A virtual bass generating circuit used in a speaker is used to filter out a high frequency part of an audio signal to generate a low passed audio signal, generates an even and odd audio signals respectively having even and odd harmonics of the low passed audio signal according to the low passed audio signal, subtracts an amplified low passed audio signal from an addition of an amplified even audio signal and an amplified odd audio signal to generate a first calculated audio signal, filters out a low frequency part and a high frequency part of the first calculated audio signal to generate a band passed audio signal, and adds the band passed audio signal and the audio signal to generate a second calculated audio signal with enhanced even and odd harmonics of the audio signal.