Lena Torres
Sound is measured in decibels (dB), which is a relative measurement of sound intensity, or how much energy a pressure wave has. Decibels are named in honour of Alexander Graham Bell, the inventor of the telephone and the audiometer, a device that measures hearing ability. The decibel is used for a wide range of measurements in science and engineering, but most prominently for sound power in acoustics. The decibel scale is useful because the human perception of sound intensity approximates the logarithm of intensity rather than a linear relationship. The quietest noises that the human ear can hear are around 10dB, while sounds of 130dB are considered painful.
| Characteristics | Values |
|---|---|
| Sound intensity or volume | Measured in decibels (dB) |
| Quietest noises for the human ear | Around 10 dB |
| Pain threshold for the human ear | 130 dB |
| Normal conversation | 60-70 dB |
| Jet taking off | 140 dB |
| Sound pressure level (Lp) | Logarithm to the base 10 of the ratio of the time-mean-square of sound pressure to the square of the reference value 20 micro Pascals |
| Time-weighted sound level (LAF or LAS) | Logarithm to the base 10 of the ratio of the running time average of the time-weighted square of a frequency-weighted sound-pressure signal to the square of the reference value 20 micro Pascals |
| Time-weighted sound level symbols | LAF, LAS, LCF, and weightings A or C and time weightings Fast (F) and Slow (S) |
| Sound exposure level (LAE) | Logarithm to the base 10 of the ratio of A-weighted sound exposure over time intervals (T) to the reference value of sound exposure |
| Frequency | Measured in hertz (Hz) |
| Pitch | Change in the frequency of the sound wave |
| Wavelength | Distance between one wave and the next |
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What You'll Learn
Decibels (dB)
The decibel originated in the early 20th century as a unit of measurement for transmission loss and power in telephony in the Bell System in the United States. It is named after Alexander Graham Bell, the inventor of the telephone and the audiometer, a device used to measure hearing ability. The bel, a unit of logarithmic power ratio, is also named after Bell but is rarely used, with the decibel being preferred for a wide range of measurements in science and engineering, particularly sound power in acoustics, electronics, and control theory.
The decibel is defined as ten times the logarithm with base 10. This means that a change in power by a factor of 10 corresponds to a 10 dB change in level. When expressing root-power ratios, a change in amplitude by a factor of 10 corresponds to a 20 dB change in level. The decibel scales differ by a factor of two, allowing for consistency between power and root-power quantities in linear systems. The use of decibels is particularly advantageous when dealing with transmission chains, as it is more convenient to add decibel values than multiply individual factors.
While the decibel is recognised by international bodies such as the International Electrotechnical Commission (IEC) and the International Organization for Standardization (ISO), it is not included in the International System of Units (SI). The IEC permits the use of the decibel for both power and root-power quantities, and this recommendation is followed by many national standards bodies. Suffixes, such as dBA or dBV, are commonly used with the decibel but are not recognised by the IEC or ISO.
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Sound intensity
Sound is measured in decibels (dB), which is a unit of measurement for sound power or sound pressure. Decibels are named after Alexander Graham Bell, the inventor of the telephone and the audiometer, a device that measures hearing ability.
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Sound pressure level
Sound is measured in decibels (dB), which is a relative measurement of intensity, or how much energy a pressure wave has. Decibels are named after Alexander Graham Bell, the inventor of the telephone and the audiometer, a device that measures hearing ability. The decibel originated in the measurement of transmission loss and power in early 20th-century telephony.
The human ear can hear sounds from 0 decibels (so quiet you can barely hear them) to around 130 decibels, which is considered painful. The decibel is a logarithmic unit, meaning it measures the ratio of a sound's pressure level relative to a reference value. This reference value is set at the quietest sound the average human ear can hear: 20 µPa (micro pascals).
The cochlea, a snail-shaped organ inside the inner ear, allows us to hear. It responds to a certain range of frequencies or pitches of sound. The cochlea responds best to frequencies in the range of human speech and does not respond as well to very high or low frequencies. In frequencies that the ear responds to best, measurements for dBA are just as high as they are in dB. However, a lower-frequency sound that the ear does not process as effectively will have a lower output level.
Small increases in dBA levels can have a big impact on hearing health. As dBA rises, hearing damage becomes more likely. You can measure sound in dBA with a sound level meter, such as an app provided by the National Institute for Occupational Safety and Health.
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Frequency
Sound frequency is a fundamental characteristic of acoustics, offering valuable insights into the nature and impact of sound. Frequency is measured in hertz (Hz), which quantifies the number of complete cycles a sound wave undergoes per second. In other words, it represents the number of pressure waves passing through a fixed point in one second.
For instance, a sound of 10Hz means that ten waves will pass a fixed point in one second. The frequency is directly linked to the speed of the sound wave's vibrations, with higher frequencies exhibiting more cycles per second and shorter wavelengths. Conversely, lower frequencies correspond to fewer cycles per second and longer wavelengths.
The distinction between high and low frequencies is crucial in understanding sound propagation and management. Low-frequency sounds, characterized by their extended wavelengths, can travel significant distances and penetrate obstacles, making them challenging to dampen. On the other hand, high-frequency sounds, with their shorter wavelengths, are typically easier to control and contain.
In acoustics, a commonly referenced frequency is 1,000 Hz, or 1 kHz, which aligns with the peak sensitivity of human hearing. This frequency serves as a benchmark for various acoustic measurements and calibration processes. For example, the A-weighting system, used to approximate the human ear's response to sound, is centred around 1 kHz. Acoustic devices are often adjusted and calibrated using a reference signal at this frequency to ensure their accuracy in replicating human auditory perception.
Additionally, sound frequency analysis plays a vital role in various applications, from designing acoustically optimized spaces to developing audio technology and safeguarding hearing health. By employing methods like n-octave filtering and Fast Fourier Transform (FFT), acousticians and sound engineers can dissect and comprehend the intricacies of sound frequency, thereby facilitating advancements in sound design, noise control, and auditory health initiatives.
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Pitch
Sound is measured in decibels (dB), which is a unit of measurement for sound intensity or volume. Decibels are a relative measurement that compares the intensity of a pressure wave to a normal or standard pressure. The human ear can hear sounds from around 10 dB, with sounds of 130 dB or more considered painful.
However, sound is more than just volume—it also has pitch. Pitch refers to the frequency of a sound wave, or how many times a second the particles vibrate. High-frequency sounds have a high pitch, while low-frequency sounds have a low pitch. The cochlea, a snail-shaped organ inside the inner ear, allows us to hear a certain range of frequencies or pitches of sound. It responds best to frequencies in the range of human speech and does not respond as well to very high or low frequencies.
Frequency is measured in hertz (Hz), which is the number of pressure waves or vibrations that pass a fixed point in one second. For example, a sound with a frequency of 10 Hz would have 10 waves passing a fixed point in one second.
Musical notes are associated with unique frequencies, and when we combine pure notes, we create harmonics, which are the basis of all musical instruments. Pitch detection tools can be used to find the pitch of any sound, such as a person's voice or an instrument. These tools detect the sound, convert it into an electrical signal, and then interpret the frequency of the sound to display the corresponding pitch.
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Frequently asked questions
Sound is measured in decibels (dB).
A decibel is a unit of measurement for the intensity of sound, which relates to how much energy the pressure wave has. Decibels are a relative unit of measurement, comparing two pressures.
You can measure sound using a sound level meter, such as an app made by the National Institute for Occupational Safety and Health.
