Santora, M., Ige, C., Otto, J., and Egolf, D., "Modeling the Sound Pressure Loss of an Electromechanical Active Helmholtz Resonator," SAE Technical Paper 2017-01-1827, 2017.
A muffler attached to an engine attenuates sound over a dedicated frequency range. This research involves the development of an active muffler that is keyed to the revolutions per minute (rpm) of the engine and suppresses the fundamental frequency being exhausted through the tailpipe. The active muffler consists of a tracking side-branch resonator terminated with a composite piezoelectric transducer. The use of an exponential horn as a resonating cavity and terminated with a composite piezoelectric transducer is presented. This would create Electromechanical Active Helmholtz Resonator (EMAHR) creates a notch that can be moved between 200-1000 Hz. The use of acoustical-to-mechanical, mechanical-to-electrical, and analog-to-digital transformations to develop a system model for the active muffler are presented. These transforms will be presented as two-port network parameters. The use of two-port networks to model the electroacoustic system are a defining factor in the analysis. The two-port network parameters for the pipe, horn and piezoelectric transducer are discussed. Using the developed electroacoustic model in simulation the system can be further developed, specifically the load on the composite piezoelectric transducer. The load can be produced with analog-to-digital, digital, and digital-to-analog circuitry. A microcontroller can be used to perform filtering to produce the desired current from the voltage input, or response of an electrical impedance. This impedance generation with a microcontroller is briefly discussed. The sound pressure level results of the modeling are shown over the frequency range of 200-1000 Hz. The maximum sound pressure loss at these frequencies is characterized by the model for the EMAHR.