Perspectives of a Writer and Musician

Issues related to writing, publishing and playing jazz music: One man's muse.
by Al Stevens

My Photo
Name:
Location: Florida, United States

Monday, May 22, 2006

All You Never Wanted to Know About Microphones

There are many different kinds of microphones for all kinds for applications. These kinds range from the cheapest small microphone that you plug into your computer's sound card for voice mail through the most expensive studio microphones. This article attempts to explain the kinds of microphones you might encounter as an entertainer and demystify some of the jargon that identifies microphones.

Microphone Stands

The typical microphone setup has a traditional handheld microphone mounted in a stationary stand. You position yourself near the microphone when you perform. Many ventriloquists prefer this configuration. Others find it limiting because it is stationary, and their act requires them to move around the stage.

Headset Microphones

A headset microphone is mounted at the end of a support that attaches to your head and wraps around your face. The microphone is directly in front of your mouth. Some varieties of headset microphones are flesh colored to blend in with your face.
Many ventriloquists swear by headset microphones because they facilitate freedom of movement around the stage and provide the best sound pickup for such acts. Others hate them because there's this permanent appendage on their faces. You'll have to decide for yourself.

Lapel Microphones

Lapel microphones are designed for lecturers. They are usually of low quality and generally not acceptable to ventriloquists because their quality is poor, their position is too far from the speaker's mouth, and they are omni-directional, which means they pick up ambient noise.

Microphone Holders

A microphone holder is placed around your neck and has a holder in which you can insert a handheld microphone. It offers the advantages of a handheld microphone but leaves your hands free for other things.

Wireless Microphones

A wireless microphone has a built-in transmitter. The receiver is a separate box that plugs into the amplifier. Handheld wireless microphones, which can be mounted on a microphone stand or in a microphone holder, have the transmitter built into the microphone shaft. Some headset microphones are wireless.

A wireless microphone has no microphone cable, which is an advantage because you are not tethered to equipment and there are no cables on the floor to trip over.

Microphone Impedance

The impedance of a microphone is how much of a current load it puts on the amplifier. Microphones come in two impedances, high and low. Dual impedance microphones have a switch that changes the impedance. High impedance microphones have high resistance, which limits the current flow, and limits the operating length of the cable to about twenty-five feet. Low impedance microphones have low resistance, which allows a higher current flow. The cables for low impedance microphones can be much longer than those for high impedance microphones.

Phantom Power

Some microphones require an external power source, which the amplifier supplies in the cable. This power source is called “phantom power.” Some microphones have flashlight batteries embedded in the microphone shaft and provide their own power.

Condenser and Dynamic Microphones

Microphones that require power, either phantom or battery, are “condenser” microphones. They are usually more expensive than “dynamic” microphones, which require no power source to operate. For stage applications, you usually have a dynamic microphone. Studios typically use condenser microphones.

Cardioid and Omnidirectional Microphones

A Cardioid (unidirectional) microphone tends to pick up sounds from directly in front of the microphone and, to a lesser extent, from the sides of the microphone while rejecting sounds from behind the microphone. An omnidirectional microphone picks up sound from all around the microphone placement. A stage microphone is usually cardioid so that it picks up mostly the instrument or vocalist using it. Studio microphones are often omnidirectional to pick up room ambiance and the balance of an instrumental ensemble.

XLR vs Phone Plugs and Jacks

A jack is the connector receptacle that accepts a cable's plug. Plugs and jacks are classed as male and female for obvious reasons. Jacks are usually female and plugs are usually male, but not always.

Some microphones have no fixed cable attached. They require a cable with a male three-prong plug on the end that connects to the amp and a female three-prong plug on the end that connects to the microphone. The microphone itself has a male three-prong jack. Such cables are called XLR cables. Other microphones have a cable attached with a single ¼ inch male phone plug to plug into the amplifier. Such microphones are said to have RCA ¼ inch phone jack cables, which means the amplifier needs a phone jack input.

An XLR cable carries two copies of the audio signal with a common ground. One of the signals is inverted at the microphone, which puts it out of phase with the other signal, which means that when one signal's waveform is positive, the other signal's waveform is negative. The system puts the signal back in phase at the amplifier and combines the two signals. Here's why.

Long lengths of cable, such as you can have with low impedance microphones, tend to pick up noise. The two signals in an XLR cable will pick up the same noise because they have a common ground, the third lead in the cable. The system reinverts the phase of the inverted signal and combines the two signals at the amplifier end. This process puts one signal's noise out of phase with the other signal's noise. Combining two signals that are the same except that they are out of phase cancels the signal to zero amplitude. Thus, an XLR circuit is a noise-cancelling device.

The amplifier must have a microphone jack that accepts the plug on the microphone cable and matches the impedance of the microphone. Many amplifiers have both kinds of jack and support both impedances.

You sometimes see a cable with a female XLR connector on one end and a ¼ inch phone jack on the other. This cable is usually for connecting a low impedance microphone to a high impedance microphone input jack. This connection works only for short cable lengths, and the signal delivered to the amplifier is not optimal. For optimal performance in this situation or for longer cable lengths, you need an impedance-matching transformer, described next.

Impedance-matching Transformers

Impedance-matching transformers convert low impedance microphones to high impedance and vice versa. These transformers are typically tubular in shape and have the correct plug on one end and jack on the other. You can plug the transformer into the amplifier's microphone input jack and the microphone cable into the transformer's input jack

Comparing Microphones

To compare the difference between the quality of microphones listen to the two audio clips shown just below this paragraph. I recorded the two clips under identical circumstances with respect to the room and the recording equipment. The only difference between the two is that the first one uses a consumer grade dynamic high-impedence microphone such as you might buy for less than $10. The second recording uses a studio quality condensor microphone that costs in the hundreds of dollars.








Cheap Microphone








Studio Microphone

So, do you hear hundreds of dollars worth of difference? Probably not. But you hear a difference in the quality of the sound. You'd hear a much bigger difference if the application was for music. The application for this example—and for most ventriloquist acts—is speech, which does not have the dynamic range requirements of vocal or instrumental music applications.

Now, listen to this clip, which I recorded with a professional dynamic, low-impedence stage microphone designed for vocalists and which is about what a ventriloquist should use:







Stage Microphone

You can hear some difference between the stage and studio microphones, but not much. Which is a good thing when you consider that you can buy a good stage microphone for much less than the cost of a studio microphone.

The industry standard for vocal applications onstage is the Shure SM58, a cardioid dynamic low-impedance vocal microphone.

0 Comments:

Post a Comment

Subscribe to Post Comments [Atom]

Links to this post:

Create a Link

<< Home