The most common kind of sound is noise. We are all surrounded by noise in our daily lives. Noise is defined as sound that has no pattern or defined pitch. Noise affects people in many ways. In addition to causing temporary and permanent hearing loss, noise interferes with speech communication, interrupts sleep, reduces human efficiency, and is believed to produce other physiological and psychological effects.
The effect of noise on the performance of various tasks has been the subject of several investigations in the laboratory and in actual work situations. When mental or motor tasks do not involve auditory (hearing) signals, the effects of noise on human performance have been difficult to assess.
Psychological effects of noise:
1. Steady noises below about 90 dB do not seem to affect performance.
2. Noise with appreciable strength around 1000 to 2000 Hz is more disruptive than low – frequency noise.
3. Noise is more likely to reduce the accuracy of work than to reduce the total quantity of work.
4. Noise appears to interfere with the ability to judge the passage of time.
5. There is a general feeling that nervousness and anxiety are caused by or intensified by exposure to noise.
Physiological effects of noise
Sudden noises are startling. They trigger a muscular reflex that may include an eye blink, a facial grimace or inward bending of arms and knees. These reflexes prepare the body for defensive action against the source of the noise. Sometimes these reflexive actions interfere with some tasks: sometimes they even cause accidents.
Constriction of blood vessels, reduction of skin resistance, change in heartbeat and secretion of saliva have been observed in human response to brief sounds. There is evidence that workers exposed to high levels of noise have a higher incidence of cardiovascular disorders such as ear, nose and throat problems and equilibrium problems than do workers at lower levels of noise.
When does noise become noise pollution? Noise pollution includes sounds that are loud, annoying or harmful to the ear. These sounds can come from sources such as jackhammers, a jet engine or highly amplified music.
Noise pollution can be harmful in several ways. Recall the way in which sound waves transfer energy through compressions and rarefactions. If the intensity of the sound wave is high enough, the energy carried can shatter windows and crack plastic.
When sound waves reach the human ear, the vibrations pass through various parts. Extremely intense vibrations can rupture the eardrum, but loudness-related hearing loss usually develops gradually. Your brain perceives sound when the auditory nerve carries a nerve impulse to the brain. The nerve is composed of many tiny nerve fibers surrounded by a fluid inside the ear. Hearing loss occurs when intense compressional waves traveling through the fluid destroys these nerve fibers. Loud sounds in the frequency range of 4000 to 20,000Hz cause most of the damage to these nerve fibers. Amplified music, motorcycles and machinery are sources of sound in this frequency range that often cause hearing loss after prolonged listening.
Controlling noise pollution (environmental acoustics)
Noise pollution can be controlled in a number of ways. Reducing the intensities of the sound waves from sources that cause noise pollution can decrease noise pollution. Acoustical engineers have quieted the noise made by many devices. For example, mufflers help quiet automobile engines. In buildings, thick heavy walls, well-sealed doors and windows, may be used to block sound. Builders use insulation to reduce sound. Industrial workers and other people exposed to intense noise should wear some form of ear protection to help prevent hearing loss.6
What is Music? Vibrations cause both music and noise, but there are some important differences. You can easily make a noise by just speaking a word or tapping a pencil on a desk, but it takes some deliberate actions to create music. Music is created using specific pitches and sound quality and by following a regular pattern.
A stringed musical instrument such as a guitar generates sound when you pluck a string. Plucking a string creates waves in the string. Because the ends of the strings are fastened, the waves reflect back and forth between the ends causing the string to vibrate at certain particular frequencies that are harmonically related to each other.
The guitar string, like most objects has a natural frequency of vibration. Plucking it causes the string to vibrate at its natural frequency.
If you were to play a note of the same pitch and loudness on a flute and on a piano, the sound wouldn’t be the same. These instruments have a different quality of sound. The quality does not refer to how good or bad the instrument sounds. Sound quality describes the difference among sounds of the same pitch and loudness. All sounds are produced by vibrations of matter, but most objects vibrate at more than one frequency. Distinct sounds from musical instruments are produced by different combinations of these wave frequencies.6
Mini-Lab: How can a hearing loss change the sounds you hear? To simulate a hearing loss, tune a radio station. Turn the volume down to the lowest level you can hear and understand. Turn the bass to maximum and the treble to minimum. If the radio does not have these controls, mask out the higher frequency sounds with heavy pads over your ears. Which voices are hardest to understand men's or women's? What letter sounds are the most difficult to hear, vowels or consonants? How could you help a person with a hearing loss understand what you say? Solution: Most hearing losses are in the higher frequencies of the speech range. Most affected are women's voices and consonant sounds. People with hearing losses should be spoken to face to face, at a steady, unrushed pace with a slight emphasis on consonant sounds.