Ribbon mics?

[Shrum]

hey guys, i have two question concerning ribbons microphones.
1: do ribbons always have two diaphragms?
2: is the diaphragm/s conductive like i.e. in condensers and carbon mics?
thanks in advance!!

[jnorman]

1. no. they are, however, typically figure 8 config where the capsule (ribbon element) picks up both from the front and rear in generally equal manner.
2. no. the ribbon element is suspended in a magentic field, and generates voltage via induction.

[rumleymusic]

They are dynamics. Most all ribbons I know of only have one aluminum diaphram. In these mics the ribbon is the diaphragm AND the inductive element, vibrating freely between two magnets (unlike other dynamic mics where the diaphragm is connected to an inductive coil). This creates a natural figure 8 pattern. LDC's need two diaphragms to create the multiple patterns, as they are naturally cardioid. LDC's create the figure 8 pattern by picking up an equal level of sound on both diaphragms with reversed polarity on the rear.

Edit, jnorman beat me to it

[Audiop]

There's also the single membrane condenser fig-8 like MKH30.

And yes, the ribbon typically made from aluminum is conductive.


/Peter

[jnorman]

peter, while aluminum is a conductive material, to my understanding, conduction does not play a part in the operation of a ribbon element.

[Corran]

Not to confuse the issue, but there are plenty of ribbons with two diaphragms / ribbons, but they aren't back-to-back like condenser diaphragms. They are next to each other, which makes the output slightly higher since you have two elements getting/sending signal.

See the Oktava ML-52, Fathead I believe, and various other mics.

[rumleymusic]

peter, while aluminum is a conductive material, to my understanding, conduction does not play a part in the operation of a ribbon element.

It "conducts" a electrostatic charge generated through induction. Conduction is just the transfer of the electrons through the wires, not a method of generating electricity.

Or so I understand

[MichaelPatrick]

Originally Posted by Shrum

hey guys, i have two question concerning ribbons microphones.
1: do ribbons always have two diaphragms?
2: is the diaphragm/s conductive like i.e. in condensers and carbon mics?
thanks in advance!!

1. No. Most designs have one ribbon (not really a diaphragm) while a few designs have two ribbons.
2. Yes. Wires connected to each end of the ribbon convey electrical energy the magnets induce to a transformer that converts the relatively low output current to a voltage high enough to be amplified.

[rumleymusic]

Yes. Wires connected to each end of the ribbon convey electrical energy the magnets induce to a transformer that converts the relatively low output current to a voltage high enough to be amplified.

Well yes, the conductive corrugated ribbon element is attached to a copper plate, where wires transfer the static charge to a transformer. But I wouldn't say it is like a condenser, that has a constant charge supplied to it.

[loujudson]

I'll chime in with a dumb question - I thought aluminum was non magnetic. If so, how does it generate a signal from a magnet? One of my private physics mysteries. How can a non-magnetic substance be induced by magnets?

L

[Howie J]

I'm going to take a shot at this just to see if my technical brain is working tonight. So, someone please correct me if I'm WAY off base. It's been a while since I really studied mic inner workings.

The aluminum ribbon can sit between two magnets since it isn't really magnetic. The air pressure caused by sound moves the ribbon back and forth within the magnetic field. The disruptions cause in the magnetic field are then translated to high/low voltages by the element and sent on down the line. It's not relying on the magnetism of the ribbon itself, but the magnets surrounding it.

I would think if the ribbon was made from something highly magnetic like iron, it would just stick to the magnet and never work. Therefore, aluminum is strong enough and flexible enough, but non-magnetic enough to be placed in a magnetic field.

Howie j

[loujudson]

Howie, I think we are both off on the same tangent. Copper is not magnetic either, but it is a conductor and the magnetism can induce electron movement in the copper of a voice coil.

You made me see that the ribbon can do the same thing, movement in the field induces electron movement. Neither has to be magnetic (ferrous is the term) just a conductor.

