Intensity, timbre and height are features, or properties of sounds. Sound intensity refers to the power of the emitting source, as well as the amount of energy what sound is capable of carrying; timbre refers to the shape of the sound oscillations and the pitch, in turn, is determined by the frequency of the sound.
Lookalso: Wave classification: what are waves and what are their main characteristics
Intensity
THE intensitysonorous measures the amount of energy that a sound wave is capable of transferring each second over an area of 1 m². The intensity is related to the amplitude of the wave and is defined by the potency issued by the source divided by the area of the sound wave front, as shown below:
I - Sound intensity (W/m²)
P - Power (W)
A - Wavefront area (m²)
The following figure illustrates the sound wave front, which is shaped Circular, since the sounds are three-dimensional and propagate with the same speed in all directions:
Through the figure, it is possible to see that, as we move a distance r, the area of the wavefront increases with the square of the distance. As it is a spherical wave, this area can be calculated by the expression 4πr².
despite the sound intensity unitbe the watt per square meter, sound intensity is commonly measured in a logarithmic scale known as bell scale, created by the inventor of the telephone, Alexander Graham Bell.
The Bell scale uses the properties of the base 10 logarithm to compare sounds of different intensities, therefore, the lowest value on this scale is also the lowest audible sound intensity value (called I0), about 10-12 W/m², also known as audibility threshold. According to this scale, sounds of different intensities are related to I0 in the following way:
N – number of bel
Applying the logarithmic properties in the presented equation, the following expression is obtained:
The calculation above allows you to calculate the number of decibels of a sound wave of intensity I. The decibel is a submultiple ten times smaller than the bel. From this, it is possible to understand that a 20 decibel sound is 10 times stronger than a 10 decibel sound, for example.
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When some sound has great intensity, we say that this sound is strong, on the contrary, it is a sound weak.
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Letterhead
O timbre it is the characteristic of sounds that allows us to differentiate a musical note emitted by a piano from a violin, for example. The timbre is the sound wave shape, each musical instrument has its own vibration mode, which results in the production of a characteristic sound.
The timbre also ensures that the human voice is different for each individual, allowing us to activate devices through voice commands, for example.
Height
The height of a sound is related to its frequency, which measures the number of oscillations that the sound wave produces every second. The measure of frequency is given in hertz (Hz).
n - number of oscillations
Δt – time interval(s)
The sound frequency can be obtained through the propagation speed and the wavelength of the sound. Watch:
v – propagation speed (m/s)
λ – wavelength (m)
f - frequency (Hz)
Human beings are not able to hear any sound frequency, in fact, our perception is quite limited: we are only able to hear frequencies that are in range from 20 Hz to 20,000 Hz, this interval is known as audible spectrum.
Any sound that has a frequency below 20 Hz is inaudible by humans and is called infrasound, on the other hand, sounds that have a frequency greater than 20,000 Hz, also inaudible to us, are known as ultrasound. Want to know more about the subject? Access our text about infrasound and ultrasound.
By Rafael Hellerbrock
Physics teacher
Would you like to reference this text in a school or academic work? Look:
HELERBROCK, Rafael. "Intensity, timbre and height"; Brazil School. Available in: https://brasilescola.uol.com.br/fisica/intensidade-timbre-altura.htm. Accessed on June 27, 2021.
