One of the most challenging tasks ever confronted by an audio engineer is amplifying
orchestral instruments on a loud stage. Problems abound, including bleed, resonance, feedback, and frustration! To solve the problem, one must first understand the environment and then deal with the challenges
When in a “classical” concert hall, orchestral instruments such as violin, cello, or upright are
usually miked using an omni-directional condenser microphone. Omnis are particularly effective at producing a natural sound as they do not focus their attention on a particular area of the instrument, but capture a larger area that includes the bow, strings, F-holes, and so on. During classical concerts, feedback problems are usually not a concern as the PA system is only used for “sound reinforcement” and SPLs rarely exceed 90dB.
Problems set in when the rock band hits the stage. Drums, electric guitars, and bass generate significant SPLs that in turn must be compensated for by turning up wedge monitors. The sound generated by the orchestral instruments is lost. To compensate, one can either try close
miking the instrument using a directional cardioid microphone that attaches to the instrument or some form of piezo pickup. The cardioid microphone can work reasonably well but is not without issues. A directional mic only captures the sound from a specific area which may or may not sound right and will inevitably pick up sounds from adjacent instruments, the PA system, and the fold-back monitors. In order to hear themselves on stage, the violins
ask for more sound from the wedge monitors and next thing you know, feedback problems set in. Things can get even worse when playing outdoors: feedback due to room acoustics is replaced by wind noise, sound pressures are
increased due to lack of room acoustics, and this often pushes engineers to use alternatives such as piezo electric transducers.
Brad Madix, FOH engineer for Rush, recently experienced this problem: “For the 2013 Clockwork Angels Tour, the production design called for setting up four violins and four cellos directly behind Neil Peart’s drums. We therefore ruled
out miking the strings pretty early on. We did experiment a little with small mics in proximity of the drums and decided we were going to get as much snare in the mic as violin. All of the players were on IEMs so even if we did mic the
strings in order to provide a proper mix to the band (not to mention the audience) we would have to also use contact mics. A combination of mics and pickups might be a good solution, but in the end we decided to go strictly with pickups.”
Part 2 will run in the August 2013 issue of Professional Sound.
Peter Janis is President of Radial Engineering, a manufacturer of professional audio products used in live touring and recording studios around the world, including the PZ-DI direct box for acoustic and orchestral instruments.
Special thanks to Brad Madix for his added input on this article.