Friday, April 30, 2010

Microphones and Accessories


One cannot make an audio recording without a microphone. It's that simple. For stereo, you need two identical microphones. You also may need more than that for highlights and ancillary ensembles such as vocal choruses and soloists. 

Ask any ten recording engineers what microphone techniques they favor, and you'll get at least thirty answers. Everyone has their favorites, many are variations on the same ones, some might seem downright bizarre. But they must work, or they wouldn't be mentioned. When we get to that part of the discussion, I will tell you my favorites and explain all of the basic ones. Microphone placement is an art, an art that is learned through experience. But before you can fly, you have to walk, so we will start with microphone types suitable for recording.

Microphone Types

There are two basic types of microphones used in recording today, the condenser mike and the dynamic mike. Years ago, amateur recordists used several other types. One type was called a piezoelectric mike, often referred to as a crystal or ceramic mike and the fourth type of microphone that recordists used to use was the carbon-button mike, ubiquitous in the 40's, 50's and even the 60's neither of these latter types are used any more. 

Dynamic Mikes

Of the types of mikes used today, probably the easiest to understand is the dynamic mike. These microphones work by moving a membrane connected to a coil of wire in a magnetic field - like a loudspeaker in reverse. The sound strikes the membrane (or diaphragm) which causes it to vibrate in sympathy with the sound striking it. This causes the coil of wire to move with it. The coil, cutting across the lines of force set-up by a permanent magnet, induces a minute electric current to flow through the coil wire. This current is analogous to the sound waves striking the diaphragm. This current is amplified and can then be sent to a public address system or to a recording medium. Dynamics of this kind are often used as PA mikes or vocalist mikes. They are valued for their ruggedness and dependability and simplicity. 

A variation of this principle is called a ribbon mike. Instead of a diaphragm and coil, the ribbon mike uses a long, thin ribbon of some lightweight foil. The ribbon is usually folded like an accordion to get more surface area. The ribbon is suspended between the poles of a very powerful magnet. When the ribbon vibrates in reaction to being hit by sound waves, it, again, cuts across the lines of magnetic force and a weak current flows along the ribbon. Both ends of the ribbon element are connected to a transformer which steps up the tiny voltage created by this current flow and matches the ribbon's impedance (which is extremely low, usually less than an Ohm) to the microphone cable and amplifying circuit. Ribbons have such feeble output that they require a lot of amplification before they are useful. Even so, throughout most of the history of commercial broadcasting, ribbons were the preferred microphone for most radio stations. The RCA 44BX microphone, which is usually the mental image most people conjure-up when they think of a microphone, is, in fact, a ribbon mike.


The famous RCA 44BX. For almost two decades this mike was the voice or both radio and television broadcasting and most recording done here in the United States. To many people, this is what they think of when someone says the word "microphone". 


Ribbons are almost always bi-directional and pick up sound equally from both the front and the back. Due to the thinness of the ribbon, they are easily damaged by blowing into them or using them out of doors on a blustery day. While ribbons like those from Royer can be made with outstandingly flat frequency response (and concurrently high prices), most ribbons don't have a lot of top end. They are good for instruments with lots of midrange such as choruses and perhaps acoustic guitars. They are often valued for their very natural, warm sound and make beautiful announcer mikes (as long as the announcer doesn't blow into them).

Condenser or Capacitor Microphones 

Probably the most often used microphone for recording is the condenser or capacitor mike, as they are sometimes called. These mikes have always offered the highest performance and most accurate translation of sound to electrical current of any microphone technology. Although, condenser mikes have been around almost as long as has radio broadcasting and "electric" recording, really good ones, of the type we now associate with the technology, didn't appear until WWII Germany.

The Germans had developed two technologies during that war that absolutely dumbfounded the espionage types in England and other Allied listening posts. German radio stations would be broadcasting concerts of, say, the Dresden State Symphony Orchestra on nights when the Allies knew for a fact that Dresden (or Berlin, or Cologne, or Munich) was, at that moment. under heavy air attack. Two other characteristics of those "phantom" broadcasts puzzled the Allied listeners: The concerts were broadcast without breaks, tics and pops, and without the "scratchy" sound that usually accompanied transcription by phonograph record. The then only known method of recording sound for later broadcast. Add to that the fact that the recordings sounded so life-like and clear; they must be live!  It wasn't until after the war, when the Allies occupied Germany and went into their radio stations did they find the answer to this puzzle. The Germans had perfected the audio tape recorder, which, due to several German innovations (like AC bias for recording) turned out recordings that were unparalleled in their wide frequency response, low distortion and noise. The second thing they found was that the research arm of the German broadcasting ministry, Telefunken, in collaboration with the Georg Neumann company, had perfected the condenser microphone. Georg Neumann, another condenser mike pioneer,  had actually invented the modern condenser mike in the early 1930s. Called the Neumann "Bottle" it was used throughout Germany and developed all during the war. In 1947, Neumann came out with the famous U47 (also sold under the Telefunken name), which, along with the later U87 became the ubiquitous form factors for condenser Mikes. So much so, that most condenser mikes today, irrespective of what they cost or where they are made, look like one or the other.

