March 29, 2018

Bandwidth is a parameter applicable to resonant frequency analysis. It determines the frequency range that can pass through a system unchanged.

Generally, the bandwidth of a resonance is computed as the distance in hertz (Hz) between the 3 decibel (dB) drop-off on each side. This value is also known as the half-power bandwidth.

Consider the resonance at 142.1Hz in Figure 4.1. Its maximum acceleration is 3.041G; 3 dB below is 2.153G.

acceleration profile displaying the resonances of a metal beam

Figure 4.1. Resonances of a metal beam.

You can compute a rough estimate of the resonance’s bandwidth by determining the distance in Hz from the point where the plot crosses 2.153G on one side of the resonance to the point where the plot crosses 2.153G on the other side.

Note: Although the 3dB bandwidth is often referred to as the half-power, we are dealing with amplitude, not power.