Acoustic membranes are flexible membranes used to produce, transmit or regulate sound, ranging from the simple to complex. In musical instruments such as drums, it is the drumhead that is vibrated to produce sound; in microphones and loudspeakers, it is diaphragms and cones that transfer sound waves to and from electricity to play music and facilitate communication. Not merely a device used to produce sound, it is also used to prevent it—barium-free viscoelastic polymers such as Acoustiblok, at merely 1/8-to-1/4-inch thickness, or Tecsound 50 heavy-duty vinyl, block out their way with their energy-converting function turning over to heat to silence walls and floors. Amazing as that is, research continues to break boundaries; ultrathin self-healing membranes composed of polyborodimethylsiloxane effectively absorb low-frequency noise (200–1000 Hz) with over 95% efficiency and restore their acoustic function once injured to open new doors to construction, automotive and aerospace applications. Such versatility—from ancient drums to innovative noise confinement—testament to the manner in which the humble yet pliable acoustic membranes find their niche in developing and diverse uses.
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👉 Acoustic membrane in the context of Idiophone
An idiophone is any musical instrument that creates sound primarily by the vibration of the instrument itself, without the use of air flow (as with aerophones), strings (chordophones), membranes (membranophones) or electricity (electrophones). It is the first of the four main divisions in the original Hornbostel–Sachs system of musical instrument classification (see List of idiophones by Hornbostel–Sachs number). The early classification of Victor-Charles Mahillon called this group of instruments autophones. The most common are struck idiophones, or concussion idiophones, which are made to vibrate by being struck, either directly with a stick or hand (like the wood block, singing bowl, steel tongue drum, handpan, triangle or marimba) or indirectly, with scraping or shaking motions (like maracas or flexatone). Various types of bells fall into both categories. A common plucked idiophone is the Jew's harp.
According to Sachs, idiophones
Acoustic membrane in the context of Drum
The drum is a member of the percussion group of musical instruments. In the Hornbostel–Sachs classification system, it is a membranophone. Drums consist of at least one membrane, called a drumhead or drum skin, that is stretched over a shell and struck, either directly with the player's hands, or with a percussion mallet, to produce sound. There is usually a resonant head on the underside of the drum. Other techniques have been used to cause drums to make sound, such as the thumb roll. Drums are the world's oldest and most ubiquitous musical instruments, and the basic design has remained virtually unchanged for thousands of years.
Drums may be played individually, with the player using a single drum, and some drums such as the djembe are almost always played in this way. Others are normally played in a set of two or more, all played by one player, such as bongo drums and timpani. A number of different drums together with cymbals form the basic modern drum kit. Many drums are played together with other instruments.
Acoustic membrane in the context of Membranophones
A membranophone is any musical instrument which produces sound primarily by way of a vibrating stretched membrane. It is one of the four main divisions of instruments in the original Hornbostel-Sachs scheme of musical instrument classification.
According to Sachs,
Acoustic membrane in the context of Vibrations of a circular drum
A two-dimensional elastic membrane under tension can support transverse vibrations. The properties of an idealized drumhead can be modeled by the vibrations of a circular membrane of uniform thickness, attached to a rigid frame. Based on the applied boundary condition, at certain vibration frequencies, its natural frequencies, the surface moves in a characteristic pattern of standing waves. This is called a normal mode. A membrane has an infinite number of these normal modes, starting with a lowest frequency one called the fundamental frequency.
There exist infinitely many ways in which a membrane can vibrate, each depending on the shape of the membrane at some initial time, and the transverse velocity of each point on the membrane at that time. The vibrations of the membrane are given by the solutions of the two-dimensional wave equation with Dirichlet boundary conditions which represent the constraint of the frame. It can be shown that any arbitrarily complex vibration of the membrane can be decomposed into a possibly infinite series of the membrane's normal modes. This is analogous to the decomposition of a time signal into a Fourier series.
Acoustic membrane in the context of Struck idiophone
Struck idiophones is one of the categories of idiophones (that is, any musical instrument that creates sound primarily by the instrument as a whole vibrating—without the use of strings or membranes) that are found in the Hornbostel-Sachs system of musical instrument classification.
Struck idiophones are categorised as 11 in the Hornbostel-Sachs system. There are two main categories of struck idiophones, directly (111) and indirectly (112) struck.