Use Direct Connections For Onstage InstrumentsJune 13, 2008 2:39 pm Live Sound
When you are setting up a PA system for use at live shows, an important general rule is to minimize the number of onstage microphones. There are two reasons for this, both having to do with feedback between the microphones and the main or monitor speakers.
The first reason to minimize the number of microphones is to avoid unnecessary sources of feedback. Every “live” microphone onstage has the potential to cause feedback, the scourge of the sound man. (The audience won’t notice if the vocal balance is a tad off. They will notice feedback.) If you can replace just one instrument microphone with some kind of direct connection, that will eliminate one more potential source of feedback!
The second reason that fewer microphones are better is that you can apply more gain to each one before feedback begins to occur. Every microphone onstage will feed back if you turn its gain up high enough. The gain applied to each microphone contributes its own small part to bringing the whole system closer to the inevitable feedback point. If fewer microphones are involved, more of the potential gain-before-feedback is available for each, allowing them to be louder.
So how do you go about limiting the microphone count? Obviously, the main vocalist(s) will each need their own mikes, and there’s nothing you can do about that. If there happens to be a group of two or three backup singers, they might be able to share a mike instead of each having their own, but in general you are kind of stuck with “one microphone per vocal.”
If you are miking a drum set, which is somewhat uncommon in smallish venues, you could think about reducing the number of mikes here too, although the loudness of the drums means that the contribution of these mikes to overall system gain is likely to be relatively small anyway. (Overheads will probably end up contributing the most.)
The Direct Approach
The way to really reduce the microphone count is this: don’t use microphones for instruments unless you have to. Instrument connections to the PA can often be made directly, rather than playing the instrument through an onstage amp and miking the amp. (See my article Using Onstage Amps vs. Playing Through the PA for info on why you would want to run your instruments through the PA in the first place.)
The easiest form of direct connection is an output from the onstage amp that you can connect directly to the stage box of the snake (or to the PA). Unfortunately, not all amps have direct output connectors. Of the ones that do, some have XLR connectors for this purpose, so you can use a regular mike cable. Others use 1/4″ connectors. In some cases, there is even a handy volume knob on the back of the amp to set the signal level appearing at the direct output connector. If so, I usually start with it set about 3/4 of the way up (i.e. on “7″).
If the amp doesn’t have a direct output, you can take a signal directly from the instrument itself using a DI (Direct Injection) box, also called a “direct box.” (Read up on the specific direct box I use here.) The direct box takes the signal from an instrument and sends it directly to the amp unchanged, tapping off a little bit of the signal through an XLR connector that you can connect to the snake (or directly to the PA) using a regular microphone cable.
Let’s say you want to use a direct box for a keyboard. Simply connect the keyboard output to the direct box’s Input connector using a guitar-type patch cord. Now run another guitar type patch cord from the direct box’s Link (or Input Thru) connector to the amp input, and run an XLR microphone cable from the direct box’s Output connector to the snake or PA. When the keyboard is played, it will be heard through the amp as usual and the signal will be available at the PA as well. Without miking the amp!
Direct boxes are often used for a keyboard or a bass guitar. They can be used on electric guitars as well, but sometimes the particular “sound” of the amp and its speaker is important and you want it in the PA sounding just that way. Here it will be necessary to “bite the bullet” and use a microphone in front of the guitar amp. Be sure to get the mike as close to the speaker as possible, and to point it away from any nearby monitor speakers to reduce the possibility of feedback.Tags: microphones, music technology -->