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The DIY Ribbon Velocity Microphone, a home project

History/Background

Not so much history, but some background on ribbon mics, and some physics.

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     The Ribbon microphone was the last of the major microphone designs to come about. The driving force of ribbon microphone development was for use for film. I've read several accounts of early ribbon history, but one thing remains the same, and that is Harry Olson's involvement.  Mr. Olson refined the ribbon microphone and sold RCA on it due to several advantages, one of the most notable being the bi-directional characteristics (figure 8 polar pattern) of ribbon microphones.  This was a fairly major concern because film cameras were VERY noisy during the period, and the microphone was positioned so the camera was in the null position of the mic (see the above illustration, source unknown). This, combined with an open area for filming to reduce sound reflections, allowed for a very quiet dialog track. 

     Another selling point was the super-flat frequency response of the ribbon.  It is the nature of ribbon mics to have a flat response, except for interference from magnet structure, casing, windscreen material, etc. And as it turned out, even the pronounced proximity effect of the mic came into play, as announcers for radio and TV discovered that they could have a bigger sounding voice if they talked very close to a ribbon mic, therefore making them sound larger than life and important.

     Ribbon mics went underground after being pushed aside by other microphone designs later.  It was considered that other designs that colored the spectrum or had greater output were more efficient for their uses.  Not really a surprise, considering the weaknesses of the ribbon design. 

     In recent years, interest in ribbon microphones has been rising.  But the new ribbon microphones (as well as the nicer old microphones) all go for a premium.  It seems that you pay for the quality of a ribbon microphones tone.  Even the Oktava ML-52, Which has a list price of $999.00, with questionable tone and other gripes I have read about, has an average street price of around 300.00.

     This was one of the reasons that I became interested in building a ribbon microphone.   All the materials are reasonably available.  Quality of such materials has dramatically improved over the last 70 years.  So why couldnt I build a great sounding Ribbon mic for a fraction of the cost that others charge?

     Aside from the transformer, I spent very little on the mic itself.  Even a quality transformer from others beside Jensen would be fairly cheap, although I cannot vouch for how quality they are, because this is something I hear from others who work on ribbon mics.   If you want QUALITY, go with the Jensen or other high-end transformer manufacturers.

    

Classic RCA 44B
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A bit about my Mic...
 
I didn't use anyone's plans, designs, or ideas when making this thing.  In fact, I flew by the seat of my pants in the initial designing and manufacture.  It just happened that when I sat down to do the math and physics, everything worked out great.
 
If you are thinking about making your own ribbon mic, I urge you to use trial and error and intelligent designing of your own.  It makes the mic uniquely YOURS, and you'll be much more proud of it.

Some advantages of Ribbon mics
 
They sound very natural.  It is the nature of a ribbon mic is to pick up sound waves in a very "un-colored" way due to the physics involved.  The relatively slack tension on the diaphram (compared to a condenser diaphram) allows for a mostly un-colored wave pickup.
 
A ribbon mic has an extremely flat frequency response (depending on the design).  Other microphones require massive design departments and exact tolerances to achive this (aside from electrets, which are cheating), but ribbons do it naturally.
 
Also, can theoretically have a frequency response that is as wide as other types of microphones, but in practice, older mics rarely went above 10-15 kiloHertz with a great tolerance.  Now, with newer materials and refinements, frequency response is better than ever.  When I get an analysis of Spike done, I will post it.
 
The ribbon microphone naturally has a bi-directional (figure of 8) polar pattern.  They can be made to be directional through the use of sound-dampening chambers and through other means.  The "null" on either side is very effective to eliminate a sound source that is not desired from a recording or performance.
 
Ribbon mics USUALLY have very little difference in frequency response and in amplitude from one side to the other.  Also, the off-axis sound is not as colored as many other mic designs.
 
The smooth sound of a ribbon mic is pleasant and works well with many instruments.
 
They are passive and have almost no self-noise, making them a great companion for digital audio when a nice preamp is used.
 
They handle high volume situations gracefully.  As long as the air itself is not moving in a way to damage the ribbon, the microphone can handle it very well.  In fact, due to the passive nature of the ribbon mic, the louder a sound source is, the better (I have yet to distort this mic I have made through conventional high-volume means).
 
Contrary to a popular belief, ribbon mics are not "dead" after the ribbon has been destroyed or broken.  There are a number of individuals and companys that re-ribbon mics for an average 100-150 dollars.  Or do it yourself.
 
Ribbon mics are not affected by temperature or humidity like condenser microphones are.  They keep on truckin', pretty much no matter what.
 
They look damn cool. They are simple, sound great, and fairly difficult to screw up when constructing one.
 
 
 

Some Drawbacks of Ribbon Mics
 
They are easy to damage.  The ribbon is very, very thin and can easily be destroyed or stretched by a soft wind (even lightly exhaling on it, in some cases!).  This makes it NOT the best choice on a bass cabinet port, close kick drum, super chunky guitar, or the woman who won't stop panting into the mic.  As a general rule, put your arm next to the sound source.  If you feel more than a tiny amount of air movement with the hairs on your arm, don't put a ribbon mic there.  There are other ways to gauge, but the idea is that if you are in a situation where the position is questionable and you have to make a decision, then don't put it there.  It will save you some trouble.
 
They require a nice QUIET preamp to be useful in a pro situation.  Like I said, they are passive and have a very, very low output.  David Royer recommends using a very quiet preamp with at least 60 dB of gain for the best performance.  I find this to be true and accurate.
 
They won't sound as crisp as a condenser.  This is partially because of the much-less tension on the ribbon than on the diaphram of the condenser, and also because of the response nature of a ribbon assembly. 
 
Depending on the design, they can have a very pronounced proximity effect.  This has to do with the time it takes the sound to travel around the microphone to reach the other side of the ribbon in relation to the on-axis sound arrival (more in the physics part). This can be an advantage or disadvantage, depending on how you look at it, I guess. 
 
It's a good idea to use very good quality cable and/or very short cable runs to eliminate any noise, capacitance or impedance problem.  Being passive does not help much.
 
Ribbon mics are very succeptible to electromagnetic intereference.  In some ways, they are virtual antennas for EMI, but if they are shielded well, this isn't so much of a problem.  Condensers have this problem as well, though.  If you've ever heard a condenser mic with the windscreen off, you know what I am talking about.  Anyway, it is a good idea to keep your distance from anything that projects an EMI signal (if at all possible).  As an example, mine is quite succeptible to my TV and computer monitor, but ignores the stupid flourecent lights in my room, which I have had problems with in some of my other mics.
 
If you are going to be building a ribbon mic, then a definite drawback will be the price of a quality transformer, Unless you read more carefully later!!! 
 
 

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