All About Mics – Part I

If one is old enough to remember Saturday morning and after-school cartoons, back when cartoons were funny and not preaching social responsibility messages to the younger folks in society, peppered in and amongst the actual entertainment were the cheesy commercials that were preaching pure unbridled consumerism to the parents of the ones who get the social responsibility message preached to them so.

Ok, so enough of my grumpy middle aged guy tirade…one of the commercials that I recalled and had me pestering my parents to buy me was Mr. Microphone. It was a relatively cheap, plastic element that picked up one’s voice and converted the output to a weak radio signal that could be broadcast to a nearby radio receiver that would then receive the signal and output it through the speaker of the radio. The trick was that one had to tune the receiver to an in between, unused broadcast frequency, or even that AM radio signal from the one station in Moose Jaw, Saskatchewan, Canada would overpower the microphone’s signal to the radio ten feet away. Did I mention that this thing was weak?

Anyway, that got my young brain working and wondering how the thing worked. I wasn’t so much interested in the radio end, but rather the microphone part. Fast forward four decades where I now know way more than I wanted to know then.


Last week, I wrote about setting up a home recording studio and one of the things I mentioned was the need for microphones, as in the plural. I reckon that there are some folks reading this that probably don’t know much more about the subject than what I did as a kid. You walk up and address the mic on the stand or pull it off the stand and start speaking or singing into the thing. The guy running the sound board is the one doing the tech magic and all the user is interested in is if they can be heard or not and if performing, if the microphone is adequately doing its job of reproducing the singer’s voice without adding any Darth Vader or Donald Duck attributes to the performance.

Well, whether one is setting up their studio or they’re looking to upgrade to a better mic for performance, it helps to know more than just which brand names are good and which ones suck for the value of the money budgeted and what to buy in order to get the best performance out of the gear for the money spent. After all, that’s really what it boils down to.

Most of the time the sales people in a store will have your best interest at heart and then sometimes, they’ve been told by the boss to move the overstock, of whatever is inflating the inventory tax payment that’s coming due, no matter what lies need to be told.

So in this Part I, I’ll describe the three most commonly used classes of microphones, and in the upcoming Part II, I’ll describe what is known as a polar pattern and the frequency response quality, along with some common mic placement patterns and the type of mics used for such placement patterns. So let’s find out about the classes of microphones, or mics, to start.

Classes of Mics

Microphones are divided into descriptive monikers that describe the transducer element that picks up the sound waves and convert them into electrical impulses.

Dynamic Mics


The most common, durable and least expensive is the Dynamic Mic. These are what most live performers use when playing at a club, a church or anything in between in a community setting. It is a completely passive design that has a body containing the salient elements called the capsule. The capsule supports the diaphragm, usually made from a polymer that is coupled to a coil that moves pursuant to the sound waves impacting the diaphragm and said motion within the permanent magnetic field of the fixed magnet induces a current that is an electronic copy of the sound waves, that flow through a transformer to increase the impedance to a usable range (around 200 ohms) and to boost the signal by about 10 dB to be sent to the next stage in the chain, the preamp or mixer.

If this sounds reminiscent to a guitar pickup or a speaker in reverse, it basically is. These mics tend to run anywhere from $10 to about $150 dollars. There are cheaper (yes, they exist) and more expensive, but this price range covers at least 90% of the common offerings. The most useful and ubiquitous examples are made by Shure, the SM57 and the SM58. If you are even half serious, no make that one quarter serious about recording or performing, whether as a vocalist, have a need to mic your cabinet or as at least one element in micing your drum kit, you need to buy one of each.

There are cheaper mics, but as I stated in a previous column, for the money, there is no point in skimping a few dollars at an unknown and probably inferior mic. There are some that are $30 to $40 more, but why spend more than you have to when, as dynamics go, it’ll be hard to beat these. The SM57 is a great instrument mic and the SM58 a great vocal mic. They can and have been used interchangeably. I’ve seen SM57’s even strapped to the coordinator rod in the inside of an open back banjo on a semi-permanent basis to allow the banjo player in a Bluegrass, Country or Celtic Rock band to be heard. The only competitive mic that I can think of is the Audix I5 as a substitute for the SM57. I have all three.


