Arcade||110|
|Busy Restaurant, School Cafeteria||85|
|Library Main Hall||35|
|Rural Area at Night||30|
Typical Loudness of Different Machinery
What Determines Loudness?
Sound is caused by waves of energy from changes in air pressure resulting from vibrations. When sound propagates in the air, air particles collide with each other from the direction of the source to your ear. Sound typically travels at 344 meters per second in the air, and loudness decreases the further from the source you are because the particles lose their energy as they travel.
The loudness of the sound is determined by the amplitude of the wave. The greater the amplitude at your ear, the louder a sound will be perceived because a greater amplitude sound wave will have more pressure and greater energy levels.
What is the Relationship Between Frequency and Loudness?
In humans, loudness varies at different frequencies. The most notable research in this field is an investigation published by Fletcher and Munson in 1933, titled “Loudness, its definition, measurement and calculation”. The experiment found the perceived loudness at different frequencies of humans, resulting in the Fletcher-Munson curve, or what is also more commonly called Equal-loudness-level Contours.
The contours are based on otologically normal people, meaning they have healthy ears. Standard BS ISO 226:2003 superseded Fletcher and Munson’s study due to the use of more modern techniques and uses the contours to derive the dBA and dBC weightings used on a sound level meter.
The contours demonstrate that our ears become less sensitive at lower frequencies. Meaning that if you played a sound at a lower frequency and higher frequency of the same dB SPL, the lower frequency sound would be perceived as being quieter than the higher frequency sound. Our ears are most sensitive around 3 kHz, which is likely no coincidence given that this is where a lot of speech information is present.
Do We Interpret Sounds Differently as We Age?
The Equal-loudness-level Contours were derived from the averaging of tests with participants aged 18-25. A young person typically has a frequency range between 20 Hz and 20 kHz. The human frequency range starts to filter off, particularly at higher frequencies, as you age. A study by Kenji Kurakata in 2009 found that participants with an average age of 70 perceived content as low as 4 kHz at a considerably lower loudness than the 18-25 group did.
If you own a decent pair of headphones or speakers that can play sounds at higher frequencies, such as up to 18 kHz, consider listening to True Love Waits by Radiohead. I’d never heard this song until about four years ago when my music teacher played it to the class while I was at school. When it had finished playing, he asked if anyone found the song difficult to listen to. I was one of the students to raise my hand. And you can see why in the frequency analysis I’ve captured below.
The song contains a high-pitched whine that I found unbearable. My teacher explained that the song contains a frequency spike at approximately 18 kHz. My friend in that class always listened to music so loud that I could audibly hear what he was listening to through his headphones while sat next to him; he was one of the people not to raise his hand.
The reason Radiohead included this unbearable noise… I’ll leave for you to think about! But note that four years on from first hearing the whine, I’m now unable to hear it.
What Are the Quietest and Loudest Sounds that You Can Hear?
The dB SPL scale, by its very definition, means that the quietest sound we can hear with healthy ears is 0 dB. With less healthy ears, this will be higher, however, even with the healthiest ears, it is not possible to hear any sound at the quietest place on Earth, the Orfield Laboratories anechoic chamber.
The founder of the laboratory, Steven Orfield, states that the chamber is so quiet that it has a negative background noise level of -9.4 dBA! In a conversation with Hearing Aid Know he said that “We challenge people to sit in the chamber in the dark – one person stayed in there for 45 minutes. When it’s quiet, ears will adapt. The quieter the room, the more things you hear. You’ll hear your heart beating, sometimes you can hear your lungs, hear your stomach gurgling loudly. In the anechoic chamber, you become the sound.”
But what is an anechoic chamber? Essentially, it is a space insulated enough so that little background noise from outside the chamber can get inside and with acoustic foam paneling to reduce the number of reflections inside the space, resulting in practically 100% sound absorption.
Most acoustics measurements had to be taken outdoors to avoid the effects of noise pollution and the reflection of sound that occurs indoors until the 1920s. This is when researchers from Bell Telephone Laboratories attempted to make an anechoic chamber.
