How Sound Waves Work: A Guide to Acoustic Science

We experience sound in different ways. Some sounds are incredibly pleasing while others may create undue stress and negatively impact wellbeing with prolonged exposure. Even though we are all familiar with sound, not all of us understand how sound waves work, and providing you with that understanding is the purpose of this article. To let you know what sound waves are, how they work, and how we can control them to create more pleasant sounding spaces.

What are Sound Waves?

All sound is a result of mechanical vibrations that travel through a medium–such as air, water, or solid materials–until they reach our ears. These vibrations, known as sound waves, radiate outward from the source and are interpreted by our brains as audible sound. Sound waves are longitudinal waves, not transverse waves, meaning the particles in the medium vibrate parallel to the direction the wave is traveling, unlike transverse waves (such as light or ripples on water), where particles move perpendicular to the wave’s direction. As the source vibrates, it creates alternating regions of compression, where molecules are pushed tightly together, and rarefaction, where they are spread apart. This process of sound propagation allows vibrational energy to move outward through the medium, carrying sound from one location to another. In essence, sound is a form of acoustic energy transfer powered by vibration and propagated through the dynamic motion of molecules.

Key Properties of Sound Waves

There are several key properties of sound waves that determine how they sound.

• Frequency (Hz): Frequency determines the pitch of a sound and refers to the vibration frequency of the sound source, or how many times it vibrates each second. Low-frequencies represent low, deep sounds, while high-frequencies represent high-pitched sounds.
• Amplitude (dB): Amplitude, measured in decibels (dB), determines how loud the sound is. Higher amplitudes equal louder sounds, while lower amplitudes equal quieter sounds.
• Wavelength: The distance between wave peaks, or wavelengths, affect both tone and perception. Shorter wavelengths correspond to higher frequencies, which we perceive as higher-pitched sounds. Longer wavelengths have lower frequencies, which we hear as lower-pitched sounds.
• Speed of Sound: The speed of sound varies based on the medium through which it travels (faster in solids, slower in gases).
• Acoustic Impedance: Another important factor in sound transmission is acoustic impedance, which is the resistance a medium offers to the propagation of sound waves. It is determined by both the density of the material and the speed of sound within it.
• Doppler Effect: The Doppler Effect refers to the change in frequency and pitch of a sound as the source and the observer move relative to one another. When the sound source approaches, the sound waves compress, causing the pitch to sound higher. As the source moves away, the waves stretch out, and the pitch sounds lower.
• Resonance and Harmonics: Resonance occurs when a sound wave interacts with an object or a structure at its natural frequency, causing the object to vibrate more intensely. This is why musical instruments are designed with specific shapes and materials to enhance resonance. Harmonics refer to the overtones that occur alongside the fundamental frequency of a sound wave, adding richness and complexity to the tone. Both resonance and harmonics play crucial roles in shaping the timbre of a sound.

How Sound Travels and Interacts in a Room

Sound waves do not simply stay confined to their original space. As they travel, they reflect off surfaces, pass through walls and floors, or travel along structural elements, leading to unwanted noise in adjacent areas. Understanding how sound travels and interacts in a room is the first step in designing effective acoustic treatment and soundproofing strategies.

Reflection and Absorption

Reflection and absorption have a significant impact on the acoustics in an environment. When sound interacts with surfaces like walls, ceilings, and floors, they are most often reflected, especially when those surfaces are hard and smooth. These reflections can create echoes, reverberation, and an overall increase in noise levels. If reflections are left unchecked, they can degrade sound clarity, reducing acoustic comfort and creating problems with concentration and focus that can lead to increased stress levels and potential health impacts.

In contrast, soft or porous materials absorb sound energy, converting it into a small amount of heat energy through a process called sound damping. This reduces the amount of sound energy that bounces back into the space and helps control acoustical issues like echo and reverberation and helps lower the ambient noise levels in the room. Absorptive materials work best when paired with sound diffusion products.

Sound diffusion refers to the process of scattering sound waves evenly throughout a space, which can help to reduce unwanted reflections and improve the overall acoustics. Diffusers are often used to ensure that sound waves are dispersed in a way that promotes clarity and balance within the room.

There are two common measures by which we select the right materials for our acoustic design:

Sound Absorption Coefficient (SAC)

The sound absorption coefficient of a material refers to its ability to absorb sound across specific frequencies, providing a standardized measure of its effectiveness. This value helps in selecting materials that will provide optimal sound control for the specific acoustical needs of a room.

Noise Reduction Coefficient (NRC)

The effectiveness of a material at absorbing sound is commonly measured using a rating called the Noise Reduction Coefficient (NRC), which ranges from 0 (no absorption) to 1 (total absorption). It is generally used to provide a simplified rating for general comparison between materials.

Properly balancing reflective and absorptive surfaces is essential for creating acoustically comfortable environments, especially in music venues and other spaces where clarity and control are critical. Some real-world applications of using acoustic treatments in these types of sound-critical spaces include:

• Concert halls using diffusers for balanced acoustics
• Large, open spaces using carpets, ceiling clouds, and baffles for reducing echo
• Offices and homes using PET (polyethylene terephthalate) felt panels for noise control

Diffraction and Refraction in Acoustic Spaces

Diffraction and refraction are two more phenomena that influence the way sound interacts with a space. Diffraction is more common in interior spaces, but there are some instances where refraction should be considered in your acoustic design.

