Thursday, December 28, 2006

The Myth of the Ribbon Microphone - Exposed! part one

"Faceless ancestors who dance about the fire of knowledge, their long shadows cast close behind them."


Be sure to read PART TWO, also. Link HERE

Before objective knowledge there was dancing, fire, and superstition.

"The Knowledge" of a London cabbie consists of a complete mental map and image of the the city roads and byways and those with The Knowledge are then qualified to transport via black cab any passenger to any location within London.

The Knowledge of Ribbon Microphones - A Codex inscribed herein for posterity - consists of the true facts and explanations about the mysterious and sometimes ancient mythology of the revered and sometimes reviled ribbon microphone.

The Myths are many and the tales told are handed down over the generations of recording aficionados and repeated almost as prayers in the scripture of the ubiquitous message boards, where no false word is ever erased, and lore is mixed with fact, fiction, lies, myths, heresy, pure falsities, and half-truths.

And then there is the phenomenon of repetition, whereby the truth is manufactured, where errors are repeated, often over and over, until they become accepted facts, despite the lack of supporting evidence. Like parrots, the falsehood is recanted, passed down through generations, and finally accepted without question.

Here are a few myths to get us started:

Vintage Myths - those myths based on lore, history, and New Old Stock

Myth: "Nothing sounds like/as good/mellow like an old RCA 44, 77, (insert an old mic here)"
Fact: These mics were good and produced excellent sound, but have low output and relatively high noise levels, and are highly variable. Most of the vintage ribbon mics have a steep roll off beginning at 10 KC. If you can put up with unpredictable performance, they may be for you. I have three RCA 77DXs here in the lab at the moment. You can bet they sound good, but different.

Myth: "Such and such has New Old Stock ribbon material (magnets/grille cloth/blueprints/uncle/DNA) which is the best"
Fact: Old ribbon material is likely to be inferior to modern materials. Aluminum oxidizes slowly but corrosion can produce pinholes, while precipitation (age/heat) hardening causes embrittlement, and fracture. Present day aluminum is produced in precise thickness and with better purity than was available even 20 years ago. This is due to demand for thin foils in other parts of the electronics industry, such as capacitors.

The Saggy Baggy Ribbon Myths - Things may droop over time, also with ribbons?

Myth: "Ribbon mics should be stored vertically".
Fact: No. The weight of a typical "large ribbon" is around 0.0018 grams, and a thin ribbon is about 1/4 that. If that is enough to cause sagging, then something is very wrong. Ribbon microphones of any vintage can be used and stored in any position.

Myth: "Just closing the case will blow the ribbon"
Fact: This is quite doubtful. Once again, if the air pressure is enough to damage the ribbon then most of ribbon microphones out there today are already blown. Several manufacturers including us supply ribbon microphones in horizontal cases with top lids. I think you would have to try to slam it very hard, over and over, to show any change to the ribbon tension.

Myth: "Crowley and Tripp uses a vertical storage box to prevent ribbon sagging."
Fact: We did this so you can see it and because we thought it looked better and was more convenient, and that it might cause the user to grab it from the mic locker more often rather than laying flat in the dark recesses of the cabinet. You can lay the box down on its side, turn it upside down - it doesn't matter at all because gravity has only the most minute influence on the ribbon.

Myth: "All ribbon microphones are fragile"
Fact: Modern ribbon microphones are not at all fragile.

Myth: "Move the ribbon mic slowly"
Fact: Nonsense. I saw an intern walking across the studio holding the microphone like it was a lit candle. This was very amusing.

Myth: "Loud sounds will shatter the ribbon"
Fact: Loud? Not loud like loud music loud, at least. No. Detonation of high explosives, maybe. Do not try this.

Phantastic Phantom Myths - Images of smoke, fire and destruction.

Myth: "Phantom power will destroy a ribbon microphone"
Fact: Not usually. Phantom power correctly applied does so evenly, so there is no net force on the ribbon.

Myth "Phantom power will not destroy a ribbon microphone"
Fact: Usually. Phantom power can stretch an aluminum foil ribbon. Any signal that is applied unevenly, such as 1. through a patchbay which is a bad idea anyway, or 2. by hot swapping cables, WILL boink the aluminum foil ribbon in passive ribbon mics.

Myth: "Phantom power will demagnetize the magnets"
Fact: I had to include this one since it was so interesting, and impossible.

Oft-Repeated Mythicisms - merely annoying, or insidiously harmful?

Myth" "Ribbon mics are dark sounding"
Fact: Some are, more modern ones are less so, and a couple are neutral to bright sounding. You choose.

Figure Eight Type Myths - fundamental things about sound in general actually...

Myth: "The back of a ribbon mic is usually brighter than the front"
Fact: This is definitely not so. Most good quality ribbon mics, ours included, are perfectly symmetric in response. The only difference from front to back, of course, is the phase. We think it's slightly embarassing at times to have to explain why this sounds different to people wearing headphones. No offense! Avoid uncomfortable social gaffes and use your phase reverse switch.

