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1/3 octave band

The distance (bandwidth) between two frequencies that have a roughly 4:5 ratio (. In a logarithmic notation, the width of a 1/3 octave band is one-third of the width of an octave.

Absorption Coefficient

The measure of how much sound energy is absorbed by a material when sound waves pass through it.

Acoustical Design Load (ADL)

Acoustical design load refers to the load relevant for the acoustical performance of the specific isolator and is typically the sum of 100% dead load (DL) + 25% or 33% live load (LL) of the supported structure. For structural integrity and failure calculations, total load (TL) is considered as well. With the performance of most load-bearing isolators being load-dependent, it is imperative to use the typical loading condition(s), not the worst-case loading condition.

Airborne noise

Amplitude in Acoustics

The maximum displacement of particles in a sound wave from their rest position, representing the loudness of the sound.

Amplitude in Vibration

The maximum displacement from the equilibrium position during a vibration cycle.


In the context of acoustics and vibration, damping refers to the process of reducing or dissipating the energy of oscillations or vibrations in a system. When an object or structure is subjected to vibrations, it tends to vibrate at its natural frequency. In the absence of damping, these vibrations would continue indefinitely due to the conservation of energy. However, damping mechanisms are introduced to absorb or dissipate the energy of the vibrations, causing them to decay over time. Damping is essential in various engineering applications to control and manage vibrations. It serves several purposes, including: Energy Dissipation: Damping materials or devices absorb the mechanical energy generated by vibrations and convert it into heat. By dissipating the energy, the amplitude of the vibrations decreases, leading to a reduction in potential damage or discomfort. Vibration Control: Damping is used to control undesirable vibrations in mechanical systems, structures, and machinery. By introducing appropriate damping mechanisms, engineers can prevent excessive oscillations, which could lead to component failure or reduced performance. Resonance Suppression: Damping is particularly effective in reducing the effects of resonance, which occurs when a vibrating system is subjected to forces at or near its natural frequency. Without damping, resonance can cause amplified vibrations, potentially leading to structural failure or malfunction. Noise Reduction: In acoustics, damping materials are used to reduce noise by absorbing sound energy and preventing its reflection or transmission. This is especially important in architectural acoustics and automotive industries to improve sound quality and comfort. Damping can be achieved through various methods, including: Viscous Damping: Using viscous fluids or dampers that generate resistance to motion, converting kinetic energy into heat. Viscous damping is commonly found in shock absorbers and various mechanical systems. Structural Damping: Incorporating materials with inherent damping properties, such as viscoelastic materials, which naturally dissipate energy due to their internal friction. Tuned Mass Dampers: Adding a secondary mass system tuned to a specific frequency to counteract vibrations in larger structures like buildings and bridges. Active Damping: Implementing active control systems that measure vibrations and apply counteracting forces to reduce unwanted oscillations. The appropriate level of damping depends on the specific application and engineering requirements. Insufficient damping can lead to resonance and excessive vibrations, while excessive damping may result in reduced system efficiency or performance. Therefore, engineers carefully analyze and design damping systems to achieve optimal results in various acoustical and vibration scenarios.


The decibel (dB) is a logarithmic unit used to express the relative intensity or level of a sound, signal, or power with respect to a reference level. It is widely used in acoustics, electronics, telecommunications, and various scientific and engineering fields to quantify and compare the magnitude of different quantities. In acoustics, the decibel is commonly employed to measure sound pressure level (SPL) and sound intensity level (SIL), providing a convenient way to describe the loudness or intensity of sounds. The decibel scale allows for a wide range of values to be represented in a more manageable and easily interpretable format. The formula to calculate the decibel level is: dB = 10 * log10 (P / Pref) Where: dB is the decibel level. P is the measured sound pressure or power being evaluated. Pref is the reference sound pressure or power level. The reference level (Pref) is typically chosen based on established standards. For sound pressure level, the commonly used reference is 20 microPascals (μPa), which is considered the threshold of human hearing at a frequency of 1,000 Hz. For power measurements, the reference level is often 1 milliwatt (mW) or 1 picowatt (pW) depending on the application. Some common examples of sound levels in decibels include: 0 dB: The threshold of human hearing at 1,000 Hz. 20 dB: A quiet whisper at a close distance. 60 dB: Normal conversation level. 90 dB: A lawnmower or heavy city traffic. 120 dB: A rock concert or a jet engine at takeoff. The decibel scale is logarithmic, which means that a 10 dB increase represents a tenfold increase in sound intensity or power. For example, a sound that is 10 dB louder than another is 10 times more intense. Similarly, a 20 dB increase signifies 100 times more intensity, and so on. Using decibels allows engineers, audiologists, and other professionals to measure and communicate sound levels and signal strengths accurately, especially when dealing with a vast range of values that may vary from barely audible to potentially harmful levels.

