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So far we have been talking about systems that have a single resonance frequency. The peak in the graph in section 4.2.1 is very sharp which means that driving the system at any frequency other than $$2.5\text{ Hz}$$ will not produce a very large amplitude vibration. Many systems, including musical instruments, have a wide range of frequencies at which the system will resonate. Several different resonance curves appear in the graph below. Notice that, although there is always a single resonance frequency for any one curve (the frequency of the peak), there are many frequencies near resonance that will cause almost the same amplitude of vibration. The width of the resonance curve is called the Quality or Q-factor. The higher the Q-factor, the narrower the curve and the more selective the system is about what frequencies will excite it into resonance.
Figure $$\PageIndex{1}$$