What is Acoustics? Understanding the Beautifully Interesting Science of Sound
Acoustics is an important part of music and sound, yet there’s so much more to the science of it than assisting in the design of instruments and concert halls.
An everyday example of acoustics you may have encountered is how we’re all better singers when we’re in the shower. There’s a good reason for that, and it is really quite fascinating.
WHAT IS SOUND?
Sound is made up of vibrations created by pressure waves in the air. Once these vibrations leave the source and travel into your ear, they cause your eardrums to vibrate and stimulate thousands of tiny hairs inside your cochlea, a tube-like structure within your inner ear.
The hairs moving back and forth in time with the vibrations create electric signals. These then travel through the auditory nerve and are received by the brain and perceived as sound.
WHAT IS ACOUSTICS?
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Acoustics is the scientific field that deals with the transmission, production, control, reception, and effects of sound.
Not only is it a key element in the design of musical instruments and architectural spaces, but it’s also used in sonar, medical ultrasounds, noise control, electroacoustic communication, bioacoustics, seismology and thermoacoustic refrigeration.
Acoustics was originally divided into two branches: diacoustics and catacoustics.
Diacoustics studies refracted sounds and the medium that they pass through. Catacoustics is the study of how sounds bounce off different surfaces, this is also known as the echo effect.
Today, both of these fields work side-by-side, harmonising their efforts.
Sound is created by vibrations travelling as waves (vibrating particles), which are then reflected by other surfaces. The harder you hit a drum skin, the bigger the vibration it causes.
Soundwaves start silent, or at the “zero line”, and the wave rises above the zero line to indicate the relevant change in pressure.
As well as passing through the particles in the surrounding environment, the vibrations must also pass through their initial source before travelling into your ear.
The speed of the sound waves, better known as the sound’s frequency, is measured in Hertz (Hz).
The average piano can make sound waves that range in frequency between 27.5 Hz and 4186 Hz, whereas the human audible spectrum is between 20Hz and 20Khz.
Anything below 20Hz is referred to as subsonic, and although we can’t hear these sounds, we can feel the vibrations they make.
All sound above 20Khz is called ultrasonic. Again, the human ear can’t pick up anything in this frequency range, but there are certain animals and sound equipment that can.
SOUND PRESSURE LEVEL
The human ear is also capable of registering sound that ranges from very soft to excruciatingly loud. When measuring sound pressure level (SPL), a sound level meter is used and it presents its readings on a decibel (dB) scale.
Despite 3dB being the common level at which sound is picked up by the average listener, our ears are able to hear sounds as soft as 1dB.
A normal conversation registers between 60dB and 65dB, whereas the sound pressure level on a busy street could reach as high as 85dB. The threshold of pain from sound pressure is around 120-140dB.
The amount of energy used to create vibration waves dictates the range of a sound from almost-silent, to very loud. More energy equals more sound. Amplitude is the “maximum displacement or distance moved by a point on a vibrating body or wave measured from its equilibrium position”.
The equilibrium position refers to the “zero line” on the sound wave scale; in another word, silence.
The further away from this state a sound is, the higher its amplitude. When the wave’s amplitude steadily decreases due to losing energy, it has been “damped”.
WHAT FACTORS AFFECT ACOUSTICS
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Numerous factors come into consideration when dealing with acoustics, such as where the initial vibration was made, what the vibrating medium is made of, what the sound wave needs to travel through/around before it enters your ear and if the sound is also reflecting off of another surface and being heard more than once.
Because the shape, size, and material of instruments and rooms vary, the science of physics comes into great use when designing something acoustically.
Here we’ll cover everything for you without writing any equations on a whiteboard.
An instrument is considered part of acoustics if it produces sound naturally without electrical assistance.
The fundamentals of musical acoustics revolve around how each instrument creates sound. Basically, they all cause vibrations, but how they do so is split into three categories: wind, string and percussion.
Depending on which instrument is being played, sound pressure is generated from the string, bar, membrane or plate. That vibration passes through the rest of the instrument, and then through the air and into our ears.
However, that sound can vary depending on the environment it's heard in.
With regard to room design and architectural acoustics, there are many shapes and sizes that people make use of. The three most common are open-plan, hard rooms, and rooms with absorbent ceilings.
Rooms with absorbent ceilings draw away reverberating sound around the venue, at the cost of a lower sound level.
Hard rooms have as few absorption properties as possible and include walls and ceilings that reflect most of the sounds made. This causes greater acoustics and increased amplification.
Open-plan rooms have corridors and areas where sound moves freely. In order to control sound in these spaces, these rooms depend on absorbent ceilings, furnishings and floor surfaces, as well as the location of the workstations and other objects.
FURNISHING AND OBSTRUCTIONS
Tables, chairs, walls, and even people in attendance have to be taken into account when dealing with acoustics. Because the vibrating particles have been bouncing off of so many different surfaces on their way to your ear, each of the obstructions can affect the sound that you eventually hear.
Depending on what else is in the room, the sound may be dampened by insulation, or be made smoother by porcelain in your bathroom. This is why your shower-time renditions sound so good.
Try listening to something in the same room as the speakers first and then compare the sound when listening to it in the next room. There will not only be a reduction in the volume, but you will notice other differences in the sound.
HOW ARE OUR EARS AFFECTED BY ACOUSTICS?
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If it wasn’t for acoustics, humans wouldn’t be able to process sound. When the vibrating sound particles make their way to us and into our ears, they make everything else around them vibrate as they squeeze their way inside our heads.
It’s not quite that simple, however, as the human ear is an amazing bit of equipment in its own right.
It consists of a series of intricate parts that do their own thing with the sound waves, after which passes down the production line.
The pinna is the first stop on the sound wave’s journey through our bodies. Also known as the auricle, the funnel-shaped outer ear catches sound energy and amplifies it inward to the next part of the ear.
THE AUDITORY CANAL
The main function of the auditory canal is to navigate sound waves to the middle ear and the eardrum. Despite being separate from the other parts of the ear, many experts consider this one-inch-long passageway as part of the outer ear.
THE MIDDLE EAR
It’s the job of the middle ear to trap airwaves and move them via the eardrum. The eardrum then pushes the air into the eustachian tube, which is located behind the nasal cavity.
This tube connects the middle ear to the back of the throat, and its main purpose is to drain fluid from the ears.
THE INNER EAR
Once the airborne sound wave leaves the middle ear, it arrives in the inner ear and is received by a tiny piece of solid bone called the cochlea.
Coiled up like a seashell, the cochlea is home to thousands upon thousands of tiny hairs. These hairs act as transmitters, and they turn sound pressure patterns into electrochemical signals.
Once they’ve done their job, the signals shoot towards the brain via the auditory nerve and are processed as sound.
THE WONDERFUL WORLD OF ACOUSTICS
Now that you’ve learned the basics of acoustics, there’s a good chance you’ll head your own investigations into how some of your most-loved songs and noises sound under different conditions and in different environments.
You should also be equipped with the tools to recognise and understand why things sound different in hard rooms, underwater, in an open field at a festival, and when the source of vibration comes from different instruments.
Best of all, you should know how acoustics cause you to hear all of these wonderful things, whether you’re in a concert hall with the world’s best acoustic architecture or listening on your favourite pair of headphones.
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Writer | DB Damage
DB Damage is a freelance content writer passionate about creative subjects like music, film, and video games. He studied IT and music technology at college and has a background in managing and promoting local bands.