One of the difficulties that a musician faces while performing live on stage is not being able to hear himself or his fellow performers well enough. This happens because some instruments naturally produce louder sounds than others. The drums for example could easily overpower everyone else on stage. Meanwhile the vocalist also has no instrument other than his own vocal chords and will probably have a hard time hearing himself sing when the whole band is playing. This difficulty is also brought on by the size of the stage. It can be so big that musicians spread across it won't be able to hear each other without pushing their instrument amplifier's volume higher or playing and singing louder than a good performance would require. Monitor speakers are specifically made to solve this problem. The sound coming from the stage goes to a mixing board and is fed back into the monitors which are positioned near where the musicians are on stage.
- Guard against feedback. The biggest danger with monitor speakers is feedback. This occurs when a microphone and a speaker face each other or are near to each other. What happens is that the sound captured by the mic goes out of the monitor and then is directly captured again by the mic thus forming a loop. This will produce a high pitched whine that will quickly grow in volume and drown everything out. The immediate solution to avoid feedback is to cut down the volume of the speakers but this could short change the performers who may need to hear the monitor mix louder. Feedback occurs at specific frequencies so to solve this dilemma; one can cut down the specific frequency rather than the actual volume. This could be done through a graphic equalizer set up between the mixing board and the amplifier driving the monitors. Initially set all the frequency gains on the equalizer to zero and push the amplifier gain just high enough to create a small amount of feedback. Isolate which frequency the feedback is occurring by pushing each frequency gain control up to the maximum one at a time. If feedback occurs pull the particular frequency gain down to a negative number. If no feedback occurs pull the gain back to zero.
- Ask the musicians what they want to hear. The monitor mix is largely determined by what the performers want to hear on stage. Ideally each musician gets one monitor speaker and he may want to hear more of a particular instrument or only certain instruments and not the whole band. Drummers for example tend to want to hear a little of everything but with an emphasis on the bass which is natural since they need to work tightly together to set the rhythmic foundation of the performance. Conversely bassists want to hear a clear kick and snare drum on their monitors. Guitarists generally want to hear the other guitarists on stage and the vocals. Vocalists naturally want to hear themselves sing and want to hear the rhythm guitar too so that they know if they're still in tune. Almost everyone needs to hear the kick drum as this basically beats out the groove. It's important therefore for a sound technician responsible for the monitor mix to communicate well with the performers so that he can handle and deliver their preferences.
The sound that comes out of monitors is the mixed differently from the sound that comes out of the front-of-house speakers, which are the large main speakers that are pointed at the audience. The audience needs to hear the best possible mix of the live performance. What comes out of the monitors however only serve to guide the musicians. So monitors mixes don't have to sound exceptionally good, they just need to be clear.