Acoustics is a branch of physics devoted to the study of production, transmission, and reception of sound. Acoustics is defined by ANSI/ASA S1. 1-2013 as:
“The science of sound including its production, transmission, and effects including biological and psychological effects,” and;
“Those qualities of a room that, together, determine its character with respect to auditory effects.” This is sometimes referred to as room acoustics.
This piece looks at the fundamentals of acoustics. But first, here are some properties of sound waves:
Wave Cycle and Wave Period
Depending on whether the sound is moving longitudinally or in an oscillating manner, its wave cycle can be defined differently. If it’s moving longitudinally, it can be defined as a single complete vibration but if oscillating, a single complete oscillation. The period (T) of a sound wave, on the other hand, is the amount of time it takes a wave to complete one full cycle.
Speed of Sound
Despite a common reference to the speed of sound as though it were a fixed value, it isn’t. For example for a sound traveling at sea level with a temperature of 32 degrees fahrenheit , the speed is 740 MPH or 331 m/s. If the temperature changes to 68 degrees fahrenheit, then speed changes to 767 MPH or 343 m/s.
Depending on the pressure, density, and temperature of the medium through which sound is traveling, it can either travel fast or slowly. Nonetheless, the higher the pressure and the greater the density, the higher the speed of sound.
This is the number of waves going through a given point in the interval of one second. It is measured in Hertz (HZ) where a Hz is equal to one oscillation per second.
This is the distance between two adjacent crests of a sound wave. The higher the frequency of a sound wave, the shorter the wavelength and the lower the frequency, the longer the wavelength.
Sound Amplitude and Intensity
Amplitude is simply the “size” of a wave or the maximum displacement of a vibrating material. Sound intensity is then simply known as the “volume” of a sound wave or the rate at which a wave moves energy per unit of an area. Intensity is measured in watts per square meter.
Fundamentals of acoustics
1. Production of Sound Waves
The number of ways in which sound is produced are endless. Nonetheless, sound waves are vibrations and to produce sound therefore, vibration must first be produced. Here, we discuss two common ways of producing sound:
Musical instruments produce vibrations that result in sound especially stringed instruments. In other instruments like trumpets, vibrations are produced as a result of the musician blowing into them. Others like drums produce pure vibrations.
The Human Voice
The human voice is arguably the greatest of all sound producing mechanisms. The mechanisms of producing the human sound are quite complicated. However, we can all agree that it begins with the vibrations of the vocal cords.
Electronic Sound Amplification
Sound waves are a form of energy and the fact that they are energy means that these waves can be converted into other forms of energy. This is exactly what sound amplification devices do once sound has been produced by the original source.
For example, a loudspeaker receives sound waves and turns them into electrical energy. This electrical energy is then pushed through to an amplifier and then to a loudspeaker. The loudspeaker now transforms the electrical energy back to sound which has now been greatly amplified.
2. Transmission (propagation) of Sound Waves
For a sound that has been produced to move from one point to the next, it must be propagated or transmitted through a medium. Air is a great medium for sound to travel through which explains why if something falls near you, you would hear but if something were to fall in a vacuum, it wouldn’t be heard.
However, a medium alone is not enough for sound waves to move. Pressure aids a great deal in the transmission of sound. That’s why astronauts often say that “In space, no one can hear you scream.” There is therefore a combination of pressure and air required. Regardless, air by itself is not the only way sound waves can be transmitted, it just happens to be the most common. Sound waves can move through three basic mediums:
Liquid (for example, water)
Solid-like metal bars, strings etc
Reception of Sound Waves
A number of devices can now be used to receive sound waves. Among them is the ability to record by tape recorders and other whatnots. But just as the human voice was the greatest sound producing mechanism, so is the human ear the greatest way for sound reception.
Although objects can produce vibrations with unlimited frequencies, the human ear can only detect a range of these frequencies. Those between 20 to 1800 Hz can be heard by us. The rest are known as undetectable sounds. When the sound frequency is below 20 Hz, the sound is known as infrasonic and when the frequency is above 1800 Hz, the sound is known as ultrasonic. Ultrasonic and intrasonic sound waves can be used in industrial or research applications.
3. Applications of Acoustics
There is a myriad applications of acoustics around us in a number of devices and technologies. Some of them are:
Radios, televisions, telephones, music players etc.
The hearing aid
Construction of concert halls and auditoria
The areas of use of acoustics cover a wide range that keeps expanding by day. This can only show that the importance of acoustics is nothing to undermine just as it’s potential for the future.