Properties Of Sound: How We Produce, Interpret And Hear Sounds

Properties of Sound

The following will go over concepts of sound. This includes how sound moves while affected by states of matter and the temperature of the environment, interpreting sounds in the form of a sound wave on a pressure wave over time graph, and how we are able to process sounds.

How Sound Moves

Sounds are vibrations that travel as a pressure wave through all substances. They travel in soundwaves that bounce and get absorbed. “Very simply, sound is the vibration of any substance”(The Soundry, n.d.). Sounds spread out like a domino effect with molecules and atoms as dominos. Although, Sound doesn’t last forever. As sound spreads further from its source it dissipates. This is because the energy is finite and molecules spread the kinetic energy as they hit each other and spreading. Naturally, as the energy spreads, it gets thinned out into nothingness. “The same amount of energy is now spread over a much larger spherical surface, it is naturally less intense”(Sound Proof Cow, n.d.). The intensity of sounds is measured with decibels.

When sound hits an object it either bounces and echoes or it is absorbed. This is dependant on the structure of the obstacle it hits. For example, the way a theater is designed is to keep the sounds within and even to preserve the sound to reach the viewer. Smooth walls often direct sound to certain spots while rough walls can spread sound in a multitude of directions. ”Smooth walls have a tendency to direct sound waves in a specific direction … Rough walls tend to diffuse sound, reflecting it in a variety of directions”(The Physics Classroom, n.d.) Sound can also go through refraction or diffraction. Refraction is when sounds change direction because of a change in medium. Diffraction is when sound bends when passing through an object.

Soundwaves travel through molecules of matter as a medium. A medium is anything that transfers energy, for sound, matter transfers sound energy. Soundwaves need a medium of matter to travel sounds cannot travel through a vacuum such as space. “Sound waves can travel only through matter. Since there’s almost no matter in interstellar space, sound can’t travel through it”(Strickland, 2008, P.3). Each state of matter conducts sound differently. In gases, there is a lot of space between molecules so, each molecule has to travel far to hit another molecule. In liquid, since, there is less space between molecules the sound travels more than 4 times faster. In solids, molecules are tightly packed together so, sound travels even faster through solids. Molecules move and vibrate other molecules then move back to there original positions. So, as the pressure wave that is a sound wave moves, there are points in space that are denser or less dense than other points.

As sounds are affected by the states of matter, temperature also affects sounds. Temperature is ultimately the measure of how much molecules move. High temperature means a high amount of energy among molecules. Molecules vibrate more if they have more energy therefore, in colder conditions sound moves less effectively while in hotter conditions they move more effectively. “Molecules at higher temperatures have more energy, thus they can vibrate faster. Since the molecules vibrate faster, sound waves can travel more quickly”(NDT Resource Center, n.d.).

Interpreting Sound Waves

Soundwaves have four important parts: wavelength, frequency, amplitude, and period.

The wavelength is how long one cycle is. Since sound waves are repeating, one cycle is the pattern that is repeated. The period is the time required for a single wavelength to pass. Amplitude is how high the wave goes, so higher the wave the larger the amplitude. Frequency is how fast the vibration is which is expressed in hertz, cycles per second. Frequency also determines the pitch of a sound, high frequency means high pitch, low frequency means low pitch. Since molecules move in a way that they return to their positions a pattern of condensation and rarefactions forms in a pressure wave. Condensations are when molecules group up and become dense. Rarefactions are when the density of molecules decreases. So, in air pressure, time graph, there are points where the air pressure increases and decreases over and over again,

How We Hear Sound

We hear sound through our ears, it takes in sound and sends signals to our brain. It does this with the structure of the outer ear, middle ear, and inner ear. The outer ear contains the pinna/ auricle, auditory canal, and eardrum. The pinna, also known as the auricle, is the structure that brings sound together into the ear. It is the part of the ear that is outside of the head and made of cartilage. “The primary purpose of the pinna is to collect sound. It does so by acting as a funnel, amplifying the sound and directing it to the ear canal”(The Soundry,n.d.). Sound is directed through the pinna into the auditory canal and into the eardrum. The canal is used to protect the eardrum physically from dust which is then carried out of the ear as the new skin replaces old skin. The eardrum is composed of a layer of skin, a layer of fiber and elastic material, and a lining that makes mucus. Sounds vibrate the eardrum which transfers the vibration into the middle ear section.

The middle ear is composed of the ossicles and the eustachian tube. The ossicles are a series of small bones: incus, stapes, and malleus. These bones bring the vibrations through the middle ear to the outer ear. “The vibration of the eardrum initiates movement of the three ear bones … The malleus, which is directly attached to the eardrum, immediately moves in response to the vibrations. This motion, in turn, moves the incus which triggers the activation of the stapes”(Davidson Hearing Aids, n.d.).

These vibrations are then brought to the inner ear. The inner ear is composed of the cochlea and auditory nerve. “Once the vibrations cause the fluid inside the cochlea to ripple, a traveling wave forms along the basilar membrane. Hair cells—sensory cells sitting on top of the basilar membrane—ride the wave”(NIDCD, 2018). The hair cells have stereocilia that when bent, open up and put chemicals into the cells. The chemicals then make an electrical signal that is brought to the brain and translated into sounds. The pattern of the electrical signal is then somehow turned into what is perceived as sounds. The sound wave energy changes forms multiple times. It changes from sound energy to mechanical, by the eardrum, to a form of hydraulic energy, in the cochlea, to electric energy by chemicals in the hair cells.