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Ribbon microphones……what they are. (Wednesday, 3 July, 2024)
Recently, I bought the Beyerdynamic M 160 double ribbon microphone to record violin and cello (see Grow). Ribbon microphones are considered by many as the most natural-sounding microphone ever made. The first commercially produced ribbon microphones appeared in the early 1930s. The ribbon microphone was also known as the velocity microphone and was the last of the four basic microphone types developed, following the dynamic, condenser, and carbon microphones.
The ribbon’s natural sound can also be made to sound warm, big, and syrupy (Bing Crosby-like) when placed within two or three feet of the talent (generally, you can’t close-talk a ribbon without having a greatly exaggerated bass characteristic; proximity effect). An adequate breath filter in front of the ribbon is also necessary to protect the delicate ribbon (NEVER blow into a ribbon mic).
The active element is of course the ribbon, consisting of a very thin corrugated aluminum ribbon clamped under light tension and mounted between the poles of a strong magnet. The extremely low impedance of the ribbon (typically on the order of 0.2 ohm) is fed directly into a step-up transformer to match low-impedance lines (50, 250, or 600 ohms).
Ribbons are fragile
Ribbon mics have a reputation for being delicate and fragile. This is due, in part, to the extremely thin ribbon material that is suspended in the magnetic gap. Most people aren’t aware of just how thin that ribbon is. On the classic Coles 4038, the ribbon thickness is 0.6 microns; on AEA ribbon mics, it is 1.8 microns; and Royer ribbon mics are either 2.5 or 4 microns thick. To put that in perspective, a typical human hair is about 100 microns (0.001 inches) thick, or more than 50 times as thick as the ribbon in an AEA R84. With this in mind, it’s easy to understand why the extremely delicate aluminum ribbon must be handled with care and protected from blasts of wind or plosives.
Image: The Coles 4038, Royer R-121, and AEA ribbon microphones
Active vs. Passive Ribbon Mics
An active ribbon includes onboard electronics that allow the mic to deliver its full potential to a mic preamp regardless of the preamp’s input impedance. The big advantage is that active ribbon mics are more consistent with a range of preamps with different input impedances and typically have stronger output levels than passive ribbons. While passive ribbon microphones deliver fantastic sound quality when paired with the right preamp, active ribbon mics make it easier to accomplish that sound.
I use a Beyerdynamic M 160 microphone together with the ART MPA II microphone pre-amp that allows the adjustment of the input impedance.
Image: The ART MPA II microphone pre-amp with variable input impedance.
Velocity microphone
A ribbon microphone is a type of velocity microphone. A velocity microphone responds to the velocity of air molecules passing it rather than the Sound Pressure Level (SPL), which is what most other microphones respond to. Very old ribbon mics could be destroyed from the air velocity created just by carrying them across a room. A ribbon mic works by loosely suspending a small element (usually a corrugated strip of metal) in a strong magnetic field. This “ribbon” is moved by the action of air molecules and when it moves it cuts across the magnetic lines of flux causing a signal to be generated. Naturally ribbon mics have a figure 8 polar pattern. Ribbon mics were the first commercially successful directional microphones.
From audiomasterclass.com:
There are two basic types of microphone – omnidirectional and figure-of-eight, which can be made in either dynamic or capacitor forms. Cardioid and hypercardioid microphones are hybrids, combining features of both the omni and figure-of-eight.
The omnidirectional microphone works on the pressure principle. The diaphragm, which picks up sound vibrations in the air, is completely open at one side, but completely closed at the other.
The sound vibration is either pushing the diaphragm against the fixed pressure of the air on the other side, or it is reducing the pressure on the front of the diaphragm allowing the pressure behind to push it out.
One of the features of pressure in a gas is that it pushes equally in all directions. That makes the mic omnidirectional then.
The figure-of-eight microphone on the other hand has both sides of the diaphragm fully open to the air. So it doesn’t compare the incoming sound pressure with a fixed pressure on the other side of the diaphragm like the omnidirectional microphone. Instead it compares the pressure of the sound wave on one side with the pressure of that same sound wave after it has traveled through to the other side.
Yes, it is a tiny difference in pressure, but strong enough to move the diaphragm.
The velocity microphone… it doesn’t really exist. However you will see the term used frequently, particularly in relation to ribbon microphones because they come closest to being a true velocity mic.
A velocity microphone, if it existed, would respond to the actual velocity of the air molecules striking the diaphragm.
For this to happen though, the diaphragm would have to be so light that it could respond instantaneously, and so thin that there was no pressure difference between the two sides of the diaphragm. In practice, the diaphragm is too heavy to acquire the velocity of the air molecules and it has significant thickness.
But a microphone that doesn’t make it as a velocity mic, because its diaphragm is too heavy and thick, is still sensitive to pressure gradient. So in practice, these microphones are pressure gradient mics.
So now you know it – the difference between pressure, pressure gradient and velocity microphones.
Image. The principle of a ribbon microphone.
Image. The pressure and pressure gradient principle.
Beyerdynamic M 160 Double Ribbon Microphone
The Beyerdynamic M 160 Double Ribbon Microphone is a timeless classic in the world of professional audio recording. Renowned for its distinctive sound quality and robust build, this microphone has earned its place in studios and on stages worldwide. Its unique double ribbon design offers a smooth, natural sound that captures the essence of any audio source with remarkable accuracy. With a heritage dating back to its introduction in the 1950s, the M 160 remains a favored choice among sound engineers and recording artists who seek unparalleled fidelity and warmth in their recordings.
