Diaphragm (acoustics)
Encyclopedia
In the field of acoustics
, a diaphragm is a transducer
intended to faithfully inter-convert mechanical motion and sound. It is commonly constructed of a thin membrane or sheet of various materials. The varying air pressure of the sound waves imparts vibrations onto the diaphragm which can then be captured as another form of energy. (or the reverse)
In a loudspeaker
, a diaphragm (generally, but not exclusively cone shaped
) is the thin, semi-rigid membrane
attached to the voice coil, which moves in a magnetic gap, vibrating the diaphragm, and producing sound
. Diaphragms are also found in headphones
, and microphones.
Similarly, the eardrum
uses this same principle, using a diaphragm to stimulate nerves to transmit a neural "image" of sound to the brain
.
In loudspeakers, cellulose fiber (paper) has historically been the most common material used for the diaphragms, based on its low mass, and controllable acoustic properties. Synthetic fibres and binders may be added to provide specific properties. Other materials used for diaphragms include: polypropylene
(PP), polycarbonate
(PC), Mylar (PET), silk
, glassfibre, carbon fibre, titanium
, aluminium
, aluminium-magnesium
alloy, nickel
, and beryllium
.
In a phonograph
reproducer, the diaphragm is a flat disk of typically mica
isinglass that converts the mechanical vibration imparted on the needle from the recorded groove into sound. In the case of acoustic recording the reproducer converts the sound into the motion of the needle that scribes the groove on the recording media.
Acoustics
Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...
, a diaphragm is a transducer
Transducer
A transducer is a device that converts one type of energy to another. Energy types include electrical, mechanical, electromagnetic , chemical, acoustic or thermal energy. While the term transducer commonly implies the use of a sensor/detector, any device which converts energy can be considered a...
intended to faithfully inter-convert mechanical motion and sound. It is commonly constructed of a thin membrane or sheet of various materials. The varying air pressure of the sound waves imparts vibrations onto the diaphragm which can then be captured as another form of energy. (or the reverse)
In a loudspeaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
, a diaphragm (generally, but not exclusively cone shaped
Speaker cone
A speaker cone, loudspeaker cone or diaphram can be manufactured from various materials depending on driver implementation , desired frequency response for each driver, and cost....
) is the thin, semi-rigid membrane
Acoustic membrane
An acoustic membrane is a thin layer that vibrates and are used in acoustics to produce or transfer sound, such as a drum, microphone, or loudspeaker....
attached to the voice coil, which moves in a magnetic gap, vibrating the diaphragm, and producing sound
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
. Diaphragms are also found in headphones
Headphones
Headphones are a pair of small loudspeakers, or less commonly a single speaker, held close to a user's ears and connected to a signal source such as an audio amplifier, radio, CD player or portable Media Player. They are also known as stereophones, headsets or, colloquially, cans. The in-ear...
, and microphones.
Similarly, the eardrum
Eardrum
The eardrum, or tympanic membrane, is a thin membrane that separates the external ear from the middle ear in humans and other tetrapods. Its function is to transmit sound from the air to the ossicles inside the middle ear. The malleus bone bridges the gap between the eardrum and the other ossicles...
uses this same principle, using a diaphragm to stimulate nerves to transmit a neural "image" of sound to the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
.
In loudspeakers, cellulose fiber (paper) has historically been the most common material used for the diaphragms, based on its low mass, and controllable acoustic properties. Synthetic fibres and binders may be added to provide specific properties. Other materials used for diaphragms include: polypropylene
Polypropylene
Polypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...
(PP), polycarbonate
Polycarbonate
PolycarbonatePhysical PropertiesDensity 1.20–1.22 g/cm3Abbe number 34.0Refractive index 1.584–1.586FlammabilityV0-V2Limiting oxygen index25–27%Water absorption – Equilibrium0.16–0.35%Water absorption – over 24 hours0.1%...
(PC), Mylar (PET), silk
Silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...
, glassfibre, carbon fibre, titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
, aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
, aluminium-magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
alloy, nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
, and beryllium
Beryllium
Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...
.
In a phonograph
Phonograph
The phonograph record player, or gramophone is a device introduced in 1877 that has had continued common use for reproducing sound recordings, although when first developed, the phonograph was used to both record and reproduce sounds...
reproducer, the diaphragm is a flat disk of typically mica
Mica
The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition...
isinglass that converts the mechanical vibration imparted on the needle from the recorded groove into sound. In the case of acoustic recording the reproducer converts the sound into the motion of the needle that scribes the groove on the recording media.