After WWII, both Telefunken (Left) and Neumann (right) came out with the first successful condenser mikes for recording, the U47. Here in the USA, they unseated the RCA 44BX as the microphone of choice for recording and broadcasting, ushering-in the era of high-fidelity - just in time for FM broadcasting and the LP. 

Operation

The condenser mike works in one of two ways. Both types work because the diaphragm and the back plate of the microphone element form a small capacitor of about 40-50 picofarad. In the most common application, this capacitor is charged with a polarizing voltage which is used to control an amplifying device such as the grid of a tube, the base of a bipolar transistor or the gate of an FET. The sound striking the diaphragm varies the capacitance of the mike capsule coupling more or less voltage to the control element of the amplifying device causing that device to conduct either more or less and the resultant signal is analogous to the sound striking the diaphragm. The second method uses a similar capacitor to the above example, but instead of that capacitor controlling the coupling of voltage to the microphone circuitry, this second method has the capacitor as part of a tuned RF oscillator circuit. The audio, striking the diaphragm, changes the frequency of the oscillator, also as an analog of the sound being picked-up. At the output of the microphone, a detector circuit called a discriminator strips the RF frequency from the signal leaving only the audio modulation. This works a lot like an FM radio, and indeed,  is often called an FM microphone. While there are still some FM microphones being made, most condenser mikes are of the first type.


The biggest drawback to the condenser mike has always been it's requirement for an external power supply to polarize the capacitor mike capsule and to drive the electronics. Pre-solid-state, most condenser mikes relied upon dedicated power supplies and special cables with multi-pin connectors to connect the mike to the supply. These cables had to carry both the audio and the various voltages such as the B+ and filament voltage for the tube(s) as well as the polarizing voltage for the capsule. Generally speaking, the link from the power supply to the recording console was via standard XLR cables. Extension cables between the mike and power supply were non-standard and usually quite expensive. After condenser mikes became solid-state, in the late 1960's, the separate power supply was abandoned in favor of so-called phantom power. Phantom powering uses 48 volts (this came from the telephone industry) DC which is piggy-backed on the same wires that carry the audio from the microphone to the mixing console. The DC doesn't affect the audio and today, most mixers have the 48 volt phantom-powering power supply built in. More expensive mixers allow you to apply the phantom-power individually to each microphone input, while cheaper mixers merely allow one to turn it on or off globally to all microphone input circuits. 


The Electret Condenser Microphone


In the late 1960's after solid-state electronics became possible inside the microphone itself, the need for tubes and the high-voltages they require was obviated. This allowed practical application of a type of condenser microphone capsule called an electret. An electret is a stable dielectric material with a permanently embedded static electric charge. Due to the high electrical resistance and chemical stability of the materials used, the electret device will retain it's charge for hundreds of years. Although the electret principle was discovered in the 1920's, it didn't become practical until two Bell Labs engineers designed one using a thin Teflon coated metal foil as the electret in 1962. The combination of the two maturing technologies, the materials technology for the electret itself, and the use of the FET transisitor for the amplifier, suddenly made this kind of microphone practical. Due to the fact that an electret condenser microphone does not need a polarizing voltage, and the FET amplifier in the mike draws very little current, suddenly, small, cheap condenser mikes which ran on batteries became possible. The biggest application for these mikes, became, of course, in telephones to replace the century-old carbon button mike. The improvement in voice quality was apparent to everyone who heard one of the new electret miked phones.


Schematic of a typical Electret Condenser Microphone showing how simple it is. Often, these mikes can be powered by a single watch battery yet provide long battery life and better performance than the cheap carbon, crystal, or dynamic mikes that they have replaced. 





 It wasn't long before companies like Sony, in Japan, were applying electret principles to recording microphones. In the early 1970's, Sony introduced the ECM-22p a professional quality electret that could be powered by either a nine-volt battery or via standard 48-volt phantom-powering. The ECM-22p sported rugged build quality, and surprisingly decent frequency response. Sony spec'd the mike at 40-15,000 Hz, but I've found that the two that I owned to be rather bass-shy. However they are great on the top end and midrange and make excellent drum mikes. After having owned them for almost 30 years, I can say that they still work as well today as the did when new (although the Eveready #206 9V batteries are somewhat hard to come by these days - thank Sony for making them standard phantom-power compatible).