I think I understood this in sixth grade, but ribbons are just so magical compared to a coil of copper... and there are aluminum voice coils too, so it shouldn't be so odd.

L

[MichaelPatrick]

Originally Posted by rumleymusic

Well yes, the conductive corrugated ribbon element is attached to a copper plate, where wires transfer the static charge to a transformer. But I wouldn't say it is like a condenser, that has a constant charge supplied to it.

Did someone say ribbon elements are like a condenser or have a static charge?

[Thomas W. Bethe]

From the www

How Does a Ribbon Mic Work

A ribbon microphone is a type of dynamic mic in which a thin, corrugated strip of aluminum suspended between two poles of a strong magnet serves as the diaphragm and voice coil. The ribbon reacts to velocity of air particles (rather than the pressure, as with moving-coil dynamic mics) and as it moves within the magnetic flux field, it generates a small AC voltage proportional to this velocity. Clamps attached to either end of the ribbon also serve as contact terminals: Wires carry the signal to a step-up transformer, which then raises the output voltage and boosts the output impedance to a usable level for a preamp, typically around 150 to 300 ohms.

Because the ribbon element responds to sound waves arriving from the front or back, but is insensitive to sound coming from the sides, most ribbon mics have a natural bidirectional polar pattern, which makes them ideal for eliminating unwanted noise between two sources or for use in M/S and Blumlein stereo recording configurations. Classic ribbon designs do not contain internal electronics — just the ribbon, magnets, transformer and occasionally a passive highpass filter network.

and

Ribbon microphones use a thin, usually corrugated metal ribbon suspended in a magnetic field. The ribbon is electrically connected to the microphone's output, and its vibration within the magnetic field generates the electrical signal. Ribbon microphones are similar to moving coil microphones in the sense that both produce sound by means of magnetic induction. Basic ribbon microphones detect sound in a bidirectional (also called figure-eight) pattern because the ribbon, which is open to sound both front and back, responds to the pressure gradient rather than the sound pressure. Though the symmetrical front and rear pickup can be a nuisance in normal stereo recording, the high side rejection can be used to advantage by positioning a ribbon microphone horizontally, for example above cymbals, so that the rear lobe picks up only sound from the cymbals. Crossed figure 8, or Blumlein pair, stereo recording is gaining in popularity, and the figure 8 response of a ribbon microphone is ideal for that application.

Other directional patterns are produced by enclosing one side of the ribbon in an acoustic trap or baffle, allowing sound to reach only one side. The classic RCA Type 77-DX microphone has several externally-adjustable positions of the internal baffle, allowing the selection of several response patterns ranging from "Figure-8" to "Unidirectional". Such older ribbon microphones, some of which still give very high quality sound reproduction, were once valued for this reason, but a good low-frequency response could only be obtained if the ribbon was suspended very loosely, and this made them fragile. Modern ribbon materials, including new nanomaterials[4] have now been introduced that eliminate those concerns, and even improve the effective dynamic range of ribbon microphones at low frequencies. Protective wind screens can reduce the danger of damaging a vintage ribbon, and also reduce plosive artifacts in the recording. Properly designed wind screens produce negligible treble attenuation. In common with other classes of dynamic microphone, ribbon microphones don't require phantom power; in fact, this voltage can damage some older ribbon microphones. Some new modern ribbon microphone designs incorporate a preamplifier and, therefore, do require phantom power, and circuits of modern passive ribbon microphones, i.e., those without the aforementioned preamplifier, are specifically designed to resist damage to the ribbon and transformer by phantom power. Also there are new ribbon materials available that are immune to wind blasts and phantom power.

[Audiop]

Originally Posted by Corran

Not to confuse the issue, but there are plenty of ribbons with two diaphragms / ribbons, but they aren't back-to-back like condenser diaphragms. They are next to each other, which makes the output slightly higher since you have two elements getting/sending signal.

Yes, ribbon mic's are like ribbon tweeters/loudspeakers so two wires in paralell mechanically (but in series electrically) means a more effective motor/generator than the single wire.

In a dynamic loudspeaker (which ribbons are a type of) the higher the flux in the magnetic field and the longer the wire of the voice coil the higher the voltage sensitivity.


/Peter

[Audiop]

Originally Posted by jnorman

peter, while aluminum is a conductive material, to my understanding, conduction does not play a part in the operation of a ribbon element.

Originally Posted by rumleymusic

It "conducts" a electrostatic charge generated through induction. Conduction is just the transfer of the electrons through the wires, not a method of generating electricity.

Or so I understand

Without a conductive material there will be no current flowing in the ribbon and the transformer windings. :-)

There's no electrostatic charge in ribbons as we find in condensers or ESL/electrostatic loudspeakers like Martin Logans and Quad for example.

These are the two dominant transducers princips >electrostatic and dynamic.

One works as a big capacitor and the other like an inductor.


/Peter

[rumleymusic]

There's no electrostatic charge in ribbons as we find in condensers or ESL/electrostatic loudspeakers like Martin Logans and Quad for example.

These are the two dominant transducers princips >electrostatic and dynamic.

My mistake in terminology. I need to brush up on my physics. But the ribbon element does generate a small static charge through electromagnetic induction, correct?

[loujudson]

Daniel, it is not a static charge but current flow.

L

[mixedupsteve]

It's actually a voltage that is produced by the induction. When that voltage is connected in a circuit there will be a current flow.

[rumleymusic]

Thank you for the clarification guys.

[Marik]

Originally Posted by Shrum

hey guys, i have two question concerning ribbons microphones.
1: do ribbons always have two diaphragms?
2: is the diaphragm/s conductive like i.e. in condensers and carbon mics?
thanks in advance!!

1. As it already was mentioned, ribbons can be single or double. Depending on design parameters the double ribbons have a few ways of arrangement:

a. Side by side (like old Grampians, Oktava ML52, and Chinese ones), or
b. One behind another (like Beyers double ribbons and new Audio Technica).

In turn, either type can be connected whether
I. In series (Oktava), or
II. In paralel (Beyer).

Ideally, with optimised transformer there should be no difference in the output sensitivity between those two, however, their noise parameters are slightly different.

2. As it was mentioned, the ribbon has to be conductive. Moreover, because source resistance translates into noise, the more conductive materials results in a quiter (hiss) operation. It would be logical to expect that thicker foils would result in lower noise, however, the thickness also adds mass, so the sensitivity goes down and we come back to S/N issues.

Historically, Aluminum became material of choice, as the best compromise between its electrical conductivity, compliance, strength and lightness.

Best, Mark Fouxman
Samar Audio & Microphone Design

[Corran]

Huh, I didn't know there were ribbon designs with two ribbons in front of each other.

Doesn't that mean that a sound from the front wouldn't move the ribbon in the back, since the other ribbon is in the way? If so, what's the point?

[rumleymusic]

Huh, I didn't know there were ribbon designs with two ribbons in front of each other.

Doesn't that mean that a sound from the front wouldn't move the ribbon in the back, since the other ribbon is in the way? If so, what's the point?

The elements are isolated in these mics by a baffle it seems (looking at the pic on AT's site). AT says it is for increased sensitivity.

[Marik]

Originally Posted by Corran

Huh, I didn't know there were ribbon designs with two ribbons in front of each other.

Doesn't that mean that a sound from the front wouldn't move the ribbon in the back, since the other ribbon is in the way? If so, what's the point?

There is quite a complicated relationship there, which comes to damping factor, different time delay and phase shift between front and rear, different effective mass, etc.
I made a few prototypes with that arrangement using large ribbons with conventional corrugation, which turned to be very fussy and complicated to tune and needed very high precision mechanical part. Small ones (like Beyer) are much more forgiving, but again, small ribbons have different sonics.

Best, M