The M160 has two ribbons, mounted back-to-front just 0.5mm apart. The use of the second ribbon is said to increase the mic’s sensitivity, although it still measures at a modest 1.0 mV/Pa.
The corrugation pattern is identical to the M130 and M500, but unlike nearly every other ribbon microphone on the market, is that the ribbon is creased vertically as well as corrugated horizontally, making the ribbon somewhat rigid as compared to the ribbon element in other microphones.
The ribbons in the M160 measure 1.42 mm in width, and approximately 15.62 mm in length.
Bill Bottrell, producer for Michael Jackson, recorded the guitar track for the world hit “Black or White” himself with a Beyerdynamic M160 double-ribbon microphone.
Image: The Beyerdynamic M 160 double ribbon hypercardioid microphone
Features
- Double Ribbon Design: Provides exceptional transient response and a natural, detailed sound.
- Hypercardioid Polar Pattern: Offers excellent off-axis rejection, making it ideal for isolating the sound source. Most ribbons have a figure-8 polar pattern. However, for my home studio and applications, I felt a hypercardioid was more appropriate.
- Frequency Response: Ranges from 40 Hz to 18 kHz.
- High SPL Handling: Capable of handling high sound pressure levels, making it versatile for various recording applications.
- Compact Size: Its sleek and compact form factor makes it easy to position in tight spaces (one of the reasons I bought this ribbon, and it is even smaller and lighter than I thought).
- Low Self-Noise: Ensures a clean and clear recording with minimal background noise.
- NO PHANTOM POWER!!!
Image: The Beyerdynamic M 160 frequency response of my specific microphone
Comparison to Other Ribbon Microphones
When compared to other ribbon microphones, the Beyerdynamic M 160 stands out due to its unique double ribbon configuration. Most ribbon microphones, such as the Royer R-121 or the AEA R84, utilize a single ribbon design. While these microphones are renowned for their warm and natural sound, the double ribbon design of the M 160 provides an even more refined and detailed capture, particularly in the high-frequency range. Additionally, the M 160’s hypercardioid polar pattern offers better directional control and isolation compared to the figure-eight pattern commonly found in other ribbon microphones. This makes the M 160 a more versatile choice in environments where bleed from other instruments or ambient noise is a concern.
Typical Applications
The Beyerdynamic M 160 is celebrated for its versatility and is used in a variety of recording scenarios, including:
- Orchestral and Acoustic Instruments: Ideal for capturing the intricate details of strings, woodwinds, and brass. I bought this microphone for the recording of violin and cello.
- Electric Guitar Amps: Provides a rich and detailed sound, capturing both the warmth and bite of the amplifier.
- Drum Overheads: Excellent for recording cymbals and providing a balanced overall drum kit sound.
- Vocal Recording: Offers a natural and intimate vocal capture, making it suitable for both studio and live settings.
- Room Ambience: Its sensitivity and frequency response make it perfect for capturing the natural acoustics of a recording space.
Why the M 160 is Suitable for Recording String Instruments
The Beyerdynamic M 160 excels in recording string instruments, such as the violin, due to its smooth frequency response and detailed sound reproduction. The double ribbon design captures the nuanced harmonics and subtle dynamics of the violin, providing a rich and warm sound that is true to the instrument’s character. The hypercardioid polar pattern helps to isolate the violin from other instruments or background noise, ensuring a clean recording even in less-than-ideal acoustic environments.
Additionally, the M 160’s ability to handle high sound pressure levels without distortion allows it to accurately capture the full range of the violin, from delicate pizzicato notes to powerful, sustained bowing. Its low self-noise ensures that the subtleties of the violin’s sound are not lost in the recording, making it an excellent choice for solo performances, chamber music, and orchestral recordings alike.
Image: Applications of the Beyerdynamic M Series microphones
History
Some history about Ribbon microphones can be found at Shure.com and at AEA. In the early 1920s, Drs. Walter Schottky and Erwin Gerlach co-invented the first ribbon microphone at Telefunken. A few years later, Dr. Harry F. Olson of RCA started developing ribbon microphones using field coils and permanent magnets. The RCA Photophone Type PB-31 was commercially manufactured in 1931, greatly impacting the audio recording and the broadcasting industries. Radio City Music Hall in New York City employed PB-31s in 1932. The following year, the RCA 44A came on the scene. Its tone and pattern control helped reduce reverberation. RCA kept building improved versions of its ribbons through the 1970s.
Image. History of the Beyerdynamic M-Series microphones.
To understand how ribbon microphones work, here is an excerpt from “Microphones Explained for Beginners”, an article that appeared in the August 1938 issue of Radio-Craft magazine:
“The ribbon microphone is so named because the armature is a light corrugated ribbon of aluminum alloy. The aluminum ribbon is suspended in the field of a permanent magnet and when sound waves strike the ribbon, it vibrates, cutting the magnetic lines of force. Whenever a moving conductor cuts lines of magnetic force, a voltage is induced in the conductor.”
Image. August 1938 issue of Radio-Craft magazine.
Image. Early sketch of the ribbon microphone
Image. Shure Engineer Ben Bauer’s 1939 lab notebook sketch of the Model 50. Note the ribbon is labeled as “conductor” in the drawing.
References
Last updated on September 7th, 2024 at 01:41 pm
