Shure Blog

Blog

 
By Shure Notes|  Comment(s)

Live Sound Reinforcement

Acoustic Instruments

The following article is an excerpt from Shure Notes, Issue #26.

Of course you know how to mic your lead singer, your bassist and your lead guitar player. But what happens when you add acoustic instruments like fiddles or horns — maybe even a dulcimer or dobro?

Experiment with a variety of microphone and positions until you hear what you want. Remember though, you can probably get there faster by understanding basic characteristics of the mic and the instrument, understanding frequency response and reducing pickup of unwanted sounds (that can also produce feedback).

General Guidelines

Before we jump into specific mic techniques for live sound reinforcement of horns and stringed instruments, here are some helpful suggestions:

  1. Try to get the sound source to sound good acoustically before you mic it.
  2. Use a microphone with a frequency response that is limited to the frequency range of the instrument, if possible, or filter out frequencies below the lowest fundamental frequency of the instrument.
  3. To find a good starting microphone position, try closing one ear with your finger, listen to the sound source with the other ear and move around until you find a spot that sound good. Put the mic there. (Save your hearing! Don’t put your ear too close to very loud sound sources. If you want to know more, check out our Hearing Conservation issue.)
  4. The closer a microphone is to a sound source, the louder the sound source is compared to reverberation and ambient noise. Also the Potential Acoustic Gain is increased – that means the system can produce more level before feedback occurs. Each time the distance between the microphone and the sound source is halved, the sound pressure level of the microphone (and the system) will increase by 6dB. This is the Inverse Square Law.
  5. Place the microphone only as close as necessary. Too close a placement can color the sound source’s tone quality or timbre by picking up only one part of the instrument.
  6. Use as few microphones as necessary to get a good sound. Every time the number of mics doubles, the Potential Acoustic Gain of the system decreases by 3 dB. This means that the volume level of the system must be turned down for every extra mic added in order to prevent feedback. Also, the amount of noise picked up increases along with the likelihood of interference effects such as comb filtering.
  7. When multiple microphones are used, follow the 3-to-1 Rule: the distance between the microphones should be at least three times the distance from each microphone to its intended sound source.

Fighting Feedback, Handling Noise and Distortion

You can avoid most of these problems by taking a few precautionary steps.

Avoiding Feedback

  • Place mics as close as possible to the sound source – as far as possible from unwanted sound sources like loudspeakers or other instruments.
  • Aim unidirectional mics on-axis – toward the sound source.
  • Aim unidirectional mics away from undesired sources – 180° off-axis for cardioid, 126° off-axis for supercardioid.

Reducing Handling Noise and Stage Thumps

  • Use a shock mount.
  • Use an omnidirectional microphone.
  • Use a unidirectional microphone with a shock mount.

Eliminating Distortion
If you are miking very loud instruments and the sound from your loudspeakers is distorted, the microphone signal may be overloading your mixer’s input. To correct it:

  • Use a microphone with a built-in attenuator.
  • Use an in-line attenuator.
  • Use the input attenuator on your mixer to reduce the signal level from the microphone.

Miking Brass and Stringed Instruments

Microphone technique is still a matter of personal taste — whatever technique produces the best sound for the instrument, the musician and song is the right one to use. While there are some mics and placement suggestions that may be more obvious choices than others, there isn’t one that’s ideal. Sharpen your listening skills and trust your ears.

Get Adobe Flash player

Note:
With the saxophone, the sound is fairly well distributed between the finger holes and the bell. Miking close to the finger holes will result in key noise. The saxophone has sound characteristics similar to the human voice. A shaped response microphone designed for voice works well.

Shure Mics:

  • Beta98H/C™
  • KSM44
  • KSM32
  • KSM27
  • Beta 57A®
  • Beta 98 S
  • Beta 56®A
  • SM57

Get Adobe Flash player

Note:
The sound from these instruments is very directional. Placing the mic off axis with the bell of the instrument will result in less pickup of high frequencies.

Shure Mics:

  • Beta98H/C™
  • KSM44
  • KSM32
  • KSM27
  • Beta 57A®
  • Beta 98 S
  • Beta 56®A
  • SM57

Shure Mics:

  • KSM141
  • KSM137
  • KSM109
  • KSM44
  • KSM32
  • KSM27
  • SM81
  • SM94

Get Adobe Flash player

Shure Mics:

  • KSM141
  • KSM137
  • KSM109
  • KSM44
  • KSM32
  • KSM27
  • SM81

Shure Mics:

  • MC50B
  • MC51B

Resource Room

For more information on instrument miking, download Shure’s educational booklet, Microphone Techniques for Live Sound Reinforcement. Other good sources of information: the MIX Audio Series book, “Professional Microphone Techniques”, and Yamaha’s “Exploring Sound Reinforcement” DVD, available online or at your local music dealer or bookstore.

Share: Google Plus