Interesting Facts

Basic Principles of Sound

Sounds are variations of pressure in the air. The variations of pressure cause imperceptible movement of molecules in the air.These movements of the molecules are waves, but not like the waves we see in the ocean. As the energy of a sound wave passes through the air it causes successive areas of compression of air particles (or areas of high presure) and successive areas of rarefaction of air particles (or areas of low pressure). If you could see the waves you would see compressions and rarefactions of air molecules passing in all directions from the source of the sound. It is necessary to have a medium so that the compressions can occur. Most of the time the meduim is air, but the medium can also be water or metal. In a vacuum there is no air. Consequently there is no sound in a vacuum because there is no medium. You can determine the length of the waves if you measure from the centre of one compression to the center of the next compression. When the length of the waves are short the frequency is high and the sound is high-pitched. When the length of the waves are long, the frequency is low and the sound is low-pitched. The definition of frequency is the number of vibrations completed per unit of time. The wavelength of the note "middle C" is 1.2 metres. The frequency is 256 Hertz. A Hertz is equal to 1 vibration per second. A human can hear frequencies between about 20 Hertz to about 20 000 Hertz. We use decibels to measure the intensity of sound. The decibel is a logarithmic measurement. So, with each increase of 3 decibels the intensity of the sound doubles!

The Ear

The ear is the reception organ of sound. The external part of the ear captures the sound waves and guides them toward the ear drum. The ear drum is a membrane which vibrates like a drum. It is attached to 3 tiny bones in the middle ear. These bones are called the hammer, the anvil and the stirrup. They amplify and transmit the movements of the ear drum to the inner ear. The inner ear is filled with liquid. The cochlea is situated here. Inside the cochlea are 15,000 cells which have tiny hairs or cilia on them. Sound vibrations cause these tiny hairs to move which in turn stumulates the auditory nerve to send electrical signals to the brain.

The Exposure of Classical Musicians to Excessive Noise

Hearing loss can be caused by exposure to excessive noise. Men are at even greater risk to this type of hearing loss than women. When a person is exposed to very loud sounds, they develop a temporary hearing loss, but their ears can recover in 14 hours in a quiet environment. However if a person is exposed repeatedly to excessive noise they will develop irreversible damage to their hearing! At first the hearing loss is at the frequency of about 4000 Hertz, so that the person will not be able to hear fairly high-pitched sounds. Later the person will no longer be able to hear sounds at higher or lower frequencies than 4000 Hertz. The first symptoms of hearing loss are often ringing in the ears, or tinnitus, and when the person starts to have difficulty hearing conversation.

When a classical musician plays in an orchestra, he or she is exposed to very loud sounds. Naturally when a lot of musicians are playing their instruments at the same time, there is a lot of noise. Also, in an orchestra, musicians have to sit very close to each other. The musicians in the brass section, especially the trumpet or trombone players, and the percussion players produce extremely loud sounds. This is dangerous for their ears as well as for the ears of the musicians sitting near them. Once my cello teacher had to sit in front of ten trumpets. He said that it was extremely painful for his ears! Usually cellists sit in one of the least dangerous sections of the orchestra. They are seated quite far from the brass and percussion sections. Also a cellist sits behind his own instrument, and so sits behind the "f-holes" in his cello.The f-holes are two thin holes in the cello which are shaped like the letter "f". The sounds he makes escape from the f-holes and are directed away from his ears.

The violin can be more dangerous to the ears of the violinist because he or she holds the violin under their chin and extremely close to their left ear. Flute and piccolo players hold their instruments very close to their right ears. Also the sounds they produce are very high-pitched or of a high frequency. The ciliated cells of the cochlea which detect high-frequency sounds are the most easily damaged of the sensory cells.

There are special problems for musicians who play in an orchestra pit, such as during an opera or a musical theatre production. The sound levels in the pit are very high because it is hard for the sound waves to escape from the enclosed area. In addition the musicians play louder than normal so that the audience can hear them.

Other classical musicians are also in danger of exposure to excessive noise. For example, the conductor has to stand directly in front of the entire orchestra, so he is in the centre of all of the sound. As well, music teachers listen to high levels of sound for many hours in a day, especially if they teach in the school system, where they teach large classes of students.

Protecting Classical Musicians Against Hearing Damage

Modifying the environment in which musicians play can help protect them from being exposed to excessive noise. Covering the walls or ceiling with accoustic panels can help to absorb some of the sound. It is also possible to separate the chairs of the members of the brass and percussion sections by a few meters from the other musicians. Sometimes transparent acrylic barriers are installed on the backs of the musicians' chairs. This helps prevent the musician sitting in the chair from the sound coming from behind him. However one of the problems is that the musician sitting in a chair behind a barrier will be exposed to even greater sound levels because sound will be reflected back at him or her. Sometimes orchestras place the brass section on risers to raise those musicians above the other musicians in the orchestra. The hope is that the sound from their instruments will be projected above the heads of the other musicians.

Musicians can also wear special "musician's ear-plugs" which are either stock or custom-made. These ear-plugs diminish the intensity of the music, but they do not distort the music. I have a pair of the stock triple-flanged musician's ear-plugs. Children, who are still growing, cannot wear the custom-made type of ear-plug because as they grow their ear canals change shape so that the custom-made ear-plugs no longer have a snug fit.

My ear-plugs

It is also very important to have a hearing examination every one to two years. In British Columbia there are regulations governing noise in the workplace and requiring hearing protection for some workers. If a worker is exposed to sound levels above 82 decibels, the employer must do sound level checks. A worker should not be exposed to average sound levels of more than 85 decibels during an 8 hour work day. Peak sound levels should not exceed 140 decibels, however in other countries this peak limit is lower because studies have shown that ear damage can occur at much lower peak levels.

 

WORKERS’ COMPENSATION BOARD

SOUND-EXPOSURE LIMITS

 

dBA level

Maximum allowable exposure time

82

16 hours

85

8 hours

88

4 hours

91

2 hours

94

1 hour

97

30 minutes

100

15 minutes

103

7. 5 minutes

Chart from SHAPE (Safety and Health in Arts Production and Entertainment (www.shape.bc.ca)

TYPICAL SOUND LEVELS

Approximate dBA level

 

Sound

45-55

Normal conversation at arm’s length

60-70

Piano played at moderate levels

75-85

Chamber music in small auditorium

80

Telephone dial tone

85

City traffic from inside car with open windows

90

Train whistle at 150 m.

92-95

Piano played loudly

94

Average personal stereo on 5

95

Subway train at 60 m

105-120

Amplified rock music at 1-2 m

107

Lawnmower

110

Power saw

120-137

Symphonic music peak

140

Jet engine at 40 m

150

Rock music peak

 Chart from SHAPE (Safety and Health in Arts Production and Entertainment (www.shape.bc.ca)

 

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