Acoustics is the study and analysis of sound properties. Understanding the elements of the trade allows you to create more subtle and organic soundtrack. Sound is the aural perception of vibrations. Noise is not organized or harmonious and music is organized. This is not clearly defined especially after World War 2 era, which is, known as Modernism. Post Modernism artist such as John Cage, Harry Parch, and Tan Dan set the stage. Periodic sound consists of the three P’s. These three P’s are Production, Propagation and Perception. Production is the vibrating body or mass that which energy is transferred and is the source of sound. Propagation is the medium through which the sound wave travels. Perception is the receptor of the sound. The human ear is a good example, or a microphone. These three P’s are also know as Generation, Transmission, and Reception. Psycho acoustics is the scientific study of sound, or the perception of sound. Pitch is how high or low a sound is perceived. Loudness is the subjective impression of the strength or weakness of the sound. The acoustical equivalent would be frequency and amplitude. Pitch is basically the psychological perception of how high or low a sound is. Frequency is the specific measurement of the rate of repetition of a vibrating mass. There are treble pitches, Bass pitches, Tenor pitches, and Alto pitches. Bass is Low, Tenor is low middle range, and Alto is upper middle range. The subjective perception of how loud or soft a sound is the loudness. The strength or weakness of the air pressure made by the sound can be measured and is know as the Amplitude. The magnitude is also measured and is know as the Volume. This includes Frequency, Pressure, Harmonics, and surface properties that all take place in the space for a specific length of time. Tambre quality is known for it’s rich tone and is very important in music. This can be related back to a choir of 200 or the over all quality of sound that comes from an Orchestra.
A waveform is how we analyze sound that travels longitudinally. By breaking it down in to this wave we can then analyze it and it’s components. Sinusoidal or Simple Harmonic Motion (SHM) is the periodic wave because it repeats over and over. This is one of the more simple of waveform. The sine waveform contains a single frequency and no harmonic content. Complex periodic contains inconsistent and irregular waveform but still repeats consistently. Most sounds that you hear around you everyday consist of complex and random waveforms.
Next, we will take about some of the primary characteristics of sound that make up the waveform. First, we have Frequency. This is the rate at which a vibrating mass, electrical signal, or acoustic generator reiterates a complete cycle of compression and rarefaction. A cycle is represented by 360 degrees of a circle and plays a major part in the phase of waveforms. The sine is divided into polar halves. One half is above the standard reference line and the other half is below the standard reference line. Frequency is measured in Hertz (Hz). That brings us to Hertz and is named after Heinrich Rudolf Hertz. Hertz is the number of times a cycle happens per second. If something produces 300 cycles it is know to have a frequency of 300 Hz.
Humans can hear a range of Hertz between 20 Hz and 20Khz. Anything below the 20 Hz is know to be Subsonic, and anything above 20 KHz is know to be Ultrasonic. Then we have Amplitude. This is the amount of sound pressure created in normal atmospheric pressure.
“ The Law of Conservation of Energy. Sound Intensity and the Inverse – Squared Law is summarized by saying that the surface area of intensity impact area is squared every time the distance doubles.” (Cancellaro, 20).
Next we have the Wavelength of sound. This is physical distance of a complete cycle. A wavelength that is longer is known to have a lower frequency and a lower sound. Wavelength and Frequency are directly related.
“ Air consist of many different types of molecules: 78% nitrogen, 21% oxygen, and the remaining 1% contains argon, carbon dioxide, neon, helium, krypton, xenon, methane, nitrous oxide, and hydrogen. Molecules in air are in constant motion, colliding and bouncing off of each other at moderately high speeds of about 1000 miles per hour.” (Cancellaro, 23).
Envelope is another characteristic of the waveform and is the attack and delay character of the wave. Harmonics also is another characteristic and consists of the base frequencies and higher frequencies that make up musical tones. Additionally, Surface Effects and Propagation is also a characteristic of the waveform. This characteristic includes how the waveform will encounter objects or react to other mediums boundary. Boundary behavior is how sound reacts when it leaves one and encounters another.
Reflection reflects an identical wave back from the surface that it encounters and then it decays. A circle indicates the Angle of Incidence with a horizontal line through it. Diffusion scattering happens with sound is reflected back from an irregular surface, in many different angles. Diffraction is how sound bends around objects that it encounters and cast an acoustic shadow.
Anything that cancels out a signal or enhances it is considered Constructive and Destructive Interference. Constructive interference increases the amplitude and destructive interference decreases the amplitude.
Beats are a mixture of frequencies with zero disturbance and doubling amplitude. Beats can be calculated by subtracting the higher and lower frequency. Anything higher than 30 Hz to 40 Hz the beat phenomenon does not exist. In it’s place is two frequencies know as and interval.
“ The path a sound takes to eventually get into your computer is one of the most important aspects to understand in the recording and playback process. Recording sound is a skill knowing the difference between device types and what they can do to a recording.” (Cancellaro, 34)
A current is the flow of charges from one place to another and is measured in Amperes. Voltage pushes the current and measuring it is an important part of sound integrity and amplitude. A Transducer converts energy from one form to another. A good example of this is a microphone or speaker. Magnetism is the theory of electromagnetic induction and plays a major role in microphones as it converts sound waves into electric impulses.
There are three types of Microphones: Dynamic, Condenser, and Ribbon. The most common is a dynamic microphone because it is tough and durable but has limited frequency response. A Condenser microphone requires an external power supply known as phantom power. The ribbon microphone has a built in transformer that boost the levels. The dynamic range of sound that the microphone can provide to the recording device.
Each microphone is different and can have varies based on construction and design. How a microphone responds to sound pressure levels or SPL is know as frequency response. Directionality is the area around the head of the microphone that is the polar pattern that the microphone responds to. There is on-axis and off-axis. Off- axis is always 180 degrees from the on angle axis. There are two directional categories, omni directional and directional and four sub categories. These categories are Cardoid, Hypercardoid, Super Cardoid, and Bidirectional.
Last but not least we have the Loudspeakers. Brands such as Trannoy, JBL, Genelec, M-Audio, Alesis, Mackie, and Yamaha are to name a few. The source of power for the speakers is monitor power. Passive requires amplifiers and Active have power supply built in. Monitor speakers come in two-way and three-way. The two-way consist of a tweeter and a woofer known as drivers. The three-way consists of a tweeter, midrange, and woofer driver. Crossovers are responsible for directing power to the drivers.
In conclusion, we have learned that all sound comes from a vibration. Also, how air and objects around us play a major role in how a sound waveforms are manipulated. Furthermore, The primary characteristics of sound such as frequency, wavelength, amplitude, envelope, harmonics, surface effects and velocity. The importance of microphones and capturing quality sound. Lastly, Loudspeakers, their components and the role they play in producing sound.
Exploring Sound Design for Interactive Media, Cancellaro, Joseph