What’s a Decibel, and How Loud is Too Loud?
Updated: Jan 2, 2020
According to the Encyclopaedia Britannica a Decibel (dB), is "the unit for expressing the ratio between two physical quantities, usually amounts of acoustic or electric power, or for measuring the relative loudness of sounds.”
But to the general public, what does this actually mean? What exactly is a decibel equivalent to? Is it a boiling kettle or a footstep? And what exactly does the upper limit of 85 decibels equate to in real terms – is it an F15 flying overhead or the noise of a pneumatic drill? In this, our inaugural blog, we’d like to demystify this unit of measurement and help you understand what it means in real terms and why it’s so important to assess its impact on the environment.
How was the unit created?
We have the great Alexander Graham Bell to thank for the ‘bel’ in Decibel. The unit was actually created by Bell Telephone Laboratories. After the telephone was created, engineers needed to be able to quantify audio levels, in order to be able to assess the quality of transmissions. The unit was named the ‘bel’, and a decibel is one tenth of a bel. A one decibel difference in loudness is the is the smallest difference detectable by the human ear.
Because human ears don’t hear all sounds and frequencies, when it comes to assessing what we hear – and how loud it’s perceived – the decibel scale is modified to an A-weighted scale. This is known as dBA and is based on a child’s hearing range.
How exactly does the human ear work?
Hearing is an extremely complex process, by which we change sound waves into electrical signals, which are then transmitted to the brain via the auditory nerve and interpreted as sound.
Ready for the science bit? Here we go….
Sound is essentially a pressure variation that travels as sound waves through air, fluid or solid mediums. These sound waves can vary in amplitude – or size – and frequency. This wavelength determines the pitch, tone or frequency of the sound.
But how do our ears detect and translate sound? Sound waves travel along the ear canal, causing the eardrum to vibrate; these vibrations are then passed to the middle ear. Three tiny bones in the middle ear – the malleus, incus and stapes – then amplify the sound vibrations, and transmit them to the inner ear. The inner ear is also known as the cochlea, and is a fluid-filled, snail-shaped structure that contains approximately 40 thousand tiny hair – or sensory – cells. The vibrations cause the fluid inside the cochlea to move and ripple, bending the hair cells, which then generate an electrical signal. The auditory nerve carries this signal to the auditory cortex in the brain, where it’s turned into the sound we know and recognise.
When hearing is impaired, it happens because the tiny hair cells in the cochlea are damaged or destroyed. Hearing loss is usually permanent, so it’s important to protect your hearing and take adequate precautions if you find yourself working in a noisy environment.
Sound levels are subjective
The hearing process is extremely sensitive, and while we can detect sounds from the quietest of whispers up to the roar of a gunshot, each person’s hearing and perception of noise will vary. For example, a teenager might be happy with the volume of music blaring out of the speakers in their room, but parents can – and usually do – find the noise emanating too much. That’s why specialists and acoustic engineers use a sound level meter to take acoustic measurements.
What is a sound level metre and how does it work?
This simple hand held device consists of a square box with a microphone sticking out at one end. It’s important that the microphone is housed separately to the main instrument as this eliminates any reflections and gives a more accurate measurement. The microphone responds to changes in air pressure caused by sound waves, producing constant changes in voltage. These electrical signals are then filtered and amplified, converting them back to a sound pressure, which is expressed as decibels.
What exactly is a decibel?
So the decibel is a unit of measurement, but to the general public, what does this mean? It’s important to understand that sound levels are on a logarithmic scale, so the numbers don’t increase like the numbers on a ruler. Every increase of 10dB is a 10-fold increase of sound intensity, so 20 decibels isn’t double the level of 10 decibels, it equates to 10 x 10 decibels, 100 times the sound level.
Here are some comparisons to help you understand what decibels equate to:
Total silence – 0dB
Rustling leaves – 10dB
Whispering – 15 dB
A ticking watch – 20 dB
Quiet conversation – 40 dB
Normal conversation – 50 dB
Quiet traffic noise – 60 dB
Loud road/motorway noise – 80 dB+
Pneumatic drill – 110 dB
Loud music through headphones and music concerts – 110 dB
Aircraft at take off – 120 dB
Fireworks – 140-160 dB
Gunshots – 140-180 dB
It’s important to note that hearing damage as a result of exposure can happen at any age; and it will happen faster depending on the sound levels and time of exposure. A short blast at dangerous levels can lead to noise-induced hearing loss; but equally, repeated exposure to loud noises over a long period of time can also damage your hearing. Studies have shown that exposure to sound levels at 85 dB for more than 8 hours can lead to permanent hearing loss; at 100 dB this permanent hearing damage can happen in as little as 15 minutes.
Noise and Health and Wellbeing
Elevated noise in the environment or workplace can cause of wide range of health problems. It won’t just impair hearing, leading to hearing loss or tinnitus, it can also cause a wide range of psychological and physical health problems. Heart disease, high blood pressure, sleep disturbance, changes to the immune system and mental health issues are but a few of the health consequences that can be attributed to noise exposure.
We’ll focus more on this issue in a future blog, but given the impact noise can have on health and wellbeing, it’s important to assess – and control – the environmental impact of noise. This is where we can help. Our team of specialists can provide help with every step of the planning process – whether you’re a contractor, property developer, planning consultant, architect or project manager. Our services extend across London and the South East. For the London office you can contact us on 020 7859 4530; for the Reading office dial 0118 207 7324. Or you can email us on firstname.lastname@example.org. Get in touch today and see how we can provide a bespoke process, helping you with every step of the process.