Early pro electret condenser Microphone the cardioid Sony ECM-22P

Although a number of electret microphones for pro use have been made, most are small-capsule mikes designed for the low-end consumer market. When I was in Japan a number of years ago, I picked up a Sony electret single-point stereo mike (ECM-929) to use with my Walkman-Pro cassette recorder. This mike has been excellent with it's M-S pick-up pattern and adjustable soundstage width. But like most electrets, it's tiny capsules make it a bit shy on bass and definitely suited only for casual recording (see the second installment of this blog for a picture of this microphone photographed with a Sony MiniDisc recorder).  


Modern Condenser Microphones

For most of the post-war era, condenser microphones were considered the Rolls-Royce of microphones. They cost a bundle. Even today, A Neumann condenser mike like an M149 can easily cost close to $6000! When I was in the recording business in the 1970's I owned a pair of "cheap" Japanese condenser microphones from Sony called C-37Ps. These had an FET amplifier in them and a single capsule that was switchable between omni-directional (non-directional) and cardioid (uni-directional). They cost well over $1000 in 1975 dollars and were considered inexpensive compared to Neumann, AKG, and Beyer condenser mikes of the time. 

Sony C-37P FET Condenser Microphones were considered "inexpensive" at about $500 each in the mid 1970's. They are still very good microphones, by the way and command top-dollar when they show up on the used market. 

Enter the Chinese

From 1949 until the death of Chairman Mao Tse-Tung, China was a closed country. They did not trade with the west, and, essentially, had no consumer markets as existed in the west. Like the Russians, the Chinese reverse-engineered (read that "copied") essential technologies from western manufacturers and simply made their own. One of these technologies was microphones. All the best condenser mikes had "Chinese copies" and they were used in both broadcasting and recording. When the Bamboo Curtain fell in the 1980's, it was found that these copies of Neumanns, AKGs, Telefunkens, Scheops, Sennheisers, Beyers et al, were actually not half bad, and available for mere pennies on the dollar compared to their western counterparts. 

As soon as trade agreements with western companies became possible, many people decided to have their own microphone designs built in China. That brings us to the present glut of excellent and cheap condenser microphones which not only are well made, but actually perform very well. It is possible to buy Chinese-built microphones from firms such as Avantone, Behringer, Samson, Rode, and many others. 

Most of these mikes are better than the classic mikes from which they are copied. The reason is that the classic Neumann and Telefunken models (not to mention AKG and Beyer) had acid-etched brass diaphragms, which, while thin and light by the standards of their day, are today, so massive that they gave these microphones a peaky, rising top end which can sound harsh, especially when used to record digitally. Modern condenser microphones, including Chinese ones, have diaphragms made from a thin Mylar plastic which has been "sputtered" with an atom-thick coating of either aluminum or even gold. The metal coating on the Mylar makes the diaphragm a conducting capacitor plate without adding any weight. The resulting diaphragm is so low in mass that it's fundamental resonance (the characteristic that gives the older mikes such an aggressive top-end) is pushed way up into the ultrasonic region of the audio spectrum, where people cannot hear it. Modern mikes, even inexpensive ones, therefore tend to have a smooth, clean sound that shames most older designs. 

One Chinese made mike that I have used and found to be just about the best mike I've ever used  is the Avantone CK-40. This stereo mike has switchable patterns between omni-directional, figure-of-eight, and cardioid and is actually two microphones in one case. The top element can be rotated either left or right 90 degrees (for a total of 180 degrees relative to the lower element). Physically, it is a close "copy" of the famous (and fabulously expensive) Telefunken ELA-M-270 from the 1950's which is still made and can still be purchased new from Telefunken USA for a mere $16,000. The CK-40, on the other hand lists for about $600 and instead of being tubed like the Telefunken, features an ultra-quiet FET preamp. 


The Avantone CK-40 (right) can be said to be a virtual "Chinese copy" of the famous Telefunken ELA-M-270 (left shown without its shock mount). Having used both an original ELA-M-270 and the CK-40, I can tell you that while both microphones are good, the Avantone is much better and, in fact, is one of the best sounding microphones this writer has ever heard.


Choosing Microphones for Your Own Recording Set-up


There are a number of characteristics that one needs to keep in mind when choosing microphones for recording. Generally speaking, the larger the capsule diameter, the better the bass. Most decent condenser mikes, these days have at least a 1-inch capsule and I would consider this a minimum for any mike that will be used for general coverage of an orchestra, symphonic band, or any ensemble with a wide range of instruments needing a solid low-end foundation. Affordable microphones that meet this criteria are, happily, fairly abundant. The Samson CO1 at around $80 is an excellent entry into this type of so-called "big-capsule" microphone as is the SM-ProAudio MC01. Both of these cardioid-only microphones are excellent performers and superb values. For multi pattern mikes, the $150 Samson CL8 is a very good pick and offers a choice of cardioid, figure-of-eight, and omnidirectional patterns. Also in this range is the excellent Behringer B-2Pro. All of these mikes have excellent, wide frequency response and solid bass performance. Of course, I cannot heap too much praise on the aforementioned Avantone CK-40 stereo mike. This dual-head single-point stereo mike has large 35mm diameter capsules and among the best low-end performance that I have heard. When coupled with this mike's smooth midrange, clean, flat top-end and wide dynamic range. it's hard to beat - at any price.


