Loudness of Sound

What is Loudness of Sound? - Characteristics of Sound

The sound is a wave. More distinctively, the sound is a wave made of vibrations in the air. When a sound is made by something, it vibrates the air molecules, which sends a chain reaction through the air until it reaches our eardrums. When our ears pick up that sound, signals are sent to our brain so that we can understand what we're hearing

The sound is a type of energy, just like heat, electricity or light. When you ring a bell, it makes a loud ringing noise. Now instead of just listening to the bell ring, put your finger on the bell after you have struck it. You will feel a sense of shaking. This movement or shaking, i.e. the back and forth motion of the body is called Vibration. The sound travels through a medium by alternately contracting and expanding parts of the medium it is travelling through. This compression and expansion generate a minute pressure difference that we identify as the sound

Characteristics of Sound

The sound that we hear around us is the type of energy generated by the vibration that moves through the air or any other medium and can be heard when it reaches a human’s ear.  So, mainly sound helps us to communicate with each other. For instance, we can hear musical instruments like tabla, flute, a guitar because of the vibration. The characteristics of the sound are as follows:

  • • Pitch

  • • Loudness

  • • Quality

  • Pitch

    Pitch is a feature of sound with the help of which a correct note can be distinguished from a grave or a flat note. We can recognize a female and male voice without seeing them. The word ‘pitch’ is frequently used in music. Pitch is based on the frequencies of the sound wave. A note has a lower pitch when the frequency is low, and a note of higher frequency has a high pitch. For instance, when a small baby says something, his or her voice has a higher frequency so in case of a baby the pitch is higher than the pitch of a man. The term shrill means a sound with a high frequency.


    The loudness is a feeling of how strong a sound wave is at a place. Every time it is termed as relative and has no dimension quantity. Loudness is calculated in decibel (dB). It is specified as:
    L = log(I), in this ‘I’ is the intensity.
    The loudness is based on the amplitude of the vibration. It will be louder when the amplitude is high. If when we remove a string of the sitar it starts vibrating with low amplitude and if we apply more energy by plucking with more force, the string will vibrate with the greater amplitude and generate a loud sound. When the amplitude of vibration increases, the sound also increases.


    The word Quality is also known as Timbre. As diverse sources generate different sounds, the timbre helps us to distinguish between them. A sound of good quality is enjoyable to listen to. The instruments are of different shapes and size and they create different harmonics of loudness hence their sound can be easily distinguished.

    4 Effects of Sound


    Now firstly, Sound affects our bodies. Our body is made up of 70% water. Sound travels well in water, so we’re very good transmitters of sound. Sound affects us physiologically in very influential ways. Since hearing is your main warning sense, a sudden sound will start a process. It releases cortisol, it increases your heart rate, makes you’re breathing fast. This is because we’ve been programmed over 1000’of years to imagine that any sudden or mysterious sound is a threat and your body gets ready to fight or flee. That happens to us a lot of times. Even though we might know that a bus is letting off its air brakes or somebody dropping a plate is not that dangerous, it yet puts us into that state.

    The 2nd way in which sound affects us is psychological. It changes our emotions and our moods. Music helps change our mood. There are different kinds of music which make us happy, sad, and excited etc.
    So music changes our mood. Still, it’s not the only sound that does that. There are ample of sounds in nature that do. Bird song, for example, makes us feel stress-free and reassured, because we’ve learned over 1000’s of years again that when the birds are singing, we’re generally pretty safe. Sound can affect our emotional state quite intensely.


    Thirdly sound affects us cognitively. The quality of work that you perform depends upon the sound around you. Nowadays, kids tell us that they do their homework much better with loud music playing. The most disturbing sound of all is the human voice. If somebody’s speaking next to you, it’s very difficult to ignore that sound. We do not have earlids and distracting human conversation hugely affects our productivity.


    Finally sound affects us behaviorally. We will try to move away from the horrible sound if we can and even descend towards pleasant sounds. Sound can cause stress and make us behave negatively. It makes us less friendly, less caring and less open-minded if we’re in a noisy setting.

    So sound changes us in 4 powerful ways and those 4 ways are running all the time. It’s significant to know this because if you start to listen deliberately to the sound around you, you could start to design your environment so that those effects are not working against you.

