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Live Sound 101: Choosing A Mic

Sound guys wear T-shirts. Usually black ones. And they typically display a line of text that’s a variation on the phrase: “I know what all the knobs and buttons do -— and it took a long time to learn.” That knowledge was what separated sound techs from performers.

Things have changed. The digital recording revolution has made it possible for performers to be more involved in their recordings at every level from the bedroom demo to the full-blown, major-label production. The curious side effect to this is that they are taking the tech that they learned in the studio and applying it to live shows, and some of them are very good at it. John Mayer, for example, can—and does—call problem frequencies from the stage and make very specific EQ requests to his sound tech at the mixing board.

But let’s get down off the big stage and apply this to the level of most working singers and musicians. Here it comes down to more of an issue of pragmatism than anything else. If you have to carry your own production (lights and sound), you’d better know how to set it up even if someone else will run it and—let’s face it—some clubs hire sound guys based more on their familial relationship with the owner than for any actual knowledge about how to create a proper mix.

HOW DO MICS WORK? Click here -

Garbage In = You Guessed It

 Think of a sound system as consisting of three parts: (1) the source; (2) the output; (3) everything in between. I know it sounds simplistic but stay with me here.

First, Let’s Talk About Transducers…

 If you didn’t sleep through all of your high school physics classes then you probably remember that energy can be neither created nor destroyed but it can change forms. A transducer is something that converts one form of energy (in this case,  acoustic energy or moving air) to another form (electricity).

There are transducers at both ends of a sound system. Your microphone converts acoustic energy (moving air) to electrical energy and a loudspeaker converts electrical energy back to acoustic energy. Everything that happens in between can be thought of as some sort of processing. And I do mean everything—be it adjusting the relative volume  of a certain source in relation to other sources (mixing), changing the strength of certain frequencies in a source (EQ or equalization), adding effects (reverb or delay), or compressing the signal. Even the amplification of the signal into something with enough power to drive a loudspeaker and move air is just another way of processing the original source.

So everything starts with “the source.” In layman’s terms, this is the instrument or voice. To the sound tech, it’s the device (human or manufactured)  that introduces the signal into the system. Sometimes this is a direct signal-like one from an electronic instrument such as a synth (in which case there is no transducer at the front end)—but most often it is a mic.

Highlight this point: If your mic(s) is not up to professional contemporary standards (it sucks!) it is highly unlikely that anything you play or sing into it will sound good.

Let’s Buy a Good Mic!

 While a vocal mic is a very personal choice for most singers, there are some guidelines that apply no matter what your career level or musical style is.
Mics come in a lot of different flavors but for our purposes we will limit things to dynamics and condensers (yes! he said with a nod to his ribbon-worshiping friends, there are some folks using ribbons—including rockers such as Aerosmith’s Joe Perry who uses Royer ribbons on his guitar amps—and they sound great; on the downside they are both too expensive and too fragile for the stage).

But this is not an article about mics, so here are the bare basics. A dynamic mic uses a magnet and a diaphram. The movement of the diaphram causes changes in the magnetic field between it and the magnet. This changing field creates a varying, low-voltage signal. A condenser microphone is similar except it uses a charged plate instead of a magnet. As a result, the mic needs power to work (typically 48 volts). That power can come from a battery or an external power supply but most often it comes from the mixing console. This is what is called phantom power; and buying a mixer without this feature is shortsighted.

When it comes to sound, general thinking says a dynamic is more road worthy but less detailed, especially in the high end. A condenser is more fragile but puts out a more “detailed” signal. Most dynamic mics also exhibit a trait called the “proximity effect,” which causes the low frequencies to be emphasized as the sound source gets closer to the mic. This is part of the reason why sound guys bitch about “mic eaters,” although being too far from the mic is just as bad (not enough energy getting to the transducer) and some artists use the proximity effect as part of “their” sound.

That is as “techy as this part is going to get, but before we put the ribbon on this first installment in the series, let’s talk about direct boxes. Instruments such as acoustic guitars with built-in pickups and keyboard can plug straight into an amp and—theoretically— straight into a sound system as well. But, for a variety of reasons (that we will get into later—including the difference between balanced and unbalanced signals and what that means in terms of signal quality and noise) they usually go through a direct box first. In simplest terms, a direct box is the nonmic signal version of a mic except that, instead of converting energy, it turns the original signal into something the system can better work with.

Once again, quality matters. Some good guitar and bass amps have built-in direct outs that sound very good. This is more common on bass amps but the ones on Line6 guitar amps generally sound just as good as a mic (some sound guys and guitarists may put a contract out on my life for that statement but, in my experience it is true). There are lots of good direct boxes available so we are not going to get into brands, but do some research before buying.

The best research is to talk to sound guys who are good and who— you respect and ask them what they like. Asking the guy behind the counter at the music store may work for you, but bear in mind that that person may or may not have any real sound experience and may or may not really know what he is talking about. I have met some guys in music stores who are an absolute wealth of knowledge. I have met others who would not know a direct box if it jumped up and bit them in the butt.

So, now we have a source and have converted it into a signal the sound system can use. Next step is getting that signal to the console, and that means cabling and wireless. Next issue. Same bat time. Same bat channel.

*Don’t Try This at Home—Unless You Want To

Got an old microphone lying around the house? Just for grins, plug it into the headphone jack of your CD player — Hear anything? This works in reverse as well. Plug a headphone into the mic input and sing into it. Granted, the quality is pretty poor, but it does illustrate the point.

 

About the author

Bill Evans