The Physics of Sound:
When dealing with any sound deadening product, it is necessary to first understand the basics of Sound:
Definition of Sound:
- Sound is an oscillation in pressure, stress, particle displacement, particle velocity, etc. in a medium
- Sound is an auditory sensation evoked by the oscillation described above.
Any audible signal is sound. The source of sound is come system in vibration. For instance, a musical system may include vibrating strings, or diaphragms, such as drum heads, cymbals, or the human voice.
These vibrations generate sound waves which travel through the surrounding medium (air) in the form of very small changes in atmospheric pressure, alternately above and below the static pressure. These changes fluctuate in a regular or irregular way.
Sound may also be transmitted in water, gases other than air, and in solids. Without a transmitting medium, sound cannot exist. In the air at room temperature vibrations travel at a constant speed of 1125 feet per second or a little over a mile in 5 seconds, in water about 5000 feet per second, and in steel about 15,000 feet per second.
Sound Quantity (Loudness)
The average deviation in atmospheric pressure above and below the static value due to a sound wave is called sound pressure. The energy expended during vib4ration is labeled intensity and is measured in energy units. Loudness is the physical response to sound pressure and intensity.
Placing a numerical value on the quantity of sound is difficult because of the tremendous sensitivity of the ear, which can detect atmospheric pressure alterations over a range of a million to one, and a range of intensities of over a trillion to one.
In order to measure and calculate this vast range of audible sound, a compact scale has been devised incorporating the decibel (dB)
Loudness varies directly, but not in a straight line, with sound pressure and intensity. A change of 3 dB is only a slightly noticeable change in loudness, while a 10dB change in the sound pressure level would be twice (or ½) as loud.
“Loudness” as identified by the ear, cannot be expressed as a single relationship between intensities, pressures, or other mathematical quantities. Two sounds with the same apparent loudness, but at different frequencies, would have large differences in sound pressure levels.
Quality of Sound
Where the quantity of sound was described as loudness and determined by static pressure deviation, quality of sound is described as tone or harmony and is dependent upon the frequency. Frequency is the number of complete cycles of vibration above and below the static pressure in a unit of time. In acoustics, frequency is expressed in units of hertz (Hz) which is equal to one cycle per second.
The human ear responds to pressure changes that occur from a rate of 16 times per second to 20,000 times per second, but is most sensitive to frequencies around 1,000 Hz. Low frequency sounds are particularly hard to hear, even though they may contain large amounts of energy units.
Click image to view animation
Click image to view animation
Sound Transmission
Sound can be transmitted from one location to another by setting up vibrations in a medium (airborne or structure-borne). Unwanted sound in a room may be the result of sound transmitted from sources outside the room. The degree to which this sound transmission is acceptable depends upon the quantity and source of the sound and the use of the adjacent space. Sound transmitted at a level below the receiving room ambient level would be acceptable.
Continued: Compare Product Options
« Previous 1 | 2 | 3 | 4 | next »