At this point the science of sound can be a little more complex and intimidating since placing a numerical value on sound is very difficult due to the extraordinary sensitivity of the human ear. The energy expanded in the process of sound propagation is labeled intensity (loudness) and is measured in energy units. The deviation of sound above and below the atmospheric pressure levels is called Sound Pressure. As will be seen later, this sensitivity difference will feature repeatedly in the control of noise. This indicates that our ears are less sensitive to low-frequency sounds than mid to high frequencies. For example, a 20-decibel sound at 1000 Hz would be perceived as the same sound level of 50 decibels at 100 Hz. The sound levels for a particular sound as defined by the level at 1000 Hz will find the same for any given frequency along the curve. (FIGURE 6) shows an equal loudness contour chart. Our ears do not perceive all sounds equally at the various frequencies or sound intensities. For the sake of simplicity, the sound intensity or pressure levels are measured in decibels. (Figure 5) shows the combination of sine waves the sounds at different loudness levels or amplitudes. Loudness:(Amplitude or Intensity) is measured by the strength of the sound, depicted as a sine wave above and below the normal atmospheric pressure. (FIGURE 4) shows several wavelengths in feet and inches as a function of frequency. In the field of music, a piano can generate sounds ranging from 20 cycles per second (Hz) all the way up to 4600 cycles per second. High-pitched sounds have very short wavelengths such as sound emitted from a whistle. Low-frequency sounds have a long wavelength and are perceived as low-pitched sounds such as the rumble of a truck. The distance between the sound compressions and rarefactions is known as wavelength. The source is the speaker’s voice, the medium through which it is transmitted is air and the receiver is the listener’s ear.Īs sound is generated by the speaker’s speech, the speaker’s voice acts like a diaphragm which causes the molecules in the air to pulsate back and forth while moving in all directions, at a speed of 1130 ft per second (770 mph).Ī single segment of a sound wave may be characterized as pressure compressions and rarefactions. (Fig 1)įor sound to be generated and heard it must have a source, a medium through which to pass and a receiver.įor purposes of this discussion, we will assume that we are talking about normal speech communications. Sound is propagated in air, much like blowing up a large balloon, which expands equally in all directions. This section is designed to help educate and guide those with little to no knowledge of Acoustical terminology. The nature of Acoustics and Noise Control can be confusing. Understanding the Nature of Sound, Acoustics and Noise Control
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