Helmholtz resonance, named after the German physicist Hermann von Helmholtz, refers to a phenomenon related to the resonant frequency of a cavity and its connection to the surrounding air. It typically arises in systems where a gas-filled cavity (such as a bottle or a hollow object) has a neck or opening that allows air to flow in and out. In simple terms, a Helmholtz resonator can be visualized as a container of air with an opening.

The term "hypersonic effect" typically refers to the phenomena associated with objects traveling at hypersonic speeds, which are defined as speeds greater than Mach 5 (five times the speed of sound in air). When an object moves at hypersonic speeds, it experiences a range of physical effects due to the extreme velocities involved, including: 1. **Shock Waves**: At hypersonic speeds, the flow of air around the object generates powerful shock waves.

The Institute of Acoustics (IOA) is a professional body in the United Kingdom dedicated to the advancement of the study and practice of acoustics. Founded in 1974, the IOA promotes the interests of those involved in acoustics, noise, and vibration control, providing a platform for professionals across various sectors, including engineering, environmental science, architecture, and audio technology.

The International Commission for Acoustics (ICA) is a scientific organization focused on the field of acoustics and its various applications. Established to promote the science and practice of acoustics worldwide, the ICA acts as a forum for international collaboration among scientists, engineers, and professionals working in this field. The commission plays a crucial role in facilitating communication and collaboration through conferences, publications, and the dissemination of acoustic research and technology.

Noise pollution refers to the excessive or harmful levels of noise in the environment, which can have detrimental effects on human health, wildlife, and overall quality of life. It is typically caused by various human activities and can include sounds from traffic, industrial operations, construction work, loud music, and other sources. Key aspects of noise pollution include: 1. **Sources**: Common sources of noise pollution include road traffic, airplanes, trains, factories, construction sites, and heavy machinery.

The Noise Reduction Coefficient (NRC) is a metric used to evaluate the sound absorption performance of a material or an acoustic treatment. It quantifies how much sound a material can absorb, thus reducing the amount of sound that reflects back into a space. The NRC is calculated as the average sound absorption across a range of frequencies, typically in the octave bands from 250 Hz to 2000 Hz.

Noise spectral density (NSD), often referred to as the power spectral density (PSD) when discussing signals, is a measure of the power distribution of a random signal or noise as a function of frequency. It characterizes how the power of a signal or noise is distributed across different frequency components. ### Key Points: 1. **Definition**: Noise spectral density quantifies the power of a noise signal per unit frequency.

Lighthill's eighth power law is a principle in aerodynamics that describes the relationship between the power required to maintain a certain flight speed and the weight of an aircraft. It is a specific observation made by Sir Michael Lighthill related to the power needed for flight in various types of airplanes, particularly those capable of high-speed flight.

Loudness is a perceptual characteristic of sound that relates to its intensity or amplitude. It is how humans perceive the strength or level of sound, and it is often measured in units such as decibels (dB). Loudness is not solely dependent on the sound's physical properties, such as pressure level, but also on how the human ear responds to different frequencies and the context in which the sound is heard.

Reverberation is the persistence of sound in a particular space after the original sound source has stopped. It occurs when sound waves bounce off surfaces like walls, ceilings, and floors, creating a series of reflected waves that continue to be heard after the direct sound. This phenomenon can be experienced in various environments, such as concert halls, cathedrals, and even in smaller rooms.

Occupational noise refers to sound that is present in a workplace environment and can potentially harm workers' health and well-being. It is typically characterized by high levels of noise that exceed certain thresholds, which may lead to hearing loss or other negative health effects over time. Occupational noise can come from various sources, such as machinery, equipment, and tools used in industries like construction, manufacturing, mining, and transportation.

A micro perforated plate (MPP) is a type of panel characterized by having a large number of small holes or perforations distributed evenly across its surface. These holes are typically much smaller in diameter compared to regular perforated plates, and the hole size can range from a few micrometers to a few millimeters.

The Minimum Audibility Curve (MAC) is a graphical representation that depicts the threshold of hearing for a typical human ear across different frequencies. Essentially, it shows the quietest sound levels (in decibels) that can be heard by an average listener at various frequencies, typically ranging from about 20 Hz to 20 kHz, which represents the average human hearing range.

A noise barrier, also known as a sound barrier or acoustic barrier, is a structure designed to reduce the impact of noise pollution from sources such as highways, railways, industrial areas, and other loud environments. These barriers are typically constructed from materials that absorb or reflect sound waves, thus preventing them from traveling beyond the barrier.

QuietRock is a brand of soundproof drywall that is specifically designed to reduce sound transmission between rooms and improve acoustic performance in buildings. It is manufactured with a combination of gypsum and a viscoelastic polymer that enhances its sound-dampening properties. QuietRock panels are often used in commercial and residential construction to help minimize noise levels, making them popular in areas such as hotels, multi-family housing, offices, and home theaters.

Submarine signals refer to a variety of acoustic signals used in underwater communication and research. These signals are typically transmitted through water and can be used for various purposes, including: 1. **Sonar Communication**: Submarines and underwater vehicles use sonar (Sound Navigation and Ranging) to communicate and detect objects in their environment. This involves sending sound waves and listening for echoes.

Shou-Wu Zhang, also known as He Shou Wu or Fo-Ti, is a traditional Chinese herb derived from the root of the plant Polygonum multiflorum. In traditional Chinese medicine (TCM), it has been used for centuries for its purported health benefits, including promoting hair health, improving vitality, and supporting liver and kidney function. The name "He Shou Wu" translates to "black-haired Mr. He," referencing a legend about a man named Mr.

Pre-echo is an audio phenomenon that occurs during sound encoding and compression, particularly in lossy formats such as MP3 or AAC. It refers to the unintended audible distortion that precedes a loud sound, often manifesting as a faint echo-like effect. This can happen due to how certain audio encoding algorithms handle transient sounds—sharp, sudden changes in sound levels.

"Presence" in the context of sound recording refers to the quality of a sound that makes it feel immediate and immersive. It is often characterized by clarity, detail, and the sense that the sound source is right in front of the listener rather than distant or artificial. This quality can be influenced by various factors, including recording techniques, microphone placement, the acoustics of the recording environment, and the equipment used.