Decibel (dB)

A unit used to measure the relative intensity of a sound, based on the logarithm of the ratio between the sound's intensity and a reference intensity.


The distance by which an elastic material is compressed when subjected to a given load or force. The deflection of elastomers is typically measured in millimeters (mm) or inches (in).


Ability and material property of an elastic material to return to its initial height after compression.


The number of cycles of a sound/vibration wave occurring in one second, measured in hertz (Hz).

Frequency Response

The range of frequencies over which a vibrating system or structure can effectively respond.

Harmonic Vibration

Vibration at integer multiples of the fundamental frequency, which can result in resonance and increased stress on a structure.

Insertion Loss

Insertion loss in acoustics refers to the reduction in sound transmission when an object, material, or structure is introduced into a sound path between a sound source and a receiver. It is a measure of how effectively the inserted object attenuates or absorbs sound energy, resulting in a decrease in the sound level that reaches the receiver. The insertion loss is typically expressed in decibels (dB) and can be calculated using the following formula: Insertion Loss (IL) = Sound Pressure Level without Insertion (Initial SPL) - Sound Pressure Level with Insertion (Final SPL) Here's a breakdown of the components in the formula: Sound Pressure Level without Insertion (Initial SPL): This is the sound level measured at the receiver (listener's position) when the sound source is emitting sound directly without any obstructions or materials in the sound path. Sound Pressure Level with Insertion (Final SPL): This is the sound level measured at the same receiver position when the sound source is emitting sound, but this time, the sound has to pass through the inserted object or material before reaching the receiver. Insertion loss is an essential parameter in acoustic design and engineering, particularly in scenarios where noise control or soundproofing is required. Common applications of insertion loss include: Soundproofing materials: Insertion loss is used to evaluate the effectiveness of various materials, such as acoustic panels, sound barriers, and insulation, in reducing sound transmission between spaces. Earplugs and earmuffs: Insertion loss is utilized to assess the efficiency of hearing protection devices in reducing the amount of noise that reaches the wearer's ears. Acoustic enclosures: When constructing enclosures around noisy equipment or machinery, insertion loss helps determine the enclosure's ability to reduce noise levels in the surrounding environment. Room acoustics: In architectural acoustics, insertion loss plays a role in evaluating the effectiveness of certain designs or materials in reducing sound transmission between rooms or controlling echoes and reverberation. It's important to note that the insertion loss is frequency-dependent. The effectiveness of sound attenuation varies with different frequencies, so insertion loss is often measured across a range of frequencies to provide a more comprehensive evaluation of the acoustic properties of the material or structure being tested.

Mass Spring System

A mass-spring system is a fundamental concept in physics and engineering that represents a simple, idealized model of a dynamic system. It consists of two main components: a mass and a spring. Mass: The mass is a physical object with mass (m) that is free to move along a straight line or in one dimension. It could be a point mass or a physical object with a significant size, depending on the application and the level of simplification required. Spring: The spring is an elastic element that exerts a force when it is stretched or compressed from its equilibrium position. It follows Hooke's law, which states that the force exerted by a spring is directly proportional to the displacement from its equilibrium position and acts in the opposite direction to the displacement. The spring constant (k) determines how stiff or soft the spring is. When you combine the mass and the spring, you get a mass-spring system. The behavior of this system can be described using Newton's second law of motion, which states that the force acting on an object is equal to the mass of the object multiplied by its acceleration (F = m * a). In this case, the force acting on the mass is the force exerted by the spring. The equation of motion for a mass-spring system is given by: m * a = -k * x where: m is the mass of the object, a is the acceleration of the mass, k is the spring constant, x is the displacement of the mass from its equilibrium position. The negative sign on the right side of the equation indicates that the force exerted by the spring opposes the direction of displacement, which is consistent with Hooke's law. The mass-spring system exhibits simple harmonic motion when it oscillates around its equilibrium position. The motion is periodic, and the system's displacement from the equilibrium position follows a sinusoidal pattern over time. The frequency of oscillation depends on the mass of the object and the stiffness of the spring. Mass-spring systems are used in various applications, including: Mechanical engineering: In designing and analyzing suspension systems, shock absorbers, and vibration isolators. Physics education: As a simple model to teach principles of oscillations and harmonic motion. Seismology: In studying the behavior of masses during earthquakes and other seismic events. Mechanical watches and clocks: As a part of the escapement mechanism in traditional timekeeping devices. The mass-spring system provides a valuable foundation for understanding more complex systems with multiple degrees of freedom and damping effects, such as in structural engineering and advanced mechanical systems.

