With the use of a low cost microphone mounted at each nozzle, a sound signature of the nozzles may be captured and stored to be used as a continuous indicator of any changes in the flow rate of the nozzles. By measuring changes in sound at each nozzle, it is possible to determine the change in flow before a change in pressure manifests into a problem in the system. The change in sound will oftentimes be significant for plugged nozzles, or nozzles that have excessive wear and flow at too high of a rate. The invention has the advantage of being relatively low cost with ceramic microphones, for example, and with little or no moving parts required. A closed loop control system may be included to compensate for nozzle degradation.
