Sound Engenering

The importance of sound

Sound is a ubiquitous component of our environment from which there is no escape. Even in the darkness of a deep underground cavern, the potholer hears the sound of the  operation of his or her body. In the dark depths of the ocean, creatures communicate by sound, which is the only form of wave that propagates over long distances in water. Only  in the reaches of cosmic space, and in high vacuums created on Earth, are atoms so isolated that the chance of interaction, and hence the existence of sound, is negligible.

Sound is one of the principal media of communication between human beings, between higher animals, and between humans and domesticated animals. Sound informs us about our environment; as a result of evolution we find some sounds  pleasant and some redolent of danger. The universal importance of music to human
beings, and its emotional impact, remain mysterious phenomena that have yet to be satisfactorily explained. Unlike our eyes, our ears are sensitive to sound arriving from all directions; as such they constitute the sensors of our principal warning system,

which is alert even when we are asleep.

So, sound is vitally important to us as human beings. But, apart from audio  engineers who capture and reproduce sound for a living, why should engineers practising in other fields have any professional interest in sound? The short answer has two parts. On the positive side, sound can be exploited for many purposes of
concern to the engineer, as indicated later in this chapter. On the negative side, excessive sound has adverse psychological and physiological effects on human beings that engineers are employed to mitigate, preferably by helping to design inherently quiet machines, equipment and systems: but failing this, by developing and applying noise control measures.

The adverse effects of excessive sound in causing hearing damage, raising stress levels, disturbing rest and sleep, reducing the efficiency of task performance, and interfering with verbal and musical communication, are widely experienced, recognized and recorded. In recent years, noise has become a major factor in influencing the marketability and competitiveness of industrial products such as cars and washing machines, as evidenced by advertising material. Many products are required to satisfy legal and regulatory requirements that limit the emission of noise into work places, homes and the general environment. Failure to meet these requirements has very serious commercial consequences.

Aircraft are not certificated for commercial operation unless they meet very stringent environmental noise limits. Road vehicles are not allowed on the road unless the y satisfy legally enforced limits on roadside noise. Train noise is currently being subjected to the imposition of noise restrictions. A less widely known adverse effect of excessive sound is its capacity to inflict serious fatigue damage on mechanical systems, such as the structures of aircraft, space rockets and gas pipelines, and to cause malfunction of sensitive components, such as the electronic circuits of Earth satellites.

Sound is vitally important to the military, particularly with the advent of automated target recognition and ranging systems. Sound is a tell-tale. It gives warning that mechanical and physiological systems are
not in good health. Sound generated by the pulmonary and cardiovascular systems provides evidence of abnormal state or operation, as foreseen by Robert Hooke over 300 years ago. The production of equipment for monitoring the state of machinery via acoustic and vibrational signals is a multimillion dollar business. The cost of monitoring is small compared with the cost of one day's outage of a 600 MW
turbogenerator, which runs into more than one million dollars. Taken together, these different aspects of the impact of sound on human beings and engineering products provide convincing reasons why acoustics is a fascinating subject of study and practice for engineers.

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Recording Studio Setup

Recording Studio Setup -  Basic information improve the quality of your productions. Remember that the final quality of your music depends on many variables, including your skills with and knowledge of sequencing techniques,  the equipment you use, the software, and the environment (meaning essentially the studio) in which you work. In fact the studio is one of the most important elements

involved in the creative process of composing your music.

 I am not talking just in terms of equipment and machines (which I will discuss in detail in a moment), but also in terms of comfort and ease of use of the working environment, qualities that are essential if you are going to spend many hours composing and sequencing your projects. Your studio should have good illumination, both natural and artificial. If you are going to use electric light as a

main source for illumination, try to avoid lights with dimmer switches, since they are known for causing interference with studio recording equipment. Acoustic isolation and acoustic treatment of the room are also important elements that will help avoid external noises and create well-balanced mixes.