Modal Analysis

The study of a structure's natural modes of vibration and their associated frequencies and shapes.

Natural Frequency

The inherent frequency at which an object or structure vibrates without any external force applied. Damping reduces the period (duration) an object or structure vibrates.


Polyurethane (abbreviated PUR or PU) is a type of polymer, developed by Otto Bayer in Germany in 1937. It is made by reacting a polyol with isocyanate to form either a polyether urethane or a polyester urethane.


In acoustics, resonance refers to a phenomenon that occurs when a vibrating system is subjected to an external force at its natural frequency, resulting in a significant increase in the system's amplitude of vibration. Resonance can occur in various acoustic systems, such as musical instruments, rooms, and mechanical structures. Key points about resonance in acoustics: Natural Frequency: Every object or system has a natural frequency at which it naturally tends to vibrate when disturbed. This frequency is determined by the object's physical properties, such as its size, shape, and material composition. For example, a tuning fork has a specific natural frequency determined by its dimensions and material. External Force: When an external force is applied to a vibrating system at or near its natural frequency, the system absorbs energy from the force and responds with an amplified vibration. This effect occurs because the force's frequency matches the system's natural frequency, leading to constructive interference and an increase in amplitude. Amplification of Sound: In acoustic systems, resonance causes an increase in the sound's volume or amplitude, making it louder and more noticeable. This effect is particularly pronounced when resonance occurs in closed spaces like rooms, where sound waves bounce back and forth, reinforcing each other at the natural frequency of the room. Resonance and Musical Instruments: Resonance plays a crucial role in the production of sound in musical instruments. For example, in string instruments like guitars or violins, plucking or bowing the strings causes them to vibrate at their natural frequencies, and the resulting sound is amplified through resonance in the hollow body of the instrument. Resonance and Room Acoustics: In room acoustics, resonance can lead to the buildup of specific frequencies, causing uneven sound distribution and creating "hotspots" or "dead spots" in a room. Proper acoustic treatment and design aim to minimize the impact of resonances on sound quality and clarity. Destructive Resonance: While resonance can be advantageous in certain applications, it can also have negative effects. Destructive resonance occurs when a vibrating system is subjected to an external force that matches its natural frequency but leads to a cancelation of vibrations. This can cause unwanted vibrations, structural damage, or even failure in certain cases. In summary, resonance in acoustics is the phenomenon where a vibrating system responds with amplified vibration when subjected to an external force at or near its natural frequency. Understanding and managing resonance are essential in various acoustic applications, including musical instrument design, room acoustics, and preventing structural problems caused by unwanted vibrations.

Resonant Frequency

The frequency at which a system or structure vibrates with the maximum amplitude when subjected to external forces.

Reverberation Time (RT)

The time it takes for a sound to decrease in intensity by 60 dB after the sound source stops.

Shock Isolation

Shock isolation in vibration refers to the process of isolating or protecting a sensitive component or equipment from the effects of sudden, high-amplitude shocks or impact forces. The purpose of shock isolation is to prevent damage, malfunction, or degradation of the isolated system due to these external shocks. Shock isolation is particularly important in situations where equipment or components are exposed to environments with high shock levels, such as in transportation, heavy machinery, aerospace, military applications, and sensitive electronic devices. Sudden shocks and impacts can cause significant mechanical stresses, leading to mechanical failure, reduced performance, or data corruption. The primary goal of shock isolation is to reduce the transmission of shock and vibration from the external environment to the isolated system. This is typically achieved by using shock-absorbing materials, isolators, or dampers, which dissipate or absorb the impact energy, protecting the sensitive equipment. Common techniques and components used in shock isolation include: Shock Absorbers: These are devices designed to absorb and dissipate the energy generated by a shock or impact. They are often made from materials with high damping properties, such as rubber or viscoelastic materials. Isolators: Shock isolators are resilient components placed between the equipment and its mounting surface. They effectively decouple the equipment from the vibrating base, reducing the transmission of shock and vibration. Isolators can be of various types, including elastomeric mounts, air springs, and tuned mass dampers. Dampers: Shock dampers use friction or fluid resistance to dampen the oscillations caused by shocks, thus reducing the amplitude of vibrations transmitted to the isolated system. Protective Casings: In some cases, sensitive equipment is enclosed within a protective casing or packaging designed to absorb and distribute the impact forces, shielding the internal components from shock and vibration. The selection of appropriate shock isolation methods and components depends on the specific requirements and characteristics of the equipment and the anticipated shock levels. Engineers and designers need to consider factors such as the weight of the equipment, the frequency and amplitude of expected shocks, and the environmental conditions in which the equipment will operate. By implementing effective shock isolation techniques, industries can safeguard their sensitive equipment and ensure its reliable performance even in harsh and dynamic environments with high shock and vibration levels.

