![]() Items such as these can be added or arranged in ways that will allow for greater sound absorption. Even in cases where these options are not viable, absorptive materials can be added to finished rooms in other ways: furniture with thick cushioning is extremely absorptive, as are thick and heavy curtains and drapes. Thick carpet with padding is also very absorptive, and acoustical ceiling tiles are designed to absorb rather than reflect sound. Fiberglass insulation is very absorptive and can be used where sound control is a concern. The use of absorptive materials can be helpful in controlling sound. Softer materials, such as carpet, foam padding, and fiberglass insulation, are far better at absorbing sound. Many common building materials, such as gypsum board, wood, concrete, brick and tile, are fairly reflective and do not absorb much sound. Surfaces that absorb sound better will not allow for reflections to bounce around as much, and will deaden the sound wave more quickly. Sound waves will continue to bounce around a room for a time after they are created if the majority of surfaces in a room is reflective. Sound absorption is the capability of a surface, or building material, to absorb sound instead of reflecting it. There are several categories of sound control for interiors: sound absorption, airborne sound transmission, and impact-sound transmission. The human voice is usually in the range of 55 to 60 dB, a loud truck or motorcycle is 80 to 100 dB, and a jet taking off or a gun firing is measured at 120 dB or more. ![]() A larger vibration at the source will cause a larger sound pressure level and, thus, a greater perceived volume. When amplitude is measured, it is actually the pressure of a sound wave striking a surface that is being measured. Systems of amplitude measurement have been developed in order to quantify sound objectively. Amplitude is the perceived loudness of the sound. Wavelength is the distance between the start and the end of a sound wave cycle. The range of human hearing goes from 16 to 20,000 Hz, with 16 being the lowest detectable pitch, and 20,000 the highest. Frequency is the number of cycles per second the sound wave itself produces, and it determines the pitch of the sound we hear. Sound has three properties: frequency, wavelength and amplitude. The energy of a sound wave is reduced by half when the distance from the source doubles. This is why structure-borne sound is often referred to as "impact noise." Sound waves radiate around the source and decrease in loudness as they travel farther away. An example would be heavy footsteps audible from the next room. Structure-borne sound is sound that travels through solid materials before we hear it. Airborne sounds are radiated from a source directly into the air, such as a loud jackhammer. The path a sound takes before it reaches our ears can be either airborne or structure-borne. When sound waves hit the eardrum and cause vibration, we perceive them through our sense of hearing. Sound energy travels from a source through air, water and solid objects. ![]() Inspectors may be interested to learn how building materials and techniques influence the transmission of sound. We rely on construction practices and materials to provide a sufficient barrier from the loud goings-on that surround us every day. Even within a building, mechanical noise from heating or air conditioning can be audible, phones ring, and voices, radios and TVs are heard through walls, and so on. Planes take off and land, traffic moves along roadways, construction crews repair roads, dogs bark, music blares, sirens sound, lawns are mowed, etc. In any heavily populated area, there is enough activity going on at once during the day to generate all kinds of sounds across the audible spectrum of human hearing.
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