I have been in a hemi-anechoic chamber, meaning that it is half an anechoic chamber as the floor is not absorptive. If you ask me, anechoic chambers make sounds very unusual. It is hard to describe the sensation of an anechoic chamber because we are so used to hearing common sounds like our voice with reflections, it is so unusual to hear a sound on its own that it gives a really eerie sensation.
Listen to this balloon pop in an anechoic chamber. It really makes you realize that a lot of what you hear is indirect reflected sound.
The loudest sound you can hear is debated. Some have said that the loudest sound you can hear is approximately 160 dB. In theory, there should be no limit to how loud something is until you can no longer hear it, but anything past 160 dB has been said to rip your eardrum!
Others have said that about 137 dBA will cause sudden hearing loss (also called acoustic shock). Either way, few people are lining up as participants for the experiment to test how loud they can hear before hearing loss occurs!
How Loud is Too Loud?
As discussed, 137 dBA is thought to cause sudden hearing loss, but how loud must a sound be to cause even slight damage? What level of sound is safe for human ears? It is not only a loud short-duration sound that can damage your ears, but also a quieter long-duration sound.
It is thought that a dBA of above 85 will start to cause damage to your ears. However, long-term exposure to noise can be just as damaging as the short-term, as demonstrated in the table below taken from The Control of Noise at Work Regulations act 2005.
|Lower Exposure Action Values||80 dBA||135 dBC||Hearing protection should be given as an option|
|Upper Exposure Action Values||85 dBA||137 dBC||Hearing protection must be worn|
|Exposure Limit Values||87 dBA||140 dBC||Should make the environment quieter as even with hearing protection the level is too loud|
L_ex is the noise exposure averaged over eight hours to align with a typical day’s work. It can be seen that a level as low as 80 dBA can cause some damage over eight hours and hearing protection should be given as an option to prevent potential hearing loss.
The employer has to ensure you are safe at work. If you sometimes feel like your workplace is too loud, ask your employer if they’ve had any tests done to ensure your ears are safe. I’ve heard of University students who have booked out equipment to measure the levels at the local gig venues they work at and have found the levels to be too loud. Be careful!
What Should You Consider When Recording Audio at Different Levels?
To capture very low and high-level sounds, you’ll need a suitable microphone. While being interviewed on A Sound Effect, Chuck Russom said that capturing loud sounds will sometimes require a microphone with a high SPL rating, such as an Avantone Pro CV-12. He also recommends setting up a backup microphone that is recording at a lower level in case the sound is louder than anticipated and causes clipping, where the peak loudness capable of recording is surpassed, causing distortion.
A similar backup microphone can be used for quieter sounds that are recording at a higher level just in case a sound is too low to be picked up. Of course, as previously discussed, sounds become quieter the further away you are, for really quiet things you might have to get really close!
Capturing the content of a high-dynamic-range will be much easier when recording to a higher bit-depth. This is because there will be more data available to represent your waveform when it has to be digitized, meaning there will be more room for any potential error. A bit-depth of 32 should be more than sufficient to easily capture loud sounds.
How Can You Measure the dB of Different Sounds Yourself?
The table at the top of this article demonstrates a range of sounds and levels you can create or find in your own home. Why not see how loud your appliances are or (the more fun option) see how loud you can shout using one of the following methods.
Professionally, dB is often measured using a sound level meter with a measurement microphone. The M2230 is a measurement microphone that has a dynamic range of 16-137 dB, this can be attached to NTi Audio XL2 to view the dB. This equipment, however, costs thousands.
A super-inexpensive way to measure dB yourself is to download a sound level meter app on your phone. I’m sure there are dozens to choose from, but I tested out Sound √, which very neatly shows the dB level and if you are in any danger of being near something too loud.
A more suitable middle ground would be to use a standard microphone and capture the sound to a device, such as your computer. You can use free software, such as Room EQ Wizard, to analyze the content. Within Room EQ Wizard, there is even a built-in SPL meter. Although the sound input was my cheap laptop microphone, which will be of poorer quality compared to a typical recording microphone, there are still a few nice features available. You can even measure the L_ex, like is measured to test if a workplace is too loud. Apparently, the is only 34.7 dBA in my room, so I know I don’t need to be worrying about my ears!