Archive for November, 2011

Acoustic Violin for Stage Performance – Acoustics Setup

November 23, 2011 Leave a comment

Twice, I had bad experiences with audio system setup with acoustic violin on stage. The problem is not because of unavailability of technology, it is because of lack of people with knowledge behind the scene. Either the acoustic instruments won’t be audible or there will be wow/ringing(that low and high frequency sounds when you point a microphone towards the speaker and increase the gain). I am an amateur violinist, as well as an electronics engineer, with a lot of fascination towards acoustics. If you are going to be on stage with an acoustic instrument, these are my ideas (untested) to avoid or reduce the problems.

Monitors are those on-stage speakers, pointing at the performer. Try to be as far from the monitor as possible. If possible, avoid monitors. Monitors were a source of great fascination for me, as, with my experiences with speakers and electret microphones, pointing a speaker to a microphone is always going to cause wow/ringing. Now I understand the trick is done by the directivity of the microphone assembly.

Microphones used for stage performances are directional. Typical ones pickup sound from the front very well, and that from the rear very poorly. Position the microphones in such a way that all the monitors are at the back side of the microphone. The front should be pointing to the instrument, preferably the f-hole (This may be a myth, but it is commonly believed, that the sound from the violin comes out through the f-hole, and hence the most loud at that point). Unfortunately the f-hole of violin is in a place, where if a microphone is placed, can obstruct the bowing. This is thus up to the artist and his style of bowing. Also there is a chance of bad sound, as the sound as the resonances from the body and other part of the violin may be quite less intense than the resonance of the air cavity, compared to actual audience. In fact it is popularly known that the sound that is heard by the audience is far better than the one heard by the performer himself. The solution is to use a more directional microphone at a greater distance from the instrument. Advanced sound engineers can consider using array microphones to achieve very high directivity.

In a typical performance, the violin is tuned to work at greater than 100Hz and typically plays at >200Hz. So the extreme low sounds can be cut off at the equaliser. This will reduce the wow effect, as the higher frequencies are more directional, and will be avoided by the directional microphone. Also to reduce the bow rubbing noise, some of the higher frequencies can be attenuated. Too low high-frequency content will fade the ‘timbre’/’colour’ of the sound. So it is up to the trained ear of the sound engineer to decide the attenuation.

Loud Speakers
Ensure that all the speakers are pointing away from the stage. Any decently constructed stage will have mechanisms to prevent reflection of the Loud Speaker from the walls.

Piezo Pickup
These are sensors used to pickup the mechanical vibration of the body(typically bridge), and convert it to electrical signal. Typically, the signals hence obtained will be of a different timbre/colour than the actual violin sound, as it doesn’t pickup the acoustic resonance. If you use this, the violin can no longer be called as acoustic. You will have to use filters to shape the violins’ timbre to the one that is audible.

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