Microphones for Instruments

In Uncategorized by tfwm

A small instrumental group has been rehearsing a special music number for weeks. The song has been perfected. They arrive at church with plenty of time to set up. The moment to begin finally arrives. The song goes as well as it had been prepared. Bravo! However, after the service, people say they wish they could have enjoyed the music instead of straining to hear. What?!? Does this sound the least bit familiar? Then this article is for you!

There are several situations that need to be considered when putting a microphone on a musical instrument: 1. Reinforcement for the main loudspeaker mix., 2. To feed the monitor loudspeakers, 3. To feed a recording.

This article will make recommendations for the selection and placement of instrument microphones. There are three basic types of microphones and many factors critical in determining the exact placement of those microphones. Some of those factors would include:
• Room characteristics.
• Sound system characteristics.
• Microphone characteristics.
• The application for which the microphone will be used.
• Your desired affect and personal preference.
• And, probably most importantly, the musicians touch.

Microphone Types and Characteristics
This article will characterize three types of microphones: vocal, instrument and boundary.

Vocal Microphone
A vocal microphone typically has its bass frequencies rolled off which compensates for the proximity effect that occurs when most directional microphones are used close up (see Figure 1). The vocal microphone is easy to recognize because the grill is typically shaped like a ball so it resembles an ice cream cone.

Some of the characteristics of a typical vocal microphone would include: cardioid or supercardioid pick-up pattern and bass roll-off frequency response curve.

Instrument Microphone
Instrument microphones are characteristically used at a distance. The low-frequency response of the microphone does not roll-off, so the response curve is relatively flat at the lower frequencies. The flat curve ensures that all the frequencies are picked up at relatively the same level. This flat pick up allows an instrument to be reproduced with a more natural sound.

Some characteristics of a typical instrument microphone would be: wide frequency response curve, flat frequency response curve and cardioid pick up pattern.

Boundary Microphone
A boundary microphone is designed to be used on a flat surface where its slim profile helps in concealing it. The boundary microphone was originally designed for recording purposes.

Its characteristics make it well suited for instrument applications, typically including: wide frequency response curve, flat response curve and half cardioid or half omnidirectional pick up patterns.

Microphone Placement
To properly place a microphone, it is essential to know the pick up pattern for your microphone. To learn your microphone’s “front” (on-axis) and “back” (off-axis) sides, refer to the microphone’s spec sheets. Or, test the microphone by speaking into it while moving it in a circle (as shown in Figure 2). The point at which the sound level drops is the “back” of the microphone.

Whenever possible, point the “back” of the microphone toward other instruments to help reduce “bleed” or pickup of the other instruments. You may also want to aim the “back” of the microphone toward any nearby monitor speaker to help reduce feedback problems.

Organ: Yes, there are times when you may want a microphone for the organ. For example, without a microphone, the organ would sound distant and indistinct on a recording. Place the microphone inside the organ pipe chamber or in the organ speaker area. A pipe organ with a swell would require a microphone outside the swell louvers. Be sure to place the microphone at a distance from a single pipe or speaker component to achieve a balanced sound.

Acoustic Guitar: Start with one of two positions. The first location (labeled A in Figure 3) is over the right shoulder of the musician (for the right handed guitarist). Locate the microphone approximately two feet above the guitar and point the “front” of the microphone at the bridge. The second location (labeled B in Figure 3) is two or three feet in front of the guitar, raised to the same height as the guitar, directly in front of the bridge.

The following are some fine-tuning tips: If you have problems with feedback or indistinct sound, gradually move the microphone closer to the guitar. If you are picking up too much string noise, gradually turn the microphone away from the neck of the guitar. If there is too much bass, turn the microphone toward the neck of the guitar. You could also experiment with a combination of a microphone and a pick up if the guitar has one.

Piano Forte: There are many approaches to microphone placement on the piano. The piano is one of few instruments that covers a wide range of frequencies and dynamics. Therefore, selection and placement are critical to achieve a quality reproduction.

Boundary microphones are well suited for placement on the lid of the piano (as shown in Figure 4). Tape the microphone to the underside of the lid. CAUTION: Be sure to ask permission first! When using a boundary microphone, point the “front” of the microphone toward the keyboard side of the lid. Have the pianist play scales from one end of the keyboard to the other. Listen for any imbalance between string sections. Adjust the position as needed or add another microphone.

Ideally, the lid would be open to full-stick for the best overall balance. If sight lines are a problem, lower the lid to the short-stick.

Please note, the use of any type of microphone under the lid when the lid is closed may produce inferior sound.

Another option is to utilize two identical, cardioid instrument microphones (as shown in Figure 5). They are positioned on a boom microphone stand. The microphones are focused at a 90 degree angle in the middle of the keyboard with the capsules side-by-side. They should be directly over the hammer section pointed toward opposite ends of the keyboard. Generally speaking, the microphones should be 12 to 24 inches above the hammers. Experiment with the height that works best for your situation.

The following are some general guidelines:

• Listen, think, then do something.
• Listen to the microphones individually.
• Remember where you were before you change something. You may want to go back to a previous position.
• Less is more.
• Don’t do anything unless you think you can make a difference.

If you need additional help finding the right microphone for your specific application, be sure to contact a local systems contractor who specializes in sound system design and installation. They are the experts to answer your questions. For other helpful articles like this about sound system and operational techniques, visit http://www.soundinstitute.com