Microphone Techniques for Choirs
By: Ron Huisinga
There are many reasons why a choir or large vocal group would need to use microphones. Perhaps the service or concert is being recorded or videotaped. Maybe the church is too dead acoustically, and the choir needs a little extra help to produce a big choral sound. You need to add some microphones. But what type? How many do you need? And where should you place them? These are the important questions to answer.
What Type of Microphone?
The choir microphone must be able to pick up voices at 6 to 10 feet away from the microphone. In other words, it must be very sensitive. A condenser microphone can have a 10 to 15 dB higher output level over a dynamic microphone. This means your sound system electronics will not have to provide as much gain or amplification in order to obtain a sufficient volume. The result is a higher signal-to-noise ratio (a lower hiss or noise) and a better dynamic range.
Flat Frequency Response
Another important thing to look for in a choir microphone is a flat frequency response. This means the microphone should pick up all the audio frequencies at the same volume. Many microphones have their low frequencies intentionally rolled-off (less sensitive). It is designed to be used close to the mouth. When this microphone is used at a distance, it will sound quite thin or tinny because of the low bass pick-up. However, when it is used as designed (within 6 inches), it will sound much better due to the bass boost, which is caused by the proximity effect.
A microphone that is designed for distance will have a flat response and will reproduce a very natural sound. This microphone also has a 2 position switch, which allows you to roll-off low frequencies if you choose.
Another very important thing to look at is the off-axis frequency response (the response from the sides and the rear of the microphone). The gain-before-feedback and the overall sound is greatly affected by how smooth or even the off-axis response is. Gain-before feedback is the maximum amplification of the sound before the sound system goes into feedback and starts squealing. The polar graphs of the microphone will give a good idea of its response.
Cardioid Pattern Microphone
In most cases, a cardioid pattern (directional) will produce more gain-before-feedback than an omni-directional microphone. The cardioid pattern can also be used to reduce the pick-up of an orchestra or audience noises.
How Many Microphones?
This is not an easy question to answer. Many factors must be taken into account, such as choir size and arrangement. One important rule to follow is the "3 to 1 Rule." That is, the distance from one microphone to the next must be at least three times the distance the first microphone is from its source of sound. This will assure minimum interaction and cancellation. If the choir is to be amplified in the church, then gain-before-feedback is always a major concern. Often, the fewer microphones that are used, the greater the chance of success. Every time the number of microphones that are on doubles, the volume before feedback will drop 3 dB. So just adding more microphones will not necessarily mean you will be able to get the choir louder. You must first move the microphones closer to the choir so the sound level reaching the microphones is louder and so the "3 to 1 Rule" is not violated. Of course, you now start picking up more of the individual voices, so the choir members may have to be shifted to provide a better balance. A good rule of thumb is to employ one high quality, high output microphone (in other words, a very sensitive microphone) for about 25 people, so a choir of up to 50 would use two microphones. Don't forget that in audio, less is often better.
Here is one formula that is very effective for up to three rows of singers. The microphones are one foot in front of the first row and 24 to 36 inches over the heads of people in the first row. The microphones are then pointed at the heads of people in the back row. This technique takes advantage of the cardioid pattern. People in the back row sing directly into the microphone's most sensitive side (front, on-axis). Now, as we move forward and down to the front row, we get closer to the microphone. However, we also get farther off-axis so the microphone is less sensitive. Therefore, the microphone picks up the front and back row voices at about the same volume.
You can also use this method to help balance a small vocal group. Just place the weaker singers in the middle (on-axis) and the stronger singers on the outside (off-axis).
Choir microphones can be set up on microphone stands with booms or installed to hang from the ceiling. The method you use depends on your visual and portability needs.
As you can see, many factors must be considered in selecting a microphone for each particular choir application.
Ron Huisinga is the co-founder of New Life Communications, Huisinga and Olsen Publishing and the Internet Sound Institute, a website devoted to educating operators and others about sound systems and operational techniques, www.soundinstitute.com.