Ribbon microphone
Encyclopedia
Electromagnetic induction
Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field. It underlies the operation of generators, transformers, induction motors, electric motors, synchronous motors, and solenoids....
. Ribbon microphones are typically bidirectional, meaning they pick up sounds equally well from either side of the microphone.
Principle of operation
Diaphragm (acoustics)
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...
is attached to a light movable coil that generates a voltage as it moves back and forth between the poles of a permanent magnet. In ribbon microphones, a voltage is induced at right angles to both the ribbon velocity and magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
direction. As the sound wave causes the ribbon to move, the induced voltage in the ribbon is proportional to the particle velocity in the sound wave. The voltage output of older ribbon microphones is typically quite low compared to a dynamic moving coil microphone and a step-up transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
is used to increase the voltage output and increase the output impedance
Output impedance
The output impedance, source impedance, or internal impedance of an electronic device is the opposition exhibited by its output terminals to an alternating current of a particular frequency as a result of resistance, inductance and capacitance...
. Modern ribbon microphones do not suffer from this problem due to improved magnets and more efficient transformers, and have output levels that can exceed typical stage dynamic microphones.
Ribbon microphones were once delicate, and expensive, but modern materials make certain present-day ribbon microphones very durable and may be used for loud rock music and stage use. They are prized for their ability to capture high-frequency detail, comparing very favorably with condenser microphones, which can often sound subjectively "aggressive" or "brittle" in the high end of the frequency spectrum. Due to their bidirectional pick-up pattern, ribbon microphones are often used in pairs to produce the Blumlein Pair
Blumlein Pair
Blumlein Pair is the name for a stereo recording technique invented by Alan Blumlein for the creation of recordings that, upon replaying through headphones or loudspeakers, recreate the spatial characteristics of the recorded signal....
recording array. In addition to the standard bidirectional pick-up pattern, ribbon microphones can also be configured to have cardioid
Cardioid
A cardioid is a plane curve traced by a point on the perimeter of a circle that is rolling around a fixed circle of the same radius. It is therefore a type of limaçon and can also be defined as an epicycloid having a single cusp...
, hypercardioid, omnidirectional, and variable polar patterns.
As many mixers are equipped with phantom power
Phantom power
Phantom power, in the context of professional audio equipment, is a method for transmitting DC electric power through microphone cables to operate microphones that contain active electronic circuitry....
in order to enable the use of condenser microphones, care should be taken when using condenser and ribbon microphones at the same time. If the ribbon microphone is improperly wired, which is not unheard of with older microphones, this capacity can damage some ribbon elements, but improvements in designs and materials have made those concerns largely a thing of the past.
History
Walter H. Schottky
Walter Hermann Schottky was a German physicist who played a major early role in developing the theory of electron and ion emission phenomena, invented the screen-grid vacuum tube in 1915 and the pentode in 1919 while working at Siemens, and later made many significant contributions in the areas of...
and Erwin Gerlach co-invented the first ribbon microphone. By turning the ribbon circuit in the opposite direction, they also invented the first ribbon loudspeaker.
In the late 1920s, Dr. Harry F. Olson
Harry F. Olson
Harry Ferdinand Olson was a prominent engineer at RCA Victor.Harry F. Olson, a pioneer in the field of 20th century acoustical engineering, was born in Mount Pleasant, Iowa to Swedish immigrant parents...
of RCA
RCA
RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
began development of ribbon microphones, first with field coils and then with permanent magnets. One of the first ribbon microphones was the RCA PB-31. Produced in 1931, it was a breakthrough technology in sound, and revolutionized the audio recording and broadcasting
Broadcasting
Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...
industries, setting a new standard in frequency response
Frequency response
Frequency response is the quantitative measure of the output spectrum of a system or device in response to a stimulus, and is used to characterize the dynamics of the system. It is a measure of magnitude and phase of the output as a function of frequency, in comparison to the input...
. The clarity and realism were unmatched by any of the condenser microphones of its day.
Just a few months later, in 1932, the PB-31 was replaced by the 44A, which was enormously successful and highly regarded for its smooth tone and defined pattern control, which not only reduced the effects of reverberation on soundstages, but also offered higher gain before feedback
Gain before feedback
In live sound mixing, gain before feedback is a practical measure of how much a microphone can be amplified in a sound reinforcement system before causing audio feedback. In audiology, GBF is a measure of hearing aid performance...
in live sound applications. The 44A was updated with improved magnetic material in the 44B/44BX models. RCA also launched the unidirectional 77A/77B models and the multi-pattern 77C/77D mics. Nearly three-quarters of a century later, many of these RCA ribbon models are still hard-working audio tools prized by engineers worldwide.
The BBC-Marconi Type A
BBC-Marconi Type A
The BBC-Marconi Type A was a ribbon microphone that was produced by the BBC and Marconi between 1934 and 1959. The microphone has been described as "iconic" and a symbol of the BBC, and has become an interface metaphor for sound recording.- History :...
was an iconic ribbon microphone produced by the BBC
BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
and Marconi
Marconi
-People:*Guglielmo Marconi, Italian-born radio pioneer*David Marconi, American screenwriter*Dominic Anthony Marconi, American Roman Catholic bishop*Enrico Marconi, also known as Henryk Marconi, architect*Gloria Marconi, Italian long-distance runner...
between 1934 and 1959. Also of note is the ST&C Coles 4038
Coles 4038
The Coles 4038 is a ribbon microphone produced by Coles Electroacoustics. The microphone was designed and patented by the BBC in the 1950s and was originally known as the STC 4038. The sound of the microphone has been described as "British" with a "BBC politeness", and its appearance has been...
(or PGS – pressure gradient single) designed by the BBC in 1954 and still used for some applications to this day. Its uses varied from talks to symphony
Symphony
A symphony is an extended musical composition in Western classical music, scored almost always for orchestra. A symphony usually contains at least one movement or episode composed according to the sonata principle...
concerts and is regarded as a delicate, fine traditional microphone.
Around 2002, relatively inexpensive ($80 – $200) Chinese
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
-manufactured ribbon microphones inspired by the RCA-44 and older Russian Oktava ribbon microphones became available.
In 2007, microphones employing ribbon elements made of strong nanomaterials
Nanomaterials
Nanomaterials is a field that takes a materials science-based approach to nanotechnology. It studies materials with morphological features on the nanoscale, and especially those that have special properties stemming from their nanoscale dimensions...
became available, offering orders of magnitude improvement in signal purity and output level.
The ribbon microphone is an electrically simple design with no active circuitry; it is possible to build one from a kit, or with basic tools and materials. The acoustic complexity of ribbon microphones is comparable to other types of air coupled transducers.