2Electroacoustic sound system

Sound is a mechanical movement of particles that is capable of inducing hearing sensation.

For interest, let's take a look at the sound propagation speeds for common types of materials (at normal pressure and temperature). In the air, it is 344 m/s, 1454 m/s in water, 3232 m/s in ice, 3837 m/s in marble, 5100 m/s in steel, and 6059 m/s in glass.

The frequency range of the sound that most people perceive starts at around 20 Hz and reaches up to about 20 kHz (the area of ​​audibility is theoretically 16 Hz to 20 kHz). With the increasing human age, the upper limit significantly decreases. The most significant range is between 2 and 4 kHz, which is the most important for speech intelligibility and the human ear is the most sensitive in this range. The highest information value of speech is transmitted in the band from 0.5 through 2 kHz.

Inverse Square Rule:

When the listening distance is doubled, the volume decreases to 25 % of the original value; doubling the listening distance increases the listening area four times. In other words, doubled distance means that the acoustic pressure is reduced to a quarter, i.e. 25 %, and the radius of the sphere is doubled, the area multiplied by four.

Inverse square rule

Decibel is a physical unit used to measure the sound intensity level. In general, however, it is a measure of the proportion of two values ​​used in many fields. It is a dimensionless measure, like a percentage, but unlike it, decibel is a logarithmic unit. The human body perceives the impulses logarithmically by their intensity (the great changes to the great impulses can be caused only by small changes of counts) - Fechner-Weber's law. The rate specified in 1923 by Bell Laboratories engineers originally served to indicate attenuation of telephone lines. For example, a 3dB decrease in attenuation means half of the power, while achieving the 3dB gain means doubling the power.