Behringer B-2Pro multi-pattern, large capsule condenser microphone shown with included accessories

There are always going to be situations where you are going to need more than just a single stereo-pair of microphones to get proper coverage of the ensemble you are recording. When recording a jazz big-band recently, I found that the stereo pair was not picking up enough of the piano. Listening to the ensemble play from the audience perspective, I could hear the piano, but when listening to the mike feed on headphones I could not. This necessitated the use of an auxiliary microphone on the piano and mixing the result into the overall pick-up from the stereo-pair. To do this I used a single cardioid SM-ProAudio MC01. This mike was placed low so that it just "peaked" over the edge of the grand piano and was aimed at the center of the raised top. I pan-potted the mike to the extreme left (the piano was on the extreme left side of the band) and raised the level on the mixer input so that the piano could just be heard in the headphones. The results were perfect.

This means that you are going to need more than just one pair of microphones. It is not necessary that these mikes have the bottom end of the main mikes as they are usually just for accent. Sometimes there will be vocalists involved and these mikes will work fine for that as well. A typical microphone complement for a modest amateur recording "kit" might be:
1- Avantone CK-40 single-point stereo mike (or equivalent such as a pair of Behringer B2 Pros on a 'T-bar'.
2- Behringer B2 Pro multi-pattern microphones (or equivalent switchable pattern mikes).
2- Samson CO1 cardioid large capsule microphones or M-ProAudio MC01(or equivalent)
2- (a matched  pair) of "lipstick" small capsule microphones (Behringer C-2, C-4 or equivalent)

 
Author's Microphone complement for location recording. Each mike has proved itself to be rugged, well made, and a good performer. 

Needed Accessories

Missing in the above pictures are two very important components. The first is microphone cable. Since you never know where you are going to end-up, it is important to always have enough. My rule of thumb is to carry 4 -50' lengths, and eight 25' lengths. This looks like a lot, but I'd rather carry too much than too little. It is rare that you'll ever need more than three or four microphones for any one gig, but you never know what you might run into or how far away from your microphones that you'll be setting-up. 

Cables

Now, about cable. Naturally, it needs to be balanced microphone cable with decent quality XLR connectors; a male on one end and a female on the other. Other than that, if you buy from a reputable source such as Shure or Hosa, you can be assured of getting decent quality. Let me clear something up about cables right now. I spent years in the aerospace industry as a wiring/cable engineer for some of our country's most leading edge rockets and satellites. I have studied wire thoroughly and I can tell you this, just between you and me: at audio frequencies, wire is wire. Oh, I know, you can spend a fortune on cables from high-end audio cable companies, but it's all bling; stuff and nonsense. No double-blind cable test has ever revealed any difference whatsoever between expensive and cheap cables. Audio cables have no sound of their own. So buy well made, reliable cables from reputable sources and don't worry about the rest. One thing is important, however, and that is to use runs as short as possible and keep the number of connectors between the console and the microphones as low as possible. In other words, one long cable is better than two or three shorter ones connected together. 

Mike Stands

Now you need something to set the mikes on. Floor stands are fairly cheap, and the best kind for location recording are the folding kind. I use four of the Euroboom OS13 stands. These microphone stands have a folding, three legged base and a column which raises to about 63" and a boom that gives another 33" of extension. They weigh only about 5 pounds each, fold very compactly and can be bought online for about $30 each. For the big (and heavy) stereo mike, I use either a Euroboom with sandbags on the legs (for stability) or I use the foldable StuBoom from On-Stage ($120). This stand extends to 80" and the counterweighted boom gives another 82" of extension. This stand is heavy, and large. I only use it where I have the room for it and I don't carry the boom very often because it won't fit in my car very comfortably (being almost 7 ' long). But it is there when I need it. Check around, you can find some very decent mike stands out there. If you have a music store in your area, you might ask them to be on the lookout for used stands for you. I once bought a huge studio boom with a cast iron base for $20 at a local music store. New ones are almost $300 today. I ended up giving it away because I couldn't easily carry it around. Deals are out there.

Next time we'll talk about microphone pick-up patterns and how to mike various instruments for best effect.









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