[Physics Class Notes] on Unit of Sound Pdf for Exam

Has a noisy situation ever left us in a grimacing and clutching situation of our ears? We can ask why some sounds seem so loud? There are many factors that generally influence how loud a sound seems including how long it lasts, the sound’s frequencies of pitches as well as the environment in which we hear the sound. 

 

Also, another important and easily measured factor is the sound intensity or volume. We can easily measure the intensity of sound which is also referred to as sound power or sound pressure in units known as a decibel. Decibels are denoted by dB and are named in honor of Sir Alexander Graham Bell. He is the inventor of both the telephone and the audiometer as well. An audiometer is said to be a device that measures how well a person can hear certain sounds. A version that is even modern is still used today to diagnose hearing loss.

SI Unit of Sound

• The SI unit of sound or more precisely frequency is hertz denoted by Hz.

• The sound intensity is the sound of power per unit area, that is the SI unit is watt per square meter W/m2.

• The pressure of the sound is the difference between the pressure caused by a sound wave and the ambient pressure of the medium it is passing through. The SI unit of the pressure of the sound is known as Pascal denoted by Pa.

• The term decibel denoted by dB is a relative unit of measure widely used in acoustics. 

• Decibel is said to be a logarithmic unit used to describe a ratio between the level that is measured and a reference or the level of threshold of 0 dB. The ratio may be the power of sound, the sound pressure or sound intensity etc. A unit of sound is any unit that is acoustic or sound measurement.

• dB, or the decibel – is the noise of sound that is the measurement which is known as decibels denoted as dB. The ratio of the pressure of the sound to the reference pressure to something.

• Sone – is said to be a unit of perceived loudness that is equal to the loudness of a 1000-hertz tone at 40 dB above threshold, starting with 1 sone.

• Phone – is a unit of loudness that is subjective.

• The Hz, or the hertz = is a unit of sound frequency.

 

What is the Unit of Loudness?

The term that is decibel which is denoted as dB – is said to be a measure of the intensity of a sound that is 1/10 of a Bel. The decibels are units that are relatively comparing two pressures. Therefore, there is a reference of pressure that must also be indicated. In underwater acoustics, the pressure reference is 1 micro pascal so the unit which is true of intensity for underwater sound in dB is referenced to 1 micro pascal. 

 

In the air, the scientists have agreed to use a reference that is of the higher pressure of 20 micro pascals. Therefore, the true unit of intensity for sounds in the air is dB referenced to as 20 micro pascals. Because they use different reference pressures the intensity of sound given in dB in water is not the same as sound intensity given in dB in air. The term that is bel is derived from the name of Sir Alexander Graham Bell who is the inventor of the telephone. The unit decibel is said to be used because a one-decibel difference in loudness between two sounds is the smallest difference that is detectable by human hearing.

 

The term Decibel – dB is a unit for expressing the ratio between two physical quantities that usually amounts to acoustic or we can say the electric power or for measuring the relative loudness which is of sounds. The one decibel that is 0.1 bel equals 10 times the common logarithm of the power ratio. Expressed as a formula which is for the intensity of a sound in decibels is 10 log10 (S1/S2), where S1 and S2 are said to be the intensity of the two sounds.

 

Soundwave

A sound wave is a pattern of disruption created by the movement of energy away from the source of the sound. Sound waves are long-distance waves. This indicates that the direction of particle vibration propagation is parallel to the path of energy wave propagation. When atoms are vibrating, they move back and forth. This constant back and forth motion creates a high-pressure and low-pressure zone in the medium. Compressions and rarefactions are the names given to these high-pressure and low-pressure zones, respectively. As a result of these areas being transmitted to the surrounding medium, sound waves pass from one medium to another.

 

Characteristics of Sound

There are three main characteristics of sound:

Amplitude – The largest displacement of vibrating particles from their typical location when sound is created is referred to as the amplitude of a sound wave. It represents the wave’s height. The amplitude of a wave is proportional to its loudness. The amount of sound energy released per second is measured as loudness. It relates the typical hearing threshold intensity with the intensity of any given sound. As a result, the sound wave with a bigger amplitude is louder, whereas the sound wave with a lesser amplitude is weaker. The meter is the SI unit of amplitude.

 

Frequency – The frequency of a sound wave is referred to as its pitch. When a wave goes through a medium, the frequency of that wave is determined by how frequently the medium’s particles vibrate. Atmospheric pressure is related to sound waves. That is, while sound waves move through the air medium, atmospheric pressure changes on a regular basis. The number of pressure fluctuations per second is also used to describe the frequency of sound waves. Sound is classified into two types based on frequency: infrasound and ultrasound. Infrasound is any sound with a frequency less than 20Hz, while ultrasound is any sound with a frequency more than 20 kHz.

 

Time Period – The time it takes for the particles in a sound wave to complete one vibration cycle is referred to as the wave’s time period. The frequency and time duration are inversely proportional.

 

Infrasound

Infrasound is a low-frequency audible sound that is frequently lower than 20 Hz. Infrasound, often known as low-statu
s sound, refers to sound waves having frequencies lower than the bottom limit of human audibility. Winds, storms, earthquakes, volcanoes, and even wind turbines may all create infrasounds. Furthermore, certain species, such as elephants, communicate with one another using infrared because low-frequency noises move quicker than high-frequency sounds.

 

Sound Pressure Level

Sound Pressure Level (SPL) is the root mean squared sound pressure of a sound in comparison to a reference value. The SPL is abbreviated as Lp. A sound pressure level is a logarithmic measure of a sound’s root mean squared (RMS) sound pressure compared to a reference value. A sine wave can depict a basic sound wave. If depicted on an oscilloscope, a sine wave diagram would be the usual output signal of a single tone noise level (a calibrator tone). Peak, Periodic Time, Peak-Peak, and RMS are the fundamental or basic properties associated with a sound wave (root-mean-square).