Summary of the world of sound

Sound is a form of energy. It can be generated, transmitted, carried, and distributed over time and distance, often containing a tremendous amount of energy. A sound only persists as long as there is energy in the system to sustain it.

At its simplest, sound is best defined as something that is audible. It’s a wave—a series of vibrations moving through a medium—within a frequency range that is perceptible to the human ear.

Sound waves can travel through gases, liquids, and solids, but they cannot propagate in a vacuum—which is why there’s no sound in outer space.

But what else should we know about sound?
Let’s take a closer look!

Sound is a longitudinal, mechanical wave. It is generated by the back-and-forth vibration of particles in the medium through which the sound travels. When an object vibrates, it sets the surrounding particles into motion. These vibrations then travel through the medium and are detected by the hearing receptors—this is what we perceive as sound.

From a physical standpoint, however, sound refers to the waves of vibrational motion themselves, regardless of whether the human ear can perceive them. In other words, sound exists even outside our range of hearing.

A medium is essential for sound to travel—it can propagate through gases, liquids, and solids, but not through a vacuum. This is why outer space is silent: there’s no medium to carry the sound vibrations.

Interestingly, the frequency of the vibrations determines what we hear:

Slower vibrations result in lower-pitched sounds.

Faster vibrations produce higher-pitched sounds (not “deep” as originally mentioned),

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Characteristics of Sound Waves

Sound waves are generally audible to the human ear when their frequency—the number of vibrations per second—falls within the range of approximately 20 to 20,000 Hz (hertz). However, this range can vary significantly from person to person, especially with age or hearing conditions.

• Frequencies below 20 Hz are called infrasound or subsonic.
• Frequencies above 20,000 Hz are known as ultrasound.

A sound wave is commonly represented as a wavy horizontal line in diagrams, but it’s important to note that this is a graphical representation, not an actual image of the wave itself. Sound is a mechanical wave, caused by pressure fluctuations as particles in a medium vibrate.

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Pressure Zones and Wave Properties

As sound travels through a medium, it creates alternating zones of:

• Compression (high-pressure areas)
• Rarefaction (low-pressure areas)

The distance between two consecutive compressions or rarefactions is called the wavelength.

Another key property is amplitude, which measures the extent of pressure change caused by the wave. It directly affects the volume of the sound:

• Large amplitude = louder sound
• Small amplitude = quieter sound

Understanding these properties helps us not only visualize how sound behaves but also how to control and manipulate it in practical settings, such as in acoustic treatment or soundproofing.

Frequency refers to the rate at which a particular sound travels through the air. It is calculated in cycles per second. The SI unit of frequency is the Hertz. Velocity can be calculated as the product of frequency and wavelength. From the formula, however, it can be inferred that there is an inverse relationship between frequency and wavelength, which means that, for example, a string twice as large as half the vibration number and a higher frequency vibration has a higher sound. The speed of sound depends on the medium: 340 meters / second in air, 1,500 meters / second in water, and finally 2,500 to 6,000 meters / second in solid matter.

As a result, sound propagates better in solids and liquids and is, therefore, more perceptible. The speed of sound can also be altered by the temperature of the medium being transmitted, albeit slightly. In warmer air, sound travels at a slightly higher speed, while in the cold air the speed travels a little lower than 340 meters per second. Because sound conductivity depends on the density of the medium, solids are better conductors than liquids and liquids are more efficient than gases. Sound waves can bounce, refract, bend, and be absorbed, as can light waves. The reflection of sound waves can result in echo – an important factor in the acoustics of theaters and auditoriums.

A sound wave can be amplified by waves from a body with the same vibration frequency, but a combination of waves with different vibration frequencies can cause beats or pulsations, or other types of interference. It is interesting to think about what this speed of 340 meters/second measured in the air means. Perhaps it is more noticeable if it is converted to kilometer/hour format, here it corresponds to 1224. At such speeds, fighter jets can travel. Supersonic aircraft can exceed the speed of sound. The popping sound that occurs at the moment of crossing is called a sound explosion.

What Is Hearing?

Hearing is a mechanical process—unlike taste or smell, which rely on chemical interactions. When we hear, the ear detects sound waves and transforms them into electrical signals that our brain can interpret. The hearing system is made up of several parts working together:

• The outer ear captures sound and directs it to the eardrum.
• The middle ear translates these vibrations to the inner ear.
• The inner ear sends the signals to the auditory nerve, which delivers them to the brain.

The brain then interprets these signals, allowing us to recognize and understand sounds. In essence, hearing begins with a vibration and ends in the brain—where sound becomes meaning.

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What Is a Decibel and How Is It Measured?

The decibel (dB) is the standard unit used to measure sound intensity. The decibel scale may seem unusual because the human ear is extremely sensitive. It can detect sounds ranging from the softest whisper to the roar of a jet engine.

To illustrate:

• A jet engine is 1 trillion times more powerful than the quietest sound we can hear.
• 0 dB represents the threshold of hearing—almost total silence.
• A sound 10 times more intense is 10 dB,
• 100 times more intense is 20 dB, and so on.

Here are examples of common sounds and their decibel levels:

• Near silence – 0 dB
• Whisper – 15 dB
• Normal conversation – 60 dB
• Lawn mower – 90 dB
• Car horn – 110 dB
• Rock concert or jet engine – 120 dB
• Firecracker or gunshot – 140 dB

Distance also plays a role—sound intensity decreases as you move farther from the source.

⚠️ Important to know: Prolonged exposure to sounds above 85 dB can lead to hearing damage.

Instant exposure to 140 dB can cause immediate injury and pain.

8 hours at 90 dB can harm your ears.