Condenser Mics


A condenser mic is a different proposition. It requires a power source as it uses the electrical property of capacitance to do the job of transduction. Condenser is an anachronistic term for capacitor. So the condenser mic sorta, kinda works like a capacitor. I’ll get into the specifics of the how the microphone works in this context.

A capacitor has two conductors in the form of a disc or a plate for each of the conductors and a voltage is present between them. In a condenser mic, one of these plates is the diaphragm that moves when struck by a sound wave and is fabricated from a relatively lightweight material. This diaphragm vibrates as it is struck by sound waves, and the induced mechanical motion serves to change the distance between the two plates. This change in distance changes the capacitance; the resulting current flow, representing the changing capacitance, is a replicated electronic version of the sound wave.

Again, the signal flows through a transformer and to the mixer or the preamp. Condenser mics require something called phantom power to energize the capacitance. This can be from a battery, an external power supply, or most commonly a current supplied by the mixing board is generally the source. This supplied power is generally in the range of about 48 volts. Price-wise, of the common mics in use, condenser mics are some of the most common in the studio and tend to be the more costly given their ubiquity.

Ribbon Mics


Ribbon mics are actually one of the older types of mics and are used quite often to capture the beautiful and rich, full frequencied tones of acoustic instruments. While formerly, they were some of the more expensive types, the process has come down in the last decade or so, due to off-shore producers. These off-shore makers are not the best examples of the class, but they will perform as advertised and capture some of the tones that any ribbon mic is renowned for.

So what is a ribbon mic? Simply put, the diaphragm that is responding to the changes in the air velocity from the sound waves. This is different than the other types that respond to the change in air pressure. Why? Because this ribbon is incredibly light weight. It is an incredibly thin sheet, a ribbon if you will, of a metal such as aluminum or an aluminum-copper alloy. Other materials can be used as can basically any electrically conductive material that can be rendered as a nanofilm on a light weight substrate. The ribbon is corrugated and suspended between the poles of a permanent magnet and electrically coupled to an output stage, generally including a transformer that sends the signal out to the preamp or mixer.

The ribbon mic has the ability to pick up sound from front or the rear due to its almost double diaphragm quality. The one diaphragm is open to the moving air in the front and back and the current flow that is induced by the movement of the ribbon in the field is bidirectional. This allows for some useful placements.

The one traditional downside is that because these ribbons have an almost gossamer-like constitution, the SPL in dB’s, or loudness they could tolerate, made them susceptible to instant death by loud sound sources and physical shock. Drop a dynamic mic and it’s no big deal. Drop a ribbon and kiss it good bye unless someone has a repair kit and the knowhow in repairing one of these.

Parking an old school ribbon mic in front of a 4x12 Celestion loaded guitar cab with Nigel Tufnel’s amp that goes to 11 is like putting a man in front of a firing squad. Now the newer ribbon mics have a much improved ability to withstand high SPL’s and are more resistant to mechanical shock. Still, I handle mine with care.

They do not require phantom power as a condenser mic and some ribbons take to phantom power like a man in the chair when the guard throws the switch. The newer ones have built in protection in the circuitry and some ribbons will require phantom power, not for the mic element itself, but for a built-in preamp. So in those cases phantom power is not death to the mic. Again, I still treat my one ribbon as though it’s a vintage RCA from 1940. Why chance it?

Conclusion

So those are the three primary microphone types that make up the majority of what’s out there and what most will purchase for live or home studio use. Next time we’ll delve into the different patterns that microphones are designed to pick up sound from, the two basic frequency response types and a few of the common placement and configuration patters for mics.

These patterns often depend on the use of the mic pick-up pattern, the frequency response and the type of element in the mic. As to Mr. Microphone - it was a piece of crap that impressed bored and music tech ignorant kids. Still, I’ve found ways to have fun with the professional wireless counterparts and if time and space permits, I’ll relate an amusing anecdote.

-Kirk Bolas - MU Columnist
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