Single Degree of Freedom (SDOF)

In mechanical and structural engineering, the term "Single Degree of Freedom" (SDOF) refers to a simplified model used to analyze the dynamic behavior of a system or structure subjected to vibration or oscillation. The SDOF model represents a linear system with a single, dominant degree of freedom, meaning that the system's response to external forces or disturbances is primarily governed by the motion of a single mass. Key characteristics of the Single Degree of Freedom model include: Mass (M): The SDOF model consists of a single point mass (M) that is assumed to be concentrated at a specific location within the system. This mass represents the effective mass of the vibrating part or component. Spring (K): A linear spring (K) is attached to the mass, providing a restoring force that is proportional to the displacement from the equilibrium position. The spring stiffness governs the system's ability to resist deformation due to applied forces. Damping (C): In some cases, damping (C) may be considered in the SDOF model to account for energy dissipation and resistance to motion. Damping represents the resistance of the system to oscillation and is often used to model the effects of friction and other energy-absorbing mechanisms. Equilibrium Position: The equilibrium position is the state where the mass is at rest and the forces acting on the system are balanced. It serves as the reference position for measuring displacements. Natural Frequency: The SDOF system has a characteristic natural frequency (ωn) at which it vibrates when displaced and then released. The natural frequency is determined by the mass and the stiffness of the spring and is a fundamental property of the system. The SDOF model is particularly useful for understanding and predicting the dynamic response of simple mechanical systems and structures under harmonic or transient loading conditions. It provides valuable insights into how the system behaves and oscillates when subjected to external forces or disturbances. Engineers often use the SDOF model as a first approximation to assess the system's stability, resonance conditions, and response amplitudes before delving into more complex multi-degree-of-freedom models for more intricate structures. While the SDOF model is limited to representing systems with a single dominant mode of vibration, it forms the foundation for more advanced and accurate analysis methods used in structural dynamics, mechanical engineering, and other fields where understanding the dynamic behavior of systems is crucial for design and optimization.

Sound Absorption

The process by which sound energy is absorbed and converted into heat by materials in a room.

Sound Diffusion

The scattering of sound waves in various directions, which can improve the uniformity of sound distribution in a room.

Sound Pressure Level (SPL)

A logarithmic measure of the sound pressure relative to a reference pressure level, usually expressed in decibels (dB).

Sound Reflection

The redirection of sound waves when they encounter a surface, typically causing echoes and influencing the acoustic characteristics of a space.

Sound Transmission Class (STC)

A rating system used to quantify how well a building partition reduces airborne sound transmission.


Techniques and materials used to reduce or block the transmission of sound between spaces.

Standing Wave

A wave pattern produced when sound waves reflecting back and forth between two surfaces interfere with each other.

Structure-Borne Sound

Structure-borne sound refers to sound waves that pulsate and radiate via a solid structure or medium before reaching the human ear. The sound of footfall from a room above, for example, would be structure-borne sound created by the impact of the footsteps resonating through the floorboards.


The oscillation or back-and-forth motion of an object around its equilibrium position.

Vibration Analysis

The process of studying and interpreting vibration data to understand the behavior of mechanical systems.

Vibration Fatigue

The progressive structural damage that occurs due to repeated vibration cycles.

Vibration Isolation

Techniques used to prevent the transmission of vibrations from one system or structure to another.

Vibration Monitoring

Continuous or periodic measurement of vibrations to assess the health and performance of machinery and structures.

Vibration Spectrum

A graphical representation showing the amplitude of vibrations at different frequencies.

Vibration Transducer

A device that converts mechanical vibrations into an electrical signal, commonly used for measurement and analysis.


The distance between two consecutive points in a sound wave that are in phase with each other, represented by the Greek letter lambda (λ).
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