text: frequency of a wave? a guitar string vibrates with the lowest possible frequency called the fundamental frequency. if the string has the length l0 = 65 cm, and the speed of a wave on the string is v = 368 m/s, then what is the frequency f of the wave on the string? when the string vibrates at its fundamental frequency, the wavelength is twice as long as the length of the string, since the only nodes are at the ends of the string. then, by frequency x wavelength = velocity, the fundamental frequency is (36800 cm/s)/(130 cm)=283.1 hz