In the field of
acoustics, a diaphragm is a
transducer intended to inter-convert mechanical vibrations to sounds, or vice versa. It is commonly constructed of a thin membrane or sheet of various materials, suspended at its edges. The varying air pressure of sound waves imparts mechanical vibrations to the diaphragm which can then be converted to some other type of signal; examples of this type of diaphragm are found in
microphone
A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and pub ...
s and the human
eardrum. Conversely a diaphragm vibrated by a source of energy beats against the air, creating sound waves. Examples of this type of diaphragm are
loudspeaker
A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or ...
cones and
earphone diaphragms and are found in
air horns.
Loudspeaker
In a dynamic
loudspeaker
A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or ...
, a diaphragm is the thin, semi-rigid
membrane
A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. ...
attached to the
voice coil, which moves in a magnetic gap, vibrating the diaphragm, and producing
sound
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.
In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by ...
. It can also be called a cone, though not all speaker diaphragms are cone-shaped. Diaphragms are also found in
headphones.
Quality midrange and bass drivers are usually made from paper, paper composites and laminates, plastic materials such as
polypropylene
Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer propylene.
Polypropylene
belongs to the group of polyolefins an ...
, or mineral/fiber filled polypropylene. Such materials have very high strength/weight ratios (paper being even higher than metals) and tend to be relatively immune from flexing during large excursions. This allows the driver to react quickly during transitions in music (i.e. fast changing transient impulses) and minimizes acoustical output distortion.
If properly designed in terms of mass, stiffness, and damping, paper woofer/midrange cones can outperform many exotic drivers made from more expensive materials. Other materials used for diaphragms include
polypropylene
Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer propylene.
Polypropylene
belongs to the group of polyolefins an ...
(PP),
polyetheretherketone (PEEK)
polycarbonate (PC),
Mylar (PET),
silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from the ...
,
glassfibre,
carbon fibre
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English
The use of the English language in current and former member countries of the Commonwealth of Nations was largely inherited fro ...
,
titanium
Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...
,
aluminium
Aluminium (aluminum in AmE, American and CanE, Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately o ...
, aluminium-
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
alloy,
nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...
, and
beryllium. A paper woofer with a peak-to-peak excursion of 0.5 inches at 60 Hz undergoes a maximum acceleration of 92 "g"s.
Paper-based cones account for approximately 85% of the cones sold worldwide. The ability of paper (cellulose) to be easily modified by chemical or mechanical means gives it a practical processing advantage not found in other common cone materials.
The purpose of the cone/surround assembly is to accurately reproduce the voice coil signal waveform. Inaccurate reproduction of the voice coil signal results in acoustical distortion. The ideal for a cone/surround assembly is an extended range of linearity or "pistonic" motion characterized by i) minimal acoustical breakup of the cone material, ii) minimal standing wave patterns in the cone, and iii) linearity of the surrounds force-deflection curve. The cone stiffness/damping plus the surround's linearity/damping play a crucial role in accuracy of the reproduced voice coil signal waveform. This is the crux of high-fidelity stereo.
The surround may be resin-treated cloth, resin-treated non-wovens, polymeric foams, or thermoplastic elastomers over-molded onto the cone body. An ideal surround has a linear force-deflection curve with sufficient damping to fully absorb vibrational transmissions from the cone/surround interface, and the "toughness" to withstand long-term vibration-induced fatigue. Sometimes the conical part and the outer surround are molded in one step and are one piece as commonly used for a
Guitar speaker.
Other types of speakers (such as
electrostatic loudspeakers) may use a thin membrane instead of a cone.
Microphone
Microphones can be thought of as speakers in reverse. The sound waves strike the thin diaphragm, causing it to vibrate.
Microphone diaphragms, unlike speaker diaphragms, tend to be thin and flexible, since they need to absorb as much sound as possible. In a condenser microphone, the diaphragm is placed in front of a plate and is
charged.
In a dynamic microphone, the diaphragm is glued to a magnetic coil, similar to the one in a dynamic loudspeaker. (In fact, a dynamic speaker can be used as a rudimentary microphone, and vice versa.)
The diaphragm in a microphone works similarly to the human
eardrum.
Other uses
In a
phonograph reproducer, the diaphragm is a flat disk of typically
mica
Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...
or
isinglass that converts the mechanical vibration imparted on the buttress 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.
See also
*
Acoustic membrane
References
{{reflist
Acoustics
Loudspeakers