    Speed of Sound

    The speed of Sound in Air
    The speed of sound is a vital parameter used in a variety of field in Physics. The distance traveled per unit time by the sound wave transmitted through a medium is known as the speed of sound. The speed of sound while traveling through air is at 20oC is 343.2 m/s which translates to 1,236 km/h.

    The speed of Sound in Solid, Liquid and Gases

    Sound can travel through solids such as wood. In fact, sound prefers traveling through solid more. In the historic days, doctors used stethoscopes consisting of thin wooden rods with broadened ends and they worked in the same way as our modern ones and performed just as well.

    The sound is nothing just a disturbance which is generated by the friction between the particles; one molecule hitting the next and so forth. Solids are extensively denser than liquids or gases. This means that the molecules are nearer to each other in solids than in liquids and in liquids than in gases. This proximity due to density means that they can collide very quickly. In fact, it takes less time for a molecule of a solid to bump into its neighboring molecule. Due to this benefit, the speed of sound in a solid is larger than in gas.

    In the same way, the density of a liquid is greater than the density of a gas. Thus, the distances between molecules are more in liquids than in solids but are less than in gases. Therefore, the speed of sound in liquids lies in between the speed of sound in solids and gases.

    We should keep in mind that the speed of sound is independent of the density of the medium when it enters a liquid or solid. As gases expand to fill the given space, density is quite consistent irrespective of the type of gas. This is obviously not in the case with solids and liquids.

    The table shown below lists the speed of sound in a range of media. The proportional deviation of speed with density is clearly visible here.

    Another important interesting fact is that in solids, sound waves can be produced either by compression or by tearing of the solid also known as Shearing. Such waves demonstrate different properties from each other and also travel at different speeds. This effect is seen evidently in Earthquakes. Earthquakes are caused due to the movement of the earth plates which then sends this turbulence in the form of waves same as the sound waves through the earth and to the surface causing an Earthquake. 
    Usually, compression waves travel at a faster speed than tearing waves which is why Earthquakes always start with an up and down motion followed after some time by side to side motion. In seismic terms, the compression waves are termed as P-waves and the tearing waves are called S-waves. S-waves are the most destructive, causing most of the damage in an earthquake.

    Loudness of sound

  • • This phenomenon of a sound is based on the amplitude of the sound wave. If the amplitude of the sound wave is large, then the sound is supposed to be loud.

  • • It is directly related to the square of the amplitude of vibration. If the amplitude of the sound wave is single, then the loudness of the sound will be doubled.

  • • It is written in decibel (dB).

  • • Sound over 80 dB becomes noise to human ears.

  • • The table given below gives us data for various sources of sound.

  • Normal Breathing10 dB
    Soft Whisper (at 5m)30 dB
    Normal Conversation60 dB
    Busy Traffic70 dB
    Average Factory80 dB

    The loudness of a sound wave is determined by its connection with the amplitude, all types of waves have a certain amplitude. For instance, a height of a wave on a calm ocean will be less than one foot where as good surfing waves might be ten feet or more in amplitude. In a storm, the amplitude might increase to 40 to 50 feet.

    Loudness, in acoustics, quality of sound that determines the intensity of auditory sensation created. The loudness of sound as perceived by human ears is generally proportional to the logarithm of sound intensity; when the intensity is very less, the sound is inaudible; when it is too high, it becomes painful and dangerous to the ear. The sound intensity that the ear can bare is roughly 1012 times greater than the amount that is just perceptible. This range can vary from person to person and with the frequency of the sound.

    A unit of loudness, called phon, has been established. The number of phons of any particular sound is equal to the number of decibels of a pure 1,000-hertz tone. The decibel scale is objective in that the intensity is defined physically and any intensity can be directly compared with the physically defined reference point. The phon scale is partly subjective in that the judgment of a listener is involved in comparing any arbitrary sound with the physically defined reference in order to set up its loudness in phons. The standard result from a large number of people then establishes the definition of equal loudness curves.
     Subjective scales were made because they tend to be more useful than a totally objective scale in telling how the ear works. 
    Generally, the physical sciences and engineering use more objective scales such as the decibel, while measurements in biological and medical fields tend to use the more subjective scales.