Diffraction is the bending and spreading of sound waves when they encounter obstacles or pass through small openings, allowing sound to travel around corners or through gaps. This effect is more pronounced at lower frequencies, which have longer wavelengths that bend more easily around objects. Diffraction is the reason we can hear sound around corners, even when there is no direct line of sight between our ears and the source of the sound.

Refraction, on the other hand, occurs when sound waves travel through different mediums or layers with varying properties like temperature or density. This can cause the sound to change speed and direction. A common example of this is sound carrying farther across a lake at night than it would during the day, due to cooling air temperature and increased density above the surface of the water. In places like large indoor spaces with HVAC systems or in long corridors and tunnels, temperature and pressure variations may be present, meaning acoustic architects must take special precautions when designing them.

Managing Sound in Different Spaces

The size and dimension of a space have significant effects on its acoustics. Many people look primarily at the surface materials when managing sound, but large rooms should be treated differently than small rooms to minimize the impact of acoustic issues like echo, reverberation, and standing waves.

Controlling Reverberation in Large Rooms

Reverberation, or reverb, refers to the prolonged sound reflections that can muddy speech or music inside a space. It occurs when sound waves bounce repeatedly between surfaces, causing a lingering echo effect that reduces clarity and can overwhelm other sounds in the environment.

Reverberation time is the duration it takes for sound to decay by 60 decibels after the source has stopped. Controlling reverb is especially important in large rooms, and a range of acoustic treatments–such as acoustic panels, ceiling clouds, and diffusers–can be used to manage it effectively.

Minimizing Echo in Small Spaces

Echo reduction is another important concept in creating great sounding spaces. Echo is caused by sound reflections off of hard, smooth surfaces, and is especially problematic in smaller spaces like home studios, offices, and meeting rooms.

Some effective solutions include:

• Installing wall treatments like acoustic panels and PET felt wall coverings to absorb reflections and reduce sharp echoes.
• Adding soft furnishings like rugs, curtains, and upholstered furniture to introduce soft surfaces that break up sound reflections.
• Strategically placing furniture to further break up sound reflections.

Example: Professional recording studios often use a combination of foam panels on walls to absorb mid- and high-frequency reflections and bass traps in corners to manage low-frequency buildup. This combination helps achieve a controlled, echo-free environment that is ideal for recording and mixing audio.

Soundproofing vs. Sound Absorption

There is a misconception that adding acoustic treatment or sound absorption products to a space is the same as soundproofing. It is not.

Soundproofing is the process of blocking sound from entering or leaving a room. It’s focused on creating a barrier to airborne or structural noise, often used in environments where privacy or external noise control is critical.

Sound transmission–how sound travels through walls, floors, and ceilings–is a key factor in this process. When sound waves pass through materials, they can either be absorbed, reflected, or transmitted. Airborne vs. structure-borne sound is an important distinction in this context.

• Airborne sound refers to sounds that travel through the air, like voices, music, or general noise. These are typically the kinds of noises we try to block in environments like offices and homes.
• Structure-borne sound, on the other hand, refers to vibrations that travel through solid materials, such as the sound from footsteps or vibrations from operating machinery.

Soundproofing materials, including acoustic insulation, aim to block or reduce both airborne and structure-borne sound transmission, preventing noise from passing through structural elements.

Sound absorption, on the other hand, is about controlling the sound within a space. It reduces echoes, reverberation, and overall ambient noise to improve sound clarity and comfort, especially in spaces like offices, classrooms, and studios.

Each process uses different materials and design strategies:

• Soundproofing materials include products like:
  • Mass-Loaded Vinyl (MLV) – a dense, flexible barrier for walls, ceilings, and floors
  • Soundproof Windows – Typically double- or triple-paned glass with air gaps and sometimes laminated layers. Designed to reduce outside noise significantly.
  • Soundproof Doors – Heavier, solid-core doors are often sealed with acoustic gaskets and door sweeps to block sound transmission.

• Sound absorption materials include products like:
  • PET Felt – a recycled, lightweight material often used in decorative acoustic panels
  • Fiberglass Acoustic Panels – highly effective for broad-frequency absorption
  • Acoustic Foam – commonly used in studios to absorb mid- and high-frequency sound reflections
  • Microperforated Aluminum Panels – used in architectural applications to reduce sound reflections without sacrificing aesthetics

Enhance Your Acoustics with the Right Materials

Using the right materials in your acoustic treatment and soundproofing plan can significantly transform acoustics in the space. Whether the goal is to reduce echo, improve speech clarity, or block unwanted external noise, material selection plays a critical role in achieving the desired acoustic performance. Architects, designers, and engineers are instrumental in this process. They assess room dimensions, intended use, and construction constraints to select materials that strike the right balance between acoustic function and aesthetic appeal–grounded in a deep understanding of how sound waves work and interact with different environments.

Material LogIQ is a trusted leader in high-performance acoustic materials, offering innovative solutions for soundproofing, sound absorption, and acoustic design. Our offerings include architectural acoustic panels designed for both commercial and residential environments, engineered materials tailored for product design and manufacturing, and custom solutions developed to meet the sound control needs of a wide range of industries.

If you would like to learn more about how we can help solve your acoustic challenges with our expertise and innovative products, contact us today to schedule a consultation.