| Sound intensity is the amount of sound power per a given area. Sound
intensity is measured in decibels (dB), and it is directly related to how
our ears perceive loudness. Decibels are logarithmic units that are used
to express the ratio of two values. For example, in electronics, decibels
are often used to express the ratio of output power to input power of an
amplifier. For sound intensity, the ratio is between a measured sound
intensity and a reference threshold sound intensity. To more accurately
reflect human hearing, a condition known as an A-contour filter can be
applied to the measurements and the resulting values are expressed as
dB(A).The logarithmic values of sound intensity translate into a general
rule of thumb that states that a sound will be twice as loud for every 10
dB increase and half as loud for every 10 dB decrease. Unfortunately, as
explained by this excellent Hewlett-Packard
document (click on the "hp PCs and acoustic noise" link),
manufacturers of low-noise components and PCs do not always use standard
methods to measure the sound levels of their products. This means that
comparing components or systems directly is not always possible. And if a
manufacturer doesn't state how it obtained its measurement, that
information isn't very useful. In such cases, you should use dB ratings to
give you a basic idea of how loud a component is and not as a value to be
used in comparison with another product. For further reference, see this
Common Noise Levels
And Typical Reactions chart (scroll down the page to see the
chart). |