Exceptions: Naked Eye is intentionally asymmetrical in response with a 3dB average 8-12 KC presence rise off the back, with no dips. (recall the embarassing phase cancellation phenomenon causes some people to misunderstand). The so-called "offset ribbon designs" are unintentionally different in tone color from front to back, I suppose because the distance from the mic body and screen to the ribbon varies from side to side. Intentional or not, it can be useful. The RCA 77DX is rather asymmetrical even in the figure eight position. This is a problem inherent in the 77C, 77D and 77DX because the local field around the ribbon motor isn't quite symmetrical to begin with, which is intentional because it is a multipattern mic.

Myth: "Ribbon mics have low output"
Fact: Modern ribbon mics have a HIGHER output than most stage dynamics. Remember that a condenser capsule has NO output and depends on the internal active electronics which are essentially a high gain voltage amplifier.

Myth: "You need a preamp with tons of gain"
Fact: No. Not only is the answer "no" but you can use your preamp wide open and unrestricted because ribbon microphones have extremely low self noise.

January 10 2007 note

Aha! I see we have stimulated a little debate about sensitivity. This is good and an opportunity to spread some numbers around.

A modern ribbon mic might be represented by a Studio Vocalist which has its stated sensitivity as -50db. This is from the standard that uses a 1 Pascal SPL at the source where 1 Pa = 94 dB, which is a little bit loud, and by measuring the actual open circuit voltage measured right at the XLR connector. You can do this measurement yourself very easily with a good multimeter, and perhaps I will take pictures of the setup and write a how-to soon.

Anyway, compare these two:

Studio Vocalist -50 db which is equal to 3.1 mV/Pa
SM57 -56 db which is equal to 1.6 mV/Pa

The Studio Vocalist appears to be more efficient at converting sound energy into an electrical voltage. What does this mean as far as "knob" gain? perhaps just a little. Can you use an SM57 with your preamp? Let me know, because if you can then you should have plenty of gain for a modern ribbon mic. If not, please let me know that, too.

In all fairness I am comparing a figure eight patterned mic with a rather big aperture to a cardioid dynamic with perhaps a little bit smaller aperture, so the two may actually be closer than the numbers. Still, here is one example of a ribbon mic with an output higher than something that you may have already used, so use your own judgement.

10 comments:

Anonymous said...

It would be interesting to see the figures and plots that bust the myth.

Bob Crowley said...

Let me knw which myth you are referring to as there are many listed above.

We have loads of numeric data on things like this.

There is also data here on the blog, for instance polar plots that show the front - back of Naked Eye, and comparative 77DX vs Proscenium frequency response/sentivity.

Anonymous said...

some modern low cost ribbon mic have low output so what about them? Why MUST you hve hi output.

Anonymous said...

To the previous comment I say: the more output means that the noise is gone and that the small sound come through pretty easily !

Anonymous said...

Condensers will still have the advantage on quiet sources and where you need the lowest noise. Ribbons cannot produce the output needed for these sources.

Bob Crowley said...

You've got to be kidding, right? The self noise is around 12 dB, and the noise immunity of our mics is extreme. This gives you a dead silent signal into a properly cabled preamp with a quiet front end. The silence is amazing in fact. The sensitivity is higher than a dynamic.

I still think you are kidding, whoever you are.

Bob

Warren said...

Hi...

What a great blog concept. Anyway, the phantom power myth busting seems a little shaky in your mind as you say "not usually" and "usually" regarding destroying a ribbon. So, do you avoid exposing your ribbons to phantom power and if they are exposed accidentally, do you worry?

Along the same line, would you be concerned about checking a ribbon microphone with a multimeter? I've read that this can also, maybe, usually, not usually, fry a ribbon. Tell me it isn't so...

Regards...

Bob Crowley said...

Hi Warren,

No it's not shaky, it's just that things aren't all that simple.

Most of the time, phantom power won't damage a ribbon mic. BUT, sometimes it can.

The myth is that it is one way or the other, absolutely. It isn't absolute. Sorry, no black or white answer to that one.

An ohmmeter can stretch a ribbon and there isn't much reason to use one on a ribbon mic anyway. Use your multimeter to measure the voltage output, not the resistance.

I worry about a lot of things, but not ribbons. Just like any other device, car, bike, etc. you are always better served by running them the right way.

Anonymous said...

The Coles 4038 is definitely very fragile. I learned from my own experience that the ribbon is very easily damaged. I don't quite understand the appeal of these any more.

Marc said...

Great post Bob and as a DIY ribboner (!) I have a boxful of bits that can surely attest to everything you've said.

The only noise problem I have comes from the amplifiers - which I'm in the process of redesigning because these modern OP Amp types produce too much noise from the front ends - presumably using either Mosfets or crummy bipolar tech.