Fundamentals of Acoustics and Audio Systems


In the previous Topic (Understanding Sound System Design ), I mentioned the important points you must know to be able to design a good sound system which I listed them as follows: 

  1. The audio system structure. 
  2. The fundamentals of acoustics and audio system. 
  3. Method of performing project survey for acoustical conditions 
  4. Sound systems Manufacturers’ catalogs and manuals 

Also I mentioned that we finish the first part which is the audio system structure through our past topics in this course; LV-1 Basic Sound System Design and Today, I will begin explaining the second part which is the fundamentals of acoustics and audio system as follows: 

The fundamentals of acoustics and audio system:


Under this part we will discuss a lot of definitions and rules that are a key for understanding sound system design.

What is Acoustics?


The Acoustics is the scientific study of sound, especially of its generation, propagation, perception and interaction with materials.

Acoustics is a wide range of science that include many topics like noise control, SONAR for submarine navigation, ultrasounds for medical imaging, thermo-acoustic refrigeration, seismology, bioacoustics, and electro-acoustic communication.

 


above is the so called "Lindsay's Wheel of Acoustics", created by R. Bruce Lindsey in 1964. This wheel describes the scope of acoustics starting from the four broad fields of Earth Sciences, Engineering, Life Sciences, and the Arts. The outer circle lists the various disciplines one may study to prepare for a career in acoustics. The inner circle lists the fields within acoustics that the various disciplines naturally lead to.

What is Sound?


Sound is a mechanical wave generated by a disturbance in an elastic medium (fig.1)

Fig (1)

Medium is simply a series of interconnected and interacting particles in its positions, if any particle is displaced from its position due to application of external energy source (fig.1), it will result in disturbance of other neighboring particles and producing a mechanical wave.

Mechanical waves are waves that require particles interaction (vibration) in a medium in order to transport their energy from one location to another and they cannot travel through a vacuum like the electromagnetic waves.

The elastic medium include three types as Gas, liquid and solid but Air is the primary form of elastic medium of concern to acoustics.

Fig (2)
 
As example; consider a tuning fork vibrating (see fig.2), The oscillatory motion of the tines creates tiny disturbances in the air which can be sensed by our ears and the resulting affect is the pulsing of compressions then Rarefactions waves which we called sound waves. 

The sound wave shape:


The sound wave will pass by three status in a disturbance period; compression, still in place and rarefaction 
as in fig.3. The wave magnitude will reach a peak point in compressions; down to zero point in “still in place” and down again to low peak in rarefactions and then repeated again. 

Fig (3)

And this will represent a sinusoidal wave for the sound-time curve as show in fig but don’t be confused actually the sound will not move (propagate) as a sinusoidal curve, it will propagate in a longitude direction from the source of sound to the sound receiver, therefore sound travelling in air as longitudinal waves not a transverse (sinusoidal) ones as shown in fig.4 for the actual experiment done in 1950 to indicate sound propagation waves.

Fig (4): sound propagation waves
 
In longitudinal waves the displacement of the medium is parallel to the propagation of the wave. A wave in a "slinky" is a good visualization as in fig.5 below.

Fig (5): Longitudinal and Transverse Waves

While For transverse waves (see fig.5) the displacement of the medium is perpendicular to the direction of propagation of the wave. Also, Transverse waves cannot propagate in a gas or a liquid because there is no mechanism for driving motion perpendicular to the propagation of the wave.

Properties of Sound:


How would you describe a sound? Is it loud or soft? High or low? Soothing or jarring? , you can answer these questions easily if you know what the properties of sound are? And the answer is in below paragraphs.

Properties of sound include the following:
  • Sound Propagation. 
  • Wavelength and Cycle. 
  • Amplitude and Loudness. 
  • Frequency and Pitch. 
  • Sound Velocity. 
  • Complex Sound waves. 
  • Audible Sound Frequency Range. 
  • Octaves. 
  • Timbre. 


In the next Topic, I will explain in detail the properties of sound. So, please keep following.

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