The transfer function is a graphical representation of resonance. The sharpness and the width of the resonance curve is dependent on the magnitude of the resistance. A large resistance produces a small increase in amplitude and a wider frequency response and vice versa. A plot of the distribution of energy across frequencies in the driving system is called the source function . Resonance is analogous to a filter.
Acoustic filters allow certain frequencies to pass unscathed while attenuating others.
The upper and lower limits of frequencies in filters are known as the upper and lower cutoff frequencies respectively and the frequency in the middle of the bandwidth is the center frequency . Resonance in Air-filled Cavities Imagine that you are sitting in an auditorium. There is a band playing on the stage. These reflected waves travel back towards the source and become mixed with the incident waves coming from the source. The reinforcement causes an increase in the amplitude of the frequencies involved while interference attenuates the frequencies.