Even though the subject of acoustic isolation and treatment goes beyond the scope of this manual, here are some basic rules to follow when building your studio. First of all try to avoid (if possible) perfectly square or rectangular rooms. These are the most problematic because the parallel walls can create unwanted phasing effects and standing waves. You will soon realize that, unless you build an environment designed specifically to host a studio, most rooms are in fact rectangular. Therefore I recommend the use of absorption panels to reduce excessive reverberation caused by reflective and parallel surfaces, such as flat and smooth walls. 

Absorption panels help reduce excessive reverberation, their main function being to stop the reflection of high frequencies. As a rule of thumb, try to avoid covering your entire studio with absorption panels since this would make your room a very acoustically dry listening environment, which not only would cause hearing fatigue but also would mislead your ears during your final mixes. In order to reduce standing waves, you should use diffusers  on the walls and ceiling of the room. The main purpose of diffusers is to reflect the sound waves at angles that are different (mostly wider) than the original angle of incidence and thereby to limit

the audio artifacts caused by parallel walls.

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A SHORT HISTORY OF THE MICROPHONE

A SHORT HISTORY OF THE MICROPHONE - The microphone pervades our daily lives through the sound we hear on radio, television and recordings, paging in public spaces, and of course

in two-way communications via telephone. In this chapter we will touch upon some of the highlights of more than 125 years of microphone development, observing in particular how most of the first 50 of these years were without the benefits of electronic amplification. The requirements 

of telephony, radio broadcast, general communications, and recording are also discussed, leading to some conjecture on future requirements.

As children, many of us were fascinated with strings stretched between the ends of a pair of tin cans or wax paper cups, with their ability to convey speech over a limited distance. This was a purely mechano-acoustical arrangement in which vibrations generated at one end were transmitted

along the string to actuate vibrations at the other end. In 1876, Alexander Graham Bell received US patent 174,465 on the scheme shown in Figure 1–1. Here, the mechanical string was, in a sense,

replaced by a wire that conducted electrical direct current, with audio signals generated and received via a moving armature transmitter and its associated receiver. Like the mechanical version, the system was reciprocal.

Transmission was possible in either direction; however, thepatent also illustrates the acoustical advantage of a horn to increase the driving pressure at the sending end and a complementary inverted horn to reinforce output pressure at the ear at the receiving end. Bell’s further experiments with the transmitting device resulted in the liquid transmitter, shown in Figure 1–2, which was demonstrated at the Philadelphia Centennial Exposition of 1876. Here, the variable contact principle

provided a more effective method of electrical signal modulation than that afforded by the moving armature.

The variable contact principle was extended by Berliner in a patent application in 1877 in which a steel ball was placed against a stretched metal diaphragm, as shown in Figure 1–3. Further work in this area was done by Blake (patents 250, 126 through 250, 129, issued in 1881), who used a platinum bead impressed against a hard carbon disc as the variable resistance element, as shown in Figure 1–4. The measured response of the Blake device spanned some 50 decibels over the frequency range from 380Hz to 2000Hz, and thus fell far short of the desired response. However, it provided a more efficient method of modulating telephone signals than earlier designs and became a standard in the Bell system for some years. 

Another interim step in the development of loose contact modulation of direct current was developed in 1878 by Hughes and is shown in Figure 1–5. In this embodiment, very slight changes in the curvature of the thin wood plate diaphragm, caused by impinging sound waves, gave rise to a fairly large fluctuation in contact resistance between the carbon rod and the two mounting points. This microphone was used by Clement Ader (Scientific American, 1881) in his pioneering two-channel transmissionsvfrom the stage of the Paris Opera to a neighboring space. It wasvHughes, incidentally, who first used the term microphone, as applied to electroacoustical devices.

 The ultimate solution to telephone transmitters came with the development of loose carbon granule elements as typified by Blake’s transmitter of 1888, shown in Figure 1–6. Along with the moving armature receiver, the loose carbon granule transmitter, or microphone, has dominated telephony up to the present. Quite a testimony to the inventiveness and resourcefulness of engineers working nearly 130 years ago.

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