# How are sound waves created

## Properties of sound¶

### Sound intensity and sound level¶

As a mechanical wave, sound does not transmit matter, but it does transmit energy. The energy flow per time is, according to the definition of the mechanical power, as sound power designated.

Definition:

The sound intensity indicates how big the sound power is on a surface meets: The sound intensity is in the unit specified.

Example:

As you can see in the example above, the sound intensity increases with the square of the distance from the sound source, so it is .

The sound power that is perceived by the ear can in turn by means of the sound intensity can be calculated by comparing this with the area of the auditory input multiplied; in the human ear, the effective area of ​​the eardrum is approximately .

Human ears have the following range of perception:

• The minimum perceptible sound power was determined in tests with different test persons as determined.
• The maximum perceptible sound power is around ; with even greater sound power, pain and irreparable damage can occur.

The large perceptual range of the human ear ( Orders of magnitude!) Has led to the introduction of a logarithmic scale for measuring volume, which is named after Alexander Graham Bell:

Definition:

The volume of sound can be measured using the so-called sound power level, which is defined as follows: The sound power level has no unit; nevertheless, the resulting numerical value is given as decibels for better clarity designated.

Examples:

The sound level scale thus forms the normal hearing range of humans on a number range between and from; Everyday noises have sound levels of around to , a normal conversation generated in Distance a sound level of approx . Sound level in decibels. The sound level always depends on the distance between the sound source and the ear or measuring device.

Since the decibel scale is a logarithmic scale, doubling the power of the sound source in no way means doubling the decibel value. Rather, the following applies in this case: A doubling of the power of a sound source only causes an increase in the sound level by . Such a difference is clearly audible, smaller sound level differences of only to are usually only recognizable by direct comparison.

Volume at different frequencies

Using the decibel scale, the human perceived volume of sounds can only be compared if they have the same frequency: the human ear reacts with different levels of sensitivity to different sound frequencies.

The guide values ​​for the decibel scale were at a sound frequency of certainly. In the Isophonic volume level figure, the bottom curve represents the minimum volume from which sounds can be heard; at this just corresponds to the value . With a frequency value of gives the curve a value of at, which means that at this frequency the sound level is around must be higher for the sound to be heard at all - this in turn requires a -fold higher sound power .

The fact that people perceive tones with low sound frequencies less intensely has the consequence that bass loudspeakers are constructed in such a way that they can emit high sound levels; Correspondingly, tweeter loudspeakers manage with only low sound power levels. The human hearing is most sensitive to frequencies in the range of to : In this range, the ear already received powers of less than to be able to perceive sound.

If you specify a volume taking into account the hearing curves shown in the figure Isophonic volume level, you write “Phon” instead of “Decibel” as the unit. It must be taken into account that a "Phon" specification is a pure numerical value, which is only named Phon for the sake of clarity.

Remarks: