What Is A Ribbon Microphone?

While dynamic and condenser microphones are well-known and popular in the recording studio and on stage, very little is known about the ribbon microphone. You can even be forgiven if you never heard of it before. What may surprise you though, is that they have been designed almost a century ago, and were the microphone of choice for nearly two decades in the broadcasting industry.

But what exactly are ribbon microphones an how do they function? 

A ribbon microphone consists of a very thin piece of correlated aluminium suspended in between the positive and negative poles of a magnet. As sound waves hit this thin piece of metal within the magnetic field, it vibrates and creates a small electrical signal which is picked up by the connections at the end end of the "ribbon".

History

The ribbon microphone was invented in the early 1920's by a collaboration between Dr Walter Schottky and Dr Erwin Gerlach.   

The warm and rich sound they were ably to produce, as well as the ability to pick up the smallest detail in high frequencies, got the attention of recording and broadcasting studios and was quickly adopted and became widely used throughout these industries.

The first commercially available ribbon microphone, the Photophone Type PB-31 was developed by RCA. It was a huge commercial success, with many finding a home in recording studios and broadcasting stations. 

In 1933, RCA released the model 44 which became one of the most successful and widely used ribbon microphones in history. So popular and successful in fact, that many are still used today in some studios. (AEA, a company manufacturing ribbon microphones, is still servicing RCA 44 microphones  today, and manufacturing 100% of parts for this classic.)

Other popular ribbon microphone of the era included the BBC-Marconi Type A and the  ST&C Coles 4038. Unbelievably, some of these microphones are still used today in some recording studios. (Talk about staying power!)

During the 1960's and 70's the much improved quality and affordability of condenser microphones caused ribbon microphones to start disappearing from recording studios and broadcasting stations. Combined with dynamic microphones ruling the stage, these microphones started fading into obscurity.

With new technology enabling ribbon microphones to be produced without many of its disadvantages and at much more affordable prices, these microphones have started to make a comeback during the early 2000's.  And there are more than a few sound engineers that cannot be more happy and satisfied with this development. 

Advantages And Disadvantages

Advantages

The exceptionally rich and natural sound quality these microphones are able to produce have already been mentioned. This is one of the main reasons they are so much adored by many recording and sound engineers.

Their ability to capture this much detail in the high frequencies of an audio track also makes them stand out. These high frequencies are often recorded very softly, but all the detail is there. This makes it easy for your DAW software to boost and bring out these details during the mixing process.

Depending on your needs, the fact that ribbon  microphones are bidirectional  can be seen as a big advantage. (Bidirectional simply means the microphone can capture sound equally well from the front and back of the microphone, with no sound from the sides of the microphone having any influence.)

Especially when doing a broadcast interview with an individual sitting across from you, with a ribbon microphone placed in the middle between you, you can get a away with using a single microphone. This same function can just as effectively used for performing a duet.

A final benefit of ribbon microphones is their ability to pick up a large amount of sound detail without being oversensitive. This characteristic allows it to pick up all the detail and variations in the sound of nearby sources while isolating it from other noises in the room.

Disadvantages

The biggest disadvantages of the ribbon microphone can narrowed down to one single characteristic of this mic. And that is the thickness of the piece of corrugated aluminium, or rather lack thereof.

The aluminium used in ribbon microphones are extremely thin. For example, the ribbon thickness of the Coles 4038 microphone is 0.6 microns. A few other ribbon microphones' ribbon thickness  vary from 1.8 to 4 microns. If you compare that to the thickness of a human hair which measures a 100 microns, you get a pretty good idea of exactly how thin this small piece of metal is. 

And it's exactly this characteristic of the ribbon microphone that makes it so delicate and fragile. This in turn can lead to 2 potentially fatal drawbacks.

1. The traditional ribbon microphone is very prone to breakage and should be handled with extreme care. Simply blowing into it or allowing a small gust of wind to hit the microphone may cause it to break. Similarly, placing it next to a loud sounding instrument like a kick-drum can have a similar result due to the air displacement and strength of the sound wave produced. Needless to say, dropping a ribbon microphone will almost certainly be fatal.
2. A second big potential problem is bending of the ribbon. Remember, the piece of ribbon is corrugated and fixed in place while under tension. Its this tension and flexibility of the ribbon that enables it to produce the necessary vibrations to generate the small electrical signals. Especially when stored away and put on its side, the ribbon can sag over time. This will cause the ribbon to bend and loose some of its shape and tension. As a result the ribbon will not respond as originally intended and produce a distorted sound or may stop functioning completely.

Apart from the disadvantages associated with the ribbon's fragile nature, another drawback is closely related to dynamic microphones. (Maybe because they fall under the "Dynamic Microphone" category and function under the same principles.) It simply means that, like the dynamic microphone, the ribbon microphone produces a very weak electrical signal.

As a result, just like traditional dynamic microphones, the resulting signal is too weak to be plugged into any interface without some kind of preamplification strengthening the signal. In the past this issue was resolved with dedicated preamplifiers. 

(Luckily, a few modern day solutions were developed to address this problem. More on that in the next section.)

One last "disadvantage" that has to be pointed out is the high price tag of ribbon microphone. Your high quality ribbon microphone are quite expensive, especially active ribbons from well-known manufacturers. This put them out of reach for the majority of home recording enthusiasts. (In its defense though,it has to be said that the quality of sound more than justify the price tag of these microphones.)

Addressing Current And Traditional Disadvantages

As I mentioned earlier the article, the ribbon microphone started making  a comeback in the early 2000's. Its return is also accompanied by technological improvements of many of the features that used to disadvantage the traditional ribbon microphone.  

One of the microphone's biggest weaknesses, its fragility and tendency to break easy, was one the first issues addressed. Shure, probably the biggest name in microphone manufacturers, developed a patented ribbon that is much stronger and durable than traditional aluminium. This enable the microphone to be used in more environments than previously possible.

They also addressed a second big problem traditional ribbon mics suffered from, which is is the tendency of the ribbon to sag and bend, especially when stored on its side for sustained periods of time. The Roswellite™ ribbons that Shure employ in their ribbon mics, have what is called shape memory. This allows the ribbon to regain its original shape after it has been subjected to some bending. (I cannot personally confirm or debunk this claim, but as a very reputable company, I am pretty confident Shure would not risk their name and reputation on any unproven claims.)

A third drawback of the ribbon microphone, the very weak electrical signal it produces, have also been addressed in more than one way. In the past dedicated dedicated preamplifiers were used to boost the weak signal to a more acceptable and usable strength.

Today, there are two ways in which you can boost the power of a ribbon microphone and both require the phantom power supplied by and audio interface or mixer. You can either use an external mic activator to give your signal a powerful and noise-free boost, or use a modern ribbon microphone with build-in amplification.

A mic activator is a compact device that plugs into your microphone's XLR cable at the one end while connecting to your input device (audio interface, mixer etc.) through another XLR cable connected at the opposite end. It uses the phantom power (48V) supplied by the audio interface/mixer to boost the signal strength with a gain of up to 25 decibels. Impressively, it does this without adding noise to the sound signal. (You can read more about mic activators in this article.)

Fortunately some microphones manufacturers stepped up to the plate and do something to directly address the weak signal produced by the ribbon. As a result quite a few ribbon microphones come standard with preamplifiers build into the microphone itself. Like mic activators they require the phantom power supplied by an audio interface or mixer to operate.

(The Audio-Technica AT4081 Phantom Powered Microphone and AEA N22 Active Ribbon Microphone are 2 good examples of these type of microphones. They carry a substantial price tag, but deliver the sound to match it.)

The biggest advantage of these active (powered) ribbon microphones, is that you don't need any additional devices or cables to enjoy the advantage of an "preamplified" ribbon microphone. Examples of these active microphones include the Audio Technica AT4081 and the AEA Microphones N22.

Possible Uses

As already mentioned, ribbon microphones receive high praise from sound engineers and recording professional for their rich, natural and well-rounded sound. This makes them especially suited for certain instruments.

The first instrument that comes to mind is the electric guitar. Ribbon microphones are almost the "industry standard" for recording electric guitars. In fact, you will be hard-pressed to find any accomplished recording professional that will disagree with this statement. They are able to get the "best of both worlds" out of the guitar by capturing the natural kick it produce in the mid-to-low range, while smoothing out any harshness produced by over-amplified mid-to-high tones.

The warm and rich sounds produced by saxophones and clarinets make ribbon microphones the ideal companion for recording these and similar instruments. The same applies to string instruments like violins and cellos. (During the 1950's and 1960's, ribbon microphones were very popular for recording symphony orchestras.)

Naturally it goes without saying that since ribbon microphones is said to closest match the way the human ear perceives sound, vocals can always be considered to be one of the sounds that can be best captured by a ribbon microphone.

Conclusion

As you can clearly see from this article, ribbon microphones came a long way from its development during the early 1920's, ruling the broadcasting and industry for nearly two decades before disappearing into obscurity during the latter part of the 20th century. And finally making a comeback in the early 2000's

Many improvement were made to mitigate the drawbacks that plagued older ribbon microphones while retaining the rich and natural sound they were famous for.

Just remember, they still are ribbon microphones. and as a result should be handled with care. They are also substantially more expensive than their condenser & dynamic counterparts. If you are looking for the most natural sounding microphone though, you will have to look long and hard for anything that comes close to the ribbon microphone!

As always, feel free to leave me any comments or suggestions you may have, and I will respond and try and get to them as soon as I can.

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Catch you in the next article and happy recording!

Wessel