WHAT IS SOUND?

Sound is energy and, like other forms of energy, can be useful to man. The vast range of possible frequencies and timbres that characterizes both speech and music makes sound an effective medium of communication. Even ultrasound – sound above the hearing range of man – has many practical uses. Most sounds don’t carry great deal of energy. The noise of a symphony orchestra playing as loudly as possible involves for example, sound energy equivalent to the light and heat energy from only a low-powered electric lamp. Our hearing sense is more easily saturated (in energy terms) than our visual sense.

Sound is a particular form of kinetic energy (energy of motion) produced when an object vibrates and a medium, such as air, vibrates in response. The sound of a car crash booms out as the surfaces of the two colliding vehicles vibrate with the force of the collision; music comes from a radio as a loudspeaker vibrates; and talking and singing result from vibration of the vocal cords.

As an object vibrates it sets the air molecules around it vibrating. Where the air molecules gather together a region of higher pressure (compression) occurs. Where they move apart a region of lower pressure (rarefaction) occurs. As compressions and rarefactions move through the air they form a sound wave. At the ear they set the eardrum vibrating and we hear sound.

If a surface vibrates more strongly, the pressure difference between the compressions and rarefactions is greater and the sound is loud. The frequency of vibrations affects the pitch, or note, of the sound. Fast vibrations produce compressions and rarefactions that are close together and the pitch is high. A slower speed of vibration causes the compressions and rarefactions to be farther apart and the sound is lower in pitch.

A sound wave moves out from its source in all directions, traveling at a speed of 1,087 ft (331 m) per second or 741 mph (1,194 kph) in air at 0ºC at sea level. The speed is slower at high altitudes as air less dense there, and faster in water and metal because these substances are more elastic than air and transmit vibrations more rapidly. The speed also correlates with temperature of the medium. Sound cannot move through a vacuum because there are no gas molecules to vibrate and transmit the sound.

Like other waves of energy, sound normally travels in straight lines, but sound can turn corners. It is reflected whenever it strikes a surface such as a wall or floor and is diffracted or spreads out as it passes through an opening such as a window.

The loudness of a sound can be measured with a decibel meter and the result given as a number of decibels (dB). The scale is logarithmic – a sound that is twice as loud as one at the threshold of hearing is 10 dB greater, not twice as great. Strictly, the meter measures the intensity of the sound, which is related to the pressure differences in the sound wave. (Loudness is the strength of the sensation received in the eardrum and transmitted to the brain). The human ear does not hear all frequencies of sound in the same way, and a low sound is perceived as being less loud than a high sound of the same intensity.

The number of the compressions occurring every second is called the frequency of the sound and is measuring in hertz (Hz), equal to cycles per second. The higher the frequency, the higher the pitch.

Noise does not have any particular pitch and covers a wide frequency range. Very loud noise is dangerous as well as a nuisance, because continuous exposure to sound of more than 100 dB – the levels produced by jet aircraft and machines in many factories – soon results in a permanent reduction in hearing ability. Low frequency noises are particularly hazardous because they do not seem to be as loud as higher pitches, and tests have shown that very high levels of low frequency sound and infrasound (sound below the hearing range of the ear) quickly result in vertigo, nausea, and other physical effects; military scientists have even experimented with using infrasound as a potential weapon.

Acoustic engineers work to reduce noise and improve sound in many ways. A consideration of acoustics in the design of a machine such as a jet engine can reduce the amount of noise it makes. Buildings can also be designed to prevent the transmission of sound through them. A steel framework tends to distribute sound throughout a building, but the use of sound-absorbing materials in and on floors, walls, and ceilings prevents sound from getting into and out of rooms. In concert halls the reflection of soft sound inside the hall is rigorously to provide an exact amount of echo and give the best quality sound. This may be assisted by electronic amplification, although very loud music loses clarity in a concert hall. Some recording studios have completely absorbent walls to remove all echo and ensure total clarity whatever the type of music being performed.

II. Read the text again carefully and answer the questions.

1. What makes sound an effective medium of communication?

2. Is our hearing or visual sense more easily saturated (in energy terms)?

3. Where does compression occur?

4. In which case is the sound loud?

5. What makes sound lower in pitch?

6. The speed of a sound wave doesn’t correlate with the temperature of the medium, does it?

7. Can sound turn corners?

8. How can the loudness of a sound be measured?

9. Why are low frequency noises particularly hazardous?

10. Is it possible to reduce noise and improve sound?

III. Which of the vocabulary units used in paragraphs 1-3 could be regarded as scientific terms?

IV. Read the translation of the forth paragraph. Compare it with the original and say if everything is right.

Если поверхность вибрирует сильнее, разница давлений между уплотнениями и разреженностями больше; и звук получается менее громким. Частотные вибрации влияют на тембр звука. Частые вибрации производят уплотнения и разреженности, располагающиеся ближе друг к другу, и тон получается более высоким. Медленная скорость вибрации вызывает уменьшение расстояния и тон звуков становится ниже.

V. Find the English equivalents of the following words and word combinations in paragraph 10.

Передача, стальной каркас, звукопоглощающие, реактивный двигатель, предотвращать, отражение, инженеры-акустики, способствовать, усиление, звукозаписывающие студии, устранять.

VI. Find passages about dynamics pitch and frequency and translate them into Russian.

VII. Choose a passage and read it aloud (1-2 minutes).

VIII. Find complex grammar structures in the text and divide them into simple ones.

IX. Find the topic sentences, key words and phrases which express the general meaning of each paragraph best of all.

X. Using the information obtained from the paragraphs make a plan of the text.

X. Speak about sound using key words, phrases, the topic sentences and the plan of the text.

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