One of the great pleasures of playing in an acoustic band is gathering with other players and feeling the resonance and harmony of all the instruments and voices working together in that close acoustic space. When playing for a larger audience, when sound reinforcement is really necessary, you can keep that acoustic essence by gathering around a single mic in the traditional bluegrass style.
Many players run into some problems with this approach with modern PA systems and sound engineers. Partly it’s a matter of expectations: the technique originated as a way to get a little more volume from essentially acoustic performances, so a band could be heard in a larger hall – any increase in volume was a win, and audiences were used to the sound of unamplified instruments. These days a lot of engineers and even audiences approach performances with an expectation of much higher volume levels and get frustrated when they can’t achieve them with this technique. Ear Trumpet Labs mics can help a lot, but it’s important to understand limitations and some techniques to get the best results.
The first point to understand is that the distance from your instrument or voice to the mic is the first gain stage in your chain. It’s a negative one – the sound level is always quieter at the mic than at the instrument, and it drops with the square of the distance. So it’s twice as quiet from one foot as from six inches away, and twice again as quiet at two feet. In order to get the same signal level in the PA, the preamp has to add that much gain back. More importantly, assuming the level of sound on the stage from the PA (mains and monitors) is the same, the microphone has to be able to deliver that much extra gain without feedback. The farther you are from the mic, the harder it will be to get the same volume from the mains without running into feedback. So the first best technique is to really work on being able to pay close to each other and to the mic. Many people place the mic too high, getting it needlessly far from instruments like the guitar and banjo, especially if vocals aren’t a major part of the band’s sound. Picture lengths of string from each sound source to the mic, and try to balance them all and keep them all as short as possible. One foot makes a big difference.
The best tool for controlling feedback is using the directionality of the mic’s pickup pattern. ETL mics like Edwina and Louise are all cardioid pattern, as are most large diaphragm condensers. The main advantage of ETL mics is that the pattern stays controlled through the whole frequency range. In a cardioid pattern, the mic has its full sensitivity in the central 30 degrees in front of the mic; by next 30 degrees, or 60 degrees from directly in front, the level has fallen off 3db; by 90 degrees (at the side of the mic) the level has dropped 6db, or in half, and is dropping very rapidly. By 30 degrees around to the back side of the mic the sensitivity is much lower, and is at its lowest directly backwards. To fight feedback you want the greatest contrast between the sensitivity directed towards your instruments and that directed towards anything coming from the PA. So keep your players to the front of the mic, ideally all within the 60 degree arc. Place your louder instruments to the sides and the quietest in the center. Keep the mic at least some distance behind the main speakers, and keep your monitor (you should only need one) a little distance behind the mic (from the band’s point of view) – don’t put the monitor right at the foot of the mic stand.
The last thing to watch out for is the one you usually have the least control over, and that is reflections and bounce-back in the room. Any sound getting back to the mic from the PA is a potential source of feedback, and low ceilings and close, reflective back walls can bounce sounds right back from the speakers. If you can get curtains or a backdrop behind you on stage, it will help a lot. Sometimes it can pay to play with angling the mic a little up or down to get its peak sensitivity away from a problematic surface.
The single-mic technique can be really rewarding in conveying a truly accurate, warm acoustic sound to a large audience. However, performers most commonly use large-diaphragm condenser mics that are really intended for the studio because of their sonic accuracy and sensitivity to capture instruments at a distance. But using mics not designed for the extreme feedback rejection needed on a live stage can be problematic. Many modern LDCs have a quite hyped high end that can be beneficial in the controlled environment of a studio, but on stage it not only makes feedback control difficult, it doesn’t sound very natural. With ETL mics, some care, and practice, you can not only get great natural acoustic sound at better volume than you ever hoped, you can even get effective monitoring on stage, which most performers never